EP4196625A1

EP4196625A1 - Resource-conserving method for zinc phosphating a metal surface

Info

Publication number: EP4196625A1
Application number: EP21735717.7A
Authority: EP
Inventors: Ralf POSNER; Christina ANGENENDT; Marc Balzer; Franz-Adolf Czika; Sebastian SINNWELL; Jan-Willem Brouwer; Kristof WAPNER
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2020-08-11
Filing date: 2021-06-28
Publication date: 2023-06-21
Also published as: JP2023538000A; MX2023001656A; CN116034185A; EP3954805A1; WO2022033759A1; US20230175138A1; KR20230050387A

Abstract

The present invention relates to a method for layer-forming zinc phosphating of metal surfaces using a colloidal, aqueous solution as an activation stage, wherein a zinc phosphate layer having a layer weight of less than 2.0 g/m² is deposited on the surfaces of zinc in the method step following the activation. The activation stage is based on a colloidal, aqueous solution containing a dispersed, particulate component, wherein the particulate component contains, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, a polymeric organic compound as a dispersant which at least in part is composed of styrene and/or an α-olefin having no more than 5 carbon atoms, wherein the polymeric organic compound has additional units of maleic acid, the anhydride thereof and/or the imide thereof and the polymeric organic compound additionally has polyoxyalkylene units. In order to form closed zinc phosphate coatings which sufficiently protect against corrosion and which can be supplied to subsequent electrophoretic painting, it is necessary that the portion of particulate components of the colloidal, aqueous solution equals at least 4 g/kg in relation to the colloidal, aqueous solution.

Description

"Resource-saving process for zinc phosphating of a metal surface"

The present invention relates to a method for layer-forming zinc phosphating of metallic surfaces using a colloidal, aqueous solution as the activation step, a zinc phosphate layer with a layer weight of less than 2.0 g/m ² being deposited on the zinc surfaces in the method step following activation. The activation stage is based on a colloidal, aqueous solution containing a dispersed particulate component, the particulate component containing, in addition to dispersed inorganic compounds of phosphates of polyvalent metal cations, a polymeric organic compound as a dispersing agent which is composed at least in part of styrene and/or an a -Olefin having not more than 5 carbon atoms, the polymeric organic compound additionally having units of maleic acid, its anhydride and/or its imide and the polymeric organic compound additionally having polyoxyalkylene units. For the formation of closed zinc phosphate coatings that provide adequate protection against corrosion and can be subjected to subsequent electrocoating, it is necessary for the proportion of particulate components in the colloidal, aqueous solution to be at least 4 g/kg, based on the colloidal, aqueous solution.

The layer-forming phosphating is a process that has been practiced and intensively studied for decades for the application of crystalline anti-corrosion coatings on metallic surfaces, in particular on materials made of the metals iron, zinc and aluminium. Zinc phosphating, which is particularly well-established for corrosion protection, takes place in a layer thickness of a few micrometers and is based on corrosive pickling of the metallic material in an acidic, aqueous composition containing zinc ions and phosphates. In the course of pickling, an alkaline diffusion layer forms on the metal surface, which extends into the interior of the solution and within which poorly soluble crystallites form, which precipitate directly at the interface with the metallic material and continue to grow there. Water-soluble compounds, which represent a source of fluoride ions, are often added to support the pickling reaction on materials made of the metal aluminum and to mask the bath poison aluminum, which in dissolved form interferes with the formation of layers on materials made of the metal. By default, the zinc phosphating is adjusted in such a way that closed, crystalline coatings are obtained with a Layer weight of at least 2 g/m ² , especially on the zinc surfaces of the components, for good corrosion protection and paint adhesion. Depending on the metal surface to be phosphated, the pickling described above and the concentration of the active components in the zinc phosphating stage must be adjusted accordingly in order to ensure correspondingly high layer weights on the surfaces of the metals iron or steel, zinc and aluminum. Zinc phosphating always begins with activation of the metallic surfaces of the component to be phosphated. The wet-chemical activation is carried out conventionally by bringing it into contact with colloidal, aqueous solutions of phosphates ("activation stage"), which are immobilized on the metal surface and serve as a growth nucleus for the formation of the crystalline coating within the alkaline diffusion layer in the subsequent phosphating. Suitable dispersions are colloidal mostly neutral to alkaline aqueous compositions based on phosphate crystallites which, in their crystal structure, exhibit only slight crystallographic deviations from the type of zinc phosphate layer to be deposited. In this context, WO 98/39498 A1 teaches in particular divalent and trivalent phosphates of the metals Zn, Fe, Mn, Ni, Co, Ca and Al, with phosphates of the metal zinc preferably being used for activation for subsequent zinc phosphating.

