Amino acid-based copolymer comprising composition for use in chemical pretreatment of metallic substrates

Abstract

The present invention relates to a method of chemical pretreatment comprising at least step 1), i.e., contacting at least one metallic surface of at least one substrate at least in portion with an aqueous composition AC being suitable to form a coating film at least in portion onto said surface, wherein AC comprises, besides water, at least constituents a1) and a2), i.e., at least one of zirconium, titanium and hafnium cations as constituent a1), and at least one copolymer, which is obtainable at least from reaction of (i) at least one amino acid comprising at least one primary amino group and / or at least two secondary amino groups with (ii) at least one constituent comprising at least two ethylenically unsaturated groups, as constituent a2), to a chemically pretreated substrate obtainable by this method, to the aqueous composition AC as such, to a concentrate usable for its preparation, to a use of composition AC for providing or improving corrosion protection and / or adhesion, to a method of coating an aforementioned chemically pretreated substrate, and to a coated substrate obtainable by said method.

Description

[0001] Amino acid-based copolymer comprising composition for use in chemical pretreatment of metallic substrates

[0002] The present invention relates to a method of chemically pretreating metallic surfaces of substrates, to a chemically pretreated substrate obtainable by this method, to a chemical pretreatment composition as such, which is suitable for use in this method, to a concentrate, from which said composition is obtainable, to a use of the chemical pretreatment composition for providing or improving corrosion protection and / or adhesion, to a method of coating an aforementioned chemically pretreated substrate, and to a coated substrate obtainable by said method.

[0003] Background of the invention

[0004] Before substrates having metallic surfaces are being lacquered, i.e., before coating layers or multilayer coating systems are applied onto their surfaces, e.g., for use in the automotive industry, they are nowadays typically subjected to an anti-corrosive chemical pretreatment by using a suitable chemical pretreatment composition.

[0005] Thin-film pretreatment systems for corrosion protection are known in the prior art. These are, e.g., based on oxides of zirconium, titanium, cerium, molybdenum, vanadium, tungsten, or other transition metals, and are used as replacement for hazardous components, like chromium and nickel, which were used for decades in trivalent or hexavalent chromate as well as tri-cationic zinc phosphate coatings. However, often such pretreatment systems are either only usable under acidic conditions or under alkaline conditions: it is usually not possible to utilize a particular composition, which has, e.g., been tailored to be suitable for use as acidic composition, also in an alkaline medium, which is disadvantageous from an economic and ecological viewpoint. In addition, even though prior art thin-film pretreatment systems often are able to provide a sufficient corrosion protection on different kinds of metal substrates, they may still suffer insufficient corrosion inhibition in particular on steel surfaces, in particular in comparison to chromate or tricationic zinc phosphate conversion coatings. Moreover, prior art thin-film pretreatments often contain nitrogen oxide or phosphorous oxide containing anionic components (NxOyz-, PxOyz) such as nitrates or phosphates, which may lead to eutrophication of water, if released in larger amounts to the environment. Due to this effect, the usage of nitrate and / or phosphate containing systems may face legal restrictions, which is undesired.

[0006] It is further known to, e.g., use polyphenols as corrosion inhibitors for corrosion protection of different kinds of metallic substrates. However, such polyphenols are often not compatible with other ingredients of chemical pretreatment systems, in particular with other polymeric constituents present therein, which may lead to undesired precipitations occurring, which in turn makes the use of such compositions disadvantageous.

[0007] The use of amino acids as corrosion inhibitors is also known in the prior art. For example, US 2018 / 023177 A1 describes applying an aqueous solution comprising amino acids selected from among alanine, arginine, aspartic acid, cysteine, glutamine, lysine, methionine, proline, serine, threonine, and a mixture thereof, to a surface of a galvanized steel substrate for corrosion protection. Further, US 2010 / 0261024 A1 describes the application of an aqueous solution comprising at least one substance being inter alia selected from glycine and glutamic acid to a metal surface such as a surface made of zinc-containing plated steel for corrosion protection. The advantage of using such corrosion inhibitors is that these may be bio-based (depending on the source of the amino acids), which is desirable from a viewpoint of sustainability. Electrochemical investigation has implied that corrosion inhibition may occur by sealing the outer porous oxide layer of the surfaces of such substrates such as an outer zinc oxide layer by means of said amino acids via an adsorption on their surface, thereby enhancing the barrier between the metal and the environment. However, a disadvantage of using comparably small organic compounds such as amino acids as corrosion inhibitors is that these sometimes destabilize the oxide layer such as the zinc oxide layer by increasing the solubility of the metal cations such as zinc cations, thereby resulting in an activation of the surface and subsequently resulting in corrosion, which is, of course, undesired.

[0008] Thus, there is a need to provide chemical pretreatment compositions suitable for formation of thin permanent coating layers on metallic substrates including particularly steel substrates, which compositions make use of easily accessible constituents having a high degree of biodegradability and sustainability, allow to be formulated both as acidic and as alkaline formulations, show an excellent compatibility with polyphenols, do not need to be necessarily formulated with nitrate and / or phosphate anions, but which lead to at least the same and preferably even to an improved corrosion resistance when applied to a metal surface, in particular when compared to coating compositions known in the prior art conventionally used for this purpose such as respective amino acid containing compositions, and which at the same time also provide an excellent substrate adhesion and an excellent adhesion to any coating layers applied on top.

[0009] Problem

[0010] It has been therefore an objective underlying the present invention to provide chemical pretreatment compositions suitable for formation of thin permanent coating layers on metallic substrates including particularly steel substrates, which compositions make use of easily accessible constituents having a high degree of biodegradability and sustainability, allow to be formulated both as acidic and as alkaline formulations, show an excellent compatibility with polyphenols, do not need to be necessarily formulated with nitrate and / or phosphate anions, but which lead to at least the same and preferably even to an improved corrosion resistance when applied to a metal surface, in particular when compared to coating compositions known in the prior art conventionally used for this purpose such as respective amino acid containing compositions, and which at the same time also provide an excellent substrate adhesion and an excellent adhesion to any coating layers applied on top.

[0011] Solution

[0012] 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. A first subject-matter of the present invention is a method of chemical pretreatment of comprising at least step 1) and optionally one or more of steps 2) and 3), namely

[0013] 1) contacting at least one metallic surface of at least one substrate at least in portion with an aqueous composition AC being suitable to form a coating film at least in portion onto said surface, wherein the aqueous composition AC comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely at least one of zirconium, titanium, and hafnium cations as constituent a1), and at least one copolymer as constituent a2), which is obtainable at least from reaction of (I) at least one amino acid comprising at least one primary amino group and / or at least two secondary amino groups with (ii) at least one constituent comprising at least two ethy lenically unsaturated groups preferably via an Aza-Michael addition reaction,

[0014] 2) optionally rinsing the coating film obtained after step 1) at least once with water and / or with at least one aqueous rinsing composition ARC, which is different from aqueous composition AC, and

[0015] 3) optionally curing or drying the coating film obtained after step 1) or 2) to give a cured or dried coating layer.

[0016] A further subject-matter of the present invention is a substrate, which is a chemically pretreated substrate being obtainable by the inventive method of chemical pretreatment as defined hereinbefore and hereinafter.

[0017] A further subject-matter of the present invention is an aqueous composition AC as defined hereinbefore and hereinafter in connection with step 1) comprising besides water at least one of zirconium, titanium, and hafnium cations as constituent a1), and at least one copolymer as constituent a2).

[0018] A further subject-matter of the present invention is a concentrate, from which the aqueous composition AC is at least obtainable by dilution with water and, optionally further, by pH adjustment.

[0019] A further subject-matter of the present invention is a use of at least one copolymer as defined hereinbefore and hereinafter as constituent a2) of composition AC, preferably when incorporated into an aqueous composition AC, more preferably into an inventive aqueous composition AC as defined hereinbefore and hereinafter, for providing or improving corrosion resistance of metallic surfaces of substrates and / or for providing or improving adhesion of metallic surfaces of substrates to one or more further coating layers present thereon. A further subject-matter of the present invention is a method of coating of at least one chemically pretreated metallic surface of at least one substrate, wherein chemical pretreatment of the at least one metallic surface has been carried out according to the inventive method of chemical pretreatment as defined hereinbefore and hereinafter or by making use of an inventive aqueous composition AC, the method of coating further comprising at least step 4), namely

[0020] 4) applying at least one coating material composition comprising at least one film-forming polymer and / or resin onto the optionally rinsed film obtained after step 1) or 2) as defined hereinbefore and hereinafter or onto the dried or cured, preferably dried, layer, which in turn is obtainable from drying or curing the film obtainable from optional step 3) as defined hereinbefore and hereinafter.

