Aqueous compositions comprising polyelectrolyte and (METH)acrylic polymer suitable for organic dipcoat applications

Abstract

The present invention relates to an aqueous coating composition comprising at least one of Zr, Ti and Hf cations a1), at least one polyelectrolyte a2), at least one polymer P as a3), which is obtainable from a polymerization of at least one (meth)acrylic monomer in the presence of at least one block copolymer BC, and said BC as a4), wherein BC contains at least two blocks B1 and B2, B1 comprising structural units SU1, wherein at least a part of SU1 contains at least one phosphorous containing moiety, which in turn is part of the side chains of SU1 and is, within each SU1, separated from the main chain of BC by at least one carbon atom, and B2 comprising structural units SU2, which are obtainable from a polymerization of at least one (meth)acrylic monomer, a concentrate for producing the aqueous coating composition by dilution with water, a method for coating an optionally pre-coated metallic substrate, which makes use of said aqueous coating composition, to a coated substrate obtainable by said method, and to several uses related to the aqueous coating composition and / or at least one of its ingredients.

Description

[0001] Aqueous compositions comprising polyelectrolyte and (meth)acrylic polymer suitable for organic dipcoat applications

[0002] The present invention relates to an aqueous coating composition, a concentrate for producing the aqueous coating composition by dilution with water, a method for coating an optionally pre-coated metallic substrate, which makes use of said aqueous coating composition, to a coated substrate obtainable by said method, and to several uses related to the aqueous coating composition and / or at least one of its ingredients.

[0003] Background of the invention

[0004] Metal substrates made, e.g., from aluminum, an aluminum alloy, steel, and / or a steel alloy, are nowadays typically generally subjected to an anti-corrosive and / or adhesion-promoting chemical pretreatment method for all sorts of different applications. Examples of such a chemical pretreatment is a pretreatment method, in which a coating such as a conversion coating, which may be an organic coating, is formed directly onto a surface of the metal (direct-to- metal applications).

[0005] One example of such a direct-to-metal application is the organic dip coating technology, where coating films of around 20 to 25 pm dry film thicknesses, which are sometimes but not necessarily pigmented, are formed on the surface of the metal substrate, in particular in case of substrate surfaces made of galvanized steel or cold rolled steel (CRS) or made of aluminum. Organic coating such as organic dip coatings may, however, not only be applied directly onto a metal surface, but also on pre-coated metal surfaces, e.g., on metal surfaces bearing already a usually thin layer for (additional) corrosion protection such as a zinc phosphate layer

[0006] Coating compositions suitable to be used in this kind of technology, in particular in the organic dip coating technology, are known in the prior art. Often, (meth)acrylic polymers, in particular (meth)acrylic copolymers, are used as polymeric binder constituents in such coating compositions. For example, WO 2021 / 008860 A1 discloses an aqueous autophoretically depositable composition comprising inter alia fluoride ions, iron(lll) ions, and at least one organic binder component dispersed in the aqueous phase, wherein said binder component comprises a copolymerizate obtainable from a water-dispersible, polymerizable (meth)acrylic acid compound and at least one acrylated mono- or diphosphate ester compound. The use of autophoretic deposition processes is, however, often disadvantageous in terms of an only insufficient corrosion protection, when autophoretically depositable compositions such as the ones disclosed in WO 2021 / 008860 A1 are applied onto metal surfaces.

[0007] It is also known to use a polymeric binder such as a (meth)acrylic polymer in combination with other organic polymers such as polyanionic polymers, e.g., polysaccharides, in particular in organic dip coat compositions, e.g., for improving the water resistance of the coatings obtained. Aqueous acidic depositable coating compositions containing inter alia polysaccharides, e.g., in form of polyelectrolytes, are known from US 2020 / 0207995 A1 and US 2017 / 0081542 A1. The coating compositions disclosed in US 2020 / 0207995 A1 inter alia comprise an NCO- reactive polymer such as polyurethane-polyacrylate hybrid polymer, said polymer being stabilized in the aqueous composition by use of suitable emulsifiers, a blocked polyisocyanate, a polyanionic polymer such as a naturally occurring anionic polysaccharide, and a complex fluoride, and are curable at baking temperatures of below 200 °C and provide a corrosion resistance to the metal surfaces once applied onto them. The coating compositions disclosed in US 2017 / 0081542 A1 inter alia comprise a stabilized dispersion of a polymeric binder such as of a polyurethane-polyacrylate hybrid polymer, a polyelectrolyte such as a polysaccharide as well as a complex fluoride. Besides the comparable complex synthesis of aforementioned hybrid polymers, the stabilization according to US 2020 / 0207995 A1 and US 2017 / 0081542 A1 necessarily is an anionic stabilization, which prevents the use of other suitable stabilization techniques, e.g., via non-ionic stabilization. Further, US 2019 / 0300722 A1 relates to stabilized polymeric binders, e.g., for use as stabilized polymeric binders according to US 2020 / 0207995 A1 and US 2017 / 0081542 A1 , such as polyurethane-polyacrylate hybrid polymers being present in an aqueous phase, which have been internally stabilized by chemical modification of suitable reactive functional groups of the binder with a suitable hydrophilic constituent such as a PEG-groups containing constituent. The binder is capable of codeposition with suitable ionogenic gel-formers such as polysaccharides once applied onto suitable substrate surfaces.

[0008] In the conventional aqueous coating compositions of the prior art it is, however, problematic that the polyelectrolyte being present therein such as a polysaccharide, which is used for co-deposition of the polymeric binder on the metallic surface, is often not compatible or not sufficiently compatible with the stabilization groups of the polymeric binder, in particular when said polymeric binder is a (meth)acrylic polymer, in particular a (meth)acrylic copolymer. Such an insufficient compatibility leads to formation of a gel and / or to a precipitation of the polymeric binder during formulation of the coating composition, which is, of course, undesired. As a further result of the aforementioned insufficient compatibility often no deposition of the coating composition onto the metallic surface at all can be achieved, since the deposition of the polymeric binder is inter alia triggered by ionogenic gelation of the polyelectrolyte such as the polysaccharide. Furthermore, the conventional aqueous coating compositions of the prior art often exhibit an insufficient water resistance, which is disadvantageous, since deposited coatings obtainable therefrom can then be at least partially washed out from the surface when performing a rinsing step. Additionally, the conventional aqueous coating compositions of the prior art often do not have a sufficient adhesion to the surfaces of the metal substrates they are applied to.

[0009] Thus, there is a need to provide aqueous coating compositions suitable to form organic coating layers on metallic substrates, in particular when applied via the organic dip coating technology, both in a direct-to-metal application and on metal surfaces already bearing a coating layer such as zinc phosphate layer or a thin conversion coating layer, in which a polyelectrolyte such as a polyanionic polymer and a polymer prepared from at least one kind of (meth)acrylic monomers and used as polymeric binder, both being present in the aqueous coating compositions, display an excellent compatibility to each other, such that an easy and smooth co-deposition of these two constituents can take place when the compositions are applied onto a metallic surface, wherein the aqueous coating compositions at the same time are able to provide both an excellent corrosion protection and an excellent water resistance once applied as coating films or layers onto the surfaces of the metallic substrates as well as an excellent adhesion to the metallic surfaces.

[0010] Problem

[0011] It has been therefore an objective underlying the present invention to provide aqueous coating compositions suitable to form organic coating layers on metallic substrates, in particular when applied via the organic dip coating technology, both in a direct-to-metal application and on metal surfaces already bearing a coating layer such as zinc phosphate layer, in which a polyelectrolyte such as a polyanionic polymer and a polymer prepared from at least one kind of (meth)acrylic monomers and used as polymeric binder, both being present in the aqueous coating compositions, display an excellent compatibility to each other, such that an easy and smooth co-deposition of these two constituents can take place when the compositions are applied onto a metallic surface, wherein the aqueous coating compositions at the same time are able to provide both an excellent corrosion protection and a water resistance once applied as coating films or layers onto the surfaces of the metallic substrates as well as an excellent adhesion to the metallic surfaces.

[0012] Solution

[0013] This objective has been solved by the subject-matter of the claims of the present application as well as by the preferred embodiments thereof disclosed in this specification, i.e. by the subject matter described herein.

[0014] A first subject-matter of the present invention is an aqueous coating composition comprising, besides water, at least constituents a1), a2), a3, and a4), which are different from one of another, namely at least one of zirconium, titanium, and hafnium cations as constituent a1), at least one polyelectrolyte as constituent a2), at least one polymer P as constituent a3), which is obtainable from a polymerization of at least one (meth)acrylic monomer in the presence of at least one block copolymer BC, and at least one block copolymer BC as constituent a4), in which presence the polymerization of the at least one (meth)acryl ic monomer for preparing the at least one polymer P has taken place, wherein said block copolymer BC contains at least two blocks B1 and B2, which are different from one another, the first block B1 comprising structural units SU1, wherein at least a part of these structural units SU1 contains at least one phosphorous containing moiety, which in turn is part of the side chains of the structural units SU1 and is, within each structural unit SU1 , separated from the main chain of the block copolymer BC by at least one carbon atom, and the second block B2 comprising structural units SU2, which are obtainable from a polymerization of at least one (meth)acrylic monomer, which is identical to or different from the at least one (meth)acry I ic monomer used for preparing the at least one polymer P.

[0015] A further subject-matter of the present invention is a concentrate for producing the aqueous coating composition according to one or more of the preceding claims by diluting the concentrate with water and if applicable by adjusting the pH value.

[0016] A further subject-matter of the present invention is a use of the aqueous coating composition according to the present invention for corrosion protection of metallic substrates, preferably after having applied the aqueous coating composition at least in portion onto a surface of an optionally pre-coated metallic substrate to form a coating film at least in portion on said surface, and / or a use of the at least one inventively used block copolymer BC as defined hereinbefore and hereinafter for stabilizing at least one inventively used polymer P as defined hereinbefore and hereinafter in an aqueous coating composition further comprising at least one polyelectrolyte as defined hereinbefore and hereinafter, preferably in an aqueous coating composition according to the present invention, and / or a use of the at least one inventively used block copolymer BC as defined hereinbefore and hereinafter for improving and / or for establishing compatibility between at least one inventively used polymer P as defined hereinbefore and hereinafter and at least one polyelectrolyte as defined hereinbefore and hereinafter, preferably in an aqueous coating composition according to the present invention.

[0017] A further subject-matter of the present invention is a method of coating of an optionally pre-coated metallic substrate comprising at least a step 1) and optionally also a step 2), namely

[0018] 1) applying the aqueous coating composition according to the present invention at least in portion onto at least one surface of at least one metallic substrate to form a coating film at least in portion onto said surface, and

[0019] 2) optionally curing or drying the coating film obtained after step 1) to give a cured or dried coating layer, wherein the obtained cured or dried coating layer preferably has a dry film thickness in a range of from 10.0 pim to 30.0 pirn.

[0020] A further subject-matter of the present invention is a substrate, which is a coated substrate being obtainable by the inventive coating method.

[0021] It has been in particular surprisingly found that the inventive aqueous coating composition is suitable for use in direct-to-metal applications and for applications, in which the metal surfaces already bear a thin coating layer such as zinc phosphate layer, in particular when applied via the organic dip coating technology, and is able to form an organic coating film and layer on the surfaces of the metallic substrate. Moreover, it has been in particular surprisingly found that the at least one polyelectrolyte such as a polyanionic polymer and the least one polymer P usable as polymeric binder, both being present in the aqueous coating compositions, display an excellent compatibility to each other, which allows a long-term stability of the aqueous composition once formulated, e.g., upon storage. It has been found that the observed excellent compatibility and the resulting stability of these two constituents is in particular due to the presence of the block copolymer BC in the aqueous coating composition, which is able to provide a sufficient stabilization of the at least one polymer P in water or aqueous media such that no other external emulsifiers are needed for stabilization, and which thus, due to said stabilization, provides for an excellent compatibility between the polymer P and the polyelectrolyte such as a polyanionic polymer, e.g., pectin.

[0022] In addition, it has been in particular surprisingly found that an easy and smooth deposition of the aqueous coating compositions and in particular an easy and smooth co-deposition of the polymer P used as main polymeric binder and the polyelectrolyte can take place, when the composition is applied onto a metallic surface. It has been found in this regard that said easy and smooth deposition of the polymeric binder is triggered by ionogenic gelation of the polyelectrolyte such as the polysaccharide.