An activation stage based on dispersions of bi- and trivalent phosphates requires a high level of process control in order to keep the activation performance constantly at an optimal level, especially when treating a series of metallic components. For the process to be sufficiently robust, neither foreign ions brought in from previous treatment baths nor aging processes in the colloidal, aqueous solution must lead to a deterioration in the activation performance. A deterioration is initially noticeable in increasing layer weights in the subsequent phosphating and finally leads to the formation of defect-rich or inhomogeneous phosphate layers. Overall, the layer-forming zinc phosphating is therefore a multi-stage process that is complex to control in terms of process engineering, which has also been resource-intensive to date, both in terms of the process chemicals and the energy to be expended. This applies in particular to the process step of zinc phosphating, which initially requires a large amount of material due to the layer formation, especially on components that have zinc surfaces, but also, combined with the required pickling rate, causes a high level of material removal into the phosphating bath. The high pickling rate means that measures to prevent or treat and dispose of Phosphating sludges must be taken, which in turn cannot do without the use of other process chemicals.

There is therefore a need to optimize the pre-treatment line for zinc phosphating, including the activation and phosphating stages, such that the overall process can be carried out in a less resource-intensive manner, especially in the pre-treatment of components that have zinc surfaces. However, a resource-saving overall process must not be at the expense of the properties of the zinc phosphating, which must be provided as a homogeneous, closed coating with high electrical penetration resistance in order to enable good protection against corrosion and a correspondingly good wraparound of the paint in a subsequent electrophoretic coating.

Surprisingly, this complex task profile can be achieved by the deposition of relatively thin phosphate coatings, for which activation using a specific polymeric dispersing agent to stabilize the colloidal component of an activation stage based on particulate phosphates is necessary, provided that it is ensured that a minimum amount of particulate components in the activation level is not undershot. Due to the extremely efficient stabilization of the particulate component that brings about the activation, the special dispersing agent ensures that high proportions of colloids can also be set in a quasi-continuous process of zinc phosphating, which surprisingly leads to improved activation of the metal surfaces and the formation of particularly thin, but more homogeneous, closed Phosphate coatings with high electrical penetration resistance.

The present invention therefore relates to a method for the anti-corrosion pretreatment of a metallic material which at least partially has surfaces of zinc, or a component which is at least partially composed of such a metallic material, in which the metallic material or the component in successive method steps first Activation (i) and then zinc phosphating (ii) is subjected, the activation in process step (i) being carried out 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 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 composed at least in part of styrene and/or an a-olefin having no more than 5 carbon atoms, the polymeric organic compound additionally having units of maleic acid, its anhydride and/or its imide and the polymeric organic compound additionally has polyoxyalkylene units, the proportion of the particulate components of the colloidal, aqueous solution being at least 4 g/kg, based on the colloidal, aqueous solution; and wherein a zinc phosphate layer with a layer weight of less than 2.0 g/m ² is deposited on the surfaces of zinc in process step (ii).

In the context of the method according to the invention, a metallic material has at least one surface of zinc if the metallic structure on this surface is composed of more than 50 at. % zinc up to a material penetration depth of at least one micrometer. This regularly applies to metallic materials that are composed of more than 50 at Iron (ZF), aluminum (ZA) and/or magnesium (ZM) can be alloyed.

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

The dispersed particulate component (a) of the colloidal, aqueous solution in activation (i) of the method according to the invention is that solids content which, after drying the retentate, undergoes 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 (K<IpScrrr ¹ ) until a conductivity below 10 pScrm 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 using the molar mass distribution curve of a sample of the respective reference variable, determined experimentally at 30° C. using size exclusion chromatography with a concentration-dependent refractive index detector and calibrated against polyethylene glycol standards. The average molar mass values are evaluated computer-aided using the strip method with a third-order calibration curve. Hydroxylated polymethacrylate is suitable as column material and an aqueous solution of 0.2 mol/L sodium chloride, 0.02 mol/L sodium hydroxide, 6.5 mmol/L ammonium hydroxide is suitable as eluent.

