EP3828306A1 - Resource-conserving method for activating a metal surface prior to phosphating - Google Patents

Abstract

The present invention relates to a method for the layer-forming phosphating of metallic surfaces using a colloidal, aqueous solution as the activation stage containing a dispersed particulate component, the particulate component containing, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, polymeric organic compounds as dispersing aids, at least in part are composed of styrene and / or an α-olefin with not more than 5 carbon atoms and maleic acid, its anhydride and / or its imide and which additionally have polyoxyalkylene units. In the activation stage of the process according to the invention, an additive of condensed phosphates can be dispensed with, so that the proportion of dissolved condensed phosphates in the colloidal, aqueous solution based on the phosphate content in the particulate component thereof, based on the element P, is less than 0.25.

Description

The present invention relates to a method for the layer-forming phosphating of metallic surfaces using a colloidal, aqueous solution as the activation stage containing a dispersed particulate component, the particulate component containing, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, polymeric organic compounds as dispersing aids, at least in part are composed of styrene and / or an α-olefin with not more than 5 carbon atoms and maleic acid, its anhydride and / or its imide and which additionally have polyoxyalkylene units. In the activation stage of the process according to the invention, an additive of condensed phosphates can be dispensed with, so that the proportion of dissolved condensed phosphates in the colloidal, aqueous solution based on the phosphate content in the particulate component thereof, based on the element P, is less than 0.25.

The layer-forming phosphating is a method that has been practiced for decades and has been intensively investigated for applying crystalline, corrosion-protective coatings to metallic surfaces, in particular to materials made of the metals iron, zinc and aluminum. The zinc phosphating, which is particularly well established for corrosion protection, takes place in a layer thickness of a few micrometers and is based on a corrosive pickling of the metallic material in an acidic aqueous composition containing zinc ions and phosphates. In the course of the pickling process, an alkaline diffusion layer develops on the metal surface, which extends into the interior of the solution and within which poorly soluble crystallites form, which precipitate directly at the interface with the metallic material and continue to grow there. To support the pickling reaction on materials made of the metal aluminum and to mask the bath poison aluminum, which in dissolved form interferes with the formation of layers on metal materials, water-soluble compounds are often added, which represent a source of fluoride ions. The zinc phosphating is always initiated with an activation of the metallic surfaces of the component to be phosphated. The wet-chemical activation takes place conventionally by bringing them into contact with colloidal, aqueous solutions of phosphates ("activation stage"), which in this respect are immobilized on the metal surface in the subsequent phosphating serve as a growth nucleus for the formation of the crystalline coating within the alkaline diffusion layer. Suitable dispersions are colloidal, mostly neutral to alkaline, aqueous compositions based on phosphate crystallites, the crystal structure of which has only slight crystallographic deviations from the type of zinc phosphate layer to be deposited. That's how she teaches WO 98/39498 A1 in this context in particular bivalent and trivalent phosphates of the metals Zn, Fe, Mn, Ni, Co, Ca and Al, where technically preferred phosphates of the metal zinc are used for activation for a subsequent zinc phosphating.

An activation stage based on dispersions of bivalent and trivalent phosphates requires a high level of process control in order to keep the activation performance constantly at an optimal level, especially when treating a series of metallic components. For the process to be sufficiently robust, neither foreign ions introduced by the entrainment of previous treatment baths nor aging processes in the colloidal, aqueous solution must lead to a deterioration in the activation performance. A deterioration is initially noticeable in increasing layer weights in the subsequent phosphating and finally leads to the formation of defective or inhomogeneous phosphate layers. When the process is carried out continuously, it is therefore necessary to chemically additive to the activation stage in order to increase the bath service life or to reduce the consumption of colloidal active components to such an extent that the phosphating can be operated economically on the basis of colloidal, aqueous solutions. In the case of activation with particulate phosphates, additives include the addition of condensed phosphates for colloid stabilization. Complexing agents are often added to mask polyvalent metal ions and water hardness introduced from previous cleaning stages in order to counteract the accelerated formation of colloid agglomerates and thus the sedimentation of the colloidally dispersed bath species. The dosage of condensed phosphates and / or complexing agents requires precise analytical monitoring, as there is both a process-critical minimum amount that must be adhered to and a system-specific upper limit, below or above which the activation performance is negatively influenced.

There is therefore a need to set up the activation stage of a pretreatment line for phosphating, in particular for zinc phosphating, which is to be based on colloidal, aqueous solutions of phosphates, with regard to its property of activating metal surfaces for phosphating, more efficiently and with greater process robustness equip. First of all, this concerns the ability of the colloidal, aqueous solution to activate the metal surfaces to be phosphated as uniformly and comprehensively as possible while using comparatively little material and thus the formation of homogeneous, finely crystalline coatings in the phosphating stage, so that with excellent paint adhesion properties, there is also a high electrical penetration resistance and in this way a correspondingly good wraparound of the paint is realized in the subsequent electrodeposition coating. Furthermore, for the aspect of the improved robustness of such a method, it is necessary that a higher tolerance to introduced and enriched foreign ions and a high stability with regard to the structural and chemical nature of the colloidal constituent is guaranteed. All of this with the aim of establishing a pretreatment line for phosphating, in particular for zinc phosphating, which can be operated in continuous operation, conserving resources and with little process engineering effort.

This complex task profile is surprisingly achieved through the use of a specific polymeric dispersing aid to stabilize the colloidal component of an activation stage based on particulate phosphates. Due to the extremely efficient stabilization of the particulate component causing the activation, the special dispersing aid ensures that even comparatively low proportions of colloids are able to bring about homogeneous, closed phosphate coatings without a significant decrease in the activation performance after the steady state of a pretreatment line has been maintained is detectable. The use of the specific dispersing aid therefore makes it possible to dispense entirely with additives with condensed phosphates and thus to significantly reduce the process engineering effort when carrying out a process for phosphating in continuous operation.