[0023] Further, it has been in particular surprisingly found that the inventive aqueous coating composition, after having applied said composition to a metal surface, is able to lead at least to the same, but preferably to an improved, substrate adhesion and adhesion to any layers applied on top, as conventionally used aqueous coating compositions, in particular due to the presence of the block copolymer BC therein and its phosphorous containing moiety within block B1 , which allows to be anchored to the metallic surface, and, further, is able to lead at least to the same, but preferably to an improved corrosion protection compared to conventional aqueous coating compositions, again in particular due to the presence of the block copolymer BC therein and its phosphorous containing moiety within block B1 , which allows to be anchored to the metallic surface.

[0024] In addition, it has been found that the inventive aqueous coating composition, after having applied said composition to a metal surface, is able to provide an excellent water resistance as well, in particular an improved water resistance, e.g., when performing a rinsing step with water, compared to conventional aqueous coating compositions.

[0025] Further, it has been found that the inventive aqueous coating composition, after having applied said composition to a metal surface, provides an excellent adhesion to the metal surface, in particular due to the presence of the at least one phosphorous containing moiety in the side chains of structural units SU1 of the first block B1 of the block copolymer BC.

[0026] Further, since, as mentioned above, no external emulsifiers / surfactants are needed for stabilization of polymer due to the fact that the use and presence of the block copolymer BC already provides an excellent stability of polymer P in water, the water and thus rinsing resistance can be improved for this reason as well, since the block copolymers BC only have a very low mobility, in contrast to conventionally used emulsifiers.

[0027] Moreover, it has been found that it is possible to include a suitable crosslinking agent such as a blocked isocyanate into the inventive aqueous coating composition, in particular in order to be able to reduce the curing temperature.

[0028] Detailed description of the invention

[0029] The term "comprising” in the sense of the present invention, in connection for example with the aqueous coating composition, preferably has the meaning of "consisting of”. With regard, e.g., to said composition referred to hereinbefore, it is possible - in addition to all mandatory constituents present therein - for one or more of the further optional constituents identified hereinafter to be also included therein. All constituents may in each case be present in their preferred embodiments as identified below.

[0030] The proportions and amounts in wt.-% (% by weight) of any of the constituents given hereinafter, which are present in each of the compositions such as the aqueous coating composition add up to 100 wt.-%, based in each case on the total weight of the respective composition.

[0031] Aqueous coating composition

[0032] The aqueous coating composition comprises, besides water, at least constituents a1), a2), a3, and a4), which are different from one of another.

[0033] The aqueous coating composition is suitable to be used in dipcoat applications such as organic dipcoat applications. This technique is known by a person skilled in the art.

[0034] Preferably, the aqueous coating composition is an aqueous acidic coating composition, which more preferably has a pH value in a range of from 0.1 to <7.0, still more preferably of from 0.5 to 6.5, even more preferably of from 1.0 to 6.0, yet more preferably of from 1.5 or 2.0 or 5.5, still more preferably of from 2.5 or 3.0 to 5.5, most preferably of from 3.5 or 3.8 to 5.5. The pH value can be in particular adjusted by using a suitable pH adjusting constituent, in particular sodium and / or potassium hydroxide and / or sodium and / or potassium and / or ammonium carbonate for alkaline adjustment, or can be in particular adjusted in case acidic adjustment is needed by at least one inorganic acid such as phosphoric and / or sulfuric and / or boric acid and / or nitric acid and / or by at least one organic acid such as methyl sulfonic acid. Preferably, phosphoric acid is used.

[0035] The aqueous coating composition preferably is a dispersion or solution. The aqueous coating composition is preferably free or essentially free of any chromium ions such as Cr(VI) cations and / or Cr(lll) cations, more preferably is free of chromium ions or comprises a maximum amount of chromium ions of <10 mg / L, calculated as metal, and / or is free or essentially free of any nickel ions such as Ni(ll) cations and / or Ni(lll) cations, more preferably is free of nickel ions or comprises a maximum amount of nickel ions of <10 mg / L, calculated as metal. “Essentially free” in this context means in each case that at least on purpose none of the aforementioned constituents is added, but it may not be ruled out that any residues of any of the constituents may be present as impurities and / or may be present in amounts being naturally present in water.

[0036] The term “aqueous” with respect to the aqueous coating composition in the sense of the present invention preferably means that the composition is a composition containing at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-% in particular at least 80 wt.-%, most preferably at least 90 wt.-% of water, based on its total content of organic and inorganic solvents including water. Thus, the aqueous composition may contain at least one organic solvent besides water - however, in an amount lower than the amount of water present.

[0037] Preferably, the aqueous coating composition contains at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-% in particular at least 80 wt.-%, of water, in each case based on its total weight.

[0038] Preferably, the amount of organic solvent(s) present in the aqueous coating composition does not exceed 5 wt.-%, yet more preferably does not exceed 2.5 wt.-%, even more preferably is at most 2.0 wt.-%, in each case based on the total weight of the composition.

[0039] Preferably, the aqueous coating composition has a solid content in a range of from 5.0 to 50.0 wt.-%, more preferably of from 7.5 to 40.0 wt.-%, even more preferably of from 10.0 to 35.0 wt.-%, still more preferably of from 12.5 to 30.0 wt.-%, even more preferably of from 15.0 to 25.0 wt.-%. The solid content is determined according to the method disclosed in the 'method' section.

[0040] Preferably, the aqueous coating composition does not comprise any sulfate and / or phosphate containing constituents such as sulfate and / or phosphate containing emulsifiers and / or surfactants. Preferably, the aqueous coating composition does not comprise any surfactants at all, despite any surfactants being subsumable under the definition of the mandatory constituents of the aqueous coating composition.

[0041] Constituent a1)

[0042] At least one of zirconium, titanium, and hafnium cations is present as constituent a1) in the aqueous coating composition.

[0043] Preferably, at least one of zirconium and titanium cations, more preferably zirconium cations, are present as constituent a1). Preferably, the aqueous coating composition comprises the at least one of zirconium, titanium, and hafnium cations as constituent a1) in an amount in a range of from 5 to 50 000 mg / L, more preferably of from 7.5 to 40 000 mg / L, even more preferably of from 10 to 30 000 mg / L, still more preferably of from 12.5 to 20 000 mg / L, yet more preferably of from 15 to 10 000 mg / L, even more preferably of from 20 to 8000 mg / L, still more preferably of from 25 to 6 000 mg / L, most preferably of from 50 to 3000 mg / L, in each case calculated as metal.

[0044] Preferably, a precursor metal compound is used to generate constituent a1). Preferably, the precursor metal compound is water-soluble. Solubility is determined at a temperature of 20°C and atmospheric pressure (1.013 bar). Particularly preferred zirconium, titanium, and / or hafnium compounds for use as precursor compounds are the complex fluorides of these metals. The term “complex fluoride” includes the single and multiple protonated forms as well as the deprotonated forms. It is also possible to use mixtures of such complex fluorides. Complex fluorides in the sense of the present invention are preferably complexes of metal cations such as zirconium, titanium and / or hafnium cations formed with fluoride ions in the composition, e.g., by coordination of fluoride anions to zirconium, titanium, and / or hafnium cations in the presence of water. In case complex fluorides of at least one of zirconium, titanium and / or hafnium cations have been used as precursor compounds, the aqueous composition further comprises fluoride anions as constituent a5).

[0045] Additionally, or alternatively, zirconium cations can also be added in form of zirconyl compounds as, e.g., zirconyl nitrate, zirconyl acetate, zirconium ammonium carbonate and / or zirconium nitrate, the latter one being particularly preferred, in particular when the aqueous composition is acidic. The same similarly applies to titanium and hafnium cations Preferably, however, zirconium, titanium, and / or hafnium compounds for use as precursor compounds are the complex fluorides of these metals

[0046] The content of constituent a1) can be monitored and determined by the means of ICP-OES (optical emission spectroscopy with inductively coupled plasma). Said method is described hereinafter in the 'method' section.

[0047] Constituent a2)

[0048] At least one polyelectrolyte is present as constituent a2) in the aqueous coating composition.

[0049] The term “polyelectrolyte" is known to a person skilled in the art, e.g., from the IUPAC gold book, PAC, 2006, 78, 2067 on page 2072. In accordance therewith, the term “polyelectrolyte" in the sense of the present invention preferably means a polymer, in which a portion such as a substantial portion of its structural and constitutional units contains ionic and / or ionizable groups. In the sense of the present invention the terms “polyelectrolyte”, “polymer electrolyte” and “polymeric electrolyte" are interchangeable.

[0050] The at least one polyelectrolyte preferably takes part, besides the at least one polymer P and the at least one block copolymer BC, in the deposition on the surface of the substrate, when the aqueous coating composition is applied thereon. It is hence preferably co-deposited besides polymer P and block copolymer BC. Preferably, the at least one polyelectrolyte is selected from polyanionic polymers, more preferably from polyanionic polymers having at least one kind of functional groups selected from acid groups, even more preferably from polyanionic polymers having at least one kind of functional groups selected from acid groups that are convertible into a salt, still more preferably selected from polyanionic polymers having at least one kind of functional groups selected from carboxyl acid groups, sulfonic acid groups, and mixtures thereof, yet more preferably selected from polyanionic polymers having carboxyl acid groups. It is possible that the at least one kind of functional groups are present in a partially esterified and / or partially amidated and / or partially epoxidized form.

[0051] Preferably, the at least one polyelectrolyte is present in the aqueous coating composition in form of a colloidal solution.

[0052] Preferably, the at least one polyelectrolyte has a number average molecular weight Mn(preferably determined by means of gel permeation chromatography using pullulan standards and an aqueous 0.05% by weight solution of sodium azide) in a range from 5 000 to 500 000 g / mol, more preferably from 20 000 to 250 000 g / mol and most preferably from 25 000 to 200 000 g / mol.

[0053] Preferably, the at least one polyelectrolyte is present in the aqueous coating composition in an amount of 0.01 wt- % to 5.0 wt.-%, more preferably in an amount of 0.05 wt.-% to 2.5 wt.-%, most preferably in an amount of 0.1 wt- % to 1.0 wt.-% by weight, based on the total weight of the aqueous coating composition.

[0054] Preferably, the at least one polyelectrolyte is used in the form of its ammonium salt and / or phosphonium salt. Among these, particular preference is given to the salts thereof with ammonia and / or tertiary amines, for example trialkylamines such as, in particular, trimethylamine, triethylamine and / or tributylamine, and / or salts thereof with tertiary phosphines, for example trialkylphosphines such as tri-t-butylphosphine or tri-n-butylphosphine and / or triphenylphosphine. It is likewise possible to use quaternary ammonium salts and / or phosphonium salts. A preferred quaternary ammonium cation is, for example, tetra-n-butylammonium, and a preferred quaternary phosphonium cation is, for example, tetra-n-butylphosphonium. Likewise usable are salts with DABCO (1,4- diazabicyclo[2.2.2]octane).

[0055] Preferably, the at least one polyelectrolyte is selected from, in each case preferably anionic, synthetic, semisynthetic and natural polyelectrolytes, and mixtures thereof, more preferably from synthetic, and natural polyelectrolytes, and mixtures thereof, even more preferably from natural polyelectrolytes.

[0056] Preferred natural polyelectrolytes are naturally occurring polyelectrolytes, more preferably selected from nucleic acids, proteins, teichoic acids, naturally occurring polyamino acids, polypeptides, and polysaccharides, even more preferably selected from polysaccharides, yet more preferably selected from anionic polysaccharides. In case of polyamino acids and polypeptides, the acidic amino acids used for their preparation especially include those that bear at least one further carboxyl group as well as the obligatory amino group and carboxyl group. The amino acids are preferably linked to one another via peptide bonds, it being immaterial whether these are alpha peptide bonds, omega peptide bonds, and / or isopeptide bonds.

[0057] Examples of suitable polysaccharide are polysaccharides (i) comprising glucuronic acid and / or galacturonic acid units, such as those selected from the group of the pectins, gum arable, tragacanth, karaya, gum ghatti, xanthan and gel Ian, (II) comprising guluronic acid and / or mannuronic acid units, such as, in particular, alginates, (iii) naturally occurring sulfated and optionally additionally carboxylated polysaccharides, for example agar, carrageenan, chitosan, chondroitin sulfate, and / or heparin.

[0058] Very preferably, the at least one polyelectrolyte is selected from polyanionic polysaccharides at least containing carboxyl groups, especially those bearing exclusively carboxyl groups or carboxylate groups. Among these, in turn particular preference is given to pectins, alginates and / or gellans. Most preferred are pectins.