The method according to the invention is characterized in that above a quantity of particulate components of 4 g/kg in the colloidal, aqueous solution, homogeneous, closed zinc phosphate coatings grow on the surfaces of the metallic materials even at unusually low layer weights, which one with zinc phosphate coatings of the prior art Technically equivalent paint primer for subsequent electrocoating with excellent paint coverage at the same time. Irrespective of this, the present invention aims at the deposition of homogeneous, closed zinc phosphate coatings on the surfaces of zinc, so that according to the invention it is assumed that in process step (ii) a zinc phosphate coating with a layer weight of more than 0.5 g/ m ² , preferably greater than 1.0 g/m ² .

The reduction in the layer weight also enables a shorter wet-chemical exposure time or contact time with the acidic aqueous composition of the zinc phosphating, which in turn correlates with both a lower pickling removal and a shorter overall pre-treatment time. A further reduction in the layer weight or the contact time in the zinc phosphating can be achieved if the proportion of the particulate components in the colloidal, aqueous solution is further increased, so that methods according to the invention are preferred in which the proportion of the particulate components of the colloidal, aqueous solution is at least 6 g/kg, particularly preferably at least 8 g/kg, particularly preferably at least 10 g/kg.

However, the achievable layer weight reduction in zinc phosphating is even greater Increasing the proportion of colloids in the activation stage is only marginal and increasingly competes with disadvantages in the process control and lower colloid stability in the activation stage. It is therefore preferred to limit the proportion of the particulate components in the colloidal, aqueous dispersion to 20 g/kg, particularly preferably to 15 g/kg, in each case based on the colloidal, aqueous solution.

In the method according to the invention, the layer coverage of zinc phosphate on the surfaces of zinc should be limited to 2.0 g/m ² for resource-saving operation of the pretreatment line. According to the invention, due to the minimum amount of particulate components in the colloidal, aqueous dispersion of the activation stage, a sufficiently homogeneous and closed zinc phosphate coating with excellent paint gripping behavior is provided in a subsequent electrocoating. The activation of the zinc surfaces in process step (i) of the process according to the invention is so effective that a further reduction in the layer thickness and thus a further reduction in material consumption in the zinc phosphating stage in process step (ii) is possible. Accordingly, preference is given in process step (ii) to limiting the layer weight of zinc phosphate on the surfaces of zinc to less than 1.8 g/m ² , particularly preferably to less than 1.6 g/m ² , particularly preferably to less than 1 5 g/ ^m2 . The coating weight can be limited in the course of the process either by reducing the contact time with the acidic, aqueous composition for zinc phosphating in process step (ii) and/or by increasing the proportion of the particulate components of the colloidal, aqueous dispersion in process step (i). . In the context of the present invention, the layer weight of zinc phosphate is determined by detaching the zinc phosphate layer with aqueous 5% by weight CrOs as a pickling solution, which is applied immediately after zinc phosphating and rinsing with deionized water (K<1 ScnT ¹ ) at 25 °C for 5 min is brought into contact with a defined area of the phosphated material or component and subsequent determination of the phosphorus content in the same pickling solution with ICP-OES. The layer weight of zinc phosphate results from multiplying the surface-related amount of phosphorus by a factor of 6.23.

A particular further advantage of the method according to the invention is that, in addition to zinc surfaces, the surfaces of iron and aluminum are also very effectively activated in method step (i) and in method step (ii) also very homogeneous, closed zinc phosphate coatings with a comparatively low layer weight accessible to these surfaces. Accordingly, components are preferably treated according to the invention which, in addition to zinc surfaces, also have iron and/or aluminum surfaces, in process step (ii) preferably also a zinc phosphate layer with a layer weight of less than 2.0 g/m on iron and aluminum surfaces ² , more preferably less than 1.8 g/m ² , more preferably less than 1.6 g/m ² , and most preferably less than 1.5 g/m ² , but preferably at least 0.5 g/m 2 ² , particularly preferably at least 1.0 g/m ² is deposited. Similarly, a metallic material has at least one surface made of iron or aluminum if the metallic structure on this surface is composed of more than 50 at. % iron or aluminum up to a material penetration depth of at least one micrometer.

Furthermore, it has been shown in the context of the present invention that the condensed phosphates dissolved in water, which are often additized for colloid stabilization in the activation stages in processes of the prior art, are only of secondary importance for maintaining consistently good phosphate coatings. It is remarkable and surprising for the person skilled in the art that in the method according to the invention, which is based on an activation stage based on the particulate component (a), which is contained in an amount of at least 4 g/kg based on the colloidal aqueous solution, on which Additization of condensed phosphates can be largely or completely dispensed with. In a preferred embodiment of the method according to the invention, the proportion of condensed phosphates dissolved in water in the activation stage, based on the phosphate content of the at least one particulate compound in the colloidal aqueous solution, based on the element P, is less than 0.25, particularly preferably less than 0. 20, more preferably less than 0.15 and most preferably less than 0.10.

