Chemical pretreatment method for metallic substrates including pre-rinse treatment step

Abstract

The present invention relates to a method of chemical pretreatment of a metallic surface of a substrate comprising at least steps 1) and 2), i.e., contacting the metallic surface at least in portion with an aqueous pre-rinse composition PRC, which comprises at least zirconium cations and copper cations (step 1)), and contacting at least the pre-rinsed portion of the metallic surface obtained after step 1)) at least in portion with an aqueous composition AC, which comprises zirconium cations, copper cations, and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof, a method of coating the surface of the substrate that has undergone the aforementioned chemical pretreatment method, a substrate obtainable by these methods, and a kit-of-parts comprising an aqueous pre-rinse composition PRC or a concentrate thereof, and an aqueous composition AC or a concentrate thereof.

Description

[0001] Chemical pretreatment method for metallic substrates including pre-rinse treatment step

[0002] The present invention relates to a method of chemical pretreatment of a metallic surface of a substrate, a method of coating the surface of the substrate that has undergone such a chemical pretreatment method, a substrate obtainable by these methods, and a kit-of-parts comprising an aqueous pre-rinse composition PRC or a concentrate thereof, and an aqueous composition AC or a concentrate thereof.

[0003] Background of the invention

[0004] Before substrates having metallic surfaces are being lacquered, they are nowadays typically subjected to pretreatment processes including an anti-corrosive chemical pretreatment method by using a suitable chemical pretreatment composition prior to applying subsequent coating steps such as an electrodeposition coating step, a coating with primer fillers, basecoats and clearcoats or powder coats. In particular, when substrates intended to be used in the automotive industry have undergone said chemical pretreatment, usually an electrodeposition coating layer is subsequently applied on top of their conversion-coated surfaces for further protection against corrosion and the above mentioned further coating layers are then in turn applied on top of the electrodeposition coating layer.

[0005] WO 2023 / 275270 A2 relates to a process for a pretreatment of a plurality of components in series at least partially composed of iron and / or steel, wherein said components initially pass through a first conversion stage followed by a rinsing stage and a subsequent second conversion stage, wherein specific pH ranges have to be applied for each of the agents used for conversion coating and rinsing. The mandatory use of these at least three different stages is, however, disadvantageous at least from an ecological and in particular economic point of view. The same applies to the necessity of pH control according to WO 2023 / 275270 A2, in particular also for the agent used for rinsing.

[0006] The current pretreatment processes including a conventional chemical pretreatment method do not always give satisfactory results for all kinds of metallic substrates such as cold rolled steel (CRS), onto which a multilayer coating system as described hereinbefore is further present, in particular in terms of sufficient anticorrosion properties and a sufficiently high stone chipping resistance.

[0007] Thus, there is a need to provide a chemical pretreatment method, which allows to obtain chemically pretreated metallic substrates such as substrates intended to be used in the automotive industry, in particular substrates at least partially made of CRS, which, after further conventional coating layers used in the automotive industry have been applied on top of them, display a sufficiently high corrosion resistance, in particular an improved corrosion resistance compared to metallic substrates, which have undergone only a conventional chemical pretreatment method, and which at the same time also exhibit a sufficiently high stone chip resistance, in particular an improved stone chip resistance compared to metallic substrates, which have undergone only a conventional chemical pretreatment method. Problem

[0008] It has been therefore an objective underlying the present invention to provide a chemical pretreatment method, which allows to obtain chemically pretreated metallic substrates such as substrates intended to be used in the automotive industry, in particular substrates at least partially made of CRS, which, after further conventional coating layers used in the automotive industry have been applied on top of them, display a sufficiently high corrosion resistance, in particular an improved corrosion resistance compared to metallic substrates, which have undergone a conventional chemical pretreatment method, and which at the same time also exhibit a sufficiently high stone chip resistance, in particular an improved stone chip resistance compared to metallic substrates, which have undergone a conventional chemical pretreatment method.

[0009] Solution

[0010] 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.