[0021] A further subject-matter of the present invention is a substrate, which is a coated substrate being obtainable by the inventive method of coating as defined hereinbefore and hereinafter.

[0022] It has been in particular surprisingly found that composition AC can be used as chemical pretreatment composition, which is suitable for forming a thin permanent coating layer such as a conversion coating layer on metallic substrates including particularly steel substrates or multi-metallic substrates including at least portions of steel.

[0023] Furthermore, it has been in particular surprisingly found that composition AC allows making use of easily accessible constituents, in particular in form of copolymer constituent a2), which has a high degree of biodegradability, since it is at least partially based on at least one amino acid such as naturally occurring amino acids, e.g., lysine and / or arginine. It has been found that using constituent a2) is also advantageous from the viewpoint of sustainability for the same reasons.

[0024] In addition, it has been found that composition AC allows to be formulated both as acidic and as alkaline formulation. In particular, it has been found in this context that copolymer constituent a2) shows a high stability against changes of the pH value, which allows the use of these copolymers, which may have pH values themselves varying, e.g., from pH 2.0 to pH 11 .0, both in acidic and in alkaline conditions combined with various other ingredients such as metal complexes and salts. This broadens their field of application and protection of a multitude of surfaces such as aluminum alloys, magnesium, galvanized steel, and steel, as well as of multi-metal surfaces. It has also been found in this context that copolymer constituent a2) is stable in the presence of various inorganic compounds, including metal-fl uoride complexes such as Ti / Zr-fluoride complexes (particularly in acidic medium) and fluoride- free complexes (in both acidic and in alkaline medium).

[0025] Further, it has been found that composition AC shows an excellent compatibility with polyphenols, when such polyphenols are also present. It has been found that stable complexes of the polyphenols such as tannic acid and constituent a2) are formed, which prevent the polyphenols from precipitating in alkaline composition. Additionally, it has been found that composition AC does not need to be necessarily formulated with nitrate and / or phosphate anions, but nonetheless shows an excellent corrosion resistance when applied on a metallic surface as permanent coating layer.

[0026] Moreover, it has been in particular surprisingly found that composition AC can be effectively used as chemical pretreatment composition in a chemical pretreatment method and that the chemically pretreated metallic substrates as such or chemically pretreated metallic substrates bearing further coating layers such as an electrodeposition coating layer, show an excellent corrosion resistance, in particular when compared to coating compositions known in the prior art conventionally used for this purpose such as respective amino acid containing compositions. It has been in particular surprisingly found in this regard, that this effect is a result of the presence of the copolymer constituent a2) in composition AC. It has been found in this context that constituent a2) as such or any complexes formed thereof with the aid of optionally present polyphenols, is able to adsorb on the outer metal oxide layer being present on suitable metal substrates such as substrates made of steel, e.g., galvanized steel, which are able to prevent or at least to significantly reduce any dissolution of the oxide layer and formation of metal cations such as zinc cations, and to provide a high barrier between the metal and its environment. It has been particularly found that the unique configuration of the polymer structure of constituent a2) - incorporation of amino acid units into the polymer backbone and immobilization of these units within the polymer chain - prevents not only the dissolution of the metal, but also provides multiple ligands that can adsorb to the metallic surface thereby isolating the porous metal oxide from the corrosive environment.

[0027] Finally, it has been in particular surprisingly found that composition AC can be effectively used as chemical pretreatment composition in a chemical pretreatment method and that the chemically pretreated substrates shown an excellent substrate adhesion and, in addition, an excellent adhesion to any layers applied on top, in particular to an electrodeposition coating layer applied on top of the chemical pretreatment layer. It has been in particular surprisingly found in this regard, that this effect is a result of the presence of copolymer constituent a2) in composition AC.

[0028] Detailed description of the invention

[0029] The term "comprising” in the sense of the present invention, in connection for example with the inventively used or inventive aqueous composition AC, 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 add up to 100 wt.-%, based in each case on the total weight of the respective composition. Pretreatment method including chemical pretreatment step 1)

[0031] A first subject-matter of the present invention is a method of chemical pretreatment of at least one metallic surface of at least one substrate comprising at least step 1) and optionally one or more of steps 2) and 3). The method may comprise further steps performed prior to step 1) and / or after each of steps 1), 2) and 3).

[0032] Chemical pretreatment is a term known by a person skilled in the art and in particular is part of a pretreatment method.

[0033] The term "pretreatment” as used herein is preferably used in accordance with the term "surface pretreatment'' as defined in Rdmpp Lexikon "Lacke und Druckfarben” (Publisher: Ulrich Zorll, Editor: Hans-Jurgen P. Adler - Stuttgart; New York: Thieme, 1998; term: "Oberflachenvorbehandlung” page 417). On metallic substrates or substrates having metallic surfaces, according to DIN 50902: 1994-07, the first step(s) of a surface treatment is / are often one or more (chemical) cleaning step(s) with aqueous or non-aqueous cleaning compositions (also called "surface preparation step”). Consequently, as it will be outlined hereinafter, the method may comprise one or more further optional steps performed prior to step 1).

[0034] The term "chemical pretreatment” is used in accordance with EN ISO 4618:2006 (E / F / D) (term: 2.41 "chemical pretreatment”), which represents any chemical process applied to a surface prior to the application of a coating material. According to this standard, e.g., treatments like chromatizing (chromating) and phosphatizing and oxalating, which can be subsumed under the term "conversion treatment”, belong to the chemical pretreatment and thus are to be distinguished from (subsequent) coating steps, wherein coating materials, i.e., coating compositions such as powder coating compositions, electrodeposition coating compositions, aqueous or non-aqueous liquid coating materials are applied. Besides conversion treatments such as chromatizing (chromating) and phosphating, the chemical surface pretreatment may be achieved with passivation compositions and thin-film forming compositions in general, including the aqueous composition AC, which is mandatorily used as chemical pretreatment composition in step 1). Hence, step 1) of the method represents a chemical pretreatment step and the aqueous composition AC used therein represents a chemical pretreatment composition.

[0035] In accordance with the above internationally valid definitions of a "pretreatment” of metallic substrates, the pretreatment method according to the present invention preferably encompasses surface preparing cleaning steps besides the chemical pretreatment step 1).

[0036] Preferably, the pretreatment method does not contain any step involving any treatment with chromium ions such as Cr(VI) ions and / or Cr(lll) ions. Preferably, the chemical pretreatment step 1) is the only chemical pretreatment step of the pretreatment method. Hence, preferably, other chemical pretreatment compositions than the aqueous composition AC applied in step 1) are not used.

[0037] Substrate

[0038] The substrate used in step 1) contains 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

[0039] The at least one metallic surface of the substrate may be optionally pre-coated, but preferably is not pre-coated.

[0040] 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.

[0041] 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.

[0042] Optional steps performed prior to step 1 )

[0043] As mentioned hereinbefore and in accordance with the above internationally valid definition of a "pretreatment” of metallic substrates, the pretreatment method according to the present invention preferably encompasses surface preparing cleaning steps besides the chemical pretreatment step 1). Prior to step 1) one or more of the following optional steps can be performed in this order:

[0044] Step A-1): cleaning and subsequently rinsing the surface of the substrate,

[0045] Step B-1): subjecting the surface of the substrate to acidic or alkaline pickling, i.e., etching, and subsequently optionally rinsing the surface of the substrate,

[0046] 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 compositions AC and ARC or alternatively with an aqueous alkaline composition or pH-neutral aqueous composition, each of these compositions being also different compositions AC and ARC, and

[0047] Step D-1): rinsing the surface of the substrate obtained after the contact according to step C-1) and / or B-1).

[0048] Alternatively, steps A-1) and B-1) may be performed in one step, which is preferred. Preferably, both steps A-1) and B-1) are performed. Optional step C-1) preferably serves to remove oxides, undesired alloy components, the skin, brushing dust etc. from the surface of the substrate and to thereby activate the surface for the subsequent conversion treatment in step 1). Preferably, the at least one mineral acid of the composition in step C-1) is sulfuric acid and / or nitric acid, more preferably sulfuric acid. As it will be outlined hereinafter, in step A-1) a cleaning composition can be used, which is different from or identical to composition AC. Rinsing step D-1) and the optional rinsing being part of step A-1) are preferably performed by using deionized water or tap water. Preferably, step D- 1) is performed by using deionized water.