[0059] Preferred semi-synthetic polyelectrolytes are anionic semi-synthetic polyelectrolytes such as subsequently sulfated, phosphated and / or carboxylated natural polyanionic polymers, for example carboxymethylated polysaccharides. The anionic natural polysaccharides described hereinbefore may be provided with further anionic groups and / or neutral polysaccharides, for example glycogen, amylose, cellulose, starch, dextrans, fructans, callose, curdlan, chitin, polysaccharides formed from tara gum, guar gum and / or locust bean gum, lignosulfates, glucomannans and amylopectin or even polysaccharides bearing amino groups, such as chitosan, may be sulfated, phosphated and / or carboxylated.

[0060] Preferred synthetic polyelectrolytes are anionic synthetic polyelectrolytes such as polymers that are obtained by a fully synthetic route and are composed of or comprise acidic amino acids such as, in particular, synthetic poly amino acids and synthetic polypeptides. In addition, synthetic polyelectrolytes can also be selected from for example, polyvinylsulfonic acid, poly (meth)acrylic acid, and the copolymers of acrylic acid and / or methacrylic acid with acrylic esters, methacrylic esters, acrylamide, styrene, and other acrylic, methacrylic or vinylic monomers.

[0061] Most preferably, the aqueous coating composition comprises at least one pectin as polyelectrolyte.

[0062] Preferably, the pectins usable with preference have a degree of esterification of the carboxyl groups in a range from 5% to 75% and / or a degree of substitution (DS) of 1 % to 75%, based on a repeat polysaccharide unit. Preferably, the pectins usable with preference have a degree of amidation of the carboxyl groups in a range from 1 % to 50% and / or a degree of epoxidation of the carboxyl functions of up to 80%, based on a repeat polysaccharide unit. Suitable polyelectrolytes such as particularly pectins for use as constituent a2) are, e g. , known from EP 3 658638

[0063] B1.

[0064] Constituents a3) and a4)

[0065] At least one polymer P is present as constituent a3) in the aqueous coating composition, which polymer P is obtainable from a polymerization of at least one (meth)acrylic monomer in the presence of at least one block copolymer BC. Said at least one block copolymer BC, in which presence the polymerization of the at least one (meth)acrylic monomer for preparing the at least one polymer P has taken place, is also present in the aqueous coating composition, i.e., as constituent a4),

[0066] Preferably, an aqueous dispersion of at least one polymer P and at least one block copolymer BC is prepared first and then incorporated into the aqueous coating composition.

[0067] Block copolymer BC

[0068] Block copolymer BC contains at least two blocks B1 and B2, which are different from one another. The block copolymer BC may comprise one or more further blocks, each of which are different from one another and also different from both blocks B1 and B2. However, preferably, the block copolymer BC is composed of the two blocks B1 and B2 and does not contain any further blocks. Hence, preferably the block copolymer BC is a diblock copolymer, more preferably a linear diblock copolymer. Preferably, each of block B1 and B2 comprises or is composed of monomeric units, which comprise side chains.

[0069] A person skilled in the art is aware of the term “block copolymer”. Block copolymers are copolymers obtained by adding at least two different ethy lenical ly unsaturated monomers, two different mixtures of ethy leni cally unsaturated monomers or by adding an ethylenically unsaturated monomer and a mixture of ethylenically unsaturated monomers at different times in the practice of a controlled polymerization, wherein an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers is initially charged at the start of the reaction. At the time of adding the further ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers or adding ethylenically unsaturated monomers in multiple installments, the ethylenically unsaturated monomers added at the start of the polymerization can be already completely reacted, or still be partly non-polymerized. As a result of such a polymerization, block copolymers may have at least one transition in their structural units along the polymer chain (polymer backbone), said transition marking the boundary between the individual blocks. Suitable block copolymer structures are e.g. AB diblock copolymers, ABA triblock copolymers or ABC triblock copolymers. Block copolymers, which are preferably used according to the present invention, are AB diblock copolymers.

[0070] The at least one block copolymer BC preferably contains a polymer main chain as backbone and the at least two blocks B1 and B2 being different from one another, wherein part of the backbone is a part of block B1 and another part of the backbone is part of block B2. Preferably, the at least one block copolymer BC is bound, more preferably bound in a non-covalently manner, to at least part of the polymer P, more preferably to at least part of the surface of polymer P, by means of at least part of its block B2.

[0071] Preferably, the at least one block copolymer BC, in which presence the polymerization of the at least one (meth)acrylic monomer for preparing the polymer P has taken place, is bound to at least part of the polymer P, more preferably to at least part of the surface of polymer P, even more preferably to at least part of the surface of a polymeric core formed by the at least one polymer P by means of at least part of its block B2, still more preferably via at least one kind of physical interactions. Examples of such physical interactions are van der Waals interactions and any hydrophobic interactions, e.g., hydrophobic effects, by which at least part of block B2 of the block copolymer is bound to the polymer P. Preferably, the at least one block copolymer BC is non-covalently bound to at least part of the surface of the polymeric core by means of at least part of its block B2. Preferably, each block B2 of each block copolymer BC bound to at least part of the surface of the polymeric core faces the surface of the polymeric core.

[0072] Block copolymer BC is preferably an amphiphilic block copolymer. The first block B1 is preferably a hydrophilic block, e.g., an ionic block, in particular a block, which is more hydrophilic than the second block B2, and which preferably allows a stabilization of the block copolymer in water or in an aqueous medium. The second block B2 is preferably a hydrophobic block, e.g., a lipophilic block, in particular a block, which is more hydrophobic than the first block B1 , and allows to be bound to at least part the surface of the polymer P.

[0073] Preferably, the number average molecular weight of the block copolymer BC is in a range of from 500 to 10 000 g / mol, more preferably of from 600 to 8 000 g / mol, even more preferably of from 800 to 6 000 g / mol. The number average molecular weight is determined according to the method disclosed in the 'methods' section.

[0074] Preferably, the block copolymer BC is obtainable by a controlled radical polymerization technique. Examples thereof are ATRP (atom transfer radical polymerization) and RAFT (reversible addition-fragmentation chain-transfer polymerization). The RAFT polymerization technique is known to a person skilled in the art, e.g., from WO 2022 / 228846 A1. The ATRP polymerization technique is also known to a person skilled in the art. For preparation of the block copolymer BC preferably at least one suitable chain transfer agent is used, at least when the block copolymer is prepared via RAFT, more preferably at least one chain transfer agent suitable for RAFT polymerization. In case of ATRP polymerization preferably an agent such as a copper halide is used. Examples of suitable chain transfer agents are dithioesters, thiocarbamates, xanthates, thiols, such as dodecyl mercaptan, secondary alcohols, and halocarbons, such as carbon tetrachloride.

[0075] In particular in case the block copolymer is obtainable by ATRP for preparing the first block B1, preferably at least one monomer is used, which is able to be used to generate precursor monomeric units forming a block B1a of the block copolymer, wherein at least part of the moieties defining block B1a, in particular at least part of the side chains of block B1 a, are able to be subjected to chemical transformation after preparation of the block copolymer, which results in phosphorous containing moieties, in particular within or as the side chain, and which thus allow the block B1 defined hereinbefore and hereinafter to be formed. For example, glycidyl (meth)acrylate can be used a monomer for generating a precursor block B1 a, which then, after formation of the block copolymer including the second block B2, is subjected to a treatment with a suitable phosphorous containing agent such as phosphoric acid, phosphonic acid, and / or any derivatives thereof, which leads, upon epoxide ring-opening, to formation of, e.g., phosphonic acids group in the side chain of block B1 a and hence to the formation of block B1 as defined hereinbefore and hereinafter.

[0076] Most preferably, the block copolymer BC is prepared via ATRP polymerization. The monomers used are polymerized via an oil in water emulsion polymerization. Advantages of the ATRP technique are that ATRP allows for precise control over the polymer chain growth by utilizing a reversible transfer process. In ATRP, the polymerization reaction typically involves a transition metal catalyst, such as copper, and a halogen-containing initiator. The reaction proceeds preferably through a series of steps of

[0077] A) Initiation: The halogen-containing initiator, often a bromide or chloride, reacts with the transition metal catalyst to generate an active species known as an "initiator radical" or "activator complex."

[0078] B) Activation and Propagation: The initiator radical reacts with a monomer, abstracting a hydrogen atom from its carbon-carbon double bond, which generates a carbon-centered radical. This carbon-centered radical then reacts with a monomer, incorporating it into the growing polymer chain.

[0079] C) Reversible Transfer: The transition metal catalyst facilitates the reversible transfer of the active radical species back to the initiator radical or activator complex. This transfer process allows for control over the polymerization kinetics and molecular weight distribution.

[0080] D) Termination: The polymerization can be terminated by various mechanisms, including radical-radical coupling or reaction with a terminating agent. This termination process helps control the polymer chain length and molecular weight.

[0081] By manipulating the monomer feed and reaction conditions, different monomers can be incorporated into the polymer chain, resulting in tailored material properties. ATRP allows for the incorporation of various functional groups into the polymer structure. By using functional monomers or post-polymerization modification techniques, specific functionalities can be introduced, expanding the range of potential applications. ATRP can be performed under a broad range of reaction conditions, making it compatible with various solvents, temperatures, and monomer types. This compatibility enables the synthesis of polymers with different properties and architectures.

[0082] Preferably, the at least one block copolymer BC is present in the aqueous coating composition in an amount in a range from 0.1 wt.-% to 10.0 wt.-%, more preferably of from 0.5 wt.-% to 7.5 or to 5.0 wt.-%, even more preferably of from 1.0 wt.-% to 2.5 or to 2.0 wt.-%, based in each case on the total weight of the sum of polymer P and block copolymer BC. Preferably, the at least one block copolymer BC is present in the aqueous coating composition in an amount in a range of from 0.05 wt.-% to 5.0 wt.-%, more preferably of from 0.07 to 3.5 wt.-%, yet more preferably of from 0.10 to 3.0 or to 2.0 wt.-%, based in each case on the total weight of the aqueous coating composition.

[0083] Block B1

[0084] The first block B1 comprises structural units SU1 , wherein at least a part of these structural units SU1 contains at least one phosphorous containing moiety, which in turn is part of the side chains of the structural units SU1 and is, within each structural unit SU1 , separated from the main chain of the block copolymer BC by at least one carbon atom.

[0085] Preferably, the at least one phosphorous containing moiety of at least a part of the structural units SU1 of the first block B1 of the block copolymer BC is part of a functional group being present within a side chain in each structural SU1 , which contains the at least one phosphorous containing moiety.

[0086] Preferably, the number average molecular weight of the first block B1 of the block copolymer BC is in a range of from 200 to 4 000 g / mol, more preferably of from 300 to 3 000 g / mol, even more preferably of from 400 to 2 000 g / mol. The number average molecular weight is determined according to the method disclosed in the 'methods’ section.

[0087] Preferably, the amount of the first block B1 of the block copolymer BC is in a range of from 70.0 to 30.0 wt.-%, more preferably of from 65.0 to 350 wt.-%, even more preferably of from 60 0 to 40.0 wt.-%, based on the total weight of the block copolymer BC

[0088] If the amount of the first block B1 is too high, e.g. exceeds 70 or 65.0 wt.-%, based on the total weight of the block copolymer BC, the water solubility of the block copolymer may be too high to be effectively usable as an emulsifier and / or surfactant for stabilizing the polymer P in water or in an aqueous medium, and this may lead to an undesired destabilization of the dispersion of polymer P in water or an aqueous medium.

[0089] Preferably, the at least one phosphorous containing moiety of at least a part of the structural units SU1 of the first block B1 of the block copolymer BC is selected from phosphonic acid groups, phosphonic acid ester groups (at least partially esterified phosphonic acid groups), at least partially esterified phosphoric acid groups, and salts of each of these groups such as for example phosphonates or phosphates, more preferably is selected from phosphonic acid groups and salts thereof, even more preferably is selected from phosphonic acid groups. The phosphonate ester groups and phosphate ester groups can in each case be completely or only partially esterified groups. For example, a phosphate ester group includes both a phosphate monoester group and also a phosphate diester group and also a phosphate tri-ester group. It is clear to those skilled in the art that a completely esterified phosphonic acid group or a completely esterified phosphoric acid group cannot be present in the form of a salt. Suitable alcohols for the partial or complete esterification of the phosphonate ester groups and phosphate ester groups are preferably Ci-s aliphatic alcohols, particularly preferably C1-8 alkyl alcohols such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, and tert-butanol.