• (a1) mindestens eine partikuläre anorganische Verbindung, die aus Phosphaten polyvalenter Metall-Kationen zumindest teilweise ausgewählt aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith zusammengesetzt ist, und
• (a2) mindestens eine polymere organische Verbindung, die zumindest zum Teil zusammengesetzt ist aus Styrol und/oder einem α-Olefin mit nicht mehr als 5 Kohlenstoffatomen sowie Maleinsäure, dessen Anhydrid und/oder dessen Imid und die zusätzlich Polyoxyalkylen-Einheiten aufweist, erfolgt,

wobei in der kolloidalen, wässrigen Lösung der Anteil an in Wasser gelösten kondensierten Phosphaten bezogen auf den Phosphatgehalt der mindestens einen partikulären Verbindung jeweils bezogen auf das Element P kleiner als 0,25 ist.The present invention therefore relates to a method for the anticorrosive pretreatment of a metallic material selected from zinc, iron or aluminum or a component which is at least partially composed of such metallic materials, in which the metallic material or the component is first activated in successive method steps (i ) and then subjected to phosphating (ii), in particular zinc phosphating, the activation in process step (i) by bringing the metallic material into contact or the component with a colloidal, aqueous solution contained in the dispersed particulate component (a) of the solution

• (a1) at least one particulate inorganic compound which is composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and / or hureaulite, and
• (a2) at least one polymeric organic compound which is at least partly composed of styrene and / or an α-olefin with no more than 5 carbon atoms and maleic acid, its anhydride and / or its imide and which additionally has polyoxyalkylene units, takes place,

wherein in the colloidal, aqueous solution the proportion of condensed phosphates dissolved in water, based on the phosphate content of the at least one particulate compound, based in each case on the element P, is less than 0.25.

The dispersed particulate component (a) of the colloidal, aqueous solution in the activation (i) of the process according to the invention is that solid fraction which, after drying the retentate of an ultrafiltration, of a defined partial volume of the aqueous dispersion with a nominal exclusion limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off) remains. The ultrafiltration is carried out with the addition of deionized water (κ <1 μScm ^-1 ) until a conductivity below 10 μScm ^{-1 is} measured in the filtrate.

In the context of the present invention, an organic compound is polymeric if its weight-average molar mass is greater than 500 g / mol. The molar mass is determined via the molar mass distribution curve of a sample of the respective reference size, which was determined experimentally by size exclusion chromatography with a concentration-dependent refractive index detector at 30 ° C. and calibrated against polyethylene glycol standards. The evaluation of the molar mass mean values is carried out with the aid of a computer using the strip method with a calibration curve of the 3rd order. A suitable column material is hydroxylated polymethacrylate and an aqueous solution of 0.2 mol / L sodium chloride, 0.02 mol / L sodium hydroxide, 6.5 mmol / L ammonium hydroxide as an eluent.

The process according to the invention is characterized in that the addition of condensed phosphates can be dispensed with in the activation stage. On the one hand, condensed phosphates dissolved in the aqueous phase of activation fulfill the task To mask permanent water hardness and, on the other hand, based on experience, the specific task of stabilizing the proportion of the phosphates hopeite, phosphophylilite, scholzite and / or hurealite on a colloidal level and thus keeping it permanently available for activation. It is remarkable and surprising for the person skilled in the art that in processes according to the invention which are based on an activation stage based on the particulate constituent (a), the addition of condensed phosphates can be dispensed with.

This advantage over conventional activation baths is particularly important when phosphating components in series, i.e. during ongoing operation of a pretreatment line for phosphating. In a preferred embodiment of the method according to the invention, a large number of specific components, which at least partially consist of zinc, iron or aluminum, are treated in series. A pretreatment in series is when the large number of components is brought into contact with the colloidal, aqueous solution in the system tank of the activation stage, the individual components being brought into contact one after the other and thus separated from one another and the components subsequently are fed to the phosphating. The system tank is the container in which the colloidal, aqueous solution is located for the purpose of activation for phosphating in series.

Overall, in the context of the present invention, the addition of condensed phosphates can be completely dispensed with, so that only those small amounts of condensed phosphates are to be found in the activation that result from upstream cleaning stages with the component to be pretreated, in particular when treating a large number of components in series, get into the activation stage. In a preferred embodiment of the method according to the invention, the proportion of condensed phosphates dissolved in water in the colloidal aqueous solution based on the phosphate content of the at least one particulate compound (a1) based on the element P is below 0.20, particularly preferably below 0.15, very particularly preferably below 0.10.

It is also preferred in this context that the proportion of condensed phosphates dissolved in water in the colloidal, aqueous solution, calculated as P, is less than 20 mg / kg, preferably less than 15 mg / kg, particularly preferably less than 10 mg / kg, based on is the colloidal, aqueous solution.

In the context of the present invention, condensed phosphates are metaphosphates and polyphosphates, preferably polyphosphates, particularly preferably pyrophosphate. The condensed phosphates are preferably in the form of compounds of monovalent cations, preferably selected from Li, Na and / or K, particularly preferably Na and / or K, before.

The proportion of condensed phosphates can be determined analytically from the difference in the total phosphate content in the non-particulate component of the colloidal, aqueous solution with and without oxidative digestion, for example by means of peroxodisulfate, the dissolved orthophosphate proportion being quantified by means of photometry. Alternatively, if polyphosphates are used as condensed phosphates, an enzymatic digestion with a pyrophosphatase can take place instead of the oxidative digestion. The non-particulate component of the colloidal, aqueous solution is the solids content of the colloidal, aqueous solution in the permeate of the previously described ultrafiltration after it has been dried to a constant mass at 105 ° C - i.e. the solids content after separation of the particulate component (a) by means of ultrafiltration.

The high tolerance of the method according to the invention with respect to entrained foreign ions also makes it possible for the cleaning steps, rinsing steps and also the activation step itself to be carried out with process water instead of deionized water. In this way, the method according to the invention is operated in a particularly resource-saving manner. It is therefore preferred according to the invention that the colloidal, aqueous solution is activated at least 0.5 mmol / L, particularly preferably at least 1.0 mmol / L, particularly preferably at least 1.5 mmol / l, but preferably not more than 10 mmol / L of alkaline earth metal ions dissolved in water.

Should the tolerance of the method according to the invention reach its limits in the individual case of the system in the case of extraordinarily high ionic strengths, e.g. high permanent water hardness and at the same time a high proportion of entrained foreign ions from previous cleaning stages, organic complexing agents can be used to mask the foreign ions in order to maintain a long bath service life. Ions are added. In this case it has to be considered whether the economic advantage that the Activation stage and, if necessary, upstream cleaning stages and rinsing with service water can be operated, is not thwarted by additives with organic complexing agents and their process monitoring in the system tank of the activation stage. Suitable organic complexing agents, which are preferred in this context, are selected from α-hydroxycarboxylic acids, which in turn are preferably selected from gluconic acid, tartronic acid, glycolic acid, citric acid, tartaric acid, lactic acid, very particularly preferably gluconic acid, and / or organophosphonic acids, which in turn are preferably selected are selected from etidronic acid, aminotris (methylenephosphonic acid), aminotri (methylenephosphonic acid)), phosphonobutane-1,2,4-tricarboxylic acid, diethylenetriaminepenta (methylenephosphonic acid), hexamethylene diamine tetra (methylenephosphonic acid) and / or hydroxyphosphonoacetic acid, particularly preferred.