[0049] Step 1)

[0050] According to step 1) the at least one metallic surface of the at least one substrate is contacted at least in portion with an aqueous composition AC being suitable to form a coating film at least in portion onto said surface. Aqueous composition AC represents a chemical pretreatment composition. By performing step 1) a conversion film (or conversion coating film or passivation film) is formed on at the portion of the surface of the substrate, which has been in contact with the aqueous composition AC. In case a cleaning step has been performed prior to step 1), preferably the cleaned portion of the surface of the substrate is subjected to step 1).

[0051] 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 the chemical pretreatment composition AC. 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 respective compositions. The "contacting” according to step 1) can be a spraying, a dipping (immersing) or a roll coating (rolling) step. The composition AC can also be applied by flooding the surface or even manually by wiping or brushing. Preferred is spraying or dipping.

[0052] The treatment time, i.e., the period of time the surface is contacted with the aqueous composition AC in step 1), is preferably from 1 seconds to 20 minutes, more preferably from 15 or 30 seconds to 10 minutes, and most preferably 45 seconds to 5 minutes, as for example 1 to 3 minutes.

[0053] The temperature of the aqueous composition AC 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.

[0054] The aqueous composition AC 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.

[0055] Preferably, the film obtainable after step 1) - preferably after drying according to optional step 3) - has a coating weight determined by XRF (X-ray fluorescence spectroscopy) of 0.5 to 500 mg / m2, more preferably 1 to 400 mg / m2, even more preferably 2 to 350 mg / m2, still more preferably 3 to 300 mg / m2, of silicon, zirconium, zinc, copper, titanium and / or hafnium ions, calculated as metals or elements.

[0056] Aqueous composition AC used in step 1)

[0057] The aqueous composition AC comprises, besides water, at least constituents a1) and a2), which are different from one of another. At least one of zirconium, titanium and hafnium cations is present as constituent a1), and the at least one copolymer is present as constituent a2). The aqueous composition AC used in step 1) represents a "chemical pretreatment composition”.

[0058] Preferably, the aqueous composition AC has a pH value in a range of from 0.1 to 13.0, more preferably of from 0.5 to 12.0, even more preferably of from 1.0 to 11.5, still more preferably of from 2.0 to 11.0.

[0059] Preferably, the aqueous composition AC is an aqueous acidic composition, 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 to 5.5, still more preferably of from 2.0 to 5.0. Alternatively, and also preferably, the aqueous composition AC is an aqueous alkaline or neutral, more preferably alkaline composition, and preferably has a pH value in a range of from >7.0 to 13.0, more preferably of from 7.5 to 12.5, yet more preferably of from 8.0 to 12.0, even more preferably of from 8.5 to 11.5, still more preferably of from 9.0 or 11.0. Most preferably, the aqueous composition AC is an aqueous acidic composition. 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.

[0060] The aqueous composition AC can be a dispersion or solution. Preferably, it is a solution. Solubility is determined at a temperature of 20°C and atmospheric pressure (1 .013 bar).

[0061] Preferably, the aqueous composition AC used in step 1) has a temperature in a range 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.

[0062] The aqueous composition AC used in step 1) 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 preferably 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, and / or is preferably free or essentially free of any boron ions such as B(lll) cations and / or B(l V) cations, more preferably is free of boron ions or comprises a maximum amount of boron ions of <10 mg / L, calculated as boron, and / or is preferably free or essentially free of any phosphate anions, more preferably is free of phosphate anions or comprises a maximum amount of phosphate anions of <10 mg / L, calculated as phosphate.

[0063] "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.

[0064] The term "aqueous” with respect to the aqueous composition AC used in step 1) 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. Preferably, the aqueous composition AC does not or essentially does not contain any organic solvent(s).

[0065] Preferably, the aqueous composition AC contains 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, in each case based on its total weight. Preferably, the aqueous composition AC is free or is essentially free of organic solvents. "Essentially free” in this context means that at least on purpose organic solvents are not added, but it may not be ruled out that any of these may be present as impurities. Preferably, the amount of organic solvent(s) present in the aqueous composition AC does not exceed 5 wt.-%, yet more preferably does not exceed 2.5 wt.-%, even more preferably is lower than 2.0 wt.-%, most preferably is at most 1.0 wt.-% or at most 0.5 wt.-% or at most 0.1 wt.-%, in each case based on the total weight of the composition.

[0066] Constituent a1)

[0067] At least one of zirconium, titanium, and hafnium cations, preferably at least one of zirconium and titanium cations, more preferably at least zirconium cations, is present as constituent(s) a1) in the aqueous composition AC.

[0068] Preferably, the aqueous composition AC comprises the at least one of zirconium, titanium, and hafnium cations in an amount in a range of from 1 to 4 000 mg / L, more preferably of from 5 to 2 000 mg / L, even more preferably of from 10 to 1 500 mg / L, still more preferably of from 12.5 to 1 000 mg / L, yet more preferably of from 15 to 750 mg / L, even more preferably of from 20 to 500 mg / L in each case calculated as metal.

[0069] Preferably, a precursor metal compound is used to generate the at least one metal cation being present in composition AC as constituent a1). Preferably, the precursor metal compound is water-soluble. 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 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 a3).

[0070] Additionally, or alternatively, zirconium can also be added in form of zirconyl compounds as, e.g., zirconyl nitrate, zirconyl acetate, and / or zirconium carbonate, in particular when the aqueous composition is alkaline, and / or zirconium nitrate, the latter one being particularly preferred, in particular when the aqueous composition is acidic. The same applies to titanium and hafnium.

[0071] The content of the at least one metal cation 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. Constituent a2)

[0072] At least one copolymer is present as constituent a2) in the aqueous composition AC, which is obtainable at least from reaction of (i) at least one amino acid comprising at least one primary amino group, preferably at least two primary amino groups, and / or at least two secondary amino groups with (ii) at least one constituent comprising at least two ethylenically unsaturated groups.

[0073] The at least one copolymer being present as constituent a2) is obtainable via an Aza-Michael addition reaction. This type of reaction is known by a person skilled in the art. Examples thereof are, e.g., disclosed in EP 0 977 780 A1 and GB 1 351 918 A. For the Aza-Michael addition reaction to take place in order to form the copolymer a2) by making use of constituent (ii), at least one amino acid with at least one primary amino group is necessary, which can lead to formation of bis-addition products as intermediates. Alternatively or additionally, at least one amino acid with at least two secondary amino group can be used.

[0074] The term "amino acid” is known by a person skilled in the art. In consistency therewith, an amino acid in the sense of the present invention is preferably a preferably organic monomeric compound, which has at least one carboxylic acid group and at least one primary amino group, preferably at least two primary amino groups, and / or at least two secondary amino groups. Preferably, the amino acid (i) used is selected from naturally occurring amino acids. Preferably, the amino acid (i) used has at least two primary amino groups.

[0075] Preferably the at least one amino acid (i) used is selected from the group consisting of alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine, and mixtures thereof, wherein each amino acid is preferably present in its naturally occurring stereoisomeric form. More preferably the at least one amino acid (i) used is selected from the group consisting of lysine, arginine, histidine, asparagine, glutamine, and tryptophan, and mixtures thereof, even more preferably selected from group consisting of lysine, arginine, asparagine, and glutamine, and mixtures thereof, yet more preferably selected from group consisting of lysine, arginine, and mixtures thereof.

[0076] Preferably, the at least one copolymer is present in composition AC an amount in a range of from 5 to 50 000 mg / L, more preferably of from 10 to 30 000 mg / L, even more preferably of from 15 to 20 000 mg / L, still more preferably of from 20 to 10 000 mg / L, yet more preferably of from 25 to 5 000 mg / L, even more preferably of from 30 to 4 000 mg / L, yet more preferably of from 35 to 3 000 mg / L, even more preferably of from 40 to 2 500 mg / L, yet more preferably of from 45 to 2 000 mg / L, most preferably of from 50 to 2 000 or to 1 500 or to 1 000 mg / L.

[0077] Preferably, the at least one copolymer, being present as constituent a2) in composition AC, has a weight average molecular weight in a range of from 1 000 g / mol to 15 000 g / mol, more preferably of from 2 000 g / mol to 10 000 g / mol. Preferably, the at least one copolymer, being present as constituent a2) in composition AC, bears free carboxylic acid groups or deprotonated forms and / or salts thereof.

[0078] Preferably, the at least one copolymer, being present as constituent a2) in composition AC, contains at least 5 and up to 1 000, more preferably at least 7 and up to 500, even more preferably at least 8 and up to 300, still more preferably at least 10 and up to 100, structural units derived from the at least one amino acid (I) used for its preparation, wherein the structural units derived from the at least one amino acid are preferably structural units derived from at least one of L-lysine, L-arginine, and histidine.