[0090] If only a part of the structural units SU1 of the first block B1 of the block copolymer BC contains the at least one phosphorous containing moiety, the remaining part preferably comprises at least one functional group per structural unit SU1 not containing the at least one phosphorous containing moiety, which is preferably selected from OH- groups and carboxyl groups, more preferably is selected from carboxyl groups, e.g., by using (meth)acrylic acid as additional monomer(s) for preparing the first block B1, or is selected from OH-groups, e.g., by using poly (ethylene glycol)(meth)acrylate (PEGMA) as additional monomer for preparing the first block B1.

[0091] Preferably, each structural unit SU1 of the first block B1 of the block copolymer BC contains the at least one phosphorous containing moiety, or in that only a part of the structural units SU1 of the first block B1 of the block copolymer BC contains the at least one phosphorous containing moiety and the remaining part of the structural units SU1 of the first block B1 of the block copolymer BC contains at least one carboxylic acid group or a salt thereof.

[0092] Preferably, each structural unit SU1 of the first block B1 of the block copolymer BC contains the at least one phosphorous containing moiety, or in that only a part of the structural units SU1 of the first block B1 of the block copolymer BC contains the at least one phosphorous containing moiety and the remaining part of the structural units SU1 of the first block B1 of the block copolymer BC contains at least one OH-group. Suitable monomers for generating said remaining part of the structural units SU1 of the first block B1 of the block copolymer BC are preferably OH-group(s) containing hydrophilic monomers, more preferably OH-group(s) containing non-ionic hydrophilic monomers. The hydrophilic character of such monomers is preferably achieved by the presence of alkylene oxide units such as ethylene and / or propylene oxide units in the chemical structure of the monomers.

[0093] For preparation of at least part of the first block B1 any suitable ethylenically unsaturated monomer can be used, which contains at least one phosphorous containing moiety, and which allows said moiety to be part of the side chains of the structural units SU1 of the block copolymer BC once prepared, such that, within each structural unit SU1 , said moiety is separated from the main chain of the block copolymer BC by at least one carbon atom, preferably by at least two carbon atoms. Hence, e.g., it is not possible to use vinyl phosphonic acid or derivatives thereof as suitable monomer for generating block B1 , since the phosphonic acid groups thereof as phosphorous containing moiety would be directly bound to the main chain of the block copolymer, the main chain being formed from polymerized vinyl units, and hence said moiety would not be separated from the main chain by at least one carbon atom.

[0094] Preferably, at least one ethylenically unsaturated monomer, which contains at least one phosphorous containing moiety is used, wherein said at least one monomer can be a (meth)acrylic monomer as, e.g., in case 2- (meth)acryloyloxyethyl phosphate, 3-(meth)acryloyloxypropyl phosphate, 4-(meth)acryloyloxybutyl phosphate, 10- (meth)acryloyloxydecyl dihydrogen phosphate, ethyl-2-[4-(dihydroxyphosphoryl)-2-oxabutyl] (meth)acrylate and 2,4,6-trimethylphenyl-2-[4-(dihydroxyphosphoryl)-2-oxabutyl] (meth)acrylate. Preferred monomers for generating the block B1 are 2-(meth)acryloyloxyethyl phosphate, 3-(meth)acryloyloxypropyl phosphate, 4- (meth)acryloyloxybutyl phosphate, and mixtures thereof.

[0095] It is also possible to introduce the phosphorous containing moiety afterwards in a polymer analogous reaction and to form block B1 in this manner from a suitable precursor block B1 a. Preferably, in case of introducing said moiety after the polymerization has taken place, a monomer comprising a suitable moiety for later modification is used for polymerization to generate said precursor block B1a. Preferably, at least one monomer selected from the group consisting of preferably (meth)acrylic monomers having at least one epoxide group is used. Most preferred is glycidyl (meth)acrylate. For introducing the at least one phosphorous containing moiety a suitable phosphorous containing compound is used, preferably a compound having at least one phosphorous containing group, which can react with the epoxide moiety after ring opening of the epoxide group and form the at least one phosphorous containing moiety. Preferably, the phosphorous containing compound is selected from the groups consisting of phosphoric acid including polyphosphoric acid, P2O5, and phosphoryl chloride, as well as phosphonic acid and / or esters and / or derivatives thereof such as octyl phosphonic acid, and leads to formation of at least one phosphorous containing moiety selected from phosphonic acid groups and / or esters and / or salts thereof.

[0096] Preferably, block B1 of the block copolymer BC contains only monomeric units derivable from at least one suitable ethylenically unsaturated monomer, which contains at least one phosphorous containing moiety, or contains monomeric units derivable from at least one suitable ethylenically unsaturated monomer, which contains at least one phosphorous containing moiety, in an amount in a range of from 60 to 99 wt.-%, preferably of from 65 to 95 wt.-%, more preferably of from 70 to 90 wt.-%, and monomeric units different therefrom derivable from the at least one monomer containing at least one carboxyl group such as (meth)acryl ic acid and / or from the at least one preferably hydrophilic monomer containing at least one OH-group such as PEGMA in an amount in a range of from 1 to 40 wt.-%, preferably of from 5 to 35 wt.-%, more preferably of from 10 to 30 wt.-%.

[0097] The sum of all monomers used for preparing the block B1 , of course, adds up to 100 wt.-% in each case.

[0098] Preferably, the amounts of monomeric units in wt.-% derivable from at least one ethylenically unsaturated monomer, which contains at least one phosphorous containing moiety, exceeds the amounts of any further monomeric units also present in block B1. Block B2

[0099] The second block B2 of the block copolymer BC comprises structural units SU2, which are obtainable from a polymerization of at least one (meth)acrylic monomer, which is identical to or different from the at least one (meth)acrylic monomer used for preparing the at least one polymer P.

[0100] As suitable monomers for preparing the second block B2 of the block copolymer BC the same kind of monomer can be used as described hereinafter in connection with preparation of polymer P.

[0101] Preferably, at least one non-functionalized and preferably hydrophobic (meth) aery lie monomer is used as monomer ml for preparing the second block B2, more preferably at least one (meth)acrylic ester of an aliphatic C1-C30- monoalcohol. Preferably, block B2 contains only monomeric units mu1 derived from the at least one (meth)acrylic monomer ml and no other monomeric units besides monomeric units ml .

[0102] Preferably, the number average molecular weight of the second block B2 of the block copolymer BC is in a range of from 200 or 300 to 6 000 g / mol , more preferably of from 300 or 400 to 5000 g / mol, even more preferably of from 400 or 500 to 4 000 or 3 000 g / mol. Preferably, the number average molecular weight of the second block B2 exceeds the number average molecular weight of the first block B1. The number average molecular weight is determined according to the method disclosed in the 'methods’ section.

[0103] Preferably, the amount of the second block B2 of the block copolymer BC is in a range of from 30.0 wt.-% to 70.0 wt.-%, more preferably of from 35.0 wt.-% to 65 0 wt.-%, even more preferably of from 40 0 to 60.0 wt.-%, based on the total weight of the block copolymer BC.

[0104] Polymer P

[0105] The at least one polymer P is obtainable from a polymerization of at least one (meth)acrylic monomer, said polymerization taking place in the presence of the at least one block copolymer BC.

[0106] Preferably, the at least one polymer P is a (meth)acrylic homopolymer in case precisely one kind of (meth)acrylic monomers is used for its polymerization, or is a (meth)acrylic copolymer in case at least two kinds of (meth)acrylic monomers, which are different from one another, or at least one kind of (meth)acrylic monomers and at least one kind of further monomers are used for its polymerization, wherein said at least one kind of further monomers are ethylenically unsaturated monomers, which are not (meth)acrylic monomers.

[0107] The term "(meth)acrylic" means "acrylic” and / or “methacrylic”. Similarly, “(meth)acrylate" means acrylate and / or methacrylate. The polymer P can be regarded as a “(meth)acrylic polymer”, since it is formed at least partially from “acrylic monomers” and / or “methacrylic monomers”, but it additionally may contain non-acrylic and / or nonmethacrylic monomeric units if other ethylenically unsaturated monomers such as vinyl monomers, e.g., styrene, are additionally used for its preparation. Preferably, the polymer P is formed from more than 20 wt.-%, even more preferably of from more than 25 wt.-%, still more preferably of more than 30 wt -%, yet more preferably of more than 35 wt.-%, of (meth)acrylic monomers.

[0108] The polymerization performed for preparing the polymer P preferably is an emulsion polymerization.

[0109] Preferably, the aqueous coating composition comprises the at least one polymer P in form of a (meth)acrylic polymeric core, since the at least one polymer P is a (meth)acrylic polymer, more preferably a (meth)acrylic copolymer.

[0110] Preferably, the at least one polymer P is present in the aqueous coating composition in form of a polymeric core and wherein the at least one block copolymer BC is bound, preferably bound in a non-covalently manner, to at least part of the surface of said polymeric core by means of at least part of its block B2.

[0111] Preferably, the at least one polymer P is present in the aqueous coating composition in an amount in a range of from 90.0 wt.-% to 99.9 wt.-%, more preferably of from 95.0 wt.-% to 99.5 wt.-%, even more preferably of from 98.0 wt.-% to 99.0 %, based in each case on the total weight of the sum of polymer P and block copolymer BC.

[0112] Preferably, the at least one polymer P is present in the aqueous coating composition in an amount in a range of from 5.0 wt.-% to 30.0 wt.-%, more preferably of from 7.5 to 25.0 wt.-%, even more preferably of from 10.0 to 20.0 wt.-%, based in each case on the total weight of the aqueous coating composition.

[0113] Preferably, the total amount of the sum of polymer P and block copolymer BC in the aqueous coating composition is in a range of from 5.0 wt.-% to 35.0 wt.-%, more preferably of from 7 5 to 30.0 wt.-%, even more preferably of from 10.0 to 25.0 wt.-%, based in each case on the total weight of the aqueous coating composition.

[0114] Preferably, polymer P, more preferably in conjunction with the at least one polyelectrolyte, represents a film-forming polymer, and, hence functions as polymer binder.

[0115] Preferably, the amount of the at least one polymer P being present in the aqueous coating composition exceeds the amount of the at least one polyelectrolyte. Polymer P hence preferably functions as the main binder in the aqueous coating composition.

[0116] Preferably, the at least one polymer P comprises at least one kind of functional groups, more preferably selected from functional groups, which are reactive towards isocyanate groups, even more preferably selected from OH- groups, amino groups, and thiol groups, still more preferably selected from OH-groups.

[0117] Preferably, the at least one (meth)acrylic monomer used for preparing polymer P is selected from nonfunctionalized, (meth)acrylic monomers, functionalized (meth)acrylic monomers, and mixtures thereof, more preferably is selected from (meth)acrylic esters of aliphatic Ci-Cgo-monoalcohols, which optionally contain at least one functional group, said at least one functional group being preferably selected from hydroxyl groups, ether groups, carbonyl groups, amino groups, epoxide groups, carboxylic acid groups, and sulfur atoms containing functional groups such as thiol groups, thioether groups, thioester groups and / or thiocarboxylic acid groups, and mixtures thereof.

[0118] Preferably, at least one non-functionalized and preferably hydrophobic (meth) aery lie monomer is used as monomer ml for preparing polymer P, more preferably at least one (meth)acrylic ester of an aliphatic Ci-Cso-monoalcohol.

[0119] Examples of suitable monomers ml, i.e., of (meth)acrylic esters of aliphatic Ci-Cao-monoalcohols, which can be used, are methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate), i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 3- propylheptyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate and / or isobornyl (meth)acrylate. Most preferred are methyl (meth)acrylate, ethyl (meth)acrylate, n- propyl (meth)acrylate), i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, lauryl (meth)acrylate, and / or 2-ethylhexyl (meth)acrylate.

[0120] Preferably, at least one functionalized (meth)acrylic monomer is used as monomer m2 for preparing polymer P, in particular in combination with the at least one monomer ml, wherein monomer m2 is preferably at least one (meth)acryl ic ester of a functionalized aliphatic Ci-Cso-monoalcohol.

[0121] Examples of suitable monomers m2, which can be used, are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 3- phenoxy-2-hydroxypropyl (meth)acrylate, glycerol mono (meth)acrylate, acrylic acid, methacrylic acid, glycidyl (meth)acrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl acrylate, N,N-dimethylaminopropyl methacrylate, 2-(N,N-diethylamino)ethyl (meth)acrylate, 2-(N,N- dimethylamino)ethyl (meth)acrylate, 3-dimethylaminoneopentyl (meth)acrylate, 2-N-morpholinoethyl (meth)acrylate, 2-(tert-butylamino)ethyl (meth)acrylate, and / or 2-diisopropylaminoethyl (meth)acrylate. Most preferred are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, and / or 4-hydroxybutyl methacrylate.