Furthermore, it is preferred in this context that the proportion of condensed phosphates dissolved in water in the colloidal, aqueous solution of the method according to the invention, calculated as P, is less than 100 mg/kg, particularly preferably less than 20 mg/kg, particularly preferably less than 15 mg /kg, and most preferably less than 10 mg/kg based on the colloidal aqueous solution. Overall, within the scope of the present invention, the additization of condensed phosphates can also be dispensed with entirely, so that only small amounts of condensed phosphates are found in the activation, which are also present from upstream purification stages the component to be pretreated, especially when treating a large number of components in series, reach the activation stage.

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.

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 using peroxodisulphate, with the dissolved orthophosphate proportion being quantified by photometry. Alternatively, if polyphosphates are used as condensed phosphates, instead of the oxidative digestion, an enzymatic digestion with a pyrophosphatase can take place. The non-particulate component of the colloidal, aqueous solution is the solids content of the colloidal, aqueous solution in the permeate of the ultrafiltration described above after it has been dried to constant mass at 105° C.—i.e. the solids content after the particulate component (a) has been separated off by means of ultrafiltration.

The high tolerance of the method according to the invention to entrained foreign ions also makes it possible for the cleaning stages upstream of the activation stages, rinsing stages and also the activation stage itself to be run 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 in the activation contains 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 plant-specific individual cases with exceptionally high ionic strengths, e.g Bath life organic complexing agents are added to mask the foreign ions. In this case, it must be considered whether the economic advantage that the activation stage and any upstream cleaning stages and rinsing can be operated with process water is counteracted by adding organic complexing agents and monitoring them in the system tank of the activation stage. Suitable organic complexing agents, which are preferred in this context, are selected from a-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 from etidronic acid, aminotris(methylenephosphonic acid), aminotri(methylenephosphonic acid)), phosphonobutane-1,2,4-tricarboxylic acid, diethylenetriaminepenta(methylenephosphonic acid), hexamethylenediaminetetra-(methylenephosphonic acid) and/or hydroxyphosphonoacetic acid, particularly preferably from etidronic acid.

To maintain a stable activation performance, organic complexing agents should only be added to such an extent that their amount in the colloidal, aqueous solution is preferably not more than twice, particularly preferably not more than 1.5 times, based on the amount of alkaline earth metal metal ions and most preferably is not greater than equimolar to the amount of alkaline earth metal metal ions.

The colloidal, aqueous solution in activation (i) of the method according to the invention preferably has an alkaline pH, particularly preferably a pH above 8.0, particularly preferably above 9.0, but preferably below 11.0 , whereby compounds that influence the pH value, such as phosphoric acid, caustic soda, ammonium hydroxide or ammonia, can be used 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.

Good activation performance requires the use of polyvalent metal cations in the form of phosphates, which should be present in the dispersed particulate component (a) in a correspondingly high proportion for activation. Accordingly, the proportion of phosphates is contained in the at least one particulate inorganic Compound (a1), based on the dispersed particulate component (a) of the colloidal, aqueous solution, 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 obtained from the drying of the retentate of the ultrafiltration (a) in a reaction furnace with supply of a CO2-free oxygen stream at 900 ° C without admixture of catalysts or other additives is pyrolyzed until an infrared sensor in the outlet of the reaction furnace delivers a signal identical to the CO2-free carrier gas (blank value). The phosphates contained in the inorganic particulate component are determined directly from the acid digestion as the phosphorus content by means of atomic emission spectrometry (ICP-OES) after acid digestion of the same with aqueous 10% by weight HNO3 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, composed primarily 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, more preferably at least partially selected from hopeite and/or phosphophyllite and most preferably at least partially selected from hopeite. Activation within the meaning of the present invention is therefore essentially based on the phosphates in particulate form contained in the activation stage. Without taking crystal water into account, hopeites stoichiometrically include Zn ₃ (PO4)2 and the variants Zn ₂ Mn(PO4)3 and Zn ₂ Ni(PO4)3 containing nickel and manganese, whereas phosphophyllite consists of Zn ₂ Fe(PO4)3, and scholzite consists of Zn ₂ Ca(PO4)3 and hureaulite consists of Mn ₃ (PO4)2. The existence of the crystalline phases hopeite, phosphophyllite, scholzite and / or hureaulite in the aqueous dispersion according to the invention can, after separating 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 diffractometric methods (XRD).

