CN118176323A

CN118176323A - Multi-stage treatment of activated zinc-based phosphating of metal parts having zinc surfaces

Info

Publication number: CN118176323A
Application number: CN202280072614.3A
Authority: CN
Inventors: R·波斯纳; M·巴尔策; K·瓦普内尔; J-W·布劳沃
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2021-11-02
Filing date: 2022-10-28
Publication date: 2024-06-11
Also published as: WO2023078791A1; EP4174211A1

Abstract

The invention relates to a method for the corrosion protection pretreatment of a plurality of components arranged in series, wherein each component arranged in series has at least partially a zinc surface and is subjected to successive method steps for depositing iron and for phosphating zinc systems. In the method step for depositing iron, the coating to be established is at least 10 milligrams of elemental iron per square meter of zinc surface. Zinc-based phosphating after the iron deposition is carried out by means of an acidic aqueous composition comprising, in addition to zinc ions, phosphate ions and free fluoride, a particulate component dispersed in water, which at least partially comprises hopeite, phosphophyllite, phosphogalvanneate and/or rhodochrosite, and provided by means of an aqueous dispersion of these crystalline solids stabilized with at least one polymeric organic compound.

Description

Multi-stage treatment of activated zinc-based phosphating of metal parts having zinc surfaces

The invention relates to a method for the corrosion protection pretreatment of a plurality of components arranged in series, wherein each component arranged in series has at least partially a zinc surface and is subjected to successive method steps for depositing iron and for phosphating (zinc phosphation) of the zinc series. In the method step for depositing iron, the coating to be established is at least 10 milligrams of elemental iron per square meter of zinc surface. Zinc-based phosphating after the iron deposition is carried out by means of an acidic aqueous composition comprising, in addition to zinc ions, phosphate ions and free fluoride, a particulate component dispersed in water, which comprises at least in part hopeite, phosphophyllite, phosphogalvanneate and/or rhodochrosite, and is provided by means of an aqueous dispersion of these crystalline solids stabilized with at least one polymeric organic compound.

Stratified phosphating is a process for applying crystalline corrosion protection coatings to metal surfaces, particularly metallic iron, zinc and aluminum materials, which has been used for decades and has been under intense research. Zinc-based phosphating is particularly well established for corrosion protection, performed in a layer thickness of a few microns, and is based on the corrosive pickling of metallic materials in an acidic aqueous composition containing zinc ions and phosphate. During the pickling process, an alkaline diffusion layer forms on the metal surface, which layer expands into the interior of the solution and forms therein poorly soluble crystallites, which precipitate directly at the interface with the metal material and continue to grow there. In order to support the pickling reaction on the metallic aluminium material and mask the toxic aluminium bath (which in dissolved form hampers the formation of layers on the metallic material), it is usual to add water-soluble compounds as fluoride ion sources.

Zinc-based phosphating is adjusted in such a way as to obtain a uniform, closed and dense crystalline coating on the surface of metallic iron, zinc and aluminum. Otherwise, good corrosion protection and good coating base cannot be achieved. Uniform, closed coatings in zinc-based phosphating are generally reliably achieved by a layer weight of 2g/m ². Depending on the metal surface to be phosphated, the concentration of the active components in the above-mentioned pickling and zinc-based phosphating stages must be adjusted accordingly to ensure a correspondingly high layer weight on the surface of the metallic iron or steel, zinc and aluminum.

Another property of zinc-based phosphating, which is important for corrosion protection and coating adhesion (especially for good electrocoating properties), is that the deposition process is self-limiting, i.e. dissolution of the phosphate layer, which occurs at the acidic pH of zinc-based phosphating, is in steady-state equilibrium with growth or continued growth of phosphate crystallites, and thus the layer weight no longer increases, which will be an indication of the growth of a coating that is crystalline but porous and thus not densely crystalline. In the case of technical zinc-based phosphating processes, this means that in the case of treatment times of usually about 20 seconds to 5 minutes, which is of interest in terms of factory technology and cost efficiency, in the zinc-based phosphating wet-chemical process step the formation of a uniform, closed and crystalline zinc phosphate coating must be achieved and the self-limiting thickness of the coating has been ideally reached. This is technically ensured by the fact that: the coating grows with as high a number density of phosphate crystallites as possible, so that the layer formation reaches a self-limiting range and thus a predetermined limit layer thickness with as low a layer weight as possible.

In order to obtain such a uniform, closed coating of phosphate crystallites of high density or high number density, zinc-based phosphating is always initiated in the prior art by activating the metal surface of the component to be phosphated. The activation is generally a wet-chemical process step, which is generally carried out by means of contact with an aqueous colloidal solution of a phosphate ("activation stage"), which, when fixed on a metal surface, acts as a growth nucleus in the subsequent phosphating for forming a crystalline coating in the alkaline diffusion layer, resulting in a high number density of grown crystallites and thus in turn in a dense crystalline zinc phosphate layer, which also has excellent corrosion protection and, due to its high charge transfer resistance, also has excellent electrocoating properties.

In this case, suitable dispersions are predominantly neutral to alkaline aqueous compositions based on colloids of phosphate crystallites, whose crystal structure has only small crystallographic deviations from the type of zinc phosphate layer to be deposited. In this context, WO 98/39498A1 teaches in particular divalent and trivalent phosphates of metals Zn, fe, mn, ni, co, ca and Al, it being technically preferable to use phosphates of metallic zinc for the subsequent activation of the zinc-based phosphating.

The activation stage based on divalent and trivalent phosphate dispersions requires a high level of process control to constantly maintain the activation performance at an optimal level, especially when treating a range of metal parts. To ensure that the process is sufficiently robust, foreign ions carried in the aqueous colloid solution from previous treatment baths or aging processes must not lead to deterioration of the activation performance. The deterioration is initially significant upon increasing the layer weight in the subsequent phosphating and eventually leads to the formation of defective, non-uniform or less dense phosphate layers. Thus, in general, layered zinc-based phosphating with upstream activation is a multi-stage process whose control is technically complex and has been carried out in a resource-intensive manner until now, both in terms of process chemicals and in terms of energy to be consumed.

In the field of automotive manufacturing, where the invention is particularly relevant, various metallic materials are increasingly used in composite structures and joined together. Various steels are still used in body construction, mainly because of their specific material properties, but lighter and lighter metals such as aluminum are also used, in particular to significantly reduce the weight of the entire body. In particular, in the automotive industry, the challenge is often that zinc surfaces must be activated particularly well compared to steel surfaces by zinc-based phosphating methods known in the art to ensure that a dense crystalline phosphate layer with a coating weight of typically less than 5.0g/m ² is grown in zinc-based phosphating, because beyond such phosphate layer weight there is no satisfactory corrosion protection on zinc surfaces, and therefore the method is neither performed in a resource-efficient nor economical manner, also due to high phosphate consumption.

WO 2019/238573 A1 addresses a resource-saving method for zinc-based phosphating and also indirectly reduces the complexity of the multi-stage process by providing a particularly efficient activation based on specific dispersed divalent and trivalent phosphates, which activation provides an aqueous colloidal solution based on divalent and trivalent phosphates and being extremely well stabilized against sedimentation and also makes it possible to make uniform, closed and very dense zinc phosphate coatings at relatively low particle content in the activation stage, thereby also reducing the material requirements due to layer formation in zinc-based phosphating.

However, there remains a need to optimize zinc-based phosphating pretreatment lines, including an activation stage and a phosphating stage, so that the entire process can be carried out in a less resource-intensive manner, ideally with a simultaneously simplified procedure. However, the whole process of saving resources must not be at the expense of the performance of zinc-based phosphating, which must be provided as a uniform, closed and dense crystalline coating with high charge transfer resistance, in order to make possible good corrosion protection and correspondingly good coverage of the coating in the subsequent electrocoating. In particular, in the most common applications, i.e. in the sequential processing of components, this must always be ensured, wherein also economically attractive and resource-saving methods must be provided for components with zinc surfaces.

Surprisingly, this complex profile of requirements can be met when a certain amount of the particulate zinc phosphate dispersion is added to an acidic aqueous composition for zinc-based phosphating, resulting in a composition for zinc-based phosphating that is self-activating. The activation performance of the zinc phosphating pretreatment line of a series of parts can then be maintained by metering in an activation aid based on the above-described particulate zinc phosphate dispersion. This makes it possible to dispense at least partly or even completely with an activation stage upstream of the wet chemical treatment stage of zinc-based phosphating and in this way to carry out the entire process of zinc-based phosphating in a less material-intensive and energy-intensive manner and to reduce the technical complexity in the form of a separate activation stage, which was previously absolutely necessary in the prior art. The decisive factor for the economic and resource-saving operation of the pretreatment line according to the invention for satisfactory phosphating of components comprising zinc surfaces in sequence is the wet-chemical step upstream of the zinc-based phosphating for depositing iron coatings on zinc surfaces, which results in a significant reduction of the weight of the phosphate layer on these surfaces, thus reliably achieving the object of the invention of providing a constant satisfactory corrosion protection value with low material consumption on components comprising zinc surfaces in sequence.

The invention therefore relates to a method for the corrosion protection pretreatment of a plurality of components arranged in series, wherein each component of the series has at least in part a zinc surface and is first subjected to a wet-chemical method step (i) for depositing iron on the zinc surface, followed by a method step (ii) for phosphating zinc systems,

Wherein in process step (i) a coating of at least 10 milligrams of elemental iron is produced per square meter of zinc surface of the component, and

Wherein in process step (ii) each part is contacted with an acidic aqueous composition having free acid with a number of points greater than zero and comprising

(A) 5-50g/kg of phosphate dissolved in water, calculated as PO ₄,

(B) Zinc ion of 0.3-3g/kg,

(C) Free fluoride, and

(D) A water-dispersed particulate component comprising phosphate of a polyvalent metal cation, wherein the phosphate is at least partially selected from hopeite, phosphophyllite, phosphocalcieite and/or rhodochrosite,

Wherein the acidic aqueous composition is obtained by adding to an acidic aqueous composition comprising components (A) - (C) an amount of an aqueous dispersion comprising a water-dispersed particulate component (P) comprising

At least one particulate inorganic compound (P1), said particulate inorganic compound (P1) comprising a phosphate of a polyvalent metal cation, said phosphate being at least partially selected from hopeite, phosphophyllite, phosphogalvanneate and/or rhodochrosite,

-And at least one polymeric organic compound (P2).