[0079] Preferably, the amount of structural units in the copolymer, which are derived from the at least one amino acid used for its preparation, does not exceed 67.0 mol-%, based on the total molar amount of all structural units present. More preferably, the amount of structural units in the copolymer, which are derived from the at least one amino acid used for its preparation, is in a range of from 0.1 or 0.5 to 65.0 mol-%, even more preferably of from 1 .0 or 2.5 to 60.0 mol-%, still more preferably of from 5.0 or 10.0 to 55.0 mol-%, yet more preferably of from 15.0 or 20.0 to 50.0 mol-%, based on the total molar amount of all structural units present.

[0080] Preferably, the at least one amino acid (I) comprises precisely two amino groups, wherein at least one of these groups, more preferably both of them, are primary amino groups.

[0081] Preferably, at least one of L-lysine, L-arginine, and histidine, more preferably at least one of L-lysine and L-arginine, has been used as at least one amino acid (i) for the preparation of the at least one copolymer, being present as constituent a2) in composition AC. Most preferred is L-lysine.

[0082] Preferably, the at least one constituent (ii) comprising at least two ethylenically unsaturated groups contains precisely two ethylenically unsaturated groups. Preferably, the at least two ethylenically unsaturated groups are non-conjugated.

[0083] Preferably, the at least one constituent (ii) comprising at least two ethylenically unsaturated groups and used for preparing said copolymer and is selected from preferably monomeric compounds comprising a) at least one vinyl group and at least one (meth)acrylic group, b) at least two (meth)acryl groups, c) at least two vinyl groups, or d) mixtures of any of a) to c). Examples of preferably monomeric compounds comprising b) at least two (meth)acryl groups are di(meth)acrylates and di(meth)acrylamides, in particular of alkylene oxides such as oligo(alkylene) oxides. Examples of alkylene oxides are di(ethylene oxide), di (propylene oxide), tri (ethylene oxide), tri(propylene oxide) as well as oligo- and poly (ethylene oxides) and oligo- and poly (propylene oxides).

[0084] The term "(meth)acrylic” or "(meth)acrylate” as used herein encompasses acrylic and / or methacrylic, as well as acrylate and / or methacrylate, respectively. If precisely two ethylenically unsaturated groups are present, constituent (II) preferably represents a difunctional monomer. If more than two ethylenically unsaturated groups are present, constituent (II) preferably represents a multifunctional monomer.

[0085] Suitable difunctional monomers are divinyl benzene (DVB), divinyl cyclohexane, divinyl sulfone, diesters of diols with (meth)acrylic acid and diallyl and divinyl ethers of such diols as, e.g., ethanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, 1 ,2-propanediol di(meth)acrylate, 1 ,3-propanediol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, 1 ,3-butanediol di(meth)acrylate, 1 ,5-pentanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, 1 ,8-octanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1 ,1-, 1 ,2-, 1 ,3- and 1 ,4-cyclohexanedimethanol di(meth)acrylate, 1 ,2-, 1 ,3- or 1 ,4-cyclohexanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, methacrylic acid anhydride (MAA), ethylene glycol dimethacrylate, 1 ,3-butylene glycol dimethacrylate, methallylmethacrylamide, allyl (meth)acrylate, and N,N'- alkylene bis((meth)acrylamides) such as N,N'-methylene bis((meth)acrylamide).

[0086] Suitable multifunctional monomers are trivinylbenzene, trivinylcyclohexane, trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, pentaerythritol tetraallyl ether and pentaerythritol tri (meth)acrylate.

[0087] Preferably, constituent a2) is a non-aromatic polymer, more preferably an aliphatic polymer.

[0088] Preferably, the at least one copolymer, being present as constituent a2) in composition AC, bears -[N(R1)-(CR2R3)- C(R4R5)]- linkages in its polymer backbone, wherein the group -(CR2R3)-C(R4R5) originates from constituent (II) and the group -N(R1)-originates from amino acid (I). Preferably, R1represents H, or a C1-C10 aliphatic residue optionally containing one or more heteroatoms such as heteroatoms selected from 0, N, NH, and N(alkyl), or a C4- C10 aromatic residue optionally containing one or more heteroatoms such as heteroatoms selected from 0, N, NH, and N(alkyl). Preferably, each of R2to R5independently of one another are selected from H, or a C1-C10 aliphatic residue optionally containing one or more heteroatoms such as heteroatoms selected from 0, N, NH, and N(alkyl), or a C4-C10 aromatic residue optionally containing one or more heteroatoms such as heteroatoms selected from 0, N, NH, and N(alkyl).

[0089] Optional constituent a3)

[0090] Preferably, the aqueous composition AC further comprises fluoride anions including complex fluoride anions and free fluoride anions as constituent a3), preferably in an amount in a range of from 5 to 4 000 mg / L, more preferably of from 7.5 to 3 000 mg / L, even more preferably of from 10 to 2 000 mg / L, still more preferably of from 12.5 to 1 000 mg / L, yet more preferably of from 15 to 500 mg / L, in each case calculated as fluorine. Preferably, the complex fluorides contain zirconium and / or titanium, more preferably zirconium. Preferably, the aqueous composition AC comprises fluoride anions being present therein as complex fluoride anions as constituent a3), which are preferably coordinated to at least one of zirconium, titanium and hafnium cations in the presence of water, more preferably at least one of zirconium and titanium cations, still more preferably zirconium cations, being also present in the composition as constituent a1), more preferably in an amount of from 1 or 50 mg / L to 4 000 mg / L, still more preferably of from 10 or 100 mg / L to 2 000 or to 1 500 mg / L, yet more preferably in an amount of from 50 or 100 mg / L to 500 or 250 mg / L, calculated in each case as H2MF6 with M = Zr, Ti and / or Hf. Alternatively or additionally, fluoride anions being present as constituent a3) may be generated by adding other 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. The free fluoride content is determined by means of a fluoride ion sensitive electrode according to the method disclosed in the ‘methods' section.

[0091] Optional constituents including optional constituents a4), a5) and a6)

[0092] Optionally and preferably, the aqueous composition AC further comprises at least one organosilane and / or a hydrolysis and / or condensation product thereof as constituent a4), preferably in an amount in a range of from 0 or 5 to 20 000 or to 15 000 mg / L, more preferably of from 0 or 10 to 10 000 or to 5 000 mg / L, even more preferably of from 0 or 15 to 1 000 or to 500 mg / L, still more preferably of from 0 or 20 to 250 or to 200 mg / L, in each case calculated as elemental silicon.

[0093] The term "organosilanes” includes, e.g., organoalkoxysilanes and organosilanols. Examples of hydrolysis and / or condensation products of organosilanes are organosiloxanes and polyorganosiloxanes as well as polyorganosilanols. For the purposes of this invention, "polyorganosiloxanes” are preferably understood to mean those compounds which can be condensed from at least two organosilanols and do not form a polydimethylsiloxane. The term "organo” in "organosilane” preferably means that at least one organic group is present, which is connected directly to a silicon atom via a carbon atom and can consequently not be subjected to hydrolysis.

[0094] Preferably, optional constituent a4) has at least one functional group selected from (meth)acrylate groups, alkylaminoalkyl groups, alkylamino groups, alkyltetrasulfide groups, amino groups, aminoalkyl groups, carboxyl groups, epoxy groups, glycidoxy groups, hydroxyl groups, isocyanato groups, mercaptoalkyl groups, succinic anhydride groups, imido groups, imino groups, and / or ureido groups (urea groups).

[0095] Examples of organosilanes are, e.g., (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, bis (trimethoxysilylpropyl) amine, bis (triethoxysilylpropyl) amine, N-2-aminoethyl-3-aminopropyltrimethoxysilane, (3- butylaminopropyl)trimethoxysilan, bis(3-triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide), bis(3- trimethoxysi ly I propy l)d isu Ifi de, bis(3-tri methoxysily I propy l)tetrasu Ifide), 1 , 2-bis(tri ethoxy si ly l)eth ane, (3- mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-methylaminopropyl)triethoxysilan, (3- methylaminopropyl)trimethoxysilan, (3-glycidyloxypropyl)trimethoxysilane and / or (3- glycidyloxypropyl)triethoxysilane, and / or vinyltrimethoxysilane. The organosilane is preferably present in a hydrolyzed form thereof.