Due to the preference for the presence of phosphates, which include zinc ions and have a certain crystallinity, it is conducive to the formation of tightly adherent crystalline Zinc phosphate coatings after activation are preferred if in the process according to the invention in the colloidal, aqueous dispersion at least 20% by weight, particularly preferably at least 30% by weight, particularly preferably at least 40% by weight, of zinc in the inorganic particulate component of the colloidal, aqueous Solution based on the phosphate content of the inorganic particulate component, calculated as PO4, are included.

However, activation within the meaning of the present invention should preferably not be achieved by means of colloidal solutions of titanium phosphates, since otherwise the layer-forming zinc phosphating on iron, in particular steel, cannot be reliably achieved. 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 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 stage (i) contains less than 10 mg/kg, particularly preferably less than 1 mg/kg, of titanium in total.

The activation stage in the method according to the invention can also 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 50% by volume of the particulate components contained in the colloidal, aqueous solution do not exceed. The D50 value can be determined according to ISO 13320:2009 by means of scattered light analysis according to the Mie theory from volume-weighted cumulative particle size distributions immediately after sampling from the activation stage at 20 °C, with spherical particles and a refractive index of the scattering particles of no = 1.52 - i 0, 1 are taken as a basis.

According to the present invention, the polymeric organic compounds (a2) used as dispersants are composed in part of styrene and/or an α-olefin having not more than 5 carbon atoms and of maleic acid, its anhydride and/or its imide, and additionally comprise polyoxyalkylene -Units. These polymeric organic compounds (a2) are responsible for 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-methylbut-1-ene and/or 3-methylbut-1-ene and particularly preferably selected from isobutylene. It is clear to the person skilled in the art that the polymeric organic compounds (a2) contain these monomers as structural units in unsaturated form covalently linked to one another or to other structural units. 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 partly composed of styrene.

The polymeric organic compounds (a2) used as dispersants have polyoxyalkylene units which are preferably composed of 1,2-ethanediol and/or 1,2-propanediol, more preferably both 1,2-ethanediol and 1,2 -propanediol, the proportion of 1,2-propanediols in the total of the polyoxyalkylene units preferably being 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 total 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 the anchoring of the dispersing agent 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) have additionally also 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 there are terminal imidazole groups in the polyoxyalkylene side chain, the covalent The polyoxyalkylene units are preferably linked to the imidazole group 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 particulate component (a) also have these preferred amine numbers. The amine number is determined in each case by weighing approximately 1 g of the respective reference quantity - organic polymeric compounds (a2) or all of the polymeric organic compounds in the particulate component - in 100 ml of ethanol, using 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 HCl solution consumed in milliliters multiplied by the factor 5.61 divided by the exact mass of the sample in grams corresponds to the amine number in milligrams of KOH per gram of the respective reference value.

The presence of maleic acid, insofar as it is a component of the organic polymeric compound (a2) as the free acid and not in the form of the anhydride or imide, can impart increased water solubility of the dispersing assistant, particularly 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 but preferably less than 100 mg KOH/g, more preferably less than 70 mg KOH/g to ensure a sufficient number of polyoxyalkylene units. It is furthermore preferred if the polymeric organic compounds (a2), preferably also all of the polymeric organic compounds in the particulate component (a), have 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, determined in each case according to method A of 01/2008:20503 from European Pharmacopoeia 9.0.

For sufficient dispersion of the inorganic particulate components 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.

In a preferred embodiment, the present invention comprises a method for anti-corrosion pretreatment including an aqueous dispersion. In such a preferred process according to the invention, the colloidal, aqueous solution in process step (i) can be obtained as an aqueous dispersion diluted by a factor of 20 to 100,000, comprising: based on the aqueous dispersion, at least 5% by weight of a dispersed particulate component (A), who in turn

(A1) at least one particulate inorganic compound 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 partly composed of styrene and/or an a-olefin having not more than 5 carbon atoms, the polymeric organic compound additionally having units of maleic acid, its anhydride and/or its imide and the polymeric organic compound additionally contains polyoxyalkylene units, and 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.