Sequential pretreatment is when the sequential components are each subjected to a method step of zinc-based phosphating according to the method of the invention and are for this purpose contacted with at least one bath provided in a system tank for zinc-based phosphating, the individual components being contacted one after the other and thus at different times. In this case, the system tank is a container in which the acidic aqueous composition is located for the purpose of zinc-based phosphating by wet chemical pretreatment. The component may be contacted with the bath of the system tank either inside the system tank, for example by dipping, or outside the system tank, for example by spraying the bath stored in the system tank.

The components treated according to the invention may be three-dimensional structures of any shape and design resulting from the manufacturing process, and in particular also semi-finished products such as strips, sheets, bars, tubes etc. and composite structures assembled from said semi-finished products, said semi-finished products being interconnected preferably by means of gluing, welding and/or hemming connections to form a composite structure.

In the context of the method according to the invention, the component has at least one surface of one of metallic iron or aluminum or zinc, if more than 50 atomic% of the metallic structure on that surface (up to a material penetration depth of at least one micrometer) comprises zinc or iron or aluminum. This generally applies to components made of the corresponding metallic material, as long as more than 50 at% of the metallic material comprises zinc or iron or aluminum as homogeneous material. However, components comprising zinc surfaces are also iron materials provided with a metal coating, such as electrolytic galvanized steel or hot dip galvanized steel, which may also be alloyed with iron (ZF), aluminum (ZA) and/or magnesium (ZM).

Process step (i) -deposition of iron:

According to the invention, it is necessary to deposit at least 10 milligrams of elemental iron-based coating per square meter of zinc surface of the component. The higher iron coating advantageously reduces the weight of the phosphate layer in the subsequent process step (ii), so that in the wet-chemical process step (i) of the process according to the invention at least 20 mg, particularly preferably at least 40 mg, very particularly preferably at least 60 mg, of the elemental iron-based coating is preferably on the surface of the component formed from zinc. However, it is often observed that a significantly higher iron coating on the zinc surface proves to be disadvantageous for the process according to the invention, since in interaction with zinc-based phosphating, a poor adhesion result to the organic top coating is achieved. It is therefore preferred if, in the wet-chemical process step (i), the iron coating is limited to less than 150 mg, particularly preferably less than 120 mg, per square meter of zinc surface of the component in each case.

When contacting the sequentially arranged parts with an aqueous composition containing an active component for depositing iron in dissolved or dispersed form in an aqueous phase, there is a wet chemical treatment step in the sense of method step (i). The compositions are water-based when the proportion of water is in each case at least 50% by weight, preferably at least 70% by weight, particularly preferably at least 80% by weight, based on the total composition.

Suitable wet chemical methods for depositing iron in the desired coating are known to those skilled in the art. The deposition is generally carried out by contacting at least the zinc surface with an aqueous composition containing iron (II) and/or iron (III) ions, wherein the proportion of iron ions dissolved in the water is at least 50mg/L, preferably at least 100mg/L.

The iron coating on the zinc surface was determined by means of pickling and photometric analysis. For quantitative determination, after method step (i), a 5 wt% nitric acid solution defining the sample volume was pipetted directly onto the defined surface of the galvanized plate using a measuring cell ring and after exposure for 30 seconds at a temperature of 25 ℃ transferred to an ultraviolet measuring cuvette initially charged with a 1.0% sodium thiocyanate solution to determine absorption at a wavelength of 517nm and a temperature of 25 ℃. Calibration in the two-point method was performed by measuring the absorption values of two standard solutions of iron (III) nitrate in 5 wt% nitric acid.

In order to avoid metal deposition of noble metal elements, which impair the positive effect of the iron coating on the zinc surface on the formation of the zinc phosphate layer, and for ecological reasons, it is preferred if the aqueous composition for depositing iron in process step (i) contains less than 10mg/L total of ionic compounds of the metals copper, nickel, cobalt, particularly preferably less than 10mg/L total of ionic compounds of the metals copper, nickel, cobalt, tin, manganese, molybdenum, chromium and/or cerium, and particularly preferably less than 1mg/L in each case of ionic compounds of the metals nickel and cobalt, based in each case on the metal elements in the aqueous composition.

Similarly, in order to avoid layer formation competing with iron deposition in process step (i), it is preferred if the aqueous composition for iron deposition contains less than 20mg/L in total of water-soluble compounds of the elements Zr, ti, hf and/or Si, particularly preferably less than 5mg/L in each case, particularly preferably less than 1mg/L in each case of water-soluble compounds of the elements Zr, ti, hf or Si.

The deposition of iron on zinc from acidic aqueous compositions in the presence of iron (II) ions is described in WO 2008/135478 A1. This method is also suitable in the context of the present invention and is particularly advantageous due to its compatibility with the pH values of the subsequent phosphating of the zinc system in process step (ii). In this connection, it is therefore preferred to contact an acidic aqueous composition having a pH in the range from 2.0 to 6.0, which contains at least 50mg/L of iron (II) ions, and preferably an alpha-hydroxycarboxylic acid (preferably in a molar ratio to iron ions of from 5:1 to 1:5), and particularly preferably additionally at least one reducing agent selected from the group consisting of oxo acids of phosphorus or nitrogen and salts thereof, wherein at least one phosphorus or nitrogen atom is present in the average oxidation state, hydrazine, hydroxylamine, nitroguanidine, N-methylmorpholine-N-oxide, glucoheptonate, ascorbic acid and/or reducing sugars.

Alternatively and due to its specific efficiency in reducing the weight of the phosphate layer on the zinc surface during the subsequent zinc-based phosphating, it is particularly advantageous to deposit the iron coating from an alkaline aqueous composition, wherein the pH of the alkaline aqueous composition containing iron (II) and/or iron (III) ions is preferably not lower than 8.5, particularly preferably not lower than 9.5, very particularly preferably not lower than 10.5, but preferably not higher than 13.5, particularly preferably not higher than 12.5, and very particularly preferably not higher than 11.5.

In a preferred embodiment of such an alkaline aqueous composition, in step (i) of the process according to the invention, there is present

(A) At least 50mg/L, preferably at least 100mg/L, particularly preferably at least 200 mg/L, of iron (III) ions, and

(B) At least 100mg/L of a complexing agent selected from the group consisting of organic compounds (b 1) and/or condensed phosphates (b 2) in terms of PO4, the organic compounds (b 1) having at least one functional group selected from COOX, OPO ₃ X and/or PO ₃ X, wherein X is an H atom or an alkali metal atom and/or an alkaline earth metal atom,

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

The term "condensed phosphate" according to component (b 1) refers to metaphosphate (Me _n[P_nO_3n) which is water soluble at room temperature, biphosphate, triphosphate and polyphosphate (Me _n+2[P_nO_3n+1 ] or Me _n[H₂P_nO_3n+1) which combine an isophosphate and a cross-linked polyphosphate, wherein Me is an alkali metal atom or an alkaline earth metal atom. Of course, instead of water-soluble salts, the corresponding condensed acids of phosphoric acid can also be used for the formulation of the alkaline aqueous composition, provided that the free alkalinity is set as indicated. The mass-based proportion of the "condensed phosphate" according to component (b 1) is always calculated as the corresponding amount of PO 4. Similarly, when determining the molar ratio constituting a quantity of condensed phosphate, this quantity of condensed phosphate is always based on the equivalent weight of PO 4.

It has been found that the alkaline aqueous composition in step (i) of the process according to the invention produces an iron coating on the zinc surface which is suitable for subsequent zinc-based phosphating and that a particularly reliable dense crystalline zinc phosphate layer can be grown when the free alkalinity is less than 5 points. To apply the alkaline aqueous composition in a spray process, particularly when the free alkalinity is less than 4 points, a suitable iron coating is produced. Surprisingly, as previously mentioned, it has been found that a high iron coating exceeding 150mg/m ² on the zinc surface has proved to be disadvantageous for the process according to the invention, since in interaction with zinc-based phosphating a poor adhesion result is achieved to the organic top coating, so that the alkaline aqueous composition in step (i) has to have too high free basicity. However, the free basicity should preferably be at least 2 points in order to produce an optimal coating of at least 20mg/m ² of elemental iron-based on the zinc surface. Alkaline aqueous compositions with free basicity greater than 6 points produce high iron coatings on zinc surfaces; however, the adhesion of the optionally applied coating after step (ii) is significantly reduced by the high coating based on elemental iron, so that corrosion protection is also less effective or insufficient.

The free alkalinity is determined by titrating 2ml of the bath (preferably to 50 ml) with 0.1n acid (e.g., hydrochloric or sulfuric acid) to a pH of 8.5. The consumption of the acid solution (in ml) represents the number of points of free alkalinity.

Desirably, the alkaline aqueous composition in step (i) of the process according to the invention has a pH value of at least 9.5, particularly preferably at least 10.5. At a pH below 10.5, an iron coating of at least 20mg/m ² is formed on the zinc surface when contacted with a composition containing iron (II) and/or iron (III) ions only in the presence of a reducing agent. Such a composition for depositing an iron coating is disclosed in WO 2011/098322 A1, which contains an amino acid and a further reducing agent selected from the group consisting of oxo acids of phosphorus or nitrogen and salts thereof, wherein at least one phosphorus or nitrogen atom is present in an average oxidation state, and is thus also suitable in the context of the present invention.

In order to minimize pickling attack on the zinc surface of the component, it is further preferred that the pH of the alkaline aqueous composition in step (i) of the process according to the invention is not higher than 13.5, particularly preferably not higher than 12.5. If the component has an aluminum surface in addition to a zinc surface, it is advantageous if the pH in the composition in step (i) of the method according to the invention does not have a value above 11.5, since otherwise increased pickling attack would lead to a strongly black coloration of the aluminum surface, so-called "very black (well blackness)", which has a detrimental effect on the effectiveness of the subsequent conversion treatment, for example on the zinc-based phosphating in step (ii) of the method according to the invention, or on the acidic post-passivation of the water-soluble inorganic compounds based on elemental zirconium and/or titanium after the method according to the invention, in the case of zinc-based phosphating which is adjusted so as not to form a layer on aluminum in step (ii).