[0011] A first subject-matter of the present invention is a method of chemical pretreatment of a metallic surface of a substrate comprising at least steps 1) and 2) and optionally one or more of steps 1a), 2a) and 3), namely

[0012] 1) contacting at least one metallic surface of at least one substrate at least in portion with an aqueous prerinse composition PRC, which comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely zirconium cations as constituent a1), and copper cations as constituent a2),

[0013] 1 a) optionally rinsing at least the pre-rinsed portion of the metallic surface of the substrate obtained after step 1) at least once with water,

[0014] 2) contacting at least the pre-rinsed portion of the metallic surface of the substrate obtained after step 1) or after optional step 1 a) at least in portion with an aqueous composition AC, which is different from aqueous pre-rinse composition PRC and which comprises, besides water, at least constituents b1), b2) and b3), which are different from one of another, namely zirconium cations as constituent b1), copper cations as constituent b2), and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent b3),

[0015] 2a) optionally rinsing at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC in step 2) at least once with water, and 3) optionally curing or drying at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC obtained in step 2) or that has been rinsed according to optional step 2a).

[0016] A further subject-matter of the present invention is a chemically pretreated substrate being obtainable by the inventive method of chemical pretreatment.

[0017] 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 as defined hereinbefore and hereinafter, the method of coating comprising at least step 4), namely

[0018] 4) applying at least one coating material composition, preferably comprising at least one film-forming polymer and / or resin, onto at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC in step 2) or that has been rinsed according to optional step 2a) of the inventive method of chemical pretreatment, optionally, but preferably, after having performed drying or curing step 3) of the inventive method of chemical pretreatment.

[0019] A further subject-matter of the present invention is a coated substrate being obtainable by the inventive coating method.

[0020] A further subject-matter of the present invention is a kit-of-parts comprising an inventively used aqueous pre-rinse composition PRC as defined hereinbefore and hereinafter, which comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely zirconium cations as constituent a1), and copper cations as constituent a2), or a concentrate of said aqueous pre-rinse composition PRC, and an inventively used aqueous composition AC as defined hereinbefore and hereinafter, which is different from aqueous pre-rinse composition PRC and which comprises, besides water, at least constituents b1), b2) and b3), which are different from one of another, namely zirconium cations as constituent b1 ), copper cations as constituent b2), and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent b3), or a concentrate of said aqueous composition AC.

[0021] It has been in particular surprisingly found that both compositions PRC and AC can be effectively used as chemical pretreatment compositions together in the inventive method of chemical pretreatment, each of which is suitable of forming a coating film or layer such as a conversion coating layer on metallic surfaces of substrates including particularly ferrous substrates such as steel substrates or multi-metallic substrates including at least portions of steel, in particular on substrates at least partially made of CRS.

[0022] Moreover, it has been in particular surprisingly found that both compositions PRC and AC can be effectively used as chemical pretreatment compositions in a chemical pretreatment method and that the chemically pretreated substrates as such or chemically pretreated substrates, in particular at least partially made of CRS, bearing further coating layers such as bearing at least an electrodeposition coating layer and in particular further coating layers conventionally applied in the automotive industry, show an excellent corrosion resistance, in particular compared to respective substrates which have been chemically pretreated by using conventional chemical pretreatment compositions and methods. It has been in particular surprisingly found in this regard, that this effect is a result of the presence of the at least one hydrolysis and / or condensation product as constituent b3) being present in composition AC and of using two different compositions PRC and AC for the chemical pretreatment method, in particular of using composition PRC in a separate step preceding using composition AC.

[0023] Further, it has been in particular surprisingly found that the chemically pretreated substrates, in particular at least partially made of CRS, obtainable by the inventive chemical pretreatment method bearing further coating layers such as bearing at least an electrodeposition coating layer and in particular further coating layers conventionally applied in the automotive industry, show an excellent stone chip resistance, in particular compared to respective substrates which have been chemically pretreated by using conventional chemical pretreatment compositions and methods. It has been in particular surprisingly found in this regard, that this effect is a result of the presence of the at least one hydrolysis and / or condensation product as constituent b3) being present in composition AC, and of using two different compositions PRC and AC for the chemical pretreatment method, in particular of using composition PRC in a separate step preceding using composition AC.