[0096] Preferably, the aqueous composition AC comprises at least one organosilane and / or a hydrolysis and / or condensation product thereof as constituent a4) with at least one amino group, urea group, imido group, imino group and / or ureido group per organosilane unit, more preferably with at least one or more such as at least two amino groups per organosilane unit. Particularly preferred is 2-aminoethyl-3-aminopropyltrimethoxysilane, 2- aminoethyl-3-aminopropyltriethoxysilane, bis (trimethoxysilylpropyl) amine and / or bis (triethoxysilyipropyl) amine.

[0097] Optionally, the aqueous composition AC further comprises at least one kind of metal cations selected from the group of cations of metals of the 1stto 3rdsubgroup (copper, zinc, and scandium groups) and 5thto 8thsubgroup (vanadium, manganese and iron groups) of the periodic table of the elements including the lanthanides as well as the 2ndmain group of the periodic table of the elements (alkaline earth metal group), lithium and bismuth and / or tin. More preferably the aqueous composition AC further optionally comprises at least one kind of metal cations selected from the group consisting of cations of cerium and other lanthanides, chromium, iron, calcium, cobalt, copper, magnesium, manganese, molybdenum, nickel, niobium, tantalum, yttrium, vanadium, lithium, bismuth, zinc and tin, and mixtures thereof. Most preferred are copper and / or zinc cations.

[0098] Optionally and preferably, the aqueous composition AC further comprises zinc cations as constituent a5), preferably in an amount in a range of from 0 or 5 to 5 000 mg / L, more preferably of from 0 or 10 to 2 500 mg / L, even more preferably of from 0 or 25 to 1 000 or to 500 mg / L, most preferably of from 0 or 100 to 500 mg / L, in each case calculated as metal, and / or copper cations as constituent a6), preferably in an amount in a range of from 0 or 0.5 to 1 000 mg / L, more preferably of from 0 or 1 .0 to 500 mg / L, even more preferably of from 0 or 1 .5 to 100 mg / L, still more preferably of from 0 or 2.0 to 50 mg / L, in each case calculated as metal.

[0099] Optionally, the aqueous composition AC further comprises molybdenum cations as constituent a7), preferably in an amount in a range of from 0 or 0.5 to 1 000 mg / L, more preferably of from 0 or 1 .0 to 500 mg / L, even more preferably of from 0 or 1 .5 to 100 mg / L, still more preferably of from 0 or 2.0 to 50 mg / L, in each case calculated as metal. Optional constituent a8)

[0100] Optionally, and preferably, the aqueous composition AC further comprises at least one polyphenol as constituent a8), preferably in an amount in a range of from 1 to 3 000 mg / L, more preferably of from 5 to 2 500 mg / L, even more preferably of from 10 to 2 000 mg / L, still more preferably of from 20 to 1 500 mg / L.

[0101] If at least one polyphenol is present as constituent a8), the weight ratio of constituents a2) (copolymer) and a8) (polyphenol) to each other preferably is in a range of from 10:1 to 1 :1, more preferably of from 5:1 to 1 :1, even more preferably of from 3.5:1 to 1 :1.

[0102] Preferably, the polyphenols are obtainable from tannins including hydrolyzable and condensed tannins as well as complex tannins. Examples of hydrolyzable tannins are gallotannins and ellagitannins.

[0103] Examples of suitable polyphenols are tannic acid and tannic acid derivatives, gallic acid and gallic acid derivatives.

[0104] Further optional constituents

[0105] Optionally, the aqueous composition AC further comprises at least one pH-value adjusting constituent, preferably selected from the group consisting of nitric acid, sulfuric acid, methanesulfonic acid, acetic acid, aqueous ammonia, sodium hydroxide and sodium carbonate, wherein methanesulfonic acid and sodium carbonate are preferred. Depending on the pH value of the aqueous composition, the above constituent can be present in their fully or partially deprotonated form or in protonated forms.

[0106] Optionally, the aqueous composition AC further comprises at least one organic solvent, preferably selected from the group consisting of methanol, ethanol, ethylene glycol n-butyl ether, ethylene glycol n-propyl ether, propylene glycol n-propyl ether, propylene glycol n-butyi ether and mixtures thereof. Methanol and ethanol can be, e.g., present as reaction products of the organosilane hydrolysis.

[0107] Optionally, the aqueous composition AC further comprises at least one organic acid, preferably at least one organic acid having at least two carboxylic acid groups, e.g., galactaric acid, 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 cation being present in the composition as a1) such as Zr cations.

[0108] Optionally, the aqueous composition AC may comprise at least one water-soluble polymer different from constituent a2) such as a water-soluble polymer having at least one kind of functional groups selected from acid groups, hydroxyl groups, and mixtures thereof. Preferably, the at least one water-soluble polymer if present is a homopolymer or copolymer obtainable from polymerization of at least one kind of ethylenically unsaturated monomers, wherein at least part of said monomers bear at least one kind of functional groups selected from acid groups, hydroxyl groups, and mixtures thereof, more preferably is a homopolymer or copolymer obtainable from polymerization of at least one kind of vinyl monomers and / or (meth)acrylic monomers, wherein at least part of said monomers bear at least one kind of functional groups selected from acid groups, hydroxyl groups, and mixtures thereof.

[0109] Optional step 2)

[0110] In optional step 2) the film obtained after step 1) is rinsed at least once with water and / or at least one aqueous rinsing composition ARC, which is different from aqueous composition AC. Preferably, rinsing with water is performed, if rinsing is performed at all. The term "rinsing” preferably means, in accordance with the general understanding of this term, a removal excessive parts of the aqueous composition AC, which was contacted with the surface in the step directly preceding the optional rinsing step.

[0111] 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.

[0112] Optional step 3)

[0113] In optional step 3) the film obtained after step 1) or after optional step 2) is dried or cured to give a cured or dried coating layer.

[0114] Drying and / or curing may be performed in particular, when in a step 4) as outlined hereinafter, a coating material composition is subsequently applied. However, step 3) is only optional and, hence, further method steps such as step 4) may be carried out without drying and / or curing the film obtained after having performed step 1) or rinsing step 2). In particular, it is possible to apply a coating material composition such as an electrodeposition coating material composition in a step 4) as outlined hereinafter onto a wet film obtained after having performed step 1) or rinsing step 2).

[0115] The drying or curing step 3) 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(s) 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 a2) in composition AC. Once a film is dried, the resulting product can be regarded as a layer.

[0116] Preferably, a conversion layer formed after drying or curing, preferably drying, the film obtainable after step 3), has a coating weight determined by XRF (X-ray fluorescence spectroscopy) of: 0.5 to 500 mg / m2, more preferably of from 1 to 400 mg / m2, even more preferably of from 2 to 350 mg / m2, determined in each case as tracer element(s) such as Ti, Zr, Zn, Cu and / or Si via XRF measurements.

[0117] Preferably, a conversion layer formed after drying or curing, preferably drying, the film obtainable after step 3), has a Zr coating weight in a range of from 10 to 500 mg / m2, more preferably of from 25 to 400 mg / m2, even more preferably of from 50 to 300 mg / m2, determined in each case via XRF measurements.

[0118] Preferably, the dry layer thickness of a conversion layer formed after drying or curing, preferably drying, the film obtainable after step 3), is below 0.5 pm. Preferably, the obtained cured or dried coating layer obtained after step 3) has a dry film thickness in a range of from 1 nm to <500 nm, more preferably of from 10 nm to 250 nm, even more preferably of from 30 to 150 nm.

[0119] Substrate obtainable by chemical pretreatment method

[0120] A further subject-matter of the present invention is a substrate, which is a chemically pretreated substrate being obtainable by the inventive method of chemical pretreatment as defined hereinbefore and hereinafter.

[0121] All preferred embodiments described above herein in connection with the chemical pretreatment method and preferred embodiments thereof are also preferred embodiments of the substrate obtainable by this method.

[0122] Aqueous composition AC

[0123] A further subject-matter of the present invention is an aqueous composition AC as defined hereinbefore and hereinafter in connection with step 1) and as used in step 1) of the chemical pretreatment method comprising besides water at least one of zirconium, titanium, and hafnium cations as constituent a1), and at least one copolymer as constituent a2).

[0124] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, and preferred embodiments thereof are also preferred embodiments of the inventive composition AC. Concentrate

[0125] A further subject-matter of the present invention is a concentrate, from which the aqueous composition AC is at least obtainable by dilution with water and, optionally, further, by pH adjustment.

[0126] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, and the inventive composition AC, and preferred embodiments thereof are also preferred embodiments of the inventive concentrate.

[0127] The concentrate used to produce the aqueous composition AC typically contains the constituents of the aqueous composition AC 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 composition AC. 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.

[0128] Preferably, the aqueous composition AC 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).