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

Due to the excellent colloid stability of the particulate component (A) by means of the polymeric organic compound (A2) as a dispersing agent, the dilution is preferably carried out with deionized water (K<1 Scm ^_1 ), particularly preferably with process water, in order to make the process according to the invention as resource-saving as possible shape. Process water in the light of the technical application on which it is based 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 component, thixotropic flow behavior and thus helps counteract the irreversible formation of agglomerates in the particulate component of the dispersion, from which primary particles can no longer be separated. The addition of the thickener should preferably be controlled in such a way that the aqueous dispersion has a maximum dynamic viscosity in the shear rate range of 0.001 to 0.25 reciprocal seconds at a temperature of 25° C. of at least 1000 Pas, but preferably below 5000 Pas and preferably at shear rates above those present at the maximum dynamic viscosity at 25° C., exhibits shear-thinning behavior, ie a decrease in viscosity with increasing shear rate, so that the aqueous dispersion exhibits thixotropic flow behavior overall. The viscosity over the specified shear rate range can be determined using a plate/cone viscometer with a cone diameter of 35 mm and a gap width of 0.047 mm.

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

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), with further preference the total proportion of polymeric organic compounds in the non-particulate component of the aqueous dispersion is 4% by weight (based on the dispersion). exceeds. The non-particulate component is the solids content of the aqueous dispersion in the permeate of the ultrafiltration already described after it has been dried to constant mass at 105° C.—ie the solids content after the particulate component has been separated off by means of ultrafiltration.

Certain classes of polymeric compounds are particularly suitable thickeners 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 inventive method for providing a colloidal aqueous solution starting from the aqueous dispersion is a mixture of polymeric compounds resulting from the reaction of a polyfunctional isocyanate with a polyol and a mono- and / or diamine emerges. In a preferred embodiment, the urea urethane resin is derived from a polyfunctional isocyanate, preferably selected from 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2(4),4-trimethyl-1,6-hexamethylene diisocyanate, 1,10- Decamethylene diisocyanate, 1,4'-cyclohexylene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate and mixtures thereof, p- and m-xylylene diisocyanate, and 4-4'-diisocyanatodicyclohexylmethane, particularly preferably selected from 2,4-toluene diisocyanate and/or m-xylylene diisocyanate. In a particularly preferred embodiment, the urea-urethane resin is derived from a polyol selected from polyoxyalkylene diols, particularly preferably from polyoxyethylene glycols, which in turn are preferably composed of at least 6, particularly preferably at least 8, particularly preferably at least 10, but preferably less than 26, particularly preferably less than 23 oxyalkylene units.

According to the invention particularly suitable and therefore preferred urea urethane resins are obtainable by a first reaction of a diisocyanate, such as toluene-2,4-diisocyanate, with a polyol, such as 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. Particular preference is given to urea-urethane resins which have neither free nor blocked isocyanate groups. As a component of the aqueous dispersion from which the colloidal, aqueous solution of the process according to the invention can be obtained by dilution, such urea-urethane resins promote the formation of loose agglomerates of primary particles, which in turn are stabilized in the aqueous phase and protected against further agglomeration to such an extent that the sedimentation of the particulate component 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. g, determined in each case by the method 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 component of the aqueous dispersion, while component (A2) is essentially bound in the particulate component (A), an aqueous dispersion is accordingly required for providing the colloidal , Aqueous solution of activation preferred in which all of the polymeric organic compounds in the non-particulate component preferably have an amine number of less than 16 mg KOH / g, more preferably less than 10 mg KOH / g, particularly preferably less than 4 mg KOH/g. Furthermore, it is preferred that the urea-urethane resin has a hydroxyl number in the range from 10 to 100 mg KOH/g, 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. having. 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.

The pH of the dispersion for providing the colloidal, aqueous solution for activating the method according to the invention is usually in the range of 6.0-9.0 without the addition of auxiliaries, and such a pH range is therefore preferred according to the invention. However, it is necessary for compatibility with the actual and regularly alkaline colloidal, aqueous solution in the activation stage of advantage if the pH of the aqueous dispersion, possibly also as a result of the addition of alkaline-reacting compounds, is above 7.2, particularly preferably above 8.0. The alkalinity of the aqueous dispersion according to the invention is ideally limited, since some polyvalent metal cations have an amphoteric character and can therefore be dissolved out of the particulate component at higher pH values, so that the pH value of the aqueous dispersion is preferably below 10 and in particular preferably below 9.0.