The iron ions are present predominantly in the form of iron (III) ions at the preferred predominant pH values and are present in the alkaline aqueous composition when saturated with atmospheric oxygen. In step (i) of the process according to the invention, the proportion thereof is preferably not more than 2000mg/L. Higher proportions of iron (III) ions are detrimental to process control, since the solubility of iron (III) ions in alkaline media must be maintained by a correspondingly high proportion of complexing agent, while no more advantageous properties are obtained for iron coatings on zinc surfaces. However, in step (i) of the method according to the invention, such an alkaline aqueous composition is preferred, wherein the proportion of iron (III) ions is at least 100mg/L, particularly preferably at least 200mg/L, to ensure, on the one hand, a sufficient iron coating on the zinc surface in step (i) of the method according to the invention in a treatment time of typically less than two minutes for the method and, on the other hand, to obtain a phosphate layer of excellent layer quality on the zinc surface in step (ii) of the method according to the invention.

The complexing agent according to component (b) of the alkaline aqueous composition in step (i) of the process according to the invention is preferably contained in the following amounts: so that the molar ratio of all component (b) to iron (III) ions is greater than 1:1, and particularly preferably at least 2:1, particularly preferably at least 5. It was found that the use of a stoichiometric excess of complexing agent is advantageous for process control, since it permanently maintains the proportion of iron (III) ions in the solution. Thus, precipitation of insoluble ferric hydroxide is completely inhibited, so that the alkaline aqueous composition remains permanently stable and does not deplete iron (III) ions. At the same time, a sufficient deposition of the inorganic layer containing iron ions on the zinc surface still takes place. However, for reasons of economy and resource saving, it is preferable that the molar ratio of component (b) to iron (III) ions in composition (A) is not more than a value of 10.

In a preferred embodiment, in step (i) of the process according to the invention, the alkaline aqueous composition may additionally contain at least 100mg/L of phosphate ions. Phosphate ions in this ratio require that, in addition to iron ions, phosphate ions are also the main component of the iron-containing coating produced on the zinc surface in step (i). Such a layer has been found to be advantageous for subsequent zinc-based phosphating and provides good adhesion to subsequently applied coatings in interaction with zinc-based phosphating. Thus, in step (i) of the process according to the invention, it is further preferred that the basic aqueous composition contains at least 200mg/L, particularly preferably at least 500mg/L, of phosphate ions. The performance of the passivation layer is not further positively influenced above a phosphate ion proportion of 4g/L when the zinc surface of the component is contacted with the composition (a) in step (i) of the method according to the invention, whereby the proportion of phosphate ions in the alkaline aqueous composition in step (i) of the method according to the invention should preferably be below 10g/L for economic efficiency reasons.

Thus, the ratio of iron (III) ions to phosphate ions can vary within a wide range. In step (i) of the process according to the invention, the mass-based ratio of iron (III) ions to phosphate ions in the alkaline aqueous composition is preferably in the range from 1:20 to 1:2, particularly preferably in the range from 1:10 to 1:3. An alkaline aqueous composition having such a mass ratio of iron (III) ions to phosphate ions provides, after contact with a zinc surface, a uniform black gray layer containing phosphate ions with an easily adjustable coating based on elemental iron in the range of 20-150mg/m ².

The condensed phosphate (b 2) is capable of maintaining iron (III) ions in solution in an alkaline medium by complexation. Although there are no particular restrictions on the type of condensed phosphates that can be used in the alkaline aqueous composition in step (i) of the process according to the invention, those condensed phosphates selected from pyrophosphates, tripolyphosphates and/or polyphosphates, particularly preferably from pyrophosphates, are preferred, as they are particularly readily soluble in water and are very readily available.

As organic compound (b 1) which is likewise present in the alkaline aqueous composition as complexing agent or as a substitute for condensed phosphate (b 2), preference is given to compounds whose acid form (x=h atom) has an acid number of at least 250 in step (i) of the process according to the invention. The lower acid value imparts surface active properties to the organic compound, so that the organic compound (b 1) having an acid value of less than 250 can have a strong emulsifying action as an anionic surfactant. In this case, it is further preferable that the organic compound is not a polymer and does not exceed a number average molecular weight of 5,000u, particularly preferably 1,000 u. If the preferred acid number and optionally the preferred molecular weight are exceeded, the emulsification of the organic compound (b 1) can be so pronounced that impurities in the form of oil and drawing grease carried over from the cleaning stage via the component can only be removed from the treatment stage by means of a complicated separation process for depositing the iron coating, for example by metering in cationic surfactants, so that further process parameters have to be controlled. It is therefore more advantageous to adjust the alkaline aqueous composition in step (i) of the process according to the invention so that it is only slightly emulsified to allow for conventional separation of the floating oil and fat. Anionic surfactants also have a tendency to cause significant foaming, which is particularly disadvantageous during spray application of alkaline aqueous compositions. Thus, an organic complexing agent (b 1) having an acid number of at least 250 is preferably used in the composition in step (i) of the method according to the invention. The acid number represents the amount of potassium hydroxide (in milligrams) required to neutralize 1g of the organic compound (b 1) in 100g of water according to DIN EN ISO 2114.

Preferred organic complexing agents (b 1) in the alkaline aqueous composition in step (i) of the process according to the invention are selected from the group consisting of alpha-, beta-and/or gamma-hydroxycarboxylic acids, hydroxyethane-1, 1-diphosphonic acids, [ (2-hydroxyethyl) (phosphonomethyl) amino ] -methylphosphonic acid, diethylenetriamine penta (methylenephosphonic acid) and/or aminotri- (methylenephosphonic acid) and salts thereof, particularly preferably hydroxyethane-1, 1-diphosphonic acid, [ (2-hydroxyethyl) (phosphonomethyl) amino ] -methylphosphonic acid, diethylenetriamine penta (methylenephosphonic acid) and/or aminotri- (methylenephosphonic acid) and salts thereof.

According to the invention, such alkaline aqueous compositions containing only condensed phosphates (b 2), only organic complexing agents (b 1) or mixtures of both are therefore explicitly comprised in step (i) of the process according to the invention. However, the proportion of the organic complexing agent (b 1) in the alkaline aqueous composition may be reduced to such an extent that a complexing agent (b 2) selected from condensed phosphates is present. In a particular embodiment of the process according to the invention, the alkaline aqueous composition in step (i) contains a complexing agent (b 2) selected from condensed phosphates and organic complexing agents (b 1), wherein the molar ratio of all component (b) to iron (III) ions is greater than 1:1, but the molar ratio of component (b 1) to iron (III) ions is less than 1:1, particularly preferably less than 3:4, but preferably at least 1:5. The mixture of the two complexing agents (b 1) and (b 2) is advantageous in that the condensed phosphate in the alkaline medium is in equilibrium with the phosphate ions of the alkaline aqueous composition at elevated temperature, so that the phosphate ions consumed by the layer formation on the zinc surface are slowly replenished by the condensed phosphate. However, conversely, the presence of condensed phosphate alone is insufficient to produce an iron and phosphate based coating on zinc surfaces, so that the proportion of phosphate ions in the alkaline aqueous composition in step (i) of the process according to the invention is always preferred. However, in the presence of condensed phosphates, the deposition of sparingly soluble phosphates, such as iron phosphate, is particularly inhibited by interaction with the organic complexing agent (b 1), even at high pH values above 10.5, so that alkaline aqueous compositions containing a mixture of complexing agents in step (i) of the process according to the invention are preferred, wherein it is preferably ensured that the molar ratio of component (b 1) to iron (III) ions is at least 1:5.

In order to increase the cleaning ability of the sequential components to be treated in the method according to the invention, in step (i) the alkaline aqueous composition may additionally contain a nonionic surfactant. In this case, the nonionic surfactant is preferably selected from one or more ethoxylated and/or propoxylated C10-C18 fatty alcohols having a total of at least two but not more than 12 alkoxy groups, particularly preferably ethoxy and/or propoxy groups, some of which may be present such that they are end-capped with alkyl functions, particularly preferably methyl, ethyl, propyl or butyl functions.

In a particular embodiment of the process according to the invention, the alkaline aqueous composition in step (i) comprises

A) 0.05 to 2g/L of iron (III) ions,

B) At least 0.1g/L of a complexing agent selected from the group consisting of organic compounds (b 1) and/or condensed phosphates (b 2) in terms of PO4, the organic compounds (b 1) having at least one functional group selected from COOX, OPO ₃ X and/or PO ₃ X, wherein X is an H atom or an alkali metal atom and/or an alkaline earth metal atom,

C) Phosphate ion of 0.1 to 4g/L,

D) From 0.01 to 10g/L in total of nonionic surfactants, preferably selected from one or more ethoxylated and/or propoxylated C10-C18 fatty alcohols having a total of at least two but not more than 12 alkoxy groups, particularly preferably ethoxy and/or propoxy groups, some of which may be present such that they are end-capped with alkyl functions, particularly preferably methyl, ethyl, propyl or butyl functions,

E) The ionic compounds of the metals copper, nickel, cobalt, tin, manganese, molybdenum, chromium and/or cerium amounting to less than 10mg/L, particularly preferably less than 1mg/L in each case of the ionic compounds of the metals nickel and cobalt, in each case based on the metallic element,

Wherein no more than 10g/L of condensed phosphate (b 2) is present in the form of PO4 and the molar ratio of the sum of components (b 1) and (b 2) to iron (III) ions is greater than 1:1, and wherein 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, during the sequential treatment of step (i), the component is contacted with an aqueous composition for depositing iron, in particular an alkaline aqueous composition containing iron (II) and/or iron (III) ions, at a temperature of at least 30 ℃, particularly preferably at least 40 ℃, but not more than 70 ℃, particularly preferably not more than 60 ℃ for at least 30 seconds but not more than 4 minutes. The preferred treatment or contact time in step (i) of the method according to the invention should be chosen such that an iron coating of at least 10mg/m ², preferably at least 20mg/m ² is achieved. The treatment and contact time for achieving such a minimum coating varies depending on the type of application and in particular on the flow of the aqueous liquid acting on the metal surface to be treated. During application of the composition by spraying, the smallest iron coating forms faster than in dipping applications.

Process step (ii) -phosphating of activated zinc systems:

The zinc-based phosphating of the sequential components carried out in process step (ii) is carried out by means of an acidic aqueous composition for zinc-based phosphating, which contains a phosphate of polyvalent metal cations dispersed as a particulate component, wherein the phosphate is at least partially selected from hopeite, phosphophyllite, phosphocalcifesite and/or rhodochrosite. The acidic aqueous zinc-based phosphating is thus self-activating, without the need for separate activation in advance, and is thus obtained by the corresponding addition of an amount of aqueous dispersion to an acidic aqueous composition containing components (a) - (C) according to claim 1 of the present invention.