[0024] Detailed description of the invention

[0025] The term “comprising" in the sense of the present invention, in connection for example with the aqueous pre-rinse composition PRC, and the aqueous composition AC, preferably has the meaning of “consisting of”. With regard, e.g., to each of said compositions 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.

[0026] 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 composition PRC or AC, add up to 100 wt.-%, based in each case on the total weight of the respective composition.

[0027] Pretreatment process including chemical pretreatment method 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 steps 1) and 2) and optionally one or more of steps 1a), 2a) and 3). The method may comprise further steps performed prior to step 1) and / or after each of steps 1), 2) and 3).

[0028] Chemical pretreatment is a term known by a person skilled in the art and in particular is part of a pretreatment method.

[0029] The term "pretreatment” as used herein is preferably used in accordance with the term "surface pretreatment'' as defined in Rompp 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).

[0030] 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 2) Hence, step 2) of the method represents a chemical pretreatment step and the aqueous composition AC used therein represents a chemical pretreatment composition For the same reasons, also pre-rinse step 1) of the method represents a chemical pretreatment step and the aqueous composition PRC used therein as pre-rinse composition also represents a chemical pretreatment composition.

[0031] 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 2), which are preferably carried out prior to step 2) and also prior to prerinse step 1).

[0032] Preferably, the chemical pretreatment method (and also not any pretreatment method, of which the chemical pretreatment method is part of) does not comprise any further contacting steps, in which any composition such as a further pre-rinse composition different from PRC1 and / or such as a further aqueous composition different from AC, e.g., for use as chemical pretreatment composition, is used, which contains zirconium cations. Preferably, the chemical pretreatment method (and also not any pretreatment method, of which the chemical pretreatment method is part of) does not contain any step involving any treatment with chromium ions such as Cr(VI) ions and / or Cr(lll) ions.

[0033] Preferably, the chemical pretreatment step 2) and the pre-rinse treatment according to step 1) are the only chemical pretreatment steps of the pretreatment method. Hence, preferably, other chemical pretreatment compositions than the aqueous pre-rinse composition PRC applied in step 1) and the aqueous composition AC applied in step 2) are not used.

[0034] Substrates

[0035] 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.

[0036] The at least one metallic surface of the substrate may be optionally pre-coated, but preferably is not pre-coated.

[0037] 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.

[0038] Preferably, the at least one metallic surface of the at least one substrate is at least partially made of at least one kind of steel, at least one kind of steel alloys, at least one kind of aluminum, at least one kind of aluminum alloys, at least one kind of zinc, at least one kind of zinc alloys including zinc magnesium alloys, and / or mixtures thereof, more preferably is made at least partially of at least one kind of steel and / or at least one kind of steel alloys.

[0039] 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.

[0040] Optional steps performed prior to step 1)

[0041] 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 performed prior to step 1).

[0042] Prior to step 1) one or more of the following optional steps can, e.g., be performed in this order:

[0043] Step A-1): cleaning and optionally subsequently rinsing the surface of the substrate,

[0044] 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,

[0045] 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 PRC or alternatively with an aqueous alkaline composition or pH-neutral aqueous composition, each of these compositions being also different compositions AC and PRC, and

[0046] Step D-1): rinsing the surface of the substrate obtained after the contact according to step C-1) and / or B-1).

[0047] 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.

[0048] 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) (pre-rinse treatment step)

[0050] According to step 1) at least one metallic surface of at least one substrate is contacted at least in portion with an aqueous pre-rinse composition PRC. As outlined hereinbefore aqueous pre-rinse composition PRC represents a chemical pretreatment composition.

[0051] Preferably, the aqueous pre-rinse composition PRC is suitable to form a first coating film CF1 such as a first conversion coating film at least in portion onto the metallic surface of the substrate.

[0052] 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 aqueous pre-rinse composition PRC. If only part of the metallic surface is contacted with the aqueous pre-rinse composition PRC, 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 pre-rinse composition PRC.