To maintain a stable activation performance, the addition of organic complexing agent should only take place to such an extent that its amount in the colloidal, aqueous solution is preferably not greater than twice, particularly preferably not greater than 1.5 times, based on the amount of alkaline earth metal ions and is very particularly preferably not greater than equimolar to the amount of alkaline earth metal ions.

The colloidal, aqueous solution in activation (i) of the method according to the invention preferably has an alkaline pH value, particularly preferably a pH value above 8.0, particularly preferably above 9.0, but preferably below 11.0 , it being possible to use compounds which influence the pH value, such as phosphoric acid, sodium hydroxide solution, ammonium hydroxide or ammonia to adjust it. The “pH value” as used in the context of the present invention corresponds to the negative decadic logarithm of the hydronium ion activity at 20 ° C. and can be determined using pH-sensitive glass electrodes.

The use of polyvalent metal cations in the form of phosphates, which should be contained in a correspondingly high proportion in the dispersed particulate component (a) for activation, is necessary for good activation performance. Accordingly, the proportion of phosphates contained in the at least one particulate inorganic compound (a1) based on the dispersed particulate component (a) of the colloidal, aqueous solution is preferably at least 25% by weight, particularly preferably at least 35% by weight, particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight. The inorganic particulate component of the colloidal, aqueous solution is in turn that which remains when the particulate component (a) obtained from the drying of the retentate of the ultrafiltration is placed in a reaction _{furnace with a flow of CO 2} -free oxygen at 900 ° C without the addition of catalysts or other additives are pyrolysed until an infrared sensor in the outlet of the reaction _{furnace delivers a signal identical to the CO 2} -free carrier gas (blank value). The phosphates contained in the inorganic particulate constituent are determined as phosphorus content by means of atomic emission spectrometry (ICP-OES) directly from the acid digestion after acid digestion of the same with aqueous 10% by weight HNO _{3 solution at 25 ° C for 15 min.}

The active components of the colloidal, aqueous dispersion, which effectively promote the formation of a closed phosphate coating on the metal surfaces and in this sense activate the metal surfaces, are, as already mentioned, primarily composed of phosphates, which in turn cause the formation of finely crystalline coatings, and are therefore at least partially selected from Hopeite, phosphophyllite, scholzite and / or hureaulite, preferably at least partially selected from hopeite, phosphophyllite and / or scholzite, particularly preferably at least partially selected from hopeite and / or phosphophyllite and very particularly preferably at least partially selected from hopeite. Activation within the meaning of the present invention is therefore essentially based on the phosphates contained in the activation stage in particulate form. Without taking into account water of crystallization, hops include stoichiometrically Zn ₃ (PO ₄ ) ₂ as well as the nickel and manganese-containing variants Zn ₂ Mn (PO ₄ ) ₃ , Zn ₂ Ni (PO ₄ ) ₃ , whereas phosphophyllite made from Zn ₂ Fe (PO ₄ ) ₃ , Scholzite consists of Zn ₂ Ca (PO ₄ ) ₃ and Hureaulite consists of Mn ₃ (PO ₄ ) ₂ . The existence of the crystalline phases hopeite, phosphophyllite, scholzite and / or hureaulite in the aqueous dispersion according to the invention can after separation of the particulate component (a) by means of ultrafiltration with a nominal exclusion limit of 10 kD (NMWC, Nominal Molecular Weight Cut Off) as described above and Drying of the retentate to constant mass at 105 ° C can be demonstrated using X-ray diffraction methods (XRD).

Due to the preference for the presence of phosphates, which comprise zinc ions and have a certain crystallinity, it is preferred for the formation of firmly adhering crystalline zinc phosphate coatings after activation if, in the process according to the invention, at least 20% by weight in the colloidal, aqueous dispersion , especially preferably at least 30% by weight, particularly preferably at least 40% by weight, of zinc are contained in the inorganic particulate component of the colloidal, aqueous solution based on the phosphate content of the inorganic particulate component, calculated as PO ₄ .

Another advantage of the process according to the invention is that even small proportions of the particulate inorganic compound (a1) in the activation (i) are sufficient to achieve the full activation performance on the materials zinc, aluminum and iron. It is therefore preferred according to the invention that the proportion of the dispersed particulate component (a) of the colloidal, aqueous solution is at least 0.05 g / kg, preferably at least 0.1 g / kg, particularly preferably at least 0.2 g / kg, but preferably is not greater than 10 g / kg, particularly preferably not greater than 2 g / kg, very particularly preferably not greater than 1 g / kg in each case based on the colloidal, aqueous solution.

Activation within the meaning of the present invention should, however, preferably not be achieved by means of colloidal solutions of titanium phosphates, since otherwise the layer-forming zinc phosphating on iron, in particular steel, will not be reliable. In a preferred embodiment of the method according to the invention, the proportion of titanium in the inorganic particulate component of the colloidal, aqueous solution is therefore less than 0.01% by weight, particularly preferably less than 0.001% by weight, based on the colloidal, aqueous solution. In a particularly preferred embodiment, the colloidal, aqueous solution of activation (i) contains a total of less than 10 mg / kg, particularly preferably less than 1 mg / kg, of titanium.

The activation stage in the method according to the invention can additionally be characterized by its D50 value, above which the activation performance decreases significantly. The D50 value of the colloidal, aqueous solution is preferably below 1 μm, particularly preferably below 0.4 μm. In the context of the present invention, the D50 value denotes the particle diameter which does not exceed 50% by volume of the particulate constituents contained in the colloidal, aqueous solution. The D50 value can be determined in accordance with ISO 13320: 2009 by means of scattered light analysis according to the Mie theory from volume-weighted cumulative particle size distributions immediately after sampling from the activation stage at 20 ° C, with spherical Particles and a refractive index of the scattering particles of n _D = 1.52 - i · 0.1 are taken as a basis.

For the purposes of the present invention, the polymeric organic compounds (a2) used as dispersants which have polyoxyalkylene units are at least partially composed of styrene and / or an α-olefin having not more than 5 carbon atoms and maleic acid, its anhydride and / or its imide, and cause the extremely high stability of the colloidal, aqueous solution in the activation stage of the process according to the invention.