The aqueous dispersion described above for providing the colloidal, aqueous solution is in turn preferably obtainable by 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 from 4 to 7 parts by mass of water and grinding until a D50 value of less than 1 μm is reached, determined by means of dynamic light scattering after dilution with water by a factor of 1000, for example using Zetasizer® Nano ZS, from Malvern Panalytical GmbH; ii) Diluting the pigment paste with such an amount of water, preferably deionized water (K<1 Scm ^_1 ) or process water, and a thickener (B) that a dispersed particulate component (A) of at least 5% by weight and a maximum dynamic viscosity of at least 1000 Pa s at a temperature of 25 °C in the shear rate range of 0.001 to 0.25 reciprocal seconds; and iii) setting a pH in the range from 7.2 to 10.0 with the aid of an alkaline compound, with preferred embodiments of the dispersion being determined by selecting appropriate components (A1), (A2) and (A) in the respectively provided or required amount, as described in connection with the colloidal aqueous solution, are obtained in an analogous manner.

The aqueous dispersion can also contain auxiliaries, for example selected from preservatives, wetting agents and defoamers, which are present in the amount required for the particular function. Preferably, the proportion of auxiliaries, particularly preferably of other compounds in the non-particulate component, which are not thickeners and are not alkaline-reacting compounds, 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 K<1 Scrrr ¹ ) and has a pK _B value for the first protonation stage above 8.0.

The resource-saving process management according to the present invention is particularly useful in the zinc phosphating of components in series, ie during ongoing operation of a pre-treatment line for zinc phosphating. In a preferred embodiment of the method according to the invention, a large number of concrete components which are at least partially composed of a metallic material which has at least one surface made of zinc are therefore treated in series. A pretreatment in series is when the components of the series are first activated according to the method according to the invention and then zinc phosphated and are brought into contact with baths provided in system tanks for activation and zinc phosphating, the individual components being brought into contact one after the other and is therefore separated in time. The system tank is the container that contains the colloidal, aqueous solution for the purpose of activation or the acidic, aqueous composition for the purpose of phosphating.

There can be a rinsing step between the activation (i) and the zinc phosphating (ii) in order to reduce the carryover of alkaline components into the acidic aqueous composition for zinc phosphating, but a rinsing step is preferably omitted in order to obtain the activation of the metallic surfaces completely. A rinsing step is used exclusively for the complete or partial removal of soluble residues, particles and active components, which are carried over from a previous wet-chemical treatment step adhering to the component, from the component to be treated, without the rinsing liquid itself containing active components based on metallic or semi-metallic elements, which are already consumed by the mere contact of the metallic surfaces of the component with the rinsing liquid. Thus, the rinsing liquid can only be city water or deionized water or, if necessary, it can also be a rinsing liquid which contains surface-active compounds to improve the wettability with the rinsing liquid.

For a layer-forming zinc phosphating and the formation of semi-crystalline coatings aimed at activating the metallic materials, it is preferred that the phosphating in step (ii) by bringing the surfaces into contact with a acidic aqueous composition containing 5 - 50 g/l of phosphate ions, 0.3 - 3 g/l of zinc ions and a quantity of free fluoride. According to the invention, the amount of phosphate ions includes the orthophosphoric acid and the anions of the salts of orthophosphoric acid dissolved in water, calculated as PO4.

A quantity of free fluoride or a source of free fluoride ions is essential for the process of layer-forming zinc phosphating, insofar as components comprising surfaces of zinc as well as surfaces of iron or aluminum are to be zinc-phosphated in a layer-forming manner, as is the case, for example, in the zinc phosphating of automobile bodies, which are at least partially made of aluminum is required. In this connection it is advantageous if the amount of free fluoride in the acidic aqueous composition is at least 0.5 mmol/kg, particularly preferably at least 2 mmol/kg. The concentration of free fluoride should not exceed values above which the phosphate coatings mainly have adhesions that can be easily wiped off, since this cannot be avoided even by a disproportionately increased amount of particulate components in the colloidal, aqueous solution of the activation. It is therefore also advantageous for economic reasons and therefore preferred if, in the method 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, particularly preferably below 10 mmol/kg and particularly preferably below 8 mmol/kg.