[0053] The “contacting” according to step 1) can be a spraying, a dipping (immersing) or a roll coating (rolling) step. The aqueous pre-rinse composition PRC can also be applied by flooding the surface or even manually by wiping or brushing. Preferred is spraying, or dipping.

[0054] The treatment time, i.e., the period of time the surface is contacted with the aqueous pre-rinse composition PRC in step 1), is preferably from 1 seconds to 20 minutes, more preferably from 5 seconds to 10 minutes, even more preferably from 10 seconds to 5 minutes, still more preferably from 15 seconds to 2 minutes, yet more preferably from 20 seconds to 1 minute. Preferably, the duration of contacting step 1) is shorter than the duration of contacting step 2), more preferably in that the duration of contacting step 1) is at least twice as short as the duration of contacting step 2).

[0055] The temperature of the aqueous pre-rinse composition PRC used in step 1) is preferably of from 5 to 55 °C, more preferably of from 15 to 45 °C, and most preferably from 20 or 25 to 40 °C.

[0056] The aqueous pre-rinse composition PRC 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.

[0057] Aqueous pre-rinse composition PRC

[0058] The aqueous pre-rinse composition PRC comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely zirconium cations as constituent a1), and copper cations as constituent a2).

[0059] Preferably, the aqueous pre-rinse composition PRC used in step 1) is free or essentially free of any organosilanes and / or hydrolysis and / or condensation products thereof

[0060] Preferably, the aqueous pre-rinse composition PRC is an aqueous acidic 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 sulfuric and / or boric acid and / or nitric acid and / or by at least one organic acid such as methyl sulfonic acid. The aqueous pre-rinse composition PRC 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 pre-rinse composition PRC 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 45 °C and most preferably from 25 to 40 °C.

[0062] The aqueous pre-rinse composition PRC 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 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 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 pre-rinse composition PRC 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.

[0065] Preferably, the aqueous pre-rinse composition PRC 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.

[0066] Preferably, the amount of organic solvent(s) present in the aqueous pre-rinse composition PRC 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 0.2 wt-%, in each case based on the total weight of the composition.

[0067] Constituent a1) Preferably, the aqueous pre-rinse composition PRC comprises zirconium cations as constituent a1) in an amount in a range of from 1 or 5 to 2 000 mg / L, more preferably of from 7.5 to 1 500 mg / L, even more preferably of from 10 to 1 000 mg / L, still more preferably of from 12.5 to 750 mg / L, yet more preferably of from 15 to 500 mg / L, even more preferably of from 20 to 250 mg / L, most preferably of from 50 to 150 mg / L, in each case calculated as metal.

[0068] 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 compounds for use as precursor compounds are the complex fluorides of zirconium. 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 cations formed with fluoride ions in the composition, e.g., by coordination of fluoride anions to zirconium cations in the presence of water. In case complex fluorides of zirconium cations have been used as precursor compounds, the aqueous pre-rinse composition PRC preferably further comprises free fluoride anions as constituent a4).

[0069] Additionally, or alternatively, zirconium can also be added in form of zirconyl compounds as, e.g., zirconyl nitrate, zirconyl acetate, zirconium carbonate and / or zirconium nitrate, the latter one being particularly preferred, in particular when the aqueous composition is acidic.

[0070] The content 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.

[0071] Constituent a2)

[0072] Preferably, aqueous pre-rinse composition PRC comprises copper cations as constituent a2) in an amount in a range of from 1 to 1 000 mg / L, more preferably of from 1 to 500 mg / L, even more preferably of from 1 5 to 250 mg / L, still more preferably of from 2 to 150 mg / L, yet more preferably of from 2.5 to 100 mg / L, even more preferably of from 5 to 50 mg / L, most preferably of from 7.5 to 30 mg / L, in each case calculated as metal. It has been found that the presence of copper ions has a positive effect on increasing the Zr coating weight of the chemically pretreated substrate.

[0073] Optional constituent a3)

[0074] Preferably, at least one of, more preferably both, the aqueous pre-rinse composition PRC and the aqueous composition AC further comprises zinc cations. It has been found that the presence of zinc ions has a positive effect on the corrosion resistance.