[0129] Preferably, the concentrate is diluted with water in a weight ratio of 1 :5000 to 1 :10, more preferred 1 :1000 to 1 : 10, most preferred in a ratio of 1 :300 to 1 : 10 and even more preferred 1 :150 to 1 :50 to produce the composition AC.

[0130] Preferably, composition AC can be prepared from a concentrate by dilution of the concentrate with water.

[0131] Use

[0132] A further subject-matter of the present invention is a use of at least one copolymer as defined hereinbefore and hereinafter as constituent a2) of composition AC, preferably when incorporated into an aqueous composition AC, more preferably into an inventive aqueous composition AC defined hereinbefore and hereinafter, for providing or improving corrosion resistance of metallic surfaces of substrates and / or for providing or improving adhesion of metallic surfaces of substrates to one or more further coating layers present thereon.

[0133] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, the inventive composition AC, and the concentrate, and preferred embodiments thereof are also preferred embodiments of the inventive use. Coating method

[0134] A further subject-matter of the present invention is a method of coating of at least one chemically pretreated metallic surface of at least one substrate, wherein chemical pretreatment of the at least one metallic surface has been carried out according to the inventive method of chemical pretreatment as defined hereinbefore and hereinafter or by making use of an inventive aqueous composition AC, the method of coating further comprising at least step 4), namely

[0135] 4) applying at least one coating material composition comprising at least one film-forming polymer and / or resin onto the optionally rinsed film obtained after step 1) or 2) as defined hereinbefore and hereinafter or onto the dried or cured, preferably dried, layer, which in turn is obtainable from drying or curing the film obtainable from optional step 3) as defined hereinbefore and hereinafter.

[0136] The method of coating according to the present invention comprises at least step 4) and is performed after having carried out the inventive chemical pretreatment method as defined hereinbefore and hereinafter. The method of coating may, however, comprise one or more further additional optional steps.

[0137] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, the inventive composition AC, the concentrate and the inventive use, and preferred embodiments thereof are also preferred embodiments of the inventive coating method.

[0138] The coating material composition used in step 4) is different from each of compositions AC and ARC.

[0139] The coating material composition can be, e.g., an electrodeposition coating composition, a primer coating composition, a basecoat composition, or a topcoat including a clearcoat composition. It is, of course, possible to apply more than one composition subsequently to form a multilayer coating system, which is conventionally used, e.g., in the automotive industry.

[0140] Preferably, the coating material composition applied in step 4) is an electro-depositable, preferably a cathodically depositable, coating material composition, wherein the at least one film-forming polymer and / or resin present therein preferably is an electro-depositable, preferably a cathodically depositable, polymer. In this case preferably further coating material compositions are applied on top of the film or layer formed from said electro-depositable, preferably a cathodically depositable, coating material composition, such as a basecoat and a clearcoat composition.

[0141] Alternatively, and also preferably, the coating material composition applied in step 4) is a powder coating composition, which comprises at least one of a polymer and / or a resin selected from polyesters, epoxy resins, poly(meth)acrylate homopolymer and poly(meth)acrylate copolymers. The resulting powder coating layer may serve as top layer.

[0142] Substrate obtainable by coating method

[0143] A further subject-matter of the present invention is a substrate, which is a coated substrate being obtainable by the inventive method of coating as defined hereinbefore and hereinafter.

[0144] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, the inventive composition AC, the concentrate, the inventive use, and inventive coating method, and preferred embodiments thereof are also preferred embodiments of the inventive coated substrate.

[0145] METHODS

[0146] 1. Solid content

[0147] The solid content (non-volatile content) was determined via DIN EN ISO 3251 :2019-09 at 125 °C for 120 min.

[0148] 2. pH

[0149] A conventional pH meter is used to measure the pH value.

[0150] 3. ICP-OES

[0151] 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.

[0152] 3. Coating weight

[0153] XRF (X-ray fluorescence spectroscopy) is used for determining the coating weight in mg / m2of certain (tracer) element(s) such as Ti, Zr, Ou, Zn and / or Si in a layer such as the conversion layer resulting from applying the chemical pretreatment composition to a substrate.

[0154] 4. Free fluoride content determination

[0155] The free fluoride content is determined by means of a fluoride ion selective electrode. The electrode is calibrated using at least three master solutions with known fluoride concentrations. The calibration process results in the building of calibration curve. Then the fluoride content is determined by using of the curve.

[0156] 5. VDA corrosion test

[0157] A corrosion test according to VDA 621-415 was performed for determining the corrosion resistance of a coating on a substrate. VDA 621-415 is a cyclic corrosion test with a weekly cycle for determination of the corrosion resistance of the investigated sample. The weekly cycle consists of 1) a salt spray phase (24 h 5% NaCI salt spray at 35°C), 2) a first condensed water climate phase (96 h warm and humid period at 40°C with 85% RH (relative humidity)) and 3) a second condensed water climate phase (48 h at ambient conditions, i.e., at 25°C with 50% RH). The whole duration of the test is 10 weeks. The coated substrates were, after having performed half (5 weeks) or after having performed the full test (10 weeks) investigated for their level of creepage (undermining), determined according to DIN EN ISO 4628-8:2013-03. The smaller the values, the better the corrosion resistance. In addition, stone chip resistance, measured according to DIN EN ISO 20567-1 :2017:07, method C, after having performed the full corrosion test (10 weeks) was investigated. The smaller the score in the stone chip test, the better the resistance.

[0158] 6. Adhesion test An adhesion test (crosshatch test) was performed to ascertain the strength of adhesion of a coating on a substrate in accordance with DIN EN ISO 2409:2020-12 1 h after having prepared the coating and after another 48 h. Cutter spacing was 2 mm. Assessment took place on the basis of characteristic cross-cut values in the range from 0 (very good adhesion) to 5 (very poor adhesion). In addition, occurrence of blistering of the coating, measured according to DIN EN ISO 20567-1 :2017:07 after the aforementioned another 48 h was investigated.

[0159] 7. Average molecular weight

[0160] 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 styrene-divinylbenzene copolymers.

[0161] EXAMPLES

[0162] The following examples further illustrate the invention but are not to be construed as limiting its scope. ‘Pbw1means parts by weight. If not defined otherwise, ‘parts' means ‘parts by weight'.

[0163] 1. Polymers and their synthesis

[0164] 1.1 Polymer P1 prepared from L-lysine and dipropylene glycol diacrylate (DPGDA)

[0165] 97.46 g L-lysine (1 mol eq.) were added to 150 g of water in a four-necked flask and dissolved. The sample was heated to an internal temperature of 90 °C. For the feed, 201.89 g dipropylene glycol diacrylate (1 mol eq.) were dissolved in 150 g isopropanol and transferred to a dropping funnel. This feed was started at 50 °C internal temperature during heating and added to the receiver comprising the aqueous solution of L-lysine within 15 min using a dropping funnel. The resulting mixture was then allowed to react for 6 h at 90 °C internal temperature. Then, the resulting product was allowed to cool and transferred to a 2 L evaporation flask. The flask was attached to a rotary evaporator. Isopropanol was exchanged with water at 40 °C and 120 to 30 mbar. The vacuum was carefully lowered during this time. In this manner a clear, viscous, red-brown product was obtained having a solid content of 45.63 wt.-% and a pH value of 4.8.

[0166] 1.2 Polymer P2 prepared from L-lysine and N,N’-methylene bis(acrylamide)

[0167] 80.41 g L-lysine (1 mol eq.) was placed in a four-necked flask with 88 g of water and dissolved at 40 °C internal temperature. For the feed, 84.8 g N,N'-methylene bis(acrylamide) (1 mol eq.) was placed in 664 g water in a 1 L beaker and dissolved at 70 °C. This warm solution was transferred to a heatable dropping funnel with a thermostat setting at 80 °C. This feed was started at 40 °C internal temperature during heating to 90 °C internal temperature and dripped into the receiver comprising the aqueous solution of L-lysine in 30 min. The dropping funnel was rinsed with 50 g of water. The mixture was then allowed to react for 6 h at 90 °C internal temperature. Then, the resulting product was allowed to cool and transferred to a 2 L evaporating flask. The flask was attached to a rotary evaporator. Water, 450 g, was distilled off at 40 °C and 120 to 30 mbar. The vacuum was carefully lowered during this time. In this manner a clear, viscous, red-brown, homogeneous product was obtained. After one day, the product was diluted again with 313 g water due to its viscosity. The product had a solid content of 14.89 wt.-% and a pH value of 8.5.