The amount of free fluoride is to be determined potentiometrically at 20 °C in the respective acidic aqueous composition after calibration with fluoride-containing buffer solutions without pH buffering using a fluoride-sensitive measuring electrode. Suitable sources for free fluoride ions are hydrofluoric acid and its water-soluble salts, such as ammonium bifluoride and sodium fluoride, and complex fluorides of the elements Zr, Ti and/or Si, in particular complex fluorides of the element Si. The source of free fluoride in a phosphating according to the present invention is therefore preferably selected from hydrofluoric acid and its water-soluble salts and/or complex fluorides of the elements Zr, Ti and/or Si. Salts of hydrofluoric acid are water-soluble in the context of the present invention if their solubility in deionized water (K<1 Scm ^-1 ) at 60°C is at least 1 g/L calculated as F. In order to suppress the so-called speckle formation on the surfaces of the metallic materials made of zinc, it is preferred if the source of free fluoride is at least partially selected from complex ones in processes according to the invention in which zinc phosphating takes place in step (ii). Fluorides of the element Si, in particular from hexafluorosilicic acid and its salts. Those skilled in the art of phosphating understand the formation of specks as the phenomenon of local deposition of amorphous, white zinc phosphate in an otherwise crystalline phosphate layer on the treated zinc surfaces or on the treated galvanized or alloy-galvanized steel surfaces.

In process step (ii) of the process according to the invention, the preferred pH of the acidic aqueous composition is above 2.5, particularly preferably above 2.7, but preferably below 3.5, particularly preferably below 3.3. The proportion of the free acid in points in the acidic aqueous composition of the 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 a 10 ml sample volume of the acidic aqueous composition to 50 ml and titrating with 0.1 N sodium hydroxide solution to pH 3.6. The consumption of ml of sodium hydroxide indicates the number of free acid points.

The usual additization of 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) contains the usual accelerators such as hydrogen peroxide, nitrite, hydroxylamine, nitroguanidine and/or N-methylmorpholine N-oxide and additionally 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. An embodiment in which 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) is particularly preferred from an ecological point of view.

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

Claims

Expectations

1 . Process for the anti-corrosion pretreatment of a metallic material which at least partially has zinc surfaces, or a component which is at least partially composed of such a metallic material, in which the metallic material or the component is first activated in successive process steps (i) and then is subjected to zinc phosphating (ii), the activation in process step (i) being carried out 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 composed of phosphates of polyvalent metal cations at least partially selected from hopeite, phosphophyllite, scholzite and/or hureaulite, and

2. The 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 0.25, preferably less than 0.20 , particularly preferably less than 0.15, particularly preferably less than 0.10. Method according to one or both of the preceding claims, characterized in that the colloidal, aqueous solution in activation (i) has an alkaline pH, preferably a pH above 8.0, particularly preferably above 9.0, but preferably below 11.0. Process according to one or more of the preceding claims, characterized in that the proportion of phosphates, calculated as PO4 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% by weight , particularly preferably at least 35% by weight, particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight. Process 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 does not exceed 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 also have imidazole units, preferably such that the polyoxyalkylene units of the polymeric organic compounds (a2) at least partially an imidazole group are end-capped. Process according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution contains at least one thickener as a 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 % by weight does not exceed. Process according to one or more of the preceding claims, characterized in that the colloidal, aqueous solution has a D50 value below 1 pm, preferably below 0.4 pm. Process according to one or more of the preceding claims, characterized in that the proportion of particulate components in the colloidal, aqueous solution is at least 6 g/kg, preferably at least 8 g/kg, particularly preferably at least 10 g/kg, but preferably not greater as

20 g/kg, particularly preferably not greater than 15 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, comprising at least 5% by weight of a dispersed particulate component (A) , in turn

(A2) at least one polymeric organic compound which is composed at least in part of styrene and/or an a-olefin having no more than 5 carbon atoms, the polymeric organic compound additionally having units of maleic acid, its anhydride and/or its imide and the Polymeric organic compound additionally has polyoxyalkylene units, contains, and 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. Method according to one or both of the preceding claims, characterized in that on the surfaces of zinc in method step (ii) a zinc phosphate layer with a layer weight of less than 1.8 g/m ² , preferably less than 1.6 g/m ² , more preferably less than 1.5 g/m ² . Process according to one or more of the preceding claims, characterized in that the zinc phosphating in process step (ii) is carried out by bringing it into contact with an acidic aqueous composition containing 5 - 50 g/kg of phosphates dissolved in water, calculated as PO4, 0.3 - 3 g/kg of zinc ions and an amount of free fluoride that may contain less than 0.1 g/kg of ions of the elements nickel and cobalt in total. Method according to one or more of the preceding claims, characterized in that components are treated which, in addition to zinc surfaces, also have iron and/or aluminum surfaces and in method step (ii) preferably have a zinc phosphate layer on all zinc, iron and aluminum surfaces a layer weight of less than 2.0 g/m ² , particularly preferably less than 1.8 g/m ² , particularly preferably less than 1.6 g/m ² , and very particularly preferably less than 1.5 g/m ² is deposited.