The aqueous dispersion contains a particulate component (P) in the form of an aqueous dispersion comprising

At least one particulate inorganic compound (P1) comprising a phosphate of a polyvalent metal cation, said phosphate being at least partially selected from hopeite, phosphophyllite, phosphocalpain and/or rhodochrosite,

And at least one polymeric organic compound (P2),

Wherein the aqueous dispersion of the acidic aqueous composition used to provide zinc-based phosphating for process step (ii) is preferably added in the following amounts: the proportion by weight of phosphate of the particulate constituents from the aqueous dispersion, based on the acidic aqueous composition containing components (A) to (C), is at least 0.004g/kg, preferably at least 0.01g/kg, particularly preferably at least 0.05g/kg, very particularly preferably at least 0.08g/kg.

In an alternative or preferred embodiment, the sequentially arranged components in step (ii) of the process according to the invention are contacted with an acidic aqueous composition, wherein the acidic aqueous composition comprises

(A) 5-50g/kg of phosphate dissolved in water (calculated as PO ₄),

(B) 0.3-3g/kg zinc ion, and

(C) The free fluoride compound(s) are present,

And has free acid with a number of points greater than zero.

Wherein in process step (ii) for zinc-based phosphating, an activating aid is added continuously or discontinuously to the acidic aqueous composition in an amount sufficient under the selected conditions of zinc-based phosphating process step (ii) to maintain the properties of the acidic aqueous composition to deposit a zinc phosphate layer having a layer weight of less than 5.0g/m ², preferably less than 4.5g/m ², particularly preferably less than 4.0g/m ², very particularly preferably less than 3.5g/m ², on the hot dip galvanized steel surface (Z),

Wherein the activation aid contains a particulate component (P) in water-dispersed form, said component comprising

-And at least one polymeric organic compound (P2).

The inventive performance (hereinafter referred to as "quality of phosphating") of a zinc phosphate layer having a layer weight of less than 5.0g/m ², preferably less than 4.5g/m ², particularly preferably less than 4.0g/m ² and very particularly preferably less than 3.5g/m ², is to be examined on a substrate (Z) which has been cleaned and degreased and which has not been subjected to any further wet-chemical pretreatment step prior to contact with the acidic aqueous composition according to the inventive method in step (ii) and after deposition of iron on the zinc surface in step (i), on a hot-dip galvanized steel surface (Z). To check the phosphating quality of the acidic aqueous composition, 2% by weight in deionized water (k < 1. Mu. Scm ^-1) was used firstC-AK 1565A and 0.2 wt%/>The alkaline cleaner of C-AD 1270 cleans hot dip galvanized steel (Z) by soaking for 5 minutes at pH 11.0 and 55 ℃. The substrate (Z) cleaned and degreased in this way is rinsed with deionized water (k <1 μm ^-1) at room temperature and then, depending on the process conditions chosen, supplied to the treatment stage according to method steps (i) and (ii). According to the chosen process conditions means that the resulting target layer weight on the hot-dip galvanized steel (Z) will be below 5.0g/m ², preferably below 4.5g/m ², particularly preferably below 4.0g/m ² and very particularly preferably below 3.5g/m ², at the same temperature, application duration and bath cycle involved, and using wet chemical treatment stages suitable for the defined phosphating qualities according to the invention. Thus, in the current method according to the invention, the quality of phosphating can be determined by: the cleaned and degreased sheet of hot dip galvanized steel (Z) is introduced together with the sequentially arranged components for method steps (i) and (ii) and then the layer weight of zinc phosphate is increased on the sheet and thus the phosphating quality of the acidic aqueous composition for zinc-based phosphating is determined in method step (ii). The cleaned and degreased hot dip galvanized steel (Z) sheet is preferably rigidly connected to the component or the transport frame in its function as a test sheet for determining the phosphating quality, in order to ensure that the flow conditions during the transport of the component together with the transport frame through the phosphating bath are reproduced as similarly as possible for the test sheet. For this purpose, the test plate should ideally be connected to the component or the transport frame in such a way that the transport of the test plate together with the component and the transport frame has no influence on the flow conditions to be considered compared to transporting the component and the transport frame without such a test plate, and the flow conditions are in both cases substantially identical and thus correspond substantially to the flow conditions of at least a part of the sequentially arranged components. This can be achieved, for example, by adapting the dimensions and/or shape of the test plate to the dimensions and/or shape of the components and/or transport frames, which are in each case arranged adjacent to the test plate. In this case, it is conceivable, in particular when the test plate is arranged on an outer surface portion of the component or the transport frame, for the test component to be correspondingly smaller in size than said surface portion, for example in order to prevent the test component from protruding beyond the surface portion. Alternatively or additionally, the test component may follow the curvature or other planar deviations of the surface portions or the transport frame. It has proven to be particularly advantageous to select a sufficiently small plate portion compared to the dimensions of a suitable outer surface of the component, wherein the outer surface is particularly suitable if it is located at a position with particularly low curvature or at a position of lowest curvature of the component, and then the test plate metal is mounted substantially parallel so as to be spaced apart along the surface normal of the outer surface. The phosphating quality is directly obtained during the sequential treatment of such components, which also have the surface of the hot-dip galvanised steel (Z) as zinc surface. In a preferred embodiment of the method, such a component is preferred.

For phosphating quality it is furthermore preferred that if the contact is prolonged by one minute, the layer weight on the hot dip galvanized steel (Z) increases not more than 0.2g/m ² and thus the layer formation under the selected conditions is already within the self-limiting range, ensuring the properties of the acidic aqueous composition for zinc-based phosphating to produce a dense crystalline zinc phosphate layer in step (ii) of the process according to the invention. It is therefore preferred that in the zinc-based phosphating process step an amount of an activating aid is added which is sufficient under the selected conditions of the zinc-based phosphating process step in the process according to the invention to maintain the properties of the acidic aqueous composition to deposit a zinc phosphate layer having a layer weight of less than 5.0g/m ², preferably less than 4.5g/m ², particularly preferably less than 4.0g/m ², very particularly preferably less than 3.5g/m ² on the hot dip galvanized steel surface (Z), wherein the layer weight obtained under the selected conditions of the zinc-based phosphating process step (ii) in the process according to the invention does not increase by more than 0.2g/m ² when the contact time with the acidic aqueous composition is prolonged by 60 seconds.

In general, in the method according to the invention, the phosphating quality is determined and monitored by means of a hot-dip galvanized steel (Z) which has been cleaned and degreased as described above, the zinc-based phosphating method steps also being carried out at regular intervals during the sequential treatment, and then the layer weight determination being carried out. As already mentioned, the phosphating quality is directly obtained during the sequential treatment of such components, which also have at least one surface of the hot-dip galvanized steel (Z) as zinc surface. As long as the phosphating quality of the acidic aqueous composition is ensured by the metering of the activating aid, a uniform, closed and dense crystalline zinc phosphate coating is deposited on the component having metallic zinc, iron and aluminum surfaces within a treatment time of typically 20 seconds to 5 minutes.

The layer weight of zinc phosphate is determined within the scope of the invention by using 5% by weight of an aqueous solution of CrO ₃ as pickling solution which is brought into contact with a defined area of phosphated material or component for 5 minutes at 25 ℃ immediately after phosphating of the zinc system and rinsing with deionized water (κ <1 μm ^-1), and subsequently determining the phosphorus content in the same pickling solution by means of ICP-OES. The layer weight of zinc phosphate can be found by multiplying the amount of phosphorus relative to the surface area by a factor of 6.23.

In the process according to the invention, an activating aid is added to the acidic aqueous composition for zinc-based phosphating for the purpose of maintaining the phosphating quality in process step (ii) for zinc-based phosphating. In order to maintain the quality of the phosphating during the sequential treatment, the addition can be carried out by means of continuous or discontinuous metering into the system tank. If the pretreatment of the sequential components directly follows one another and a reduction in the phosphating quality over time can be ascertained, continuous metering is preferred, so that further a certain amount of activator can be metered in continuously over time. The advantage of this method is that after starting the pretreatment line and determining the material flow for metering in the activation aids and other active components, no further inspection of the phosphating quality is necessary as long as the sequential treatment remains unchanged in terms of time and the properties of the components to be treated and the treatment parameters in step (ii) of the zinc-based phosphating process. However, if a constant mode of operation in sequential processing cannot be ensured or is undesirable for systematic reasons, discontinuous metering of the activation aid is advantageous and may even be sensible. In this case, the phosphating quality of the acidic aqueous composition is preferably monitored continuously or at defined time intervals in step (ii), and if the layer weight on the hot-dip galvanized steel (Z) reaches a specific value of less than 5.0g/m ², preferably less than 4.5g/m ², particularly preferably less than 4.0g/m ² and very particularly preferably less than 3.5g/m ², then a defined amount of activating auxiliary is metered in. Continuous or quasi-continuous phosphating mass measurements over defined time intervals can also be carried out using surrogate data relating to the actual zinc phosphate layer weight. Non-destructive measurement of layer thickness (e.g., using eddy current or even non-contact optical measurement methods such as ellipsometry or spectral reflectance measurement) provides suitable surrogate data for zinc phosphate layer weight that can be reliably measured on the zinc surface of the part on a pretreatment line and can be correlated to actual layer weight on hot dip galvanized part steel (Z). The crystallite size and thus the determination of the roughness by means of optical profilometry can also provide surrogate data for the layer weight, since on hot-dip galvanized steel (Z) a higher layer weight is associated with a lower crystallite number density, whereas crystallites are relatively large, so that the roughness increases with layer weight.

It has been found that if the activating auxiliary is metered in continuously or discontinuously in an amount which is suitable for maintaining a steady-state amount of the particulate component (P) in the acidic aqueous composition during the pretreatment of the sequentially arranged components, said steady-state amount preferably being at least 0.001g/kg, particularly preferably at least 0.005g/kg, more particularly preferably at least 0.01g/kg, the phosphating quality is in most cases already sufficient. This applies in particular to the contact of the acidic aqueous composition by spraying, however in the case of impregnation applications, the acidic aqueous composition for zinc-based phosphating should contain a steady-state amount of the particulate component (P) of preferably at least 0.002g/kg, particularly preferably 0.01g/kg, more particularly preferably 0.02 g/kg.