The α-olefin is preferably selected from ethene, 1-propene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene and / or 3-methyl-1-butene and is particularly preferably selected from isobutylene. It is clear to the person skilled in the art that the polymeric organic compounds (a2) contain these monomers as structural units in unsaturated form with one another or with other structural units covalently linked. Suitable commercially available representatives are, for example, Dispex® CX 4320 (BASF SE) a maleic acid-isobutylene copolymer modified with polypropylene glycol, Tego® Dispers 752 W (Evonik Industries AG) a maleic acid-styrene copolymer modified with polyethylene glycol or Edaplan® 490 (Münzing Chemie GmbH) modified a maleic acid-styrene copolymer with EO / PO and imidazole units. In the context of the present invention, preference is given to those polymeric organic compounds (a2) which are at least partly composed of styrene.

The polymeric organic compounds (a2) used as dispersing auxiliaries have polyoxyalkylene units which are preferably composed of 1,2-ethanediol and / or 1,2-propanediol, particularly preferably both 1,2-ethanediol and 1,2 Propanediol, the proportion of 1,2-propanediols in the total of the polyoxyalkylene units being preferably at least 15% by weight, but particularly preferably not exceeding 40% by weight, based on the total of the polyoxyalkylene units. Furthermore, the polyoxyalkylene units are preferably contained in the side chains of the polymeric organic compounds (a2). A proportion of the polyoxyalkylene units in the totality of the polymeric organic compounds (a2) 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.

For anchoring the dispersing aid with the inorganic particulate component of the colloidal, aqueous solution, which is at least partially formed by polyvalent metal cations in the form of phosphates selected from hopeite, phosphophyllite, scholzite and / or hurealite, the organic polymeric compounds (a2) in addition, imidazole units, preferably such that the polyoxyalkylene units of the polymeric organic compounds (a2) are at least partially end-capped with an imidazole group, so that in the preferred embodiment terminal imidazole groups are present in the polyoxyalkylene side chain, the covalent linkage of the polyoxyalkylene units with the imidazole group is preferably carried out via a nitrogen atom of the heterocycle.

In a preferred embodiment, the amine number of the organic polymeric compounds (a2) is at least 25 mg KOH / g, particularly preferably at least 40 mg KOH / g, but preferably less than 125 mg KOH / g, particularly preferably less than 80 mg KOH / g, so that in a preferred embodiment all of the polymeric organic compounds in the particulate component (a) also have these preferred amine numbers. The amine number is determined in each case using a weight of about 1 g of the respective reference value - organic polymeric compounds (a2) or totality of the polymeric organic compounds in the particulate component - in 100 ml of ethanol, with 0.1 N HCl standard solution against the indicator Bromophenol blue is titrated until the color changes to yellow at a temperature of the ethanolic solution of 20 ° C. The amount of standard solution HCl consumed in milliliters multiplied by the factor 5.61 divided by the exact weight of the initial weight in grams corresponds to the amine number in milligrams of KOH per gram of the respective reference value.

The presence of maleic acid, insofar as it is a constituent of the organic polymeric compound (a2) in the form of the free acid and not in the form of the anhydride or imide, can impart increased water solubility of the dispersing aid, especially in the alkaline range. It is therefore preferred that the polymeric organic compounds (a2), preferably also all of the polymeric organic compounds in the particulate component (a), have an acid number according to DGF CV 2 (06) (as of April 2018) of at least 25 mg KOH / g have, but preferably less than 100 mg KOH / g, particularly preferably less than 70 mg KOH / g, in order to ensure a sufficient number of polyoxyalkylene units. It is also preferred if the polymeric organic compounds (a2), preferably also the entirety of the polymeric organic compounds in the particulate component (a), a hydroxyl number of less than 15 mg KOH / g, particularly preferably less than 12 mg KOH / g, particularly preferably less than 10 mg KOH / g, each determined according to method A of 01/2008: 20503 from European Pharmacopoeia 9.0.

For a sufficient dispersion of the inorganic particulate constituents in the colloidal, aqueous dispersion, it is sufficient if the proportion of the polymeric organic compounds (a2), preferably all of the polymeric organic compounds in the particulate component (a), based on the particulate component (a ) is at least 3% by weight, particularly preferably at least 6% by weight, but preferably does not exceed 15% by weight.

• bezogen auf die wässrige Dispersion mindestens 5 Gew.-% eines dispergierten partikulären Bestandteils (A), der wiederum
  • (A1) mindestens eine partikuläre anorganische Verbindung, die aus Phosphaten polyvalenter Metall-Kationen zumindest teilweise ausgewählt aus Hopeit, Phosphophyllit, Scholzit und/oder Hureaulith zusammengesetzt ist,
  • (A2) mindestens eine polymere organische Verbindung, die zumindest zum Teil zusammengesetzt ist aus Styrol und/oder einem α-Olefin mit nicht mehr als 5 Kohlenstoffatomen sowie Maleinsäure, dessen Anhydrid und/oder dessen Imid und die zusätzlich Polyoxyalkylen-Einheiten aufweist, enthält, sowie
• gegebenenfalls mindestens einen Verdicker (B), der vorzugsweise ausgewählt ist aus Harnstoffurethanharzen, besonders bevorzugt aus Harnstoffurethanharzen, die eine Aminzahl von weniger als 8 mg KOH/g, vorzugsweise von weniger als 5 mg KOH/g, besonders bevorzugt von weniger als 2 mg KOH/g aufweisen.

In a further aspect, the present invention relates to a method for anti-corrosive pretreatment based on phosphating with the inclusion of an aqueous dispersion. Such a method according to the invention relates to the anticorrosive pretreatment of a metallic material selected from zinc, iron or aluminum or of a component which is at least partially composed of such metallic materials, in which the metallic material or the component is initially activated (i) and in successive method steps is then subjected to phosphating (ii), in particular zinc phosphating, the activation in process step (i) being carried out by bringing the metallic material or at least one metallic material of the component into contact with a colloidal, aqueous solution as described above, which is available as an aqueous dispersion diluted by a factor of 20 to 100,000 comprising:

• based on the aqueous dispersion at least 5 wt .-% of a dispersed particulate constituent (A), which in turn
  • (A1) at least one particulate inorganic compound which is composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and / or hureaulite,
  • (A2) at least one polymeric organic compound which is at least partially composed of styrene and / or an α-olefin with no more than 5 carbon atoms and maleic acid, its anhydride and / or its imide and which additionally has polyoxyalkylene units, as
• optionally at least one thickener (B), which is preferably selected from urea urethane resins, particularly preferably from urea urethane resins, which have an amine number of less than 8 mg KOH / g, preferably less than 5 mg KOH / g, particularly preferably less than 2 mg KOH / g.