[0122] Optionally, at least further (meth)acrylic monomer is used as monomer m3 for preparing polymer P, which preferably is selected from (meth)acryl amide, N-hydroxy ethyl (meth)acrylamide, N-lsopropyl acrylamide, N-(2- hydroxypropyl) (meth)acryl amide, N-[3-(N,N-dimethylamino)propyl] (meth)acrylamide, 2-(N,N-diethylamino)ethyl (meth)acrylamide, N-dodecylacrylamide and N-[2-(N,N-Dimethylamino)ethyl] (meth)acrylamide, and / or N,N- Dimethyl (meth)acrylamide. Preferably, at least one further monomer is used as monomer m4 for preparing polymer P, in particular in combination with the at least one monomer ml and / or m2 and optionally m3, wherein monomer m4 is selected from ethylenically unsaturated monomers bearing precisely one ethylenically unsaturated group, which are not (meth)acrylic monomers, more preferably is selected from allyl alcohol, hydroxy styrene, styrene, hydroxyalkyl vinyl ethers such as hydroxy butyl vinyl ether, vinylbenzyl alcohol, vinyl mercapto alcohols such as vinyl mercaptoethanol, vinyl thiazoles, vinyl thiophenes, 2-vinylpyridine, 4-vinylpyridine, allyl amine, vinylimidazole, N- vinyl-pyrrolidone, vinyl acetate, N-vinylformamide, N, N-diethylamino styrene (all isomers) and N,N-diethylamino- alpha-methylstyrene (all isomers). Most preferred is styrene.

[0123] Optionally, at least one further monomer is used as monomer m5 for preparing polymer P, in particular in combination with the at least one monomer ml and / or m2 and optionally m3 and / or m4, wherein monomer m5 is selected from ethylenically unsaturated monomers bearing more than one ethylenically unsaturated group. Monomer m5 is preferably a monomer selected from vinylic and / or (meth)acrylic monomers. Preferably, it has at least two vinylic or at least two (meth)acrylic groups. Suitable difunctional monomers m5 are divinyl benzene (DVB), divinyl cyclohexane, diesters of diols with (meth)acrylic acid and diallyl and divinyl ethers of such diols as, e.g., ethanediol di(meth)acrylate, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, methallylmethacrylamide, allyl (meth)acrylate, 1 ,4-butanediol diacrylate (BDDA), 1 ,4-butanediol dimethacrylate, 1 ,5-pentanediol di(meth)acrylate, 1,6-hexandiol di(meth)acrylate, and methacrylic acid anhydride (MAA). Further suitable difunctionalized monomers m5 are PEG di (meth) acrylate, PPG di(meth)acrylate, polyglycerol di(meth)acrylates, polyurethane di(meth)acrylate resins and polyester di(meth)acrylates. Suitable polyfunctionalized monomers m5 are PEG bearing more than two (meth)acrylate groups, PPG bearing more than two (meth)acrylate groups, polyglycerols with more than two (meth)acrylate groups, polyurethanes with more than two (meth)acrylate groups and polyesters with more than two (meth)acrylate groups, polyesters of polyols with (meth)acrylic acid and the polyallyl and polyvinyl ethers of such polyols, trivinylbenzene, trivinylcyclohexane, trimethylolpropane tri (meth)acrylate, pentaerythritol tetraallyl ether and pentaerythritol tri(meth)acrylate.

[0124] Preferably, polymer P contains only monomeric units mu1 derived from the at least one (meth)acrylic monomer ml and no other monomeric units besides monomeric units ml, or contains monomeric units mu1 derived from the at least one (meth)acrylic monomer ml in an amount in a range of from 60 to 99 wt.-%, preferably of from 65 to 95 wt.-%, more preferably of from 70 to 90 wt.-%, and monomeric units mu2 derived from the at least one monomer m2 in an amount in a range of from 1 to 40 wt.-%, preferably of from 5 to 35 wt.-%, more preferably of from 10 to 30 wt.-%, or contains monomeric units mu1 derived from the at least one (meth)acrylic monomer ml in an amount in a range of from 40 to 99 wt.-%, preferably of from 50 to 95 wt.-%, more preferably of from 50 to 90 wt.-%, and monomeric units mu2 derived from the at least one monomer m2 in an amount in a range of from 1 to 60 wt.-%, preferably of from 5 to 50 wt.-%, more preferably of from 10 to 50 wt.-%, or contains monomeric units mu1 derived from the at least one (meth)acryl ic monomer ml in an amount in a range of from 30 to 98 wt.-%, preferably of from 36 to 92 wt.-%, more preferably of from 44 to 86 wt.-%, monomeric units mu2 derived from the at least one monomer m2 in an amount in a range of from 1 to 35 wt.-%, preferably of from 4 to 32 wt.-%, more preferably of from 5 to 25 wt.-%, and monomeric units mu4 derived from the at least one monomer m4 in an amount in a range of from 1 to 50 wt.-%, preferably of from 2 to 45 wt.-%, more preferably of from 5 to 40 wt.-%.

[0125] The sum of all monomers used for preparing the polymer P, of course, adds up to 100 wt.-% in each case.

[0126] Preferably, the amounts of monomeric units mu1 in wt.-% exceeds the amounts of any monomeric units mu2 also present.

[0127] As outlined hereinbefore, preferably, an aqueous dispersion of at least one polymer P and at least one block copolymer BC is prepared first and then incorporated into the aqueous coating composition. Preferably, said aqueous dispersion is prepared in that the at least one (meth)acrylic monomer used for preparing the at least one polymer P is polymerized in the presence of the at least one block copolymer BC in water or an aqueous medium to form the aqueous dispersion of the at least one polymer P.

[0128] Preferably, the at least one block copolymer BC is used in an amount in a range of from 0.1 wt.-% to 9.0 wt.-%, more preferably of from 0.4 wt.-% to 4.0 wt.-%, even more preferably of from 1.0 wt.-% to 2 0 % wt.-%, based in each case on the total weight of all monomers including the at least one (meth)acrylic monomer used for preparing the polymer P.

[0129] Preferably, the polymerization is an emulsion polymerization, more preferably an oil-in-water emulsion polymerization. The at least one (meth)acrylic monomer, which can be used as part of a monomer mixture for preparing polymer P, is preferably suitable to form an oil phase. Preferably, said oil phase is then emulsified, with the aid of the at least one block copolymer BC, into water or an aqueous medium as aqueous continuous phase, and the at least one (meth)acrylic monomer is then polymerized to form polymer P. Preferably, the first block B1 of the block copolymer BC is in the aqueous phase during and after polymerization, whereas the second block B2 of the block copolymer BC preferably is in the oil phase, said oil phase corresponding to the at least one (meth)acry I ic monomer including a monomer mixture comprising said at least one (meth)acrylic monomer used for preparing polymer P during or before the polymerization and / or said oil phase corresponding to the at least one polymer P obtained in this manner after the polymerization. Preferably, the polymerization is a free radical polymerization. Hence, preferably, one or more initiator compounds are used such as redox initiators and / or thermal initiators. Suitable thermal initiators are, e.g., dialkyl peroxides, hydroperoxides, peroxyesters, peroxyketals, diacylperoxides, peroxy(di)carbonates, persulphates and / or azo initiators. Redox initiators may include a reducing agent such as sodium sulfite, sulfur dioxide and an oxidizing compound such as ammonium persulphate or a suitable peroxide compound, such as tertiary butyl hydroperoxide.

[0130] Preferably, the polymerization is performed at a temperature in a range of from 5 to 100 °C, more preferably of from 40 to 95 °C.

[0131] Optional constituent a5)

[0132] Optionally and preferably, the aqueous coating composition further comprises fluoride anions as constituent a5), which preferably are selected from complex fluoride anions, free fluoride anions, and mixtures thereof.

[0133] Preferably, constituent a5) is present in the aqueous coating composition in an amount in a range of from 5 to 1 000 mg / L, more preferably of from 10 to 750 mg / L, even more preferably of from 15 to 500 mg / L, still more preferably of from 20 to 400 or to 300 mg / L, in each case calculated as fluorine. The amount refers to the total amount of fluoride ions including complex fluoride anions and / or free fluoride anions. Preferably, the complex fluorides, if present contain zirconium.

[0134] Preferably, the aqueous coating composition comprises both complex fluoride anions, which are preferably coordinated to at least one of zirconium, titanium, and hafnium cations, still more preferably to zirconium cations, being also present in the composition as constituent a1) in the presence of water, and free fluoride anions.

[0135] Preferably, free fluoride anions are present in an amount in a range of from 1 mg / L to 500 mg / L, still more preferably of from 5 or 400 mg / L, yet more preferably of from 10 or 300 mg / L, even more preferably of from 15 to 200 mg / L, calculated in each case fluorine. Preferably, complex fluoride anions are present in an amount in a range of from 10 mg / L to 1 000 mg / L, still more preferably of from 15 or 750 mg / L, yet more preferably of from 20 or 500 mg / L, even more preferably of from 25 to 300 mg / L, calculated in each as HsMFs with M = Zr, Ti and / or Hf.

[0136] Free fluoride anions being present as constituent a5) may be generated by adding water-soluble fluorine compounds, e.g., fluorides other than complex fluorides of Ti, Zr and / or Hf as well as hydrofluoric acid to the composition.

[0137] The free fluoride content is determined by means of a fluoride ion sensitive electrode according to the method disclosed in the ‘methods’ section. Optional constituent a6)

[0138] Optionally and preferably the aqueous coating composition further comprises at least one crosslinking agent as constituent a6), which preferably is selected from di- or polyisocyanates having free NCO-groups, di- or polyisocyanates having blocked NCO-groups, melamine resins including melamine aldehyde resins such as melamine formaldehyde resins having at least one of imino groups, alkykol groups and etherified alkylol groups, and mixtures thereof, more preferably is selected from di- or polyisocyanates having blocked NCO-groups, melamine resins including melamine aldehyde resins such as melamine formaldehyde resins having at least one of imino groups, alkykol groups and etherified alkylol groups, and mixtures thereof. Constituent a6) is in particular present, when polymer P comprises at least one kind of functional groups, which are reactive towards NCO-groups such as OH-groups.

[0139] Preferably, the at least one crosslinking agent is present in the aqueous coating composition in an amount in a range of from 1.5 to 15.0 wt.-%, more preferably of from 2.5 to 10.0 wt.-%, even more preferably of from 5.0 to 8.5 wt.-%, based in each case on the total weight of the aqueous coating composition.

[0140] Suitable di- or polyisocyanates bears on average two or more isocyanate groups, wherein the isocyanate groups may be present in a blocked form. Preferred are blocked di- or polyisocyanates. If di- or polyisocyanates with free isocyanate groups are used, they would be stored separately and only mixed with the remaining part of the aqueous coating composition shortly before the desired application time. The aqueous coating composition would then be obtainable from a 2K coating system. If di- or polyisocyanates with blocked isocyanate groups are used, which is preferred, these can be mixed with the remaining part of the aqueous coating composition any time. The aqueous coating composition would then be 1 K coating composition.

[0141] Preferably, if at least one di- or polyisocyanates is used as a6), it has an aliphatic or cycloaliphatic structure and / or a parent structure that is derived from an aliphatic or cycloaliphatic di- or polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation. Trimers, i.e., isocyanurates, of IPDI (isophorone diisocyanate) and / or HDI (hexamethylene diisocyanate) are particularly preferred.

[0142] Suitable aliphatic di- or polyisocyanates are preferably substituted or unsubstituted aliphatic di- or polyisocyanates such as tetramethylene 1,4-diisocyanate, hexamethylene 1,6-diisocyanate, 2,2,4-trimethylhexane 1,6- diisocyanate, ethylene diisocyanate, dodecane 1, 12-diisocyanate, and mixtures of the aforementioned di- or polyisocyanates. Suitable di- or polyisocyanate parent structures may be di- or polyisocyanate prepolymers having urethane structural units which are obtained by reaction of polyols with a stoichiometric excess of aforementioned aliphatic di- or polyisocyanates. Particularly preferred di- or polyisocyanate parent structures are hexamethylene diisocyanate and / or its biuret dimer and / or allophanate dimer and / or isocyanurate trimer and / or its uretdione, and also mixtures of the stated di- or polyisocyanate parent structures. Especially preferred di- or polyisocyanate parent structures are hexamethylene diisocyanate and / or its isocyanurate trimer, optionally together with its uretdione. Suitable cycloaliphatic di- or polyisocyanates are preferably substituted or unsubstituted cycloaliphatic di- or polyisocyanates such as isophorone diisocyanate, cyclobutane 1,3-diisocyanate, cyclohexane 1,3-diisocyanate, cyclohexane 1,4-diisocyanate, methylcyclohexyl diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2, 6-diisocyanate, hexahydrophenylene 1 ,3-diisocyanate, hexahydrophenylene 1,4-diisocyanate, perhydrodiphenylmethane 2,4'-diisocyanate and 4,4'-methylendicyclohexyl diisocyanate and mixtures of the aforementioned di- or polyisocyanates. Suitable di- or polyisocyanate parent structures may be di- or polyisocyanates derived from a cycloaliphatic di- or polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, more particularly the biuret dimer and / or the allophanate dimer and / or the isocyanurate trimer. The di- or polyisocyanate parent structures may be di- or polyisocyanate prepolymers having urethane structural units which are obtained by reaction of polyols with a stoichiometric excess of aforementioned cycloaliphatic di- or polyisocyanate. Particularly preferred cycloaliphatic di- or polyisocyanates are isophorone diisocyanate and 4,4’-methylenedicyclohexyl diisocyanate and / or the biuret dimers thereof and / or the allophanate dimers thereof and / or the isocyanurate trimers thereof.