The present invention thus surprisingly shows that activation of the metal surface can be carried out by metering an activation aid (as known in the prior art and as described, for example, in WO 98/39498 A1) directly into the acidic aqueous treatment solution for zinc-based phosphating in step (ii), whereby a uniform, closed and dense crystalline zinc phosphate coating with high charge transfer resistance is grown on the metal surface, wherein such a high quality phosphate coating for corrosion protection and coating adhesion is achieved on the zinc surface as a result of the deposition of iron in process step (i). The present invention exploits this effect in that the sequential treatment of the components is based on zinc-based phosphating by means of an acidic aqueous composition which contains, in addition to zinc ions, phosphate ions and free fluoride, a particulate component (P) dispersed in water, and/or on maintaining the quality of the phosphating by metering in an acidic aqueous composition for zinc-based phosphating an activating aid. For the desired phosphating quality, in this case, it is possible to switch to the separate addition of the aqueous dispersion or the metering of the activating aid, each containing the particulate component (P), without the parts arranged in succession prior to the zinc-based phosphating process step having to be subjected to a wet-chemical activation stage, for example based on the aqueous dispersion or the activating aid. This may save complete process steps including necessary bath maintenance, circulation, temperature management and chemical addition, for example using water-soluble condensed phosphates, so that for the first time an extremely resource-saving and economical operation of the pretreatment line for zinc-based phosphating is possible.

For the dispersed particulate component (P) and the at least one particulate inorganic compound (P1) or polymeric organic compound (P2), the definitions and preferred specifications listed below apply, whether the dispersed particulate component (P) is part of an aqueous dispersion for providing a self-activating acidic aqueous composition for zinc-based phosphating in process step (ii) of the process according to the invention or an activating aid for maintaining the activating properties of the acidic aqueous composition. Hereinafter, for simplicity, reference is made only to the activating aid. Accordingly, statements about the activation aids correspondingly apply to the provision of aqueous dispersions of self-activating acidic aqueous compositions for zinc-based phosphating.

The activating auxiliaries which can be used according to the invention, i.e. which maintain the phosphating quality during the metering into the acidic aqueous zinc-phosphating composition, or which are provided for the first time in step (ii) for the acidic aqueous zinc-phosphating composition, are aqueous dispersions and thus contain, in water-dispersed form, a particulate component (P) which comprises at least one phosphate salt containing polyvalent metal cations, which is at least partly selected from the group consisting of hopeite, phosphophyllite, phosphohalcone and/or rhodochrosite, and at least one polymeric organic compound (P2).

The use of polyvalent metal cations in the form of phosphates is responsible for good activation performance or suitability of the activation aids to maintain the phosphating quality of the acidic aqueous compositions for zinc-based phosphating, so that in the dispersed particulate component (P) the phosphates should be contained in sufficiently high proportions in the activation aids. The proportion of phosphate contained in the at least one particulate inorganic compound (P1) is therefore preferably at least 25% by weight, particularly preferably at least 35% by weight, more particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight, based on the particulate component (P) dispersed in the activating aid. The dispersed particulate component (P) of the activation aid is the solids content remaining after drying of a defined partial volume of ultrafiltration retentate of the activation aid, the nominal retention limit of said ultrafiltration being 10kD (NMWC: nominal molecular weight cut-off). Ultrafiltration was performed by adding deionized water (k <1 μm ^-1) until the conductivity was measured in the filtrate to be below 10 μm ^-1. The inorganic particulate component of the activation aid is thus the inorganic particulate component that remains when the particulate component (P) obtained from the dried ultrafiltration retentate is pyrolyzed in a reaction furnace by: the CO ₂ -free oxygen stream is supplied at 900 ℃ without a catalyst or other additive mixture until the infrared sensor provides the same signal at the outlet of the reactor as the CO ₂ -free carrier gas (blank value). The phosphate contained in the inorganic particle component was directly measured as phosphorus content from acid digestion after acid-digestion of the component with 10 wt% HNO ₃ aqueous solution at 25 ℃ for 15 minutes by means of atomic emission spectrometry (ICP-OES).

Once a sufficient amount of the active component of the activation aid is added to the acidic aqueous composition for zinc-based phosphating, the active component of the activation aid promotes the formation of a uniform, closed and dense crystalline phosphate coating on the metal surface, in particular on the zinc surface, and in this sense activates the metal surface, said active component comprising mainly phosphate which in turn is selected at least partly from hopeite, phosphophyllite, phosphozincite and/or rhodochrosite, preferably from hopeite, phosphophyllite and/or phosphophyllite, particularly preferably from hopeite and/or phosphophyllite, very particularly preferably from hopeite. The maintenance of the phosphating quality in the acidic aqueous composition is therefore essentially based on the phosphate in particulate form contained in the metered-in activation aid. Without considering the water of crystallization, hopeite stoichiometrically contains Zn ₃(PO₄)₂ and nickel-and manganese-containing variants Zn ₂Mn(PO₄)₃、Zn₂Ni(PO₄)₃, whereas phosphophyllite consists of Zn ₂Fe(PO₄)₃, hopeite consists of Zn ₂Ca(PO₄)₃, and rhodochrosite consists of Mn ₃(PO₄)₂. The presence of crystalline phases hopeite, phosphophyllite, phosphogalvanneate and/or rhodochrosite in the activation aid can be demonstrated by means of X-ray diffraction (XRD) after separation of the particulate component (P) by ultrafiltration with a nominal cut-off limit of 10kD (NMWC: nominal molecular weight cut-off) as described above and drying the cut-off to a constant mass at 105 ℃.

Since it is preferred that a phosphate comprising zinc ions and having a certain crystallinity is present, in the process according to the invention, in order to form a strongly adherent crystalline zinc phosphate coating, it is preferred that the activation aid comprises at least 20 wt.%, particularly preferably at least 30 wt.%, more particularly preferably at least 40 wt.% zinc in the inorganic particulate component, based on the phosphate content of the inorganic particulate component (calculated as PO ₄).

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

The polymeric organic compound (P2) stabilizing the particulate component has a significant influence on the effectiveness of the particulate component (P) metered in via the activating aid. The choice of polymeric organic compound was found to be decisive for the degree of activation of the metal surface in the acidic aqueous composition for zinc-based phosphating in step (ii), which activation is known to be caused by dispersed multivalent phosphate salts, and surprisingly, as shown in the present invention, said activation may also occur simultaneously with layer formation.

In the context of the present invention, an organic compound is a polymer if its weight average molar mass is greater than 500 g/mol. In this case, the molar mass is determined using a molar mass distribution curve of the sample with the relevant reference value, which curve is established experimentally at 30 ℃ by means of size exclusion chromatography using a concentration-dependent refractive index detector and calibrated with polyethylene glycol standards. According to the banding method, the average molar mass is evaluated by means of a computer using a third-order calibration curve. Hydroxylated polymethacrylates are suitable as column materials, and aqueous solutions of 0.2mol/L sodium chloride, 0.02mol/L sodium hydroxide and 6.5mmol/L ammonium hydroxide are suitable as eluents.

It was found that if the polymeric organic compound (P2) for dispersing the particulate inorganic compound (P1) comprises at least partly styrene and/or an alpha-olefin having not more than 5 carbon atoms, wherein the polymeric organic compound (P2) additionally has units of maleic acid, its anhydride and/or its imide in its side chains and preferably additionally has polyoxyalkylene units, particularly preferably polyoxyalkylene units, in the zinc-based phosphating process step, the maintenance of the phosphating quality and thus the activation of the metal surface is particularly well achieved when contacted with the acidic aqueous composition, i.e. with relatively small amounts of active components of the activating aid. Therefore, in the particulate component (P) of the activating aid, such a polymeric organic compound (P2) is preferable according to the present invention.

In this case, the alpha-olefin is preferably selected from ethylene, 1-propylene, 1-butene, isobutene, 1-pentene, 2-methyl-but-1-ene and/or 3-methyl-but-1-ene, particularly preferably from isobutene. It is clear to the person skilled in the art that the polymeric organic compound (P2) contains these monomers as building blocks in unsaturated form, which monomers are covalently linked to each other or to other building blocks.

Representative of suitable commercially available polymeric organic compounds (P2) are, for example,CX 4320 (BASF SE), a maleic acid-isobutylene copolymer modified with polypropylene glycol; /(I)Dispers752W (Evonik Industries AG), a maleic acid-styrene copolymer modified with polyethylene glycol; or/>490 Mu nzing 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 polymeric organic compounds (P2) which comprise styrene at least in part.

The colloidally stabilised polymeric organic compound (P2) of the particulate component (P) for the activation aid preferably has polyoxyalkylene units which in turn preferably comprise 1, 2-ethanediol and/or 1, 2-propanediol, particularly preferably comprise both 1, 2-ethanediol and 1, 2-propanediol, the proportion of 1, 2-propanediol in the total polyoxyalkylene units preferably being at least 15% by weight, but particularly preferably not more than 40% by weight, based on the total polyoxyalkylene units. Furthermore, the polyoxyalkylene unit is preferably contained in the side chain of the polymeric organic compound (P2). The proportion of polyoxyalkylene units in the total polymeric organic compound (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 the dispersibility of the compound.

In order to anchor the polymeric organic compound (P2) with the inorganic particulate component (P1) of the activating aid, which is at least partially formed by polyvalent metal cations in the form of phosphates selected from hopeite, phosphophyllite, phosphohalcone and/or rhodochrosite, and to improve the stability and activation ability of the particulate component (P) in the acidic aqueous composition of zinc-based phosphating, the organic polymeric compound (P2) also has an imidazole unit, preferably an imidazole unit in a side chain, particularly preferably as a component of the polyoxyalkylene unit of the polymeric organic compound (P2).

In a preferred embodiment, the amine number of the organic polymeric compound (P2) is at least 25mg KOH/g, particularly preferably at least 40mg KOH/g, but preferably less than 125mg KOH/g, particularly preferably less than 80mg KOH/g, and thus, in a preferred embodiment, the polymeric organic compound in the particulate component (P) of the activation aid as a whole also has these preferred amine numbers. In each case, the amine number was determined by: about 1g of the relevant reference value-the organic polymeric compound (P2) or the polymeric organic compound in the particulate component (P) as a whole-was weighed into 100ml of ethanol and the indicator bromophenol blue was titrated with 0.1N HCl titration until the color became yellow at a temperature of 20℃ethanol solution. The exact mass of the HCl titration used, in milliliters, multiplied by the factor 5.61 divided by the weight in grams, corresponds to the amine number (in mg KOH/g relative reference).