[0075] Preferably, the aqueous pre-rinse composition PRC further comprises as constituent a3) zinc cations, more 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 mg / L, still more preferably of from 0 or 50 to 750 mg / L, yet more preferably of from 0 or 100 to 600 mg / L, in each case calculated as metal.

[0076] Optional constituent a4)

[0077] Preferably, the aqueous pre-rinse composition PRC further comprises as constituent a4) free fluoride anions, preferably in an amount in a range of from 0 or 1 mg / L to 500 mg / L, still more preferably of from 0 or 5 or 400 mg / L, yet more preferably of from 0 or 10 or 300 mg / L, even more preferably of from 0 or 15 to 200 mg / L, still more preferably of from 0 or 20 to 100 mg / L calculated in each case as fluorine. The free fluoride content is determined by means of a fluoride ion sensitive electrode according to the method disclosed in the ‘methods’ section.

[0078] Free fluoride anions being present as optional constituent a4) may be generated by adding water-soluble fluorine compounds, e.g., fluorides other than complex fluorides of Zr as well as hydrofluoric acid to the composition.

[0079] Alternatively, free fluoride anions being present as optional constituent a4) may be generated by adding complex fluorides of Zr and / or of other metals such as Ti to the composition. Complex fluorides are coordinated to at least one suitable metal cation such as zirconium in the presence of water. In this case, besides free fluoride anions, the aqueous pre-rinse composition PRC preferably further comprises complex fluoride anions as well. Preferably, the total amount of fluorides (being the sum of the amount of free fluoride anions and complex fluorides) in the composition is at least 0.10 g / L, more preferably at least 0.15 g / L.

[0080] Further optional constituents of composition PRC

[0081] Optionally, the aqueous pre-rinse composition PRC 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, except of copper and zinc ions, which are already necessarily present as constituents a1) and a2). More preferably the aqueous pre-rinse composition PRC further optionally comprises at least one kind of metal cations selected from the group consisting of cations of cerium and other lanthanides, iron, calcium, cobalt, magnesium, manganese, molybdenum, niobium, tantalum, yttrium, vanadium, lithium, bismuth, and tin, and mixtures thereof.

[0082] Optionally, the aqueous pre-rinse composition PRC 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. Optionally, the aqueous pre-rinse composition PRC further comprises at least one kind of metal cations selected from titanium and hafnium cations.

[0083] Optionally, the aqueous pre-rinse composition PRC 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-butyl ether and mixtures thereof.

[0084] Optionally, the aqueous pre-rinse composition PRC 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 group 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 Zr cations being present in the composition as a1 ).

[0085] The aqueous composition may further comprise at least one of the following constituents: one or more waxes, one or more wetting agents and one or more defoamers and / or rheology additives.

[0086] Optionally, the aqueous pre-rinse composition PRC may comprise at least one water-soluble polymer 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 ethy lenically 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.

[0087] Optional step 1a)

[0088] According to optional step 1a) at least the pre-rinsed portion of the metallic surface of the substrate obtained after step 1) is rinsed at least once with water. Preferably, the water used in optional step 1a) has a pH value <5.0, more preferably <4.8, even more preferably is in a range of from 3.5 to 4.7 or of from 3.8 to 4.6 or of from 3.9 to 4.5.

[0089] The term "rinsing" preferably means, in accordance with the general understanding of this term, a removal of excessive parts of the aqueous pre-rinse composition PRC, which was contacted with the surface in step 1) directly preceding the optional rinsing step. Tap water and / or deionized water can be used for rinsing in optional step 1a). As outlined hereinbefore, optional step 1a) can be performed more than once. It is hence possible, e.g., to perform a rinsing in step 1 a) once with tap water followed by rinsing with deionized water or vice versa.

[0090] Preferably, optional rinsing step 1 a) is not performed. Accordingly, preferably no rinsing step is performed between steps 1) and 2). This has the advantage that less water to be used in total for performing the method is necessary. In addition, a rinsing zone in the setup and pretreatment line used for performing the chemical pretreatment method is not necessary.