[0143] However, aliphatic di- or polyisocyanates are preferred. Especially preferred di- or polyisocyanates are hexamethylene diisocyanate and / or its isocyanurate trimer.

[0144] Suitable melamine resins including melamine aldehyde resins such as melamine formaldehyde resins have at least one of imino groups, alkykol groups and etherified alkylol groups. Examples of alkylol groups are methylol groups.

[0145] At least some of the alkylol groups may be alkylated through further reaction with at least one alcohol to produce nitrogen-bonded alkoxyalkyl groups (etherified alkylol groups) In particular, the hydroxyl groups in the nitrogen- bonded alkylol groups may be reacted with the alcohol through an etherification reaction to produce nitrogen- bonded alkoxyalkyl groups. The alkoxyalkyl groups are available for a crosslinking reaction with, for example, suitable crosslinkable functional groups such as OH- and / or acid groups. The remaining imino groups present after the aldehyde / melamine reaction are unreactive with the alcohol used for alkylation. As outlined above the alkylol groups of the melamine resins may be partially alkylated. By “partially alkylated", it is meant that a sufficiently low amount of alcohol is reacted with the melamine resins to leave some of the alkylol groups in the melamine resins, under reaction conditions that should result in incomplete alkylation of the alkylol groups. When the melamine resins are partially alkylated, they are typically alkylated with alcohol in amounts sufficient to leave alkylol groups present in an amount of at least about 2%, more preferably of from about 10% to about 50%, even more preferably of from about 15% to about 40%, in each case based on the total number of reactive sites present in the melamine prior to reaction. Typically, the melamine resin is partially alkylated to obtain from about 40 to about 98% of alkoxyalkyl groups, more preferably of from about 50% to about 90%, even more preferably of from about 60% to about 75%, in each case based on the total number of reactive sites present in the melamine prior to reaction. Preferably, at least a portion, more preferably only a portion, of the alkylol groups such as methylol groups of the melamine resin is etherified by reaction with at least one alcohol. Any monohydric alcohol can be employed for this purpose, including methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, t-butanol, pentanol, hexanol, heptanol, as well as benzyl alcohol and other aromatic alcohols, cyclic alcohols such as cyclohexanol, monoethers of glycols, and halogen-substituted or other substituted alcohols such as 3-chloropropanol and butoxyethanol. In particular, at least a part of the alkylol groups of the melamine resin is partially modified with methanol and / or n-butanol and / or iso-butanol.

[0146] Further optional constituents

[0147] The aqueous coating composition may comprise further optional constituents as lined out in the hereinafter. The term "further comprises”, as used herein, means "in addition to the mandatory constituents. Therefore, such “further” constituents are different from any of the mandatorily present constituents.

[0148] Optionally, the aqueous coating composition further comprises at least one organosilane. Examples are, e.g., (3- aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, (3- mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane and / or (3-glycidyloxypropyl)triethoxysil ane, vinyltrimethoxysilane, in particular when the aqueous composition is acidic.

[0149] Optionally, the aqueous coating composition further comprises at least one organic acid, preferably at least one organic acid having at least two carboxylic acid groups and / or at least one organic acid having at least one carboxylic acid groups and at least one further functional group having at least one donor atom such an OH-group, e g., lactic acid, in particular when the aqueous composition is alkaline. The presence of such a compound may be helpful for stabilization of the at least one metal ion in the composition such as Zr cations.

[0150] Optionally, the aqueous coating composition further comprises at least one additive depending on the desired application. For example, it may comprise at least one additive selected from the group consisting of, light stabilizers, antioxidants, deaerators, slip additives, plasticizers, initiators for free-radical polymerizations, adhesion promoters, pigments, fillers, flow control agents, film-forming auxiliaries, flame retardants, corrosion inhibitors, siccatives, biocides, thickeners, wetting agents, levelling agents and / or matting agents. They can be used in the known and customary proportions. Preferably, their content, based on the total weight of the aqueous coating composition is 0.01 to 20.0 wt.-%, more preferably 0.05 to 15.0 wt.-%, particularly preferably 0.1 to 10.0 % by weight, even more preferably from 0.1 to 7.5% by weight, especially from 0.1 to 5.0% by weight and most preferably from 0.1 to 2.5% by weight, in each case based on the total weight of the aqueous coating composition. Concentrate

[0151] A further subject-matter of the present invention is a concentrate for producing the aqueous coating composition according to one or more of the preceding claims by diluting the concentrate with water and if applicable, i.e., optionally, by adjusting the pH value.

[0152] All preferred embodiments described above herein in connection with the aqueous coating composition and preferred embodiments thereof are also preferred embodiments of the concentrate.

[0153] The concentrate used to produce the aqueous coating composition typically contains the constituents of the aqueous coating composition to be produced in the desired proportions, but at a higher concentration. Such concentrate is diluted with water to the desired concentrations of the constituents as disclosed hereinbefore to form aqueous coating composition. If necessary, the pH value of the composition may be adjusted after dilution as well as outlined hereinbefore Of course, it is also possible to further add any of the optional constituents of the composition to the water used for dilution or to add any of the optional or some of the necessary constituents after diluting the concentrate with water. It is, however, preferred that the concentrate already contains all necessary constituents

[0154] Preferably, the aqueous coating composition is obtainable from a concentrate by dilution with water, preferably with deionized water, such that the concentrate is present in the composition after dilution in an amount of from 5 to 60 g / L, more preferably 10 to 40 g / L, even more preferably of from 15 to 30 g / L, based on the total weight of the composition (obtained after dilution of the concentrate).

[0155] Preferably, the concentrate is diluted with water in a weight ratio of 1 :5000 to 1 :10, more preferably of 1 :1000 to 1 : 10, even more preferably of 1 :300 to 1 :10, still more preferably of 1: 150 to 1 :10, yet more preferably of 1 :50 to 1 : 10, even more preferably of 1 :20 to 1 :5, most preferably of 1 :10 or 1 :5 to 1 :2, to produce the aqueous coating composition.

[0156] Preferably, aqueous coating composition can be prepared from a concentrate by dilution of the concentrate with water.

[0157] Uses

[0158] A further subject-matter of the present invention is a use of the aqueous coating composition according to the present invention for corrosion protection of metallic substrates, preferably after having applied the aqueous coating composition at least in portion onto a surface of an optionally pre-coated metallic substrate to form a coating film at least in portion on said surface. A further subject-matter of the present invention is a use of the at least one inventively used block copolymer BC as defined hereinbefore and hereinafter for stabilizing at least one inventively used polymer P as defined as defined hereinbefore and hereinafter in an aqueous coating composition further comprising at least one polyelectrolyte as defined hereinbefore and hereinafter, preferably in an aqueous coating composition according to the present invention.

[0159] A further subject-matter of the present invention is a use of the at least one inventively used block copolymer BC as defined hereinbefore and hereinafter for improving and / or for establishing compatibility between at least one inventively used polymer P as defined hereinbefore and hereinafter and at least one polyelectrolyte as defined hereinbefore and hereinafter, preferably in an aqueous coating composition according to the present invention.

[0160] All preferred embodiments described above herein in connection with the aqueous coating composition and the concentrate and in each case preferred embodiments thereof are also preferred embodiments of the aforementioned uses.

[0161] Coating method

[0162] A further subject-matter of the present invention is a method of coating of an optionally pre-coated metallic substrate comprising at least a step 1) and optionally also a step 2), namely

[0163] 1) applying the aqueous coating composition according to the present invention at least in portion onto at least one surface of at least one metallic substrate to form a coating film at least in portion onto said surface, and

[0164] 2) optionally curing or drying the coating film obtained after step 1) to give a cured or dried coating layer, wherein the obtained cured or dried coating layer preferably has a dry film thickness in a range of from 10.0 m to 30.0 pm.

[0165] All preferred embodiments described above herein in connection with the aqueous coating composition and the concentrate and the aforementioned uses and in each case preferred embodiments thereof are also preferred embodiments of the inventive method.

[0166] Step 1)

[0167] In step 1) the aqueous coating composition according to the present invention is applied at least in portion onto at least one surface of at least one metallic substrate to form a coating film at least in portion onto said surface. By performing step 1) a coating film is formed on the surface of the substrate, which has been in contact with the aqueous coating composition. The term “at least in portion” preferably means in this context, in accordance with the general understanding of said term, that in some cases it might be desired or sufficient to contact not the whole surface of the substrate with aqueous coating composition. If only part of the metallic surface is contacted with the respective composition, it is typically the same part for all steps of the method. However, generally, it is desired to contact the whole surface of the metallic substrate with the aqueous coating composition.

[0168] The “contacting” according to step 1) can be a spraying, a dipping (immersing) or a roll coating (rolling) step. The aqueous coating composition can also be applied by flooding the surface or even manually by wiping or brushing. Preferred is spraying, or dipping, most preferred is dipping.

[0169] The treatment time, i.e., the period of time the surface is contacted with the aqueous coating composition in step 1), is preferably from 1 seconds to 20 minutes, more preferably from 15 or 30 seconds to 10 minutes, and most preferably 20 seconds to 5 minutes, as for example 20 seconds to 3 minutes.

[0170] The temperature of the aqueous coating composition used in step 1) is preferably of from 5 to 50 °C, more preferably of from 15 to 45 °C or to 40 °C and most preferably from 25 to 35 °C.

[0171] The aqueous coating composition can be used as a dip coat bath. However, it can also be applied by virtually any conventional coating procedure like, e.g., spray coating, roll coating, brushing, wiping etc. as outlined above in connection with step 1). Spraying and dipping are preferred. Most preferred is dipping.

[0172] Optional step 1a)

[0173] In optional step a) the film obtained after step 1) is rinsed at least once with water or with at least one aqueous rinsing composition ARC, which is different from the aqueous coating composition. The term “rinsing” preferably means, in accordance with the general understanding of this term, a removal excessive parts of the aqueous coating composition, which was contacted with the surface in the step directly preceding the optional rinsing step.

[0174] Tap water and / or deionized water can be used for rinsing in optional step 2). As outlined hereinbefore, optional step 2) can be performed more than once. It is hence possible, e.g., to perform a rinsing in step 2) once with tap water followed by rinsing with deionized water or vice versa.

[0175] Optional step 2)

[0176] In optional step 2) the film obtained after step 1) or after optional step 1a) is dried or cured to give a cured or dried coating layer.

[0177] The drying or curing step 2) may be preferably performed (if performed at all), e.g., at a temperature in the range of 15°C to 180°C, more preferably at a temperature in the range of 25°C to 150°C, in particular at a temperature in the range of 50°C to 130°C. “Drying” in the sense of the present invention means physical drying by evaporation of in particular water originally present in the composition(s) used, whereas "curing'' further includes a chemical reaction between at least two constituents originally present in the composition® and / or between at least one constituent originally present in the composition(s) and a suitable functional group present on the metallic surface or in the conversion film, e.g., due to the presence of polymer P including its block B1 in the aqueous coating composition. Once a film is dried, the resulting product can be regarded as a layer.

[0178] Preferably, the obtained cured or dried coating layer obtained after step 3) has a dry film thickness in a range of from 12.5 pim to 27.5 pirn, more preferably of from 15.0 pirn to 25.0 pirn.