For the dispersed particulate constituent (A) and the at least one particulate inorganic compound (A1) or polymeric organic compound (A2), the same definitions and preferred specifications apply as were given above for the colloidal, aqueous solution.

Due to the excellent colloid stability of the particulate constituent (A) by means of the polymeric organic compound (A2) as a dispersing aid, the dilution is preferably carried out with deionized water (κ <1 μScm ^-1 ), particularly preferably with service water, in order to make the process according to the invention as resource-saving as possible . Process water in the light of the underlying technical application contains at least 0.5 mmol / L of alkaline earth metal ions.

The presence of a thickener according to component (B) gives the aqueous dispersion, in combination with its particulate constituent, a thixotropic flow behavior and thus contributes to counteracting the irreversible formation of agglomerates in the particulate constituent of the dispersion, from which primary particles can no longer be removed. The addition of the thickener should preferably be controlled so that the aqueous dispersions in the shear rate range of 0.001 to 0.25 reciprocal seconds have a maximum dynamic viscosity at a temperature of 25 ° C. of at least 1000 Pa · s, but preferably below 5000 Pa · s , and preferably at shear rates above that which is present at the maximum dynamic viscosity, shows shear-thinning behavior at 25 ° C., that is, a decrease in viscosity with increasing shear rate, so that the aqueous dispersion as a whole has a thixotropic flow behavior. The viscosity over the specified shear rate range can be determined using a plate / cone viscometer with a cone diameter of 35 mm and a gap width of 0.047 mm.

A thickener according to component (B) is a polymeric chemical compound or a defined mixture of chemical compounds that are used as a 0.5% by weight component in deionized water (κ <1μScm ^-1 ) at a temperature of 25 ° C has a Brookfield viscosity of at least 100 mPa · s at a shear of 60 rpm (= rounds per minute) using a size 2 spindle. When determining this thickening property, the mixture with water is to be made up in such a way that the appropriate amount of the polymeric chemical compound is added to the water phase with stirring at 25 ° C and the homogenized mixture is then freed of air bubbles in an ultrasonic bath and left to stand for 24 hours. The measured value of the viscosity is then read off immediately within 5 seconds after a shear of 60 rpm has been applied by spindle number 2.

An aqueous dispersion according to the invention preferably contains 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 according to component (B), further preferred the total proportion of polymeric organic compounds in the non-particulate component of the aqueous dispersion does not exceed 4% by weight (based on the dispersion). The non-particulate component is the solids content of the aqueous dispersion in the permeate of the ultrafiltration already described after it has been dried to constant mass at 105 ° C. - i.e. the solids content after the particulate component has been separated off by means of ultrafiltration.

Certain classes of polymeric compound are particularly suitable thickeners according to component (B) and are also readily available commercially. The thickener according to component (B) is initially preferably selected from polymeric organic compounds, which in turn are preferably selected from polysaccharides, cellulose derivatives, aminoplasts, polyvinyl alcohols, polyvinylpyrrolidones, polyurethanes and / or urea urethane resins, and particularly preferably from urea urethane resins.

A urea urethane resin as a thickener according to component (B) of the preferred method according to the invention for providing a colloidal, aqueous solution based on the aqueous dispersion is a mixture of polymeric compounds that result from the reaction of a polyvalent isocyanate with a polyol and a mono- and / or diamine emerges. In a preferred embodiment, the urea urethane resin is made from a polyvalent isocyanate, preferably selected from 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2 (4), 4-trimethyl-1,6-hexamethylene diisocyanate, 1,10- Decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate and mixtures thereof, p- and m-xylylene diisocyanate, and 4-4 ', - diisocyanatodicyclohexylmethane, particularly preferably selected from 2,4-toluene diisocyanate and / or m-xylylene diisocyanate , emerge. In a particularly preferred embodiment, the urea urethane resin is derived from a polyol selected from polyoxyalkylene diols, particularly preferably from polyoxyethylene glycols, which in turn are preferably composed of at least 6, particularly preferably at least 8, particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23 oxyalkylene units.

According to the invention particularly suitable and therefore preferred urea urethane resins are obtainable by a first reaction of a diisocyanate, for example toluene-2,4-diisocyanate, with a polyol, for example a polyethylene glycol, to form NCO-terminated urethane prepolymers, after which with a primary monoamine and / or with a primary diamine , for example m-xylylenediamine, is further implemented. Urea urethane resins which have neither free nor blocked isocyanate groups are particularly preferred. Such urea urethane resins, as a component of the aqueous dispersion from which the colloidal, aqueous solution of the process according to the invention is obtainable by dilution, promote the formation of loose agglomerates of primary particles, which, however, are stabilized in the aqueous phase and protected against further agglomeration to such an extent that the sedimentation of the particulate constituent in the aqueous dispersion is largely prevented. In order to further promote this profile of properties, urea urethane resins which have neither free or blocked isocyanate groups nor terminal amine groups are preferably used as component (B). In a preferred embodiment, the thickener according to component (B), which is a urea urethane resin, therefore has an amine number of less than 8 mg KOH / g, particularly preferably less than 5 mg KOH / g, particularly preferably less than 2 mg KOH / g, each determined by the method as described above for the organic polymeric compound (A2). Since the thickener is essentially dissolved in the aqueous phase and can therefore be assigned to the non-particulate constituent of the aqueous dispersion, while component (A2) is essentially bound in the particulate constituent (A), an aqueous dispersion is accordingly to be provided the colloidal, aqueous solution of activation is preferred, in which the totality of the polymeric organic compounds in the non-particulate component preferably has an amine number of less than 16 mg KOH / g, particularly preferably less than 10 mg KOH / g, particularly preferred has less than 4 mg KOH / g. It is also preferred that the urea urethane resin has a hydroxyl number in the range from 10 to 100 mg KOH / g, particularly preferably in the range from 20 to 60 mg KOH / g, determined according to method A of 01/2008: 20503 from European Pharmacopoeia 9.0. With regard to the molecular weight, a weight-average molar mass of the urea urethane resin in the range from 1000 to 10000 g / mol, preferably in the range from 2000 to 6000 g / mol, is advantageous according to the invention and therefore preferred, in each case determined experimentally as above in connection with the definition of a polymeric compound according to the invention described.