[0091] Step 2)

[0092] According to step 2) at least the pre-rinsed portion of the metallic surface of the substrate obtained after step 1) or after optional step 1 a) is contacted at least in portion with an aqueous composition AC. As outlined hereinbefore aqueous composition AC represents a chemical pretreatment composition.

[0093] Preferably, the aqueous composition AC is suitable to form a second coating film CF2 such as a second conversion coating film at least in portion onto at least the pre-rinsed portion of the metallic surface of the substrate, i.e., onto at least the portion of the metallic surface of the substrate, which already bears the first coating film CF1.

[0094] 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 aqueous composition AC. If only part of the metallic surface is contacted with the aqueous composition AC, 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 composition AC.

[0095] The “contacting” according to step 2) can be a spraying, a dipping (immersing) or a roll coating (rolling) step. The aqueous composition AC can also be applied by flooding the surface or even manually by wiping or brushing. Preferred is spraying, or dipping.

[0096] The treatment time, i.e., the period of time the surface is contacted with the aqueous composition AC in step 2), is preferably from 1 second to 20 minutes, more preferably from 10 seconds to 15 minutes, even more preferably from 30 seconds to 10 minutes, still more preferably from 45 seconds to 5 minutes, yet more preferably from 60 seconds to 3 minutes. Preferably, the duration of contacting step 2) exceeds the duration of contacting step 1), more preferably in that the duration of contacting step 2) is at least twice as long as the duration of contacting step 1).

[0097] The temperature of the aqueous composition AC used in step 2) is preferably of from 5 to 55 °C, more preferably of from 15 to 45 °C, and most preferably from 20 or 25 to 40 °C.

[0098] 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 2). Spraying and dipping are preferred. Aqueous composition AC

[0099] The aqueous composition AC is different from the aqueous pre-rinse composition PRC and comprises, besides water, at least constituents b1), b2) and b3), which are different from one of another, namely zirconium cations as constituent b1), copper cations as constituent b2), and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent b3).

[0100] Preferably, the aqueous composition AC is an aqueous acidic 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 sulfuric and / or boric acid and / or nitric acid and / or by at least one organic acid such as methyl sulfonic acid.

[0101] 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).

[0102] Preferably, the aqueous composition AC used in step 2) has a temperature in a range of from 5 to 50 °C, more preferably of from 15 to 45 °C or to 45 °C and most preferably from 25 to 40 °C.

[0103] The aqueous composition AC used in step 2) 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, and / or is 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.

[0104] “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.

[0105] The term “aqueous” with respect to the aqueous composition AC used in step 2) 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.

[0106] 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.

[0107] 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 0.2 wt.-%, in each case based on the total weight of the composition.

[0108] Constituent b1)

[0109] Preferably, the aqueous composition AC comprises zirconium cations as constituent b1) in an amount in a range of from 1 or 5 to 2 000 mg / L, more preferably of from 7.5 to 1 500 mg / L, even more preferably of from 10 to 1 000 mg / L, still more preferably of from 12.5 to 750 mg / L, yet more preferably of from 15 to 500 mg / L, even more preferably of from 20 to 250 mg / L, most preferably of from 50 to 150 mg / L, in each case calculated as metal.

[0110] Preferably, a precursor metal compound is used to generate constituent b1). The same precursor metal compounds discussed hereinbefore in connection with constituent a1) can be used here as well. In case complex fluorides of zirconium cations have been used as precursor compounds, the aqueous composition AC preferably further comprises free fluoride anions as constituent b5).

[0111] Additionally, or alternatively, zirconium can also be added in form of zirconyl compounds as, e.g., zirconyl nitrate, zirconyl acetate, zirconium carbonate and / or zirconium nitrate, the latter one being particularly preferred, in particular when the aqueous composition is acidic.

[0112] The content cation b1) 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.

[0113] Constituent b2)

[0114] Preferably, aqueous composition AC comprises copper cations as constituent b2) in an amount in a range of from 1 to 1 000 mg / L, more preferably of from 1 to 500 mg / L, even more preferably of from 1.5 to 250 mg / L, still more preferably of from 2 to 150 mg / L, yet more preferably of from 2.5 to 100 mg / L, even more preferably of from 