[0168] 1.3 Polymer P3 prepared from L-lysine, L-arginine and N,N’-methylene bis(acrylamide)

[0169] 40.2 g L-lysine (0.5 mol eq.) and 47.9 g L-arginine (0.5 mol eq.) were placed in a four-necked flask with 88 g of water and dissolved at 40 °C internal temperature. For the feed, 84.8 g N,N'-methylene bis(acrylamide) (1 mol eq.) was placed in 664 g water in a 1 L beaker and dissolved at 70 °C. This warm solution was transferred to a heatable dropping funnel with a thermostat setting at 80 °C. This feed was started at 40 °C internal temperature during heating to 90 °C internal temperature and dripped into the receiver comprising the aqueous solution of L-lysine and L-arginine in 30 min. The dropping funnel was rinsed with 50 g of water. The mixture was then allowed to react for 6 h at 90 °C internal temperature. Then, the resulting product was allowed to cool and transferred to a 2 L evaporating flask. The flask was attached to a rotary evaporator. Water, 450 g, was distilled off at 40 °C and 120 to 30 mbar. The vacuum was carefully lowered during this time. In this manner a clear, slightly viscous, red-orange, homogeneous product was obtained having a solid content of 36.30 wt.-% and a pH value of 8.3.

[0170] 1.4 Polymer P4 prepared from L-lysine, L-arginine and divinyl sulfone

[0171] 51.16 g L-lysine (0.525 mol eq.), 60.98 g L-arginine (0.525 mol eq.) were added to 220 g of water in a four-necked flask and heated to 90 °C internal temperature, thereby dissolving the materials. For the feed, 78.76 g divinyl sulfone (1 mol eq.) was dissolved in 220 g water and 31 g isopropanol and transferred to a dropping funnel. This feed was started at 50 °C internal temperature during heating and dripped into the receiver comprising the aqueous solution of L-lysine and L-arginine in 15 min using a dropping funnel. The reaction was exothermic, after 5 minutes the internal temperature reached 80 °C, while the outside temperature was 62 °C. The mixture was then allowed to react for 6 h at 90 °C internal temperature. Then, the resulting product was allowed to cool and transferred to a 2 L evaporating flask. The flask was attached to a rotary evaporator. The isopropanol was exchanged for water at 40 °C and 120-30 mbar. The vacuum was carefully lowered during this time. The product was supplemented with water to the initial weight. In this manner a clear, viscous, red-brown product was obtained having a solid content of 31 .26 wt.-% and a pH value of 7.6.

[0172] 1.5 Polymer P5 prepared from L-lysine, histidine and N,N’-methylene bis(acrylamide)

[0173] 36.55 g L-lysine (0.5 mol eq.) and 38.79 g histidine (0.5 mol eq.) were placed in a four-necked flask with 160 g of water and dissolved during heating at 90 °C internal temperature. For the feed, 77.09 g N,N'-methylene bis(acrylamide) (1 mol eq.) was dissolved and transferred to a dropping funnel. This feed was started at 50 °C internal temperature and dripped into the receiver comprising the aqueous solution of L-lysine and histidine in 15 min. The mixture was then allowed to react for 6 h at 90 °C internal temperature. Then, the resulting product was allowed to cool. In this manner a gel-like, fluffy solution was obtained having a solid content of 32.50 wt.-% and a pH value of 5.5.

[0174] 1.6 Polymer P6 prepared from L-lysine, histidine and divinyl sulfone

[0175] 25.58 g L-lysine (0.525 mol eq.) and 27.15 g histidine (0.525 mol eq.) were placed in a four-necked flask with 110 g of water and dissolved during heating at 90 °C internal temperature. For the feed, 39.38 g divinyl sulfone (1 mol eq.) was dissolved in 110 g and transferred to a dropping funnel. This feed was started at 50 °C internal temperature and dripped into the receiver comprising the aqueous solution of L-lysine and histidine in 30 min. The mixture was then allowed to react for 6 h at 90 °C internal temperature. Then, the resulting product was allowed to cool. In this manner a clear, brownish solution was obtained having a solid content of 29.30 wt.-% and a pH value of 7.0.

[0176] 2. Stability tests

[0177] Some of the polymers obtained were subjected to stability tests in different acidic aqueous coating compositions. Each of polymers P1 to P4 obtained in the manner as described in sections 1.1 to 1.4 was added in an amount of

[0178] I g / L to one of commercially available aqueous coating compositions A1 to A3 and was found to be stable in each of these compositions. The stability was determined visually over a period of 30 days: a clear solution indicated a stable solution after 30 days. No precipitation was observed.

[0179] Composition A1 had a pH of about 3 and contained zirconium and fluoride ions (^ZrFe). Composition A2 had a pH of about 1 and contained titanium and fluoride ions (^TiFe) as well as zinc ions and, further, an organosilane and / or condensation and / or hydrolysis products thereof. Composition A3 had a pH of about 5 and contained zirconium and fluoride ions (H2ZrFe) as well as zinc and copper ions.

[0180] Each of polymers P1 to P4 obtained in the manner as described in sections 1.1 to 1.4 was also added in an amount of 1 g / L together with tannic acid to one of commercially available aqueous coating compositions A1 to A3 as described hereinbefore. Tannic acid was used in an amount such that the weight ratio of one of P1 to P1 to tannic acid to was about 3:1. Each of polymers P1 to P4, being present in a polymer complex with tannic acid in the compositions, was found to be stable in each of these compositions A1 and A3 as well. Stability was measured in the same manner as outlined hereinbefore.

[0181] 3. Preparation of aqueous coating compositions

[0182] 3.1 A commercially available aqueous coating composition C1 was used as comparative composition.

[0183] Composition C1 had a pH value of about 4.8, contained zirconium cations in an amount of about 100 ppm, zinc cations in an amount of about 200 ppm, and copper cations in an amount of about 2 ppm. It further contained about 30 ppm of free fluoride anions.

[0184] 3.2 The commercially available aqueous coating composition C1 was used as precursor for preparing compositions

[0185] I I to I4 according to the present invention.

[0186] In case of 11 1.65 g / L of a polymer complex of P1 and tannic acid (weight ratio of P1 to tannic acid about 2:1) was added to C1.

[0187] In case of I2 1.65 g / L of a polymer complex of P2 and tannic acid (weight ratio of P2 to tannic acid about 2:1) was added to C1.

[0188] In case of I3 1.65 g / L of a polymer complex of P3 (weight ratio of P3 to tannic acid about 2:1) and tannic acid was added to C1.

[0189] In case of I4 1.65 g / L of a polymer complex of P4 (weight ratio of P4 to tannic acid about 2:1) and tannic acid was added to C1. 4. Pretreatment including chemical pretreatment method as well as subsequent coating

[0190] Two different kinds of steel substrates were used (CRS as substrate S1 and HDG as substrate S2). Each of the substrates was cleaned by making use of a commercially alkaline degreaser having a temperature of about 60 °C for about 3 minutes by spraying. Then, spray rinsing with tap water and subsequent spray rinsing with deionized water was performed (for 60 seconds each at ambient temperature).

[0191] A contacting step was then carried out, wherein the overall surface of each of the substrates was contacted with one of the chemical pretreatment compositions described hereinbefore in items 3.1 and 3.2 for 3 minutes by immersion at about 30 °C in order to form a conversion coating film onto the surface of each of the substrates.

[0192] Following the contacting step, rinsing with tap water and subsequently a rinsing with deionized water was performed (for 30 seconds each at ambient temperature).

[0193] Following the rinsing steps, a drying step was performed by warm air drying for about 8 minutes in an oven at 120 °C air temperature.

[0194] Finally, a commercially available electrodeposition (ED) coating material (Cathoguard® 800) was applied on the conversion coated surface of the substrates and baked at 175 °C for 25 minutes. The dry layer thickness of the ED coating was in a range of from 20 pm and 25 pm. Then, a commercially available basecoat and a commercially available clearcoat were applied subsequently.

[0195] 5. Investigation of the properties of the chemically pretreated (conversion coated) or coated substrates

[0196] 5.1 The coated substrates obtained, after the method described hereinbefore in item 4. had been performed, have then been investigated according to the methods described in the ‘methods' section. The results are shown in Tables 1 and 2.

[0197] Table 1 Table 2

[0198] 5.2 In addition, the chemically pretreated substrates (conversion coated substrates), prior to applying the ED coating material, have been investigated according to the method (XRF) described in the ‘methods' section as far as their Zr deposition values are concerned. The results are summarized in Table 3.

[0199] Table 3.