Without the addition of auxiliaries, the pH of the dispersion for providing the colloidal, aqueous solution for activating the method according to the invention is usually in the range from 6.0-9.0 and such a pH range is therefore preferred according to the invention. For compatibility with the actual and regularly alkaline colloidal aqueous solution in the activation stage, however, it is advantageous if the pH of the aqueous dispersion, possibly also by adding alkaline compounds, is above 7.2, particularly preferably above of 8.0. The alkalinity of the aqueous dispersion according to the invention is, since some polyvalent metal cations have amphoteric character and can therefore be leached out of the particulate constituent at higher pH values, ideally limited, so that the pH value of the aqueous dispersion is preferably below 10 and especially is preferably below 9.0.

1. i) Bereitstellen einer Pigmentpaste durch Verreiben von 10 Massenteilen einer anorganischen partikulären Verbindung (A1) mit 0,5 bis 2 Massenteilen der polymeren organischen Verbindung (A2) in Gegenwart von 4 bis 7 Massenteilen Wasser und Vermahlen bis zum Erreichen eines D50-Wert von weniger als 1 µm bestimmt mittels dynamischer Lichtstreuung nach Verdünnung mit Wasser um den Faktor 1000, bspw. mittels Zetasizer® Nano ZS, Fa. Malvern Panalytical GmbH;
2. ii) Verdünnen der Pigmentpaste mit einer solchen Menge an Wasser, vorzugsweise entionisiertem Wasser (κ<1 µScm^-1) oder Brauchwasser, und eines Verdickers (B), dass ein dispergierter partikulärer Bestandteil (A) von mindestens 5 Gew.-% und eine maximale dynamische Viskosität von mindestens 1000 Pa·s bei einer Temperatur von 25 °C im Scherratenbereich von 0,001 bis 0,25 reziproken Sekunden eingestellt ist; und
3. iii) Einstellen eines pH-Wertes im Bereich von 7,2 bis 10,0 mit Hilfe einer alkalisch reagierenden Verbindung,

wobei bevorzugte Ausführungsformen der Dispersion durch Auswahl entsprechender Komponenten (A1), (A2) und (A) in der jeweils ggf. vorgesehenen bzw. erforderlichen Menge, wie im Zusammenhang mit der kolloidalen, wässrigen Lösung beschrieben, auf analoge Weise erhalten werden.The above-described aqueous dispersion for providing the colloidal, aqueous solution is for its part preferably obtainable from

1. i) Providing a pigment paste by triturating 10 parts by mass of an inorganic particulate compound (A1) with 0.5 to 2 parts by mass of the polymeric organic compound (A2) in the presence of 4 to 7 parts by mass of water and grinding until a D50 value of less is reached as 1 µm determined by means of dynamic light scattering after dilution with water by a factor of 1000, for example by means of Zetasizer® Nano ZS, Malvern Panalytical GmbH;
2. ii) Diluting the pigment paste with such an amount of water, preferably deionized water (κ <1 μScm ^-1 ) or industrial water, and a thickener (B) that a dispersed particulate component (A) of at least 5 wt .-% and a maximum dynamic viscosity of at least 1000 Pa · s at a temperature of 25 ° C is set in the shear rate range of 0.001 to 0.25 reciprocal seconds; and
3. iii) setting a pH value in the range from 7.2 to 10.0 with the help of an alkaline compound,

preferred embodiments of the dispersion being obtained in an analogous manner by selecting corresponding components (A1), (A2) and (A) in the respective possibly provided or required amount, as described in connection with the colloidal, aqueous solution.

The aqueous dispersion can also contain auxiliaries, for example selected from preservatives, wetting agents and defoamers, which are contained in the amount necessary for the respective function. The proportion of auxiliaries, particularly preferably of other compounds in the non-particulate constituent, which are not thickeners or compounds with an alkaline reaction, is preferably less than 1% by weight. In the context of the present invention, an alkaline compound is water-soluble (water solubility: at least 10 g per kilogram of water with κ <1 μScm ^-1 ) and has a pK _B value for the first protonation stage above 8.0.

If, within the scope of the method according to the invention, reference is made to the treatment of a metallic material selected from zinc, iron or aluminum, this includes all materials which contain more than 50 at% of the respective element. Anticorrosive pretreatment always affects the surfaces of the material or component. The material can be a uniform material or a coating. Thus, according to the invention, galvanized steel types consist of both the material steel and the material zinc, whereby surfaces of iron can be exposed at the cut edges and sanded-through points, for example of an automobile body made of galvanized steel, and according to the invention, the material iron is then pretreated.

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

A rinsing step can take place between activation (i) and phosphating (ii) in order to reduce the carryover of alkaline constituents into the mostly acidic phosphating, but a rinsing step is preferably dispensed with in order to fully maintain the activation performance. A rinsing step is used exclusively for the complete or partial removal of soluble residues, particles and active components, which are carried away adhering to the component from a previous wet chemical treatment step, from the component to be treated, without active components based on metallic or semi-metallic elements being contained in the rinsing liquid itself, which are already used up simply by bringing the metallic surfaces of the component into contact with the flushing liquid. Thus, the rinsing liquid can only be city water or deionized water or, if necessary, can also be a rinsing liquid which contains surface-active compounds to improve the wettability with the rinsing liquid.

For layer-forming phosphating and the formation of partially crystalline coatings aimed at activating the metallic materials, it is preferred that the phosphating in process step (ii) by bringing the surfaces into contact with an acidic aqueous composition containing 5-50 g / kg of phosphates dissolved in water, calculated as PO ₄ and preferably additionally contains at least one source of free fluoride. According to the invention, the amount of phosphate ions comprises orthophosphoric acid and the anions of the salts of orthophosphoric acid dissolved in water, calculated as PO ₄ .

In a preferred embodiment of the present invention, the subsequent phosphating is zinc phosphating and the phosphating in process step (ii) is based on an acidic aqueous composition containing 0.3-3 g / kg of zinc ions, preferably on an acidic aqueous composition containing 5 - 50 g / l of phosphate ions, 0.3 - 3 g / l of zinc ions and a lot of free fluoride.