[0179] Substrate

[0180] The metallic substrate used in step 1) contains at least one surface, preferably at least one metallic surface. The term "metallic surface" in the sense of the present invention preferably means that the surface of the substrate used is at least partially made of at least one metal, i.e., that at least one region of said surface is made of at least one metal and / or alloy thereof. Preferably, the overall surface of the substrate is made of at least one metal and / or alloy thereof, more preferably, the whole substrate is made of at least one metal and / or alloy thereof, i.e., the substrate consists of at least one metal and / or alloy thereof. If a substrate comprises areas of different metals, such substrate is herein denoted as "multi-metallic substrate” as a subclass of metallic substrates. Such multi-metallic substrates can be subjected to step 1) of the chemical pretreatment method and can be coated in the same treatment bath

[0181] The at least one metallic surface of the substrate may be optionally pre-coated, such as with at least one zinc phosphating coating layer.

[0182] Preferably, the substrate used is an electrically conductive substrate, which is used customarily and known to the skilled person. The substrate can have all sorts of geometry and shape such as coils, foils and sheets as well as represent parts such as automotive parts including vehicle parts such as wheel parts. Particularly suitable substrates are parts of vehicle bodies or complete bodies of automobiles for production.

[0183] Preferably, the at least one surface of the substrate is at least partially made of at least one metal and / or alloy thereof, more preferably is made at least partially of at least one of steel, steel alloys, aluminum, aluminum alloys, zinc, zinc alloys including zinc magnesium alloys, and mixtures thereof, even more preferably is made at least partially of at least one of steel and steel alloys. Examples of steel and / or steel alloys are bare steel, cold rolled steel (CRS), hot rolled steel (HRS), galvanized steel (zinc plated steel) such as hot dip galvanized steel (HDG), electrolytically galvanized steel (EG), alloy galvanized steel and aluminized steel such as, for example, Galvalume®, Galvannealed® or Galfan®, as well as steel coated at least in portion with at least one kind of zinc- aluminum-magnesium alloy (ZM). Examples of aluminum alloys are aluminum magnesium alloys, aluminum magnesium silicon alloys, aluminum copper alloys, aluminum zinc alloys, and aluminum zinc copper alloys. Examples of zinc alloys are Zn / Mg alloys and Zn / Ni alloys as well as Zn / Mg / AI alloys. Optional steps performed prior to step 1)

[0184] Prior to step 1) one or more of the following optional steps can be performed in this order:

[0185] Step A-1): cleaning and subsequently rinsing the surface of the substrate,

[0186] Step B-1): subjecting the surface of the substrate to acidic or alkaline pickling, i.e., etching, and subsequently rinsing the surface of the substrate, in particular when surface is made of at least one kind of steel and / or aluminum, in each case including alloys thereof,

[0187] Step C-1): contacting the surface of the substrate with an aqueous composition comprising at least one mineral acid, said aqueous composition being different from the aqueous coating composition, and

[0188] Step D-1 ): rinsing the surface of the substrate obtained after the contact according to step C-1) and / or B-1).

[0189] Coated substrate

[0190] A further subject-matter of the present invention is a substrate, which is a coated substrate being obtainable by the inventive coating method.

[0191] All preferred embodiments described above herein in connection with the aqueous coating composition and the concentrate and the aforementioned uses and the method in each case preferred embodiments thereof are also preferred embodiments of the inventive coated substrate.

[0192] METHODS

[0193] 1. Solid content

[0194] The solid content (non-volatile content) was determined via DIN EN ISO 3251 :2019-09 at 110 °C for 60 min.

[0195] 2. pH

[0196] A conventional pH meter is used to measure the pH value.

[0197] 3. Flow time

[0198] The flow time was measured according to DIN EN ISO 2431 :2020-02.

[0199] 4. Dry film thickness

[0200] The dry film thickness was determined according to ISO 2808:2019.

[0201] 5. Neutral salt spray (NSS) testing

[0202] The NSS test was used for determining the corrosion resistance of a coating on a substrate. In accordance with DIN EN ISO 9227:2017-07 the samples under analysis were positioned in a chamber in which there was continuous misting of a 5% strength sodium chloride salt solution at a temperature of 50 °C for a duration of 72, 120, 168 or 504 hours with controlled pH. The spray mist deposited on the samples under analysis, covering them with a corrosive film of salt water. Prior to storing the samples in the chamber the substrates were cut. After storage the creepage (undermining) in [mm] was measured. Each of the tests was performed three times and an average value was determined.

[0203] 6. Cupping test

[0204] The Erichsen cupping deep drawing test was performed according to DIN EN ISO 20482:2014-03.

[0205] 7. Solvent resistance

[0206] Solvent resistance against MEK (methyl ethyl ketone) was measured according to ASTM D5402-19 (“double rub test”). Up to 50 double rubs were performed.

[0207] 8. Free fluoride content determination

[0208] The free fluoride content was determined by means of a fluoride ion selective electrode. The electrode was calibrated using at least three master solutions with known fluoride concentrations. The calibration process resulted in the building of calibration curve. Then the fluoride content was determined by using of the curve. 9. Average particle size

[0209] The average particle size was determined by dynamic light scattering in accordance with DIN ISO 13321 (October 2004). In the context of the present invention, particle size refers to the measured average particle diameter (Z- average mean).

[0210] 10. Average molecular weight of polymers P and block copolymers BC

[0211] The number average molecular weight (Mn) was determined by means of gel permeation chromatography (GPC) in accordance with DIN 55672-1 (date: August 2007). Besides the number-average molecular weight, this method may also be used to determine the weight-average molecular weight (Mw) and also the polydispersity d (ratio of weight average molecular weight (Mw) to number-average molecular weight (Mn)). Tetrahydrofuran was used as eluent. The determination was made against polymethyl methacrylate standards. The column material consists of sty rene-divi nyl benzene copolymers.

[0212] 11. ICP-OES

[0213] The amounts of certain elements in a sample under analysis, such as of zirconium, titanium, hafnium etc., is determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885 (date: September 1 , 2009). A sample is subjected to thermal excitation in an argon plasma generated by a high-frequency field, and the light emitted due to electron transitions becomes visible as a spectral line of the corresponding wavelength and is analyzed using an optical system. There is a linear relation between the intensity of the light emitted and the concentration of the element in question. Prior to implementation, using known element standards (reference standards), the calibration measurements are carried out as a function of the particular sample under analysis. These calibrations can be used to determine concentrations of unknown solutions such as the concentration of the amount of titanium, zirconium, and hafnium.

[0214] 12. Glass transition temperature

[0215] The glass transition temperature was measured by means of DSC measurements in accordance with DIN EN ISO 11357-2 (2019-03).

[0216] EXAMPLES

[0217] The following examples further illustrate the invention but are not to be construed as limiting its scope.

[0218] 1. Aqueous coating compositions

[0219] 1.1 Three types A, B and C of aqueous coating compositions were prepared. For preparation of these three types of coating compositions the constituents listed in Table 1 were mixed with each other in the sequence indicated in said Table.

[0220] Table 1

[0221] A commercially available aliphatic blocked polyisocyanate was used. Commercially available preservatives were used. A commercially available plasticizer as well as a commercially available gelling catalyst were used.

[0222] 1.2 For preparing each of the three types of coating compositions A to C different kinds of aqueous polymer dispersions AD were in turn used, namely one of AD1 , AD2, AD3, AD4, AD5, AD6, and AD7 to yield compositions of types A-AD1 to A-AD7, B-AD1 to B-AD7 and C-AD1 to C-AD7.

[0223] The preparation of AD1 to AD7 will be described hereinafter in section 2.

[0224] 2. Synthesis of aqueous polymer dispersions AD1 to AD 7

[0225] The following general procedure was carried out for preparing each of AD1 to AD7:

[0226] A 2-L stainless steel reactor equipped with a mechanical stirrer, a reflux condenser and a nitrogen inlet was charged with a mixture of water and a block copolymer dispersion containing block copolymer BC1 to obtain a mixture 1. The preparation of block copolymer BC1 will be described hereinafter in section 3. An initiator feed consisting of ammonium peroxodisulfate in water was prepared. Part of the feed was added over a period of time to mixture 1. A monomer feed consisting of water, block copolymer dispersion containing BC1 , styrene, 2- hydroxyethyl meth acrylate (HEMA), n-butylacrylate (n-BA) and methylmethacrylate (MMA) was shaken to form a pre-emulsion and continuously stirred. Part of the monomer feed was added to the mixture 1 over a certain period of time, starting sometime after the start of the initiator feed. The polymerization was continued for 30 min after the end of the feeds. The remaining initiator- and monomer feeds were then added simultaneously over the course of a certain period of time and the reaction was continued for another certain period of time before cooling to 40 °C. Each of the resulting poly(meth)acrylate dispersion was characterized by its solid content, average particle size, glass transition temperature Tg, and pH value.

[0227] For preparation of AD1 to AD7, the amounts of monomers (styrene, HEMA, BA, and / or MMA) and / or the amount of block copolymer BC1 had been varied.

[0228] AD1 had an average particle size of 241 nm, a Tgof 66 °C, a solid content of 32.5 wt.-%, and a pH value of 2.76.

[0229] AD2 had an average particle size of 198 nm, a Tgof 56 °C, a solid content of 31.7 wt.-%, and a pH value of 1.88.

[0230] AD3 had an average particle size of 217 nm, a Tgof 66 °C, a solid content of 35.2 wt.-%, and a pH value of 1.98.

[0231] AD6 had an average particle size of 314 nm, a Tgof 76 °C, a solid content of 34.3 wt.-%, and a pH value of 2.13.

[0232] 3. Synthesis of block copolymers

[0233] Block copolymer BC1 prepared via ATRP polymerization

[0234] The following general procedure was carried out for preparing BC1 :

[0235] Step A: A 1 L four neck round bottom flask fitted with a nitrogen line, a condenser, an agitator, a heating mantle, and a thermocouple was charged with p-toluenesulfonyl chloride and 2-butanone. In a 20 mL sintered vial, tris(2- pyridyl-methyl)amine, anhydrous copper dichloride and ethanol were mixed and stirred to make a bluish green homogeneous solution of the catalyst, and the solution was added to the reaction flask. The mixture was heated under nitrogen blanket. When the temperature reached about 75 °C, 2,2'-azodi (2-methylbutyronitrile), dissolved in 2-butanone, was added to the flask at once. When the temperature increased to about 75 °C again, the monomer glycidyl methacrylate was fed to the reaction flask using a monomer pump. The feeding was done at 75 °C for a total of about 5 hours. After 2 hours a mixture of 2,2'-azodi (2-methyl butyronitri le) in 2-butanone was added in one portion. After the monomer feed was finished the temperature was held at about 75 °C for another 75 minutes.

[0236] Step B: At the end of step A, further 2-butanone was added at once. Temperature dropped slightly. When the temperature reached about 75 °C again, a mixture of 2,2'-azodi(2-methylbutyronitrile) in 2-butanone was added to the flask at once. The temperature dropped slightly, and it was allowed to reach to about 75 °C. At this point, a monomer mixture of n-butyl methacrylate (BMA), 2-hydroxyethylmethacrylate (HEMA) and butyl acrylate (BA) was fed at a constant rate over the course of about 4.5 h. A mixture of 2,2'-azodi(2-methylbutyronitrile) in 2-butanone was added and the polymerization was continued at about 75 °C for another 75 minutes. The monomer conversion reached >99% and was analyzed via NMR. Step C: The resulting polymer solution from step B was mixed with a solution of phosphonic acid in 2-butanone in a 500 ml three necked flask equipped with a magnetic stirrer, a reflux condenser, a nitrogen inlet, and a thermometer. The mixture was heated to about 60 °C for 7 h before a mixture of diethanolamine in water was added. The 2-butanone was removed from the resulting mixture under reduced pressure to yield a block copolymer dispersion containing BC1.

[0237] 4. Stability investigations

[0238] Stability of some commercially available aqueous polymer dispersions, namely of Alberdingk® AC 2403, Alberdingk® 2420, Acronal® 6592, Acronal® 5560, AC 126, Acronal® S996, and Acrodur® DS 3513, has been investigated when mixed with the polyelectrolyte used for preparing compositions of types A-AD1 to A-AD7, B-AD1 to B-AD7 and C-AD1 to C-AD7. In each case, it was found that these mixtures were not stable, since a gel had been formed in each case after one day or one week latest. Hence, none of these commercially available products could be used for preparing A-AD1 to A-AD7, B-AD1 to B-AD7 and C-AD1 to C-AD7. In contrast, when mixing the polyelectrolyte with each of AD1 to AD7 no gelation occurred and the mixtures were found to be stable.

[0239] 5. Properties of the aqueous coating compositions

[0240] Some properties of the different compositions of types A-AD1 to A-AD7, B-AD1 to B-AD7 and C-AD1 to C-AD7 were measured according to the methods disclosed in the 'method' section. The results are summarized in Tables 2, 3 and 4.