It has therefore proved advantageous for the polymeric organic compound (P2), preferably also the entire polymeric organic compound in the particulate component (P), to have an acid number of at least 25mg KOH/g, but preferably less than 100mg KOH/g, particularly preferably less than 70mg KOH/g, according to DGF C-V2 (06) (month 4 of 2018) in order to ensure a sufficient number of polyoxyalkylene units. It is also preferred that the polymeric organic compound (P2), preferably also all polymeric organic compounds in the particulate component (P), have a hydroxyl number of less than 15mg KOH/g, particularly preferably less than 12mg KOH/g, very particularly preferably less than 10mg KOH/g, which hydroxyl number is in each case determined according to method a of 01/2008:20503 of european pharmacopoeia 9.0.

For stable dispersion of the inorganic particulate component in the activation aid, it is sufficient that the proportion of the polymeric organic compound (P2), preferably of the total polymeric organic compound in the particulate component (P), is at least 3% by weight, particularly preferably at least 6% by weight, but preferably not more than 15% by weight, based on the particulate component (P). The dispersed particulate component (P) of the activation aid is the solids content remaining after drying of a defined partial volume of ultrafiltration retentate of the activation aid, the nominal retention limit of said ultrafiltration being 10kD (NMWC: nominal molecular weight retention). Ultrafiltration was performed by adding deionized water (k <1 μm ^-1) until the conductivity was measured in the filtrate to be below 10 μm ^-1.

The activating auxiliaries preferably contain not more than 40% by weight of particulate component (P) based on the agent, since otherwise the stability of the dispersion and the technical handling behavior of the agent metered continuously or discontinuously into the zinc-phosphating acidic aqueous compositions by means of metering pumps are no longer ensured or at least complicated. This applies in particular to the overall low amount of particulate component (P) required to maintain the phosphating quality of the acidic aqueous composition for the reference amount of zinc phosphating. However, it is advantageous for the activation aid to be provided in the form of a dispersion which is as stable as possible and at the same time as highly concentrated as possible. This is especially achieved when dispersing the particulate inorganic compound (P1) with the preferred polymeric organic compound (P2), whereby an activating aid containing at least 5 wt%, but preferably not more than 30 wt% of the particulate component (P) based on the agent is preferably used.

In such concentrated aqueous dispersions of activating auxiliaries, i.e. those having a proportion of the particulate component (P) of 5% by weight, based on the reagent, the activating auxiliaries are additionally characterized in the process according to the invention by a D50 value of greater than 10. Mu.m, which is correspondingly preferred. Agglomerates of the dispersed particles contained in the dispersion produce thixotropic flow characteristics that facilitate the handling behavior of the activation aid. The tendency of the agglomerates to have a high viscosity at low shear favors their long shelf life, whereas the loss of viscosity when sheared renders them pumpable. Advantageous flow properties can also be obtained if the dispersion does not significantly exceed a D90 value of 150 μm; thus, according to the invention, the D90 value of the aqueous dispersion is preferably less than 150. Mu.m, preferably less than 100. Mu.m, in particular less than 80. Mu.m. In the context of the present invention, the D50 value or the D90 value represents a particle size which is not exceeded by the particle constituents contained in 50% by volume or 90% by volume, respectively, of the aqueous dispersion. According to ISO 13320:2009, the D50 value or D90 value may be determined as follows: using spherical particles and the refractive index of the scattering particles nd=1.52-i·0.1, the activation aid in the form of a concentrated aqueous dispersion was diluted to 0.05% by weight of the dispersed particle component at 20 ℃ with a corresponding amount of deionized water (k <1 μscm ^-1), immediately after which it was determined by volume-weighted cumulative particle size distribution by means of scattered light analysis according to Mie theory. Dilution was performed in such a way that an amount of concentrated dispersion corresponding to a volume of 200ml of deionized water was added to a sample container from the LA-950V2 particle size analyzer of manufacturer Horiba ltd. And mechanically circulated there into the measuring chamber (circulation pump on LA-950V2 was set: 5 stage = 1167rpm, volume flow rate 3.3 liters/min). The particle size distribution was measured within 120 seconds after the dispersion was added to the dilution volume.

The presence of a thickener is advantageous for preventing irreversible agglomeration of the primary particles of the particulate component (P), in particular if the activating aid is present in the form of the concentrated dispersion described above. Thus, in a preferred embodiment of the method according to the invention, the activation aid contains a thickening agent, preferably in an amount in the range of a shear rate of from 0.001 to 0.25 reciprocal seconds, such that the activation aid has a maximum dynamic viscosity of at least 1000 Pa-s, but preferably below 5000 Pa-s, at a temperature of 25 ℃, and preferably results in a shear thinning behavior, i.e. a decrease in viscosity with increasing shear rate, resulting in a shear rate at 25 ℃ that is higher than those present at the maximum dynamic viscosity, such that the activation aid has an overall thixotropic flow behavior. In this case, the viscosity in the specific shear rate range can be determined by means of a cone-plate viscometer with a cone diameter of 35mm and a gap width of 0.047 mm.

Within the meaning of the present invention, a thickener is a polymeric chemical compound or a defined mixture of chemical compounds, which has a Brookfield viscosity of at least 100 mpa.s at a shear rate of 60rpm (=revolutions per minute) using a No. 2 rotor as a component of 0.5% by weight in deionized water (k <1 μscm ^-1) at a temperature of 25 ℃. When determining the properties of the thickener, the mixture should be mixed with water in such a way that the corresponding amount of polymeric chemical compound is added to the aqueous phase at 25℃while stirring, and then the air bubbles in the homogenized mixture are removed in an ultrasonic bath and left for 24 hours. Then, immediately after a shear rate of 60rpm was applied with a rotor No. 2, the measurement of viscosity was read within 5 seconds.

The activating assistants preferably comprise a total of at least 0.5% by weight, but preferably not more than 4% by weight, particularly preferably not more than 3% by weight, of one or more thickeners, the total proportion of polymeric organic compounds in the non-particulate constituents of the aqueous dispersion further preferably not more than 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 described above after drying to a constant mass at 105 ℃, i.e. after separation of the particulate component by means of ultrafiltration.

Certain types of polymeric compounds are particularly suitable thickeners and are also readily commercially available. The thickener is therefore preferably selected from polymeric organic compounds which in turn are preferably selected from polysaccharides, cellulose derivatives, aminoplasts, polyvinyl alcohols, polyvinylpyrrolidone, polyurethanes and/or urea urethane resins, and particularly preferably from urea urethane resins, in particular urea urethane resins as mixtures of polymeric compounds resulting from the reaction of polyvalent isocyanates with polyols and monoamines and/or diamines. In a preferred embodiment, the urea urethane resin is derived from a polyvalent isocyanate, preferably selected from the group consisting of 1, 4-tetramethylene diisocyanate, 1, 6-hexamethylene diisocyanate, 2 (4), 4-trimethyl-1, 6-hexamethylene diisocyanate, 1, 10-decamethylene diisocyanate, 1, 4-cyclohexylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2, 6-toluene diisocyanate, 2, 4-toluene diisocyanate and mixtures thereof, p-xylylene diisocyanate and m-xylylene diisocyanate and 4,4' -diisocyanato dicyclohexylmethane, particularly preferably selected from the group consisting of 2, 4-toluene diisocyanate and/or m-xylylene diisocyanate. In a particularly preferred embodiment, the urea urethane resin is produced from a polyol selected from the group consisting of polyoxyalkylene glycols, particularly preferably from the group consisting of polyoxyalkylene glycols, which in turn preferably comprise at least 6, particularly preferably at least 8, more particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23, alkylene oxide units.

Urea urethane resins particularly suitable and therefore preferred according to the invention can be obtained by: a diisocyanate, such as toluene-2, 4-diisocyanate, is first reacted with a polyol, such as polyethylene glycol, to form an NCO-terminated urethane prepolymer, and then further reacted with a primary monoamine and/or a primary diamine, such as m-xylylenediamine. Particularly preferred are urea urethane resins having neither free nor blocked isocyanate groups. As an ingredient of the activator, this urea urethane resin promotes the formation of loose agglomerates of primary particles, which prevent further agglomeration and dissociate into primary particles upon metering into an acidic aqueous composition for zinc-based phosphating. To further facilitate this performance characteristic, it is preferable to use as a thickener a urea urethane resin having neither free or blocked isocyanate groups nor terminal amine groups. Thus, in a preferred embodiment, the thickener which is a urea urethane resin has an amine number of less than 8mg KOH/g, particularly preferably less than 5mg KOH/g, more particularly preferably less than 2mg KOH/g, which amine number is determined in each case according to the method as described previously for the organic polymeric compound (P2). Since the thickener is substantially dissolved in the aqueous phase of the activation aid and can therefore be classified as a non-particulate component, while component (P2) is substantially incorporated in the particulate component (P), an activation aid is preferred in which all polymeric organic compounds in the non-particulate component preferably have an amine number of less than 16mg KOH/g, particularly preferably less than 10mg KOH/g, more particularly preferably less than 4mg KOH/g. It is further preferred that the urea urethane resin has a hydroxyl number in the range of 10 to 100mg KOH/g, particularly preferably 20 to 60mg KOH/g, determined according to method a from european pharmacopoeia 9.0, 01/2008:20503. Regarding the molecular weight, it is advantageous and therefore preferred according to the invention for the weight average molar mass of the urea urethane resin to be in the range from 1000 to 10000g/mol, preferably in the range from 2000 to 6000g/mol, in each case determined experimentally, as described above in connection with the definition of the polymeric organic compound according to the invention.

The activation aid is an aqueous dispersion which preferably has a pH in the range from 6.5 to 8.0 and particularly preferably is free of any pH-regulating water-soluble compounds having a pK _S value of less than 6 or a pK _B value of less than 5.

The activation aid may also contain adjuvants, for example adjuvants selected from preservatives, wetting agents and defoamers, which are contained in amounts required for the function concerned. The proportion of auxiliary agents, particularly preferably the proportion of other compounds than thickeners in the non-particulate component, is preferably less than 1% by weight.