A source of free fluoride ions is essential for the process of layer-forming zinc phosphating, insofar as the layer formation on all metallic materials selected from zinc, iron or aluminum and is required, for example, in the zinc phosphating of automobile bodies that are at least partially also made of aluminum. If all surfaces of the metallic materials of a component are to be provided with a phosphate coating, the amount of particulate constituents in the activation often has to be adapted to the amount of free fluoride required for the formation of a layer in the zinc phosphating. In a method according to the invention based on activation (i) followed by zinc phosphating (ii), in which the components to be pretreated are made of metallic materials of zinc and iron, in particular steel, it is advantageous for a closed and defect-free phosphate coating if the amount of free fluoride in the acidic aqueous composition is at least 0.5 mmol / kg. If the component is also made of the metallic material aluminum and its surfaces are also to be provided with a closed phosphate coating, it is further preferred in the method according to the invention that the amount of free fluoride in the acidic aqueous composition is at least 2 mmol / kg. The concentration of free fluoride should not exceed values above which the phosphate coatings predominantly have adhesions that can be easily wiped off, since these cannot be avoided even by a disproportionately increased amount of particulate components in the colloidal, aqueous solution of activation. It is therefore also advantageous and therefore preferred for economic reasons if, in the process according to the invention, based on activation (i) followed by zinc phosphating (ii), the concentration of free fluoride in the acidic aqueous composition of zinc phosphating is below 15 mmol / kg, in particular is preferably below 10 mmol / kg and particularly preferably below 8 mmol / kg.

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

To suppress the so-called speck formation on the surfaces of the metallic materials made of zinc, it is preferred if, in those methods according to the invention in which zinc phosphating takes place in step (ii), the source of free fluoride is at least partially selected from complexes Fluorides of the element Si, in particular from hexafluorosilicic acid and its salts. Speck formation is understood by those skilled in the art of phosphating as the phenomenon of local deposition of amorphous, white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surfaces or on the treated galvanized or alloy-galvanized steel surfaces. The formation of specks is caused by a locally increased pickling rate of the substrate. Such point defects in the phosphating can be the starting point for the corrosive delamination of subsequently applied organic paint systems, so that the occurrence of specks can largely be avoided in practice. In this context, it is preferred if the concentration of silicon dissolved in water in the acidic aqueous composition of the zinc phosphating in process step (ii) is at least 0.5 mmol / kg, particularly preferably at least 1 mmol / kg, particularly preferably at least 2 mmol / kg is, however, preferably less than 15 mmol / kg, particularly preferably less than 12 mmol / kg, particularly preferably less than 10 mmol / kg and very particularly preferably less than 8 mmol / kg. The upper limits for the concentration of silicon are preferred, since above these values phosphate coatings are favored, which predominantly have loose adhesions which cannot be avoided even by a disproportionately increased amount of particulate constituents in the colloidal, aqueous solution of the activation stage. The concentration of silicon in the acidic aqueous composition dissolved in water is to be determined in the filtrate of a membrane filtration of the acidic aqueous composition, which was carried out using a membrane with a nominal pore size of 0.2 µm, by means of atomic emission spectrometry (ICP-OES).

1. (a) 5-50 g/l an Phosphat-Ionen,
2. (b) 0,3-3 g/l an Zink-Ionen, und
3. (c) mindestens eine Quelle für freies Fluorid,

erfolgt, wobei der Quotient aus der Konzentration der Phosphate im anorganischen partikulären Bestandteil der kolloidalen, wässrigen Lösung der Aktivierung in mmol/kg bezogen auf PO₄ zur Summe aus der Konzentration an freiem Fluorid und der Konzentration an Silizium jeweils in der sauren wässrigen Zusammensetzung der Zinkphosphatierung und jeweils in mmol/kg größer als 0,2, vorzugsweise größer als 0,3, besonders bevorzugt größer als 0,4, ist.With regard to the interaction between activation and zinc phosphating, it has been found that the proportion of particulate constituents that contribute to activation must be adapted to the amount of free fluoride and silicon in the zinc phosphating in order to ensure that the layer-forming phosphating on components includes aluminum as a metallic material The higher contents of free fluoride contained in the phosphating bath do not have a detrimental effect on the layer formation, which, in particular when pretreating a large number of components, results in a constant Quality of the phosphate coatings is of great importance. In this context, a method is preferred according to the invention in which a series of components is to be pretreated, which comprises components that are at least partially made of the materials zinc and aluminum, in which the components of the series are activated one after the other in successive process steps (i) and then subjected to zinc phosphating (ii), the activation in process step (i) being carried out by bringing the component into contact with a colloidal, aqueous solution as described above, which in a preferred embodiment is obtainable as a factor of 20 up to 100,000 diluted previously described aqueous dispersion, and containing the zinc phosphating in process step (ii) by bringing into contact with an acidic aqueous composition

1. (a) 5-50 g / l of phosphate ions,
2. (b) 0.3-3 g / l of zinc ions, and
3. (c) at least one source of free fluoride,

takes place, the quotient of the concentration of the phosphates in the inorganic particulate component of the colloidal, aqueous solution of the activation in mmol / kg based on PO ₄ to the sum of the concentration of free fluoride and the concentration of silicon in each case in the acidic aqueous composition of the zinc phosphating and in each case in mmol / kg is greater than 0.2, preferably greater than 0.3, particularly preferably greater than 0.4.

Insofar as the second aspect of the present invention relates to zinc phosphating in process step (ii), the preferred pH value of the acidic aqueous composition causing the zinc phosphating is above 2.5, particularly preferably above 2.7, but preferably is below 3.5, particularly preferably below 3.3. The proportion of free acid in points in the acidic aqueous composition of zinc phosphating in process step (ii) is preferably at least 0.4, but preferably not more than 3.0, particularly preferably not more than 2.0. The percentage of free acid in points is determined by diluting the 10 ml sample volume of the acidic aqueous composition to 50 ml and titrating it with 0.1 N sodium hydroxide solution up to a pH of 3.6. The consumption of ml sodium hydroxide solution indicates the number of free acid points.

The usual additives for zinc phosphating can also be carried out in an analogous manner within the scope of the present invention, so that the acidic aqueous composition in process step (ii) uses the usual accelerators such as hydrogen peroxide, nitrite, hydroxylamine, nitroguanidine and / or N-methylmorpholine-N-oxide and can also contain cations of the metals manganese, calcium and / or iron in the form of water-soluble salts, which have a positive influence on the layer formation. In an embodiment preferred for reasons of environmental hygiene, a total of less than 10 ppm of nickel and / or cobalt ions are contained in the acidic aqueous composition of the zinc phosphating in process step (ii).