[0241] Table 2: Compositions of types A-AD1 to A-AD7

[0242] - = not measured Table 3: Compositions of types B-AD1 to B-AD7

[0243] - = not measured

[0244] Table 4: Compositions of types C-AD1 to C-AD7

[0245] - = not measured

[0246] 6. Coatings obtained from the aqueous coating compositions and properties thereof

[0247] 6.1 Two different kinds of steel substrates S1 and S2 were used. S1 was a cold rolled steel (CRS) substrate. S2 was a cold rolled steel (CRS) substrate bearing a zinc phosphate coating layer.

[0248] Each of the substrates was cleaned by making use of a commercially alkaline degreaser such as Gardoclean® 5165 having a temperature of about 55 to 70 °C for about 3 minutes. Then, spray rinsing with tap water and subsequent spray rinsing with deionized water was performed (for 30 seconds each at ambient temperature).

[0249] A contacting step was then carried out, wherein the overall surface of the substrates was contacted with some of the aqueous coating compositions of types A-AD1 to A-AD7, B-AD1 to B-AD7 and C-AD1 to C-AD7 described hereinbefore in item 1. by dipping the respective substrate into a bath containing one of the aqueous coating compositions of types A-AD1 to A-AD7, B-AD1 to B-AD7 and C-AD1 to C-AD7 at a bath temperature of about 20 to 45 °C in order to form a coating film onto the surface of each of the substrates.

[0250] Following the contacting step, rinsing with tap water and subsequently a rinsing with deionized water was performed (for 30 seconds each at ambient temperature). Following the rinsing steps, a drying step was performed by warm air drying for about 10 minutes in an oven at 110 °C air temperature. The dipping times and the resulting dry layer thicknesses obtained for the experimental runs conducted are summarized in Tables 5 (for substrate S1) and 6 (for substrate 82).

[0251] Table 5 - substrate S1

[0252] Table 6 - substrate S2

[0253] 6.2 Some properties of the coated substrates obtained were measured according to the methods disclosed in the ‘method’ section. The results are summarized in Tables 7 (for substrate S1) and 8 (for substrate S2). Table 7- substrate S1

[0254] - = not measured Table 8- substrate S2

Claims

CLAIMS1. An aqueous coating composition comprising, besides water, at least constituents a1), a2), a3, and a4), which are different from one of another, namely at least one of zirconium, titanium, and hafnium cations as constituent a1 ), at least one polyelectrolyte as constituent a2), at least one polymer P as constituent a3), which is obtainable from a polymerization of at least one (meth)acrylic monomer in the presence of at least one block copolymer BC, and at least one block copolymer BC as constituent a4), in which presence the polymerization of the at least one (meth)acrylic monomer for preparing the at least one polymer P has taken place, wherein said block copolymer BC contains at least two blocks B1 and B2, which are different from one another, the first block B1 comprising structural units SU1 , wherein at least a part of these structural units SU1 contains at least one phosphorous containing moiety, which in turn is part of the side chains of the structural units SU1 and is, within each structural unit SU1, separated from the main chain of the block copolymer BC by at least one carbon atom, and the second block B2 comprising structural units SU2, which are obtainable from a polymerization of at least one (meth)acrylic monomer, which is identical to or different from the at least one (meth)acrylic monomer used for preparing the at least one polymer P.

2. The composition according to claim 1 , characterized in that it is an aqueous acidic coating composition, which preferably has a pH value in a range of from 0.1 to <7.0, more preferably of from 0.5 to 6.5, even more preferably of from 1.0 to 6.0, yet more preferably of from 1.5 or 2.0 or 5.5, still more preferably of from 2.5 or 3.0 to 5.5, most preferably of from 3.5 or 3.8 to 5.5.

3. The composition according to claim 1 or 2, characterized in that it has a solid content in a range of from 5.0 to 50.0 wt.-%, preferably of from 7.5 to 40.0 wt.-%, more preferably of from 10.0 to 35.0 wt.-%, still more preferably of from 12.5 to 30.0 wt.-%, even more preferably of from 15.0 to 25.0 wt.-%.

4. The composition according to one or more of the preceding claims, characterized in that it further comprises fluoride anions as constituent a5), which preferably are selected from complex fluoride anions, free fluoride anions, and mixtures thereof, preferably in an amount in a range of from 5 to 1 000 mg / L, more preferably of from 10 to 750 mg / L, even more preferably of from 15 to 500 mg / L, still more preferably of from 20 to 400 or to 300 mg / L, in each case calculated as fluorine, preferably in that the composition comprises both complex fluoride anions, which are preferably coordinated to at least one of zirconium,titanium and hafnium cations being also present in the composition as constituent a1) in the presence of water, and free fluoride anions.

5. The composition according to one or more of the preceding claims, characterized in that at least one of zirconium and titanium cations, preferably zirconium cations, are present as constituent a1), and / or in that the composition comprises the at least one of zirconium, titanium, and hafnium cations as constituent a1) in an amount in a range of from 5 to 50 000 mg / L, more preferably of from 7.5 to 40 000 mg / L, even more preferably of from 10 to 30000 mg / L, still more preferably of from 12.5 to 20000 mg / L, yet more preferably of from 15 to 10 000 mg / L, even more preferably of from 20 to 8 000 mg / L, still more preferably of from 25 to 6 000 mg / L, most preferably of from 50 to 3 000 mg / L, in each case calculated as metal.

6. The composition according to one or more of the preceding claims, characterized in that the at least one polyelectrolyte is selected from poly anionic polymers, preferably from polyanionic polymers having at least one kind of functional groups selected from acid groups, more preferably from acid groups that are convertible into salts, still more preferably from carboxyl acid groups, sulfonic acid groups, and mixtures thereof, yet more preferably selected from carboxyl acid groups, wherein in each case the at least one kind of functional groups can be present in a partially esterified and / or partially amidated and / or partially epoxidized form, and / or in that the at least one polyelectrolyte has a number average molecular weight in a range from 5 000 to 500 000 g / mol, preferably from 20 000 to 250 000 g / mol and most preferably from 25 000 to 200 000 g / mol.

7. The composition according to one or more of the preceding claims, characterized in that the at least one polyelectrolyte is present in the aqueous coating composition in an amount of 0.01 wt.-% to 5.0 wt.-%, preferably in an amount of 0.05 wt.-% to 2.5 wt.-%, more preferably in an amount of 0.1 wt.-% to 1.0 wt.- % by weight, based on the total weight of the aqueous coating composition, and / or in that the at least one polyelectrolyte is selected from, in each case preferably anionic, synthetic, semi-synthetic and natural polyelectrolytes, and mixtures thereof, more preferably from natural polyelectrolytes, even more preferably from polysaccharides, still more preferably from pectins.

8. The composition according to one or more of the preceding claims, characterized in that the at least one polymer P is present in the aqueous coating composition in an amount in a range of from 90.0 wt.-% to 99.9 wt.-%, preferably of from 95.0 wt.-% to 99.5 wt.-%, more preferably of from 98.0 wt.-% to 99.0 %, based on the total weight of the sum of polymer P and block copolymer BC, and / or in that the at least one block copolymer BC is present in the aqueous coating composition in an amount in a range of from 0.1 wt.-% to 10.0 wt.-%, preferably of from 0.5 wt.-% to 7.5 or to 5.0 wt.-%, more preferably of from 1 .0 wt.-% to 2.5 or to 2.0 wt.-%, based on the total weight of the sum of polymer P and block copolymer BC.

9. The composition according to one or more of the preceding claims, characterized in that the number average molecular weight of the first block B1 of the block copolymer BC is in a range of from 200 to 4000 g / mol, preferably of from 300 to 3 000 g / mol, more preferably of from 400 to 2 000 g / mol, and / or in that the number average molecular weight of the second block B2 of the block copolymer BC is in a range of from 200 or 300 to 6 000 g / mol, preferably of from 300 or 400 to 5 000 g / mol, more preferably of from 400 or 500 to 4 000 or 3 000 g / mol, wherein the number average molecular weight of the second block B2 preferably exceeds the number average molecular weight of the first block B1, and / or in that the number average molecular weight of the block copolymer BC per se is in a range of from 500 to 10 000 g / mol, preferably of from 600 to 8 000 g / mol, more preferably of from 800 to 6 000 g / mol, and / or in that the amount of the first block B1 of the block copolymer BC is in a range of from 70.0 to 30.0 wt.-%, preferably of from 65.0 to 35.0 wt.-%, more preferably of from 60.0 to 40.0, based on the total weight of the block copolymer BC, and / or in that the amount of the second block B2 of the block copolymer BC is in a range of from 30.0 wt.-% to 70.0 wt.-%, more preferably of from 35.0 wt.-% to 65.0 wt.-%, even more preferably of from 40.0 to 60.0 wt.-%, based on the total weight of the block copolymer BC, and / or in that the block copolymer BC is composed of the two blocks B1 and B2 and does not contain any further blocks and / or in that the copolymer BC is bound, preferably bound in a non-covalently manner, to at least part of the polymer P by means of at least part of its block B2.

10. The composition according to one or more of the preceding claims, characterized in that the at least one polymer P is a (meth)acrylic homopolymer in case precisely one kind of (meth)acrylic monomers is used for the polymerization, or is a (meth)acrylic copolymer in case at least two kinds of (meth)acrylic monomers, which are different from one another, or at least one kind of (meth)acrylic monomers and at least one kind of further monomers is used for the polymerization, wherein said at least one kind of further monomers are ethylenically unsaturated monomers, which are not (meth)acrylic monomers, and / or in that the at least one polymer P comprises at least one kind of functional groups, preferably selected from functional groups, which are reactive towards isocyanate groups, more preferably selected from OH- groups, amino groups, and thiol groups, even more preferably selected from OH-groups, and / or in that the at least one polymer P is present in the aqueous coating composition in form of a polymeric core and wherein the at least one block copolymer BC is bound, preferably bound in a non-covalently manner, to at least part of the surface of said polymeric core by means of at least part of its block B2.

11. The composition according to one or more of the preceding claims, characterized in that it further comprises at least one crosslinking agent as constituent a6), which preferably is selected from di- or polyisocyanates having free NCO-groups, di- or polyisocyanates having blocked NCO-groups, melamine resins including melamine aldehyde resins having at least one of imino groups, alkykol groups and etherified alkylol groups, and mixtures thereof, and mixtures thereof, more preferably is selected from di- or polyisocyanates having blocked NCO-groups, melamine resins including melamine aldehyde resins having having at least one of imino groups, alkykol groups and etherified alkylol groups, and mixtures thereof, and mixtures thereof, wherein the at least one crosslinking agent preferably is present in the composition in an amount in a range of from 1.5 to 15.0 wt.-%, preferably of from 2.5 to 10.0 wt.-%, morepreferably of from 5.0 to 8.5 wt.-%, based in each case on the total weight of the aqueous coating composition.

12. A concentrate for producing the aqueous coating composition according to one or more of the preceding claims by diluting the concentrate with water and optionally by adjusting the pH value.

13. A use of the aqueous coating composition according to one or more of claims 1 to 11 for corrosion protection of metallic substrates, preferably after having applied the aqueous coating composition at least in portion onto a surface of an optionally pre-coated metallic substrate to form a coating film at least in portion on said surface, and / or a use of the at least one block copolymer BC as defined in one or more of claims 1 and 8 to 10 for stabilizing at least one polymer P as defined in one or more of claims 1 and 8 to 10 in an aqueous coating composition further comprising at least one polyelectrolyte as defined in one or more of claims 1 , 6 and 7, preferably in an aqueous coating composition as defined in one or more of claims 1 to 11 , and / or a use of the at least one block copolymer BC as defined in one or more of claims 1 and 8 to 10 for improving and / or for establishing compatibility between at least one polymer P as defined in one or more of claims 1 and 8 to 10 and at least one polyelectrolyte as defined in one or more of claims 1, 6 and 7, preferably in an aqueous coating composition as defined in one or more of claims 1 to 11 .

14. A method of coating of an optionally pre-coated metallic substrate comprising at least a step 1) and optionally also a step 2), namely1) applying the aqueous coating composition according to one or more of claims 1 to 11 at least in portion onto at least one surface of at least one metallic substrate to form a coating film at least in portion onto said surface, and2) optionally curing or drying the coating film obtained after step 1) to give a cured or dried coating layer, wherein the obtained cured or dried coating layer preferably has a dry film thickness in a range of from 10.0 m to 30.0 pm.

15. A substrate, which is a coated substrate being obtainable by the method according to claim 14.

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