The activation aid may preferably be obtained in the form of a concentrated aqueous dispersion by:

i) Pigment pastes are provided by grinding and milling 10 parts by mass of inorganic particulate compound (P1) together with 0.5 to 2 parts by mass of polymeric organic compound (P2) in the presence of 4 to 7 parts by mass of water until a D50 value of less than 1 μm is reached, said D50 value being determined by dynamic light scattering after dilution with water by a factor of 1000 (for example by means of MALVERN PANALYTICAL GmbH Nano ZS);

ii) diluting the pigment paste with an amount of water, preferably deionized water (k < 1. Mu. Scm ^-1) or technical water and a thickener, such that at least 5% by weight of the dispersed particulate component (P) and a maximum dynamic viscosity of at least 1000 Pa.s in the shear rate range of 0.001 to 0.25 reciprocal seconds at a temperature of 25 ℃ are set,

Wherein a preferred embodiment of the activation aid is obtained in a similar manner by selecting the amounts of the respective components (P1), (P2) and the thickener which can be provided or required in each case. This concentrated aqueous dispersion has excellent stability and, due to its thixotropic flow behaviour, also has good pumpability, so that the concentrated dispersion can be metered directly into the zinc-based phosphating system tank in a controlled manner.

With respect to the acidic aqueous composition for zinc-based phosphating, it is necessary for the formation of a homogeneous, closed zinc phosphate layer that, in step (ii) of the process according to the invention, the composition contains at least

(A) 5-50g/kg of phosphate dissolved in water (calculated as PO ₄),

(B) 0.3-3g/kg zinc ion, and

(C) The free fluoride compound(s) are present,

And free acids with points greater than zero.

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

The proportion by dot of free acid in the acidic aqueous composition of zinc-based 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 spot-wise proportion of free acid was determined by diluting an acidic aqueous composition to 60ml in a sample volume of 10ml and titrating with 0.1N sodium hydroxide solution to a pH of 3.6. The ml consumption of sodium hydroxide solution indicates the number of free acid points.

The preferred pH of the acidic aqueous composition is generally above 2.5, particularly preferably above 2.7, but preferably below 3.5, particularly preferably below 3.3. "pH" as used in the context of the present invention corresponds to the negative decimal logarithm of the hydronium ion activity at 20℃and can be determined by means of a pH-sensitive glass electrode.

An amount of free fluoride or free fluoride ion source is essential to the layered zinc-based phosphating process. If the component comprising, if appropriate, in addition to the zinc surface, also the iron or aluminum surface is to be subjected to a zinc-based phosphating in a layered manner, it is advantageous, for example, in the zinc-based phosphating of motor vehicle bodies made at least in part of aluminum, if the amount of free fluoride in the acidic aqueous composition in step (ii) is at least 0.5mmol/kg, particularly preferably at least 2 mmol/kg. The concentration of free fluoride should not exceed values above which the phosphate coating has loose adhesion that can be easily wiped off, since such defects often cannot be compensated for even by increasing the metering of the activating aid or by increasing the steady-state amount of particulate component (P) in the acidic aqueous composition for zinc-based phosphating. Thus, in step (ii) of the process according to the invention, a concentration of free fluoride in the acidic aqueous composition of zinc-based phosphating of less than 15mmol/kg, particularly preferably less than 10mmol/kg, more particularly preferably less than 8mmol/kg is advantageous and is therefore also preferred.

The amount of free fluoride can be determined potentiometrically in the relevant acidic aqueous composition at 20℃by means of a fluoride-sensitive measuring electrode after calibration with a fluoride-containing buffer solution without pH buffer. Suitable sources of 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. Thus, in the phosphating process according to the invention, the source of free fluoride is preferably selected from hydrofluoric acid and its water-soluble salts and/or complex fluorides of the elements Zr, ti and/or Si. Hydrofluoric acid salts are water-soluble within the meaning of the present invention if their solubility in deionized water (k < 1. Mu. Scm ^-1) at 60 ℃ is at least 1g/L (in F).

In order to suppress so-called "pinholes" on the surface of metallic materials made of zinc, in such a method according to the invention, the free fluoride source in step (ii) is preferably at least partly selected from the complex fluorides of the element Si, in particular from hexafluorosilicic acid and salts thereof. The term "pinholes" is understood by those skilled in the phosphating arts to mean the phenomenon of localized deposition of amorphous white zinc phosphate in a crystalline phosphate layer on a treated zinc surface or on a treated galvanized or alloy galvanized steel surface.

In the process according to the invention, accelerators known in the prior art can be added to the acidic aqueous composition to form layers more rapidly. These accelerators are preferably selected from the group consisting of 2-hydroxymethyl-2-nitro-1, 3-propanediol, nitroguanidine, N-methylmorpholine-N-oxide, nitrite, hydroxylamine and/or hydrogen peroxide. It was found that when using nitroguanidine or hydroxylamine as accelerator, a relatively low metering of the activation aid is required or a low steady-state amount of the particulate component (P) has to be maintained in the acidic aqueous composition for zinc-based phosphating in step (ii), so that nitroguanidine or hydroxylamine, in particular nitroguanidine, is particularly preferred as accelerator in the acidic aqueous composition in step (ii) of the process according to the invention in view of the particularly low material use of the activation aid for maintaining the phosphating quality.

From an ecological point of view, particular preference is given to embodiments in which less than 10ppm of nickel and/or cobalt ions are contained in total in the acidic aqueous composition of zinc-based phosphating used in step (ii) of the process according to the invention.

Furthermore, in the process according to the invention, it is also possible to use additives known in the art in the zinc-based phosphating process.

Optional method steps:

In a preferred embodiment of the process according to the invention, the sequential components are therefore not contacted with a colloid-activated aqueous solution containing hopeite, phosphophyllite, middling and/or rhodochrosite, preferably phosphate of polyvalent metal cations, or slightly soluble salts of elemental Ti in the particulate component, prior to contact with the acidic aqueous composition in step (ii) of the zinc-based phosphating process. The sequential elements are particularly preferably not contacted with an aqueous colloidal solution for activating the surface of the element for zinc-based phosphating prior to contact with the acidic aqueous composition in step (ii) of the zinc-based phosphating process, and very particularly preferably not subjected to an activation stage for activating the surface of the element for zinc-based phosphating prior to contact in step (ii) of the process.

However, it is often not possible to omit the cleaning and degreasing stages as a method step upstream of zinc-based phosphating in step (ii) and iron deposition in step (i). In order to obtain a reproducible layer coating which is as uniform as possible, in a preferred embodiment of the method according to the invention, at least the metal surface of the component is cleaned and, if necessary, degreased, either in a separate cleaning stage or together with method step (i). The cleaning is preferably carried out by contact with an aqueous, preferably neutral or alkaline cleaning agent, wherein process step (i) is immediately followed by a cleaning stage, with or without an intermediate rinsing step, preferably without an intermediate rinsing step.

In the case of cleaning and optionally degreasing of components, alkaline cleaning is characterized by the following facts: metal surfaces, particularly surfaces containing metallic aluminum, whether as materials or as alloy components of hot dip galvanized steel, are pickled, which results in additional standardization of the metal surfaces and thus facilitates the growth of a uniform zinc phosphate coating.

The cleaning phase, or the combined cleaning and iron-forming phase, is preferably carried out without contact with an aqueous, preferably neutral or alkaline, cleaning agent containing a particulate component comprising hopeite, phosphophyllite, brushite and/or a slightly soluble salt of elemental Ti, since, as mentioned above, any activation of the metal surface prior to phosphating the zinc system in step (ii) can be omitted according to the invention. As previously mentioned, the rinsing step after cleaning is optional and in the context of the present invention is dedicated to the complete or partial removal from the component to be treated of the soluble residues, particles and active components carried by adhering to the component from the previous wet chemical treatment step (in this case the cleaning and degreasing phase), whereas the rinsing liquid itself does not contain active components based on metallic or semi-metallic elements that have been consumed only by contacting the metallic surface of the component with the rinsing liquid. For example, the rinse solution may simply be municipal or deionized water, or if desired, a rinse solution containing a surface active compound to enhance wettability by means of the rinse solution.

Parts:

Since the quality of phosphating on hot-dip galvanized steel is technically optimized in the method according to the invention, a method according to the invention in which at least part of the components having a sequence of zinc surfaces also comprises the hot-dip galvanized steel surface is naturally also preferred. In principle, the phosphating quality of the acidic aqueous composition maintained in step (ii) by the addition of the activating auxiliary agent makes it possible for parts manufactured in multimetal structures, such as automobile bodies, to be zinc-phosphated with very good properties and to obtain also very uniform, closed and dense zinc phosphate coatings on the surfaces of iron and aluminum. In the method according to the invention, the components arranged in a preferred order therefore also have a metallic iron surface or, in particular for lightweight structures in the manufacture of vehicle bodies, an additional aluminum surface. In a particularly preferred embodiment, particularly in the manufacture of vehicle bodies, the components have surfaces of the metals zinc, iron and aluminum next to each other.

In the process according to the invention, it is preferred that the sequentially arranged components are contacted with the acidic aqueous composition in step (ii) for at least a period of time sufficient to deposit a layer weight of at least 1.0g/m ² on the zinc surface, as this in turn ensures that a sufficiently uniform, closed zinc phosphate coating is formed on all metal surfaces of the component selected from zinc, iron or aluminium. Thus, preferred is a method according to the invention wherein a zinc phosphate layer having a layer weight of at least 1.0g/m ², preferably at least 1.5g/m ² is deposited on the zinc surface. Since the phosphating quality of the acidic aqueous composition used for phosphating zinc systems in step (ii) is preferably kept as a control variable in the process according to the invention or the acidic aqueous composition has inherent activation properties, it is also always ensured that the zinc surface of the component has a uniform, closed and dense crystalline zinc phosphate layer whose layer thickness is within self-limiting limits, so that the layer weight of the zinc phosphate layer on the zinc surface of the component, as required by the target range, is also preferably below 5.0g/m ², preferably below 4.5g/m ², particularly preferably below 4.0g/m ², very particularly preferably below 3.5g/m ².

In the method according to the invention, a good coating base for the subsequent dip coating or powder coating is prepared, in the course of which a substantially organic cover layer is applied. Thus, in a preferred embodiment of the process of the invention, the zinc-based phosphating in step (ii) is followed by dip coating or powder coating, particularly preferably electrocoating, more particularly preferably cathodic electrocoating, with or without intermediate rinsing and/or drying steps, but preferably with rinsing steps and without drying steps, which preferably contains water-soluble or water-dispersible salts of yttrium and/or bismuth in addition to the dispersed resin, which preferably comprises an amine-modified polyepoxide.

Exemplary embodiments:

To illustrate the advantages of the method according to the invention, the method described in detail below is applied sequentially to the stratified phosphating of various metal substrates and illustrates the applicability thereof to the treatment of components comprising these sequentially arranged metal substrates.

A) By means of a mixture with 0.8%M-FE 2020MU、1.2％/>M-AD ZN-2、0.5％/>M-AD FE-1 and 0.5%/>3.5%/>, C-AD 1561 mixtureAlkaline cleaning of C-AK 2020-1 (each of which is a process chemical from Henkel AG & Co. KGaA and applied to the indicated proportions with fully deionized water (k < 1. Mu. Scm ^-1)). After setting a pH value of 11.8-11.9 and a temperature of 55 ℃, the plates were first spray degreased for 1 minute at a pressure of 1 bar, then

A1 Variants without iron deposition: dip degreasing with the same cleaning solution for 3 minutes while stirring, or

A2 Variants with iron deposition): by immersing the plate in 0.8 wt%M-FE 2020 MU, 0.7 wt%/>M-AD ZN-2, 0.5 wt%/>M-AD FE-1 and 0.5 wt%3.6 Wt.%/>, C-AD 1561 mixtureIn C-AK 2020-1, which are each process chemicals from Henkel AG & Co.KGaA and applied to the indicated ratios with fully deionized water (k < 1. Mu. Scm ^-1), degreasing was carried out for 2 minutes while stirring. The treatment was performed after setting a pH of 12.0 and a temperature of 60 ℃.

B) The substrate was then thoroughly rinsed with fully deionized water (k <1 μm ^-1) for about 1 minute. Under these conditions, the blocked aqueous layer remained on the substrate for at least 30 seconds, indicating the absence of grease and oil on the substrate.

C) The substrate surface was then wetted in water and immersed directly at 52 ℃ with stirring based on fully deionized water (k <1 μscm ^-1) and 4.6 wt% without treatment in a separate activation bathM-Zn 1994MU-1 and 1 wt%/>M-AD 565 (each of which is a process chemical from Henkel AG & Co.KGaA and applied with deionized water (k < 1. Mu. Scm ^-1) to the indicated ratio) in a hydroxylamine-promoted phosphating bath for 3 minutes (free acid: 1.1 point, total acid: 26.5 points, zinc content: 0.13 wt%, accelerator content: 0.1 wt%), was added thereto/>

c1)1g/LAn aqueous zinc phosphate dispersion of M-AC 3000 (Henkel AG & Co.KGaA) prepared as described in the examples of WO 2021/104973 A1 (this corresponds to a proportion of particulate zinc phosphate of 0.2g/kg based on phosphating baths), or

c2)3g/LAn aqueous zinc phosphate dispersion of M-AC 3000 (Henkel AG & Co.KGaA) prepared as described in the examples of WO 2021/104973 A1 (this corresponds to a proportion of particulate zinc phosphate of 0.6g/kg based on phosphating bath).

D) The substrate was then thoroughly rinsed in completely deionized water (k < 1. Mu. Scm ^-1) for about 1 minute, then

E) Purged with compressed air at room temperature and then dried in an oven at 50 ℃.

The metal substrates coated in sequence according to the method are Cold Rolled Steel (CRS) plates, electrolytically galvanised steel (EG) plates, hot dip galvanised steel (HDG) plates, zinc-magnesium hot dip galvanised steel (ZM) plates and aluminium (AA 6014) plates, which are cleaned after process steps a 1) or a 2) and then pretreated after successive process steps b) to e).

In all cases a closed, uniform zinc phosphate layer was produced.

In the process sequence with the iron-forming stage (a 2-b-c1-d-e/a2-b-c 2-d-e), a coating of 82 to 105mg/m ² of iron was prepared on the HDG, EG and ZM plates. The iron coating was quantitatively determined after substrate pickling with 5 wt% HNO ₃ and subsequent photometric concentration determination based on the formation of colored thiocyanate complexes.

In the method according to the invention, a further reduction in the weight of the phosphate layer can be achieved on all galvanized sheets, which method has an iron-forming stage (see table 1) prior to phosphating of the activated zinc system, which is advantageous both in terms of process economy and in terms of downstream electrocoating and in terms of improved coverage that can be achieved there subsequently. At the same time, the layer weight produced on aluminum and cold-rolled steel sheets remains almost constant to slightly increase, so that the method according to the invention for zinc-based phosphating of components comprising the above-mentioned material mixtures is suitable.

Table 1:

/>

Claims

1. A method for the corrosion protection pretreatment of a plurality of components arranged in series, wherein each component arranged in series has at least in part a zinc surface and is first subjected to a wet chemical method step (i) for depositing iron on the zinc surface, followed by a method step (ii) for phosphating zinc systems,

(A) 5-50g/kg of phosphate dissolved in water, calculated as PO ₄,

(B) Zinc ion of 0.3-3g/kg,

(C) Free fluoride, and

Wherein the acidic aqueous composition is obtained by adding an amount of the aqueous dispersion to an acidic aqueous composition containing components (A) to (C),

Wherein the aqueous dispersion comprises a water-dispersed particulate component (P) comprising

-And at least one polymeric organic compound (P2).

2. The process according to claim 1, characterized in that the aqueous dispersion for providing the acidic aqueous composition of process step (ii) is added in such an amount that the weight proportion of phosphate of the particulate component (P) from the aqueous dispersion is at least 0.004g/kg, preferably at least 0.01g/kg, particularly preferably at least 0.05g/kg, very particularly preferably at least 0.08g/kg, based on the acidic aqueous composition.

3. The process according to one or both of the preceding claims, characterized in that in process step (ii) of the zinc-based phosphating, an amount of an activation aid containing a particulate component (P) in water-dispersed form is added continuously or discontinuously to the acidic aqueous composition, said component comprising

And at least one polymeric organic compound (P2),

Said amount being sufficient to maintain the following properties of said acidic aqueous composition under the selected conditions of process step (ii): a zinc phosphate layer having a layer weight of less than 5.0g/m ², preferably less than 4.5g/m ², particularly preferably less than 4.0g/m ², very particularly preferably less than 3.5g/m ² is deposited on the hot dip galvanized steel surface (Z).

4. The process according to one or more of the preceding claims, characterized in that in process step (ii) the polymeric organic compounds (P2) in the aqueous dispersion or the particulate component (P) of the activation aid comprise at least partially styrene and/or a-olefins having not more than 5 carbon atoms, wherein the polymeric organic compounds (P2) additionally have units of maleic acid, maleic anhydride and/or maleimide in their side chains and preferably additionally have polyoxyalkylene units, particularly preferably polyoxyalkylene units, wherein the polymeric organic compounds (P2) additionally preferably have imidazole units in the side chains.

5. The process according to one or more of the preceding claims, characterized in that in process step (ii) the acidic aqueous composition for zinc-based phosphating has a pH value of less than 3.6, preferably less than 3.4, particularly preferably less than 3.2, the free acid preferably being greater than 0.5 point, particularly preferably greater than 0.8 point, more particularly preferably greater than 1.0 point.

6. The process according to one or more of the preceding claims, characterized in that in process step (ii) the acidic aqueous composition for zinc-based phosphating contains a source of free fluoride and preferably at least 10mg/kg, particularly preferably at least 40mg/kg, but preferably not more than 200mg/kg of free fluoride.

7. The method according to one or more of the preceding claims, characterized in that in the wet-chemical method step (i) at least 20mg, preferably at least 40 mg, very particularly preferably at least 60 mg, but preferably less than 150 mg, particularly preferably less than 120 mg, of elemental iron-based coating is produced per square meter of the zinc surface of the component in each case.

8. The method according to one or more of the preceding claims, characterized in that wet chemical method step (i) is preferably carried out by contacting at least the zinc surface of the sequentially arranged component with an aqueous composition containing iron (II) and/or iron (III) ions, wherein the proportion of iron ions dissolved in water is at least 50mg/L, preferably at least 100mg/L, wherein in each case preferably less than 10mg/L total of ionic compounds of metallic copper, nickel, cobalt, tin, manganese, molybdenum, chromium and/or cerium, in particular less than 1mg/L of ionic compounds of metallic nickel and cobalt, relative to the metallic element, is contained in the aqueous composition.

9. The process according to claim 8, wherein wet chemical process step (i) is carried out by contacting with an alkaline aqueous composition having a pH value preferably not lower than 8.5, particularly preferably not lower than 9.5, very particularly preferably not lower than 10.5, but preferably not higher than 13.5, particularly preferably not higher than 12.5, and very particularly preferably not higher than 11.5, and comprising

(A) At least 50mg/L, preferably at least 100mg/L, particularly preferably at least 200mg/L, of iron (III) ions, and

(B) At least 100mg/L of a complexing agent selected from the group consisting of organic compounds (b 1) and/or condensed phosphates (b 2) in terms of PO ₄, the organic compounds (b 1) having at least one functional group selected from COOX, OPO ₃ X and/or PO ₃ X, wherein X is an H atom or an alkali metal atom and/or an alkaline earth metal atom,

10. The method according to claim 9, characterized in that the alkaline aqueous composition additionally contains at least 100mg/L, preferably at least 200mg/L, particularly preferably at least 500mg/L, but not more than 10g/L of phosphate ions, wherein the mass-based ratio of iron (III) ions to phosphate ions in the alkaline aqueous composition is in the range of 1:20 to 1:2.

11. The process according to one or both of the preceding claims 9 to 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, preferably at least 2:1, particularly preferably at least 5.

12. The method according to one or more of the preceding claims, characterized in that said sequential arrangement of components is not contacted with an aqueous colloidal solution containing hopeite, phosphophyllite, phosphogalvanneaite and/or rhodochrosite, preferably phosphates of polyvalent metal cations, or slightly soluble salts of elemental Ti in said particulate component, prior to contact with said acidic aqueous composition in step (ii) of the method of zinc-based phosphating; and preferably not contacted with an aqueous colloidal solution for activating the surface of the part for zinc-based phosphating prior to contact with the acidic aqueous composition in process step (ii); and particularly preferably does not undergo an activation stage for activating the surface of the component for zinc-based phosphating.

13. The method according to one or more of the preceding claims, characterized in that the sequentially arranged components are cleaned and optionally degreased before or in a cleaning phase together with method step (i), in particular by contact with an aqueous, preferably alkaline, cleaning agent, wherein method step (i) is followed immediately by the cleaning phase with or without an intermediate rinsing step, preferably without an intermediate rinsing step.

14. The method according to one or more of the preceding claims, characterized in that the sequentially arranged components additionally have a surface of metallic aluminum, particularly preferably additionally have surfaces of metallic aluminum and iron.

15. The method according to one or more of the preceding claims, characterized in that a zinc phosphate layer having a layer weight of at least 1.0g/m ², preferably at least 1.5g/m ² is deposited on the zinc surface.