In the method according to the invention, a good paint primer is achieved for a subsequent dip painting, in the course of which an essentially organic top layer is applied. Accordingly, in a preferred embodiment of the process according to the invention, zinc phosphating with or without an intervening rinsing and / or drying step, but preferably with a rinsing step but without a drying step, is followed by dip painting, particularly preferably electrodeposition painting, particularly preferably cathodic electrodeposition painting, which is preferably in addition to the dispersed Resin, which preferably comprises an amine-modified polyepoxide, contains water-soluble or water-dispersible salts of yttrium and / or bismuth.

Claims (16)

Process for the anticorrosive pretreatment of a metallic material selected from zinc, iron or aluminum or a component that is at least partially composed of such metallic materials, in which the metallic material or the component is first activated (i) and then phosphated (i) in successive process steps. ii), in particular zinc phosphating, the activation in process step (i) by bringing the metallic material or the component into contact with a colloidal, aqueous solution containing the dispersed particulate component (a) of the solution (a1) at least one particulate inorganic compound which is composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and / or hureaulite, and (a2) at least one polymeric organic compound which is at least partly composed of styrene and / or an α-olefin with no more than 5 carbon atoms and maleic acid, its anhydride and / or its imide and which additionally has polyoxyalkylene units, takes place, wherein in the colloidal, aqueous solution the proportion of condensed phosphates dissolved in water, based on the phosphate content of the at least one particulate compound, based in each case on the element P, is less than 0.25. Method according to claim 1, characterized in that in the colloidal-aqueous solution the proportion of condensed phosphates dissolved in water based on the phosphate content of the at least one particulate compound, based on the element P, is less than 0.20, preferably less than 0.15 , is particularly preferably less than 0.10. Method according to one or both of the preceding claims, characterized in that in the colloidal-aqueous solution the proportion of condensed phosphates dissolved in water calculated as P less than 20 mg / kg, preferably less than 15 mg / kg, particularly preferably less than 10 mg / kg based on the colloidal, aqueous solution. The method according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution at least 0.5 mmol / L, preferably at least 1.0 mmol / L, particularly preferably at least 1.5 mmol / l, but not more than 10 mmol / L of alkaline earth metal ions dissolved in water. Process according to claim 4, characterized in that the colloidal, aqueous solution contains at least one complexing agent, which is preferably selected from α-hydroxycarboxylic acids, which in turn are preferably selected from gluconic acid, tartronic acid, glycolic acid, citric acid, tartaric acid, lactic acid, very particularly preferably gluconic acid , and / or organophosphonic acids, which in turn are preferably selected from etidronic acid, aminotris (methylenephosphonic acid), aminotri (methylenephosphonic acid)), phosphonobutane-1,2,4-tricarboxylic acid, diethylenetriaminepenta (methylenephosphonic acid), hexamethylene diamine tetra (methylenephosphonic acid) and / or hydroxyphosphonic acid , particularly preferably from etidronic acid. The method according to claim 5, characterized in that the amount of complexing agents in the colloidal, aqueous solution is no greater than twice, preferably no greater than 1.5 times the molar amount of alkaline earth metal ions and particularly preferably not the equimolar amount of Alkaline earth metal ions exceeds. Method according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution in activation (i) has an alkaline pH value, preferably a pH value above 8.0, particularly preferably above 9.0, but preferably below 11.0. Method according to one or more of the preceding claims, characterized in that the proportion of phosphates calculated as PO ₄ contained in the at least one particulate inorganic compound (a1) based on the dispersed inorganic particulate component of the colloidal, aqueous solution is preferably at least 25 wt. %, particularly preferably at least 35 % By weight, particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight. Method according to one or more of the preceding claims, characterized in that the polymeric organic compounds (a2) of the colloidal, aqueous solution contain the polyoxyalkylene units in their side chains, the proportion of polyoxyalkylene units in the totality of the polymeric organic compounds (a2 ) is preferably at least 40% by weight, particularly preferably at least 50% by weight, but particularly preferably not exceeding 70% by weight. The method according to one or more of the preceding claims, characterized in that the organic polymeric compounds (a2) of the colloidal, aqueous solution additionally also have imidazole units, preferably such that the polyoxyalkylene units of the polymeric organic compounds (a2) at least partially with an imidazole group are end-capped. Method according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution contains at least one thickener as further component b), which is preferably selected from urea urethane resins, preferably from urea urethane resins, which have an amine number of less than 8 mg KOH / g , particularly preferably less than 5 mg KOH / g, very particularly preferably less than 2 mg KOH / g. Method according to one or more of the preceding claims, characterized in that the total of polymeric organic compounds in and based on the particulate component of the colloidal, aqueous solution is at least 3% by weight, preferably at least 6% by weight, but preferably 15 Wt .-% does not exceed. Method according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution has a D50 value below 1 µm, preferably below 0.4 µm. Method according to one or more of the preceding claims, characterized in that the proportion of the particulate constituents of the colloidal, aqueous solution is at least 0.05 g / kg, preferably at least 0.1 g / kg, particularly preferably at least 0.2 g / kg , but is preferably not greater than 10 g / kg, particularly preferably not greater than 2 g / kg, in each case based on the colloidal, aqueous solution. Method according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution is obtainable as an aqueous dispersion diluted by a factor of 20 to 100,000 - Based on the aqueous dispersion at least 5 wt .-% of a dispersed particulate component (A), which in turn (A1) at least one particulate inorganic compound which is composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and / or hureaulite, (A2) at least one polymeric organic compound which is at least partially composed of styrene and / or an α-olefin with no more than 5 carbon atoms and maleic acid, its anhydride and / or its imide and which additionally has polyoxyalkylene units, as - optionally at least one thickener, which is preferably selected from urea urethane resins, particularly preferably from urea urethane resins, which have an amine number of less than 8 mg KOH / g, preferably less than 5 mg KOH / g, particularly preferably less than 2 mg KOH / g exhibit. Process according to one or more of the preceding claims, characterized in that the phosphating in process step (ii) by bringing into contact with an acidic aqueous composition containing 5 - 50 g / kg of phosphates dissolved in water, calculated as PO ₄ , 0, 3 - 3 g / kg of zinc ions as well an amount of free fluoride takes place, which possibly contains a total of less than 0.1 g / kg of ions of the elements nickel and cobalt.