Claims

CLAIMS1. A method of chemical pretreatment comprising at least step 1) and optionally one or more of steps 2) and 3), namely1 ) contacting at least one metallic surface of at least one substrate at least in portion with an aqueous composition AC being suitable to form a coating film at least in portion onto said surface, wherein the aqueous composition AC comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely at least one of zirconium, titanium, and hafnium cations as constituent a1), and at least one copolymer as constituent a2), which is obtainable at least from reaction of (I) at least one amino acid comprising at least one primary amino group and / or at least two secondary amino groups with (ii) at least one constituent comprising at least two ethylenically unsaturated groups via an Aza-Michael addition reaction,2) optionally rinsing the coating film obtained after step 1) at least once with water and / or with at least one aqueous rinsing composition ARC, which is different from aqueous composition AC, and3) optionally curing or drying the coating film obtained after step 1) or 2) to give a cured or dried coating layer.

2. The method according to claim 1 , characterized in that the at least one copolymer is present in composition AC in an amount in a range of from 5 to 50 000 mg / L, preferably of from 10 to 30 000 mg / L, more preferably of from 15 to 20 000 mg / L, still more preferably of from 20 to 10 000 mg / L, yet more preferably of from 25 to 5 000 mg / L, even more preferably of from 30 to 4 000 mg / L, yet more preferably of from 35 to 3 000 mg / L, even more preferably of from 40 to 2 500 mg / L, yet more preferably of from 45 to 2 000 mg / L, most preferably of from 50 to 2 000 or to 1 500 or to 1 000 mg / L.

3. The method according to claim 1 or 2, characterized in that the at least one copolymer, being present as constituent a2) in composition AC, has a weight average molecular weight in a range of from 1 000 g / mol to 15 000 g / mol, more preferably of from 2 000 g / mol to 10 000 g / mol, and / or bears free carboxylic acid groups or deprotonated forms and / or salts thereof, and / orcontains at least 5 and up to 1 000, more preferably at least 7 and up to 500, even more preferably at least 8 and up to 300, still more preferably at least 10 and up to 100 structural units derived from the at least one amino acid (i) used for its preparation, and / or contains an amount of structural units, which are derived from the at least one amino acid used for its preparation, which is in a range of from 0.1 or 0.5 to 65.0 mol-%, preferably of from 1 .0 or 2.5 to 60.0 mol- %, still more preferably of from 5.0 or 10.0 to 55.0 mol-%, yet more preferably of from 15.0 or 20.0 to 50.0 mol-%, based on the total molar amount of all structural units present.

4. The method according to one or more of the preceding claims, characterized in that at least one amino acid having at least two primary amino groups, preferably at least one amino acid selected from lysine, arginine, asparagine, and, glutamine, more preferably selected from L-lysine, and L-arginine, has been used as at least one amino acid (I) for the preparation of the at least one copolymer, being present as constituent a2) in composition AC, and / or in that at least one constituent (II) comprising at least two ethylenically unsaturated groups and used for preparing said copolymer is selected from preferably monomeric compounds comprising a) at least one vinyl group and at least one (meth)acrylic group, b) at least two (meth)acryl groups, c) at least two vinyl groups, or d) mixtures of any of a) to c).

5. The method according to one or more of the preceding claims, characterized in that aqueous composition AC comprises the at least one of zirconium, titanium, and hafnium cations in an amount in a range of from 1 to 4 000 mg / L, more preferably of from 5 to 2 000 mg / L, even more preferably of from 10 to 1 500 mg / L, still more preferably of from 12.5 to 1 000 mg / L, yet more preferably of from 15 to 750 mg / L, even more preferably of from 20 to 500 mg / L in each case calculated as metal.

6. The method according to one or more of the preceding claims, characterized in that the aqueous composition AC has a pH value in a range of from 0.1 to 13.0, preferably of from 0.5 to 12.0, more preferably of from 1.0 to 11.5, even more preferably of from 2.0 to 11.0, or in that the aqueous composition AC is acidic and preferably has a pH value in a range of from 0.1 to <7.0, more preferably of from 0.5 to6.5, yet more preferably of from 1 .0 to 6.0, even more preferably of from 1 .5 to 5.5, still more preferably of from 2.0 or 5.0, most preferably of from 3.0 to 5.0, or in that the aqueous composition AC is neutral or alkaline, and preferably has a pH value in a range of from >7.0 to 13.0, more preferably of from 7.5 to12.5, yet more preferably of from 8.0 to 12.0, even more preferably of from 8.5 to 11.5, still more preferably of from 9.0 or 11.0.

7. The method according to one or more of the preceding claims, characterized in that the aqueous composition AC further comprises fluoride anions including complex fluoride anions and free fluoride anions as constituent a3), preferably in an amount in a range of from 5 to 4 000 mg / L, more preferably of from 7.5 to 3 000 mg / L, even more preferably of from 10 to 2 000 mg / L, still more preferably of from 12.5to 1 000 mg / L, yet more preferably of from 15 to 500 mg / L, in each case calculated as fluorine, and / or in that the aqueous composition AC comprises fluoride anions being present therein as complex fluoride anions as constituent a3), which are preferably coordinated to at least one of zirconium, titanium and hafnium cations being also present in the composition as constituent a1), more preferably in an amount of from 1 or 50 mg / L to 4 000 mg / L, still more preferably of from 10 or 100 mg / L to 2 000 or to 1 500 mg / L, yet more preferably in an amount of from 50 or 100 mg / L to 500 or 250 mg / L, calculated in each case as H2MF6 with M = Zr, Ti and / or Hf.

8. The method according to one or more of the preceding claims, characterized in that aqueous composition AC further comprises at least one organosilane and / or a hydrolysis and / or condensation product thereof as constituent a4), preferably in an amount in a range of from 5 to 20 000 or to 15 000 mg / L, more preferably of from 10 to 10 000 or to 5 000 mg / L, even more preferably of from 15 to 1 000 or to 500 mg / L, still more preferably of from 20 to 250 or to 200 mg / L, in each case calculated as elemental silicon, and / or zinc cations as constituent a5), preferably in an amount in a range of from 5 to 5 000 mg / L, more preferably of from 10 to 2 500 mg / L, even more preferably of from 25 to 1 000 or to 500 mg / L, most preferably of from 100 to 500 mg / L, in each case calculated as metal, and / or copper cations as constituent a6), preferably in an amount in a range of from 0.5 to 1 000 mg / L, more preferably of from 1.0 to 500 mg / L, even more preferably of from 1.5 to 100 mg / L, still more preferably of from 2.0 to 50 mg / L, in each case calculated as metal.

9. The method according to one or more of the preceding claims, characterized in that the aqueous composition AC further comprises at least one polyphenol as constituent a8), preferably in an amount in a range of from 1 to 3 000 mg / L, more preferably of from 5 to 2 500 mg / L, even more preferably of from 10 to 2 000 mg / L, still more preferably of from 20 to 1 500 mg / L.

10. The method according to one or more of the preceding claims, characterized in that step 3) is performed and that the cured or dried coating layer obtained after step 3) preferably has a dry film thickness below 0.5 pm and / or in that the cured or dried coating layer obtained after step 3) preferably has a Zr coating weight in a range of from 10 to 500 mg / m2, more preferably of from 25 to 400 mg / m2, even more preferably of from 50 to 300 mg / m2, determined in each case via XRF measurements.11 . The method according to one or more of the preceding claims, characterized in that the at least one metallic surface of the at least one substrate 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, preferably is made at least partially of at least one of steel and steel alloys.

12. An aqueous composition AC as defined in one or more of claims 1 to 9 or a concentrate, from which said aqueous composition AC is at least obtainable by dilution with water and, optionally further, by pH adjustment.

13. A use of at least one copolymer as defined in one or more of claims 1 to 4, preferably when incorporated into an aqueous composition AC, preferably into an aqueous composition AC according to claim 12, for providing or improving corrosion resistance of metallic surfaces of substrates and / or for providing or improving adhesion of metallic surfaces of substrates to one or more further coating layers present thereon.

14. A method of coating of at least one chemically pretreated metallic surface of at least one substrate, wherein chemical pretreatment of the at least one metallic surface has been carried out according to the method as defined in one or more of claims 1 to 11 or by making use of aqueous composition AC according to claim 12, the method of coating further comprising at least step 4), namely4) applying at least one coating material composition comprising at least one film-forming polymer and / or resin onto the coating film obtained after step 1) or 2) as defined in claim 1 or onto the dried or cured, preferably dried, layer, which in turn is obtainable from drying or curing the film obtainable from optional step 3) as defined in claim 1 or 10.

15. A substrate, which is a chemically pretreated substrate being obtainable by the method according to one or more of claims 1 to 11, or a coated substrate being obtainable by the method according to claim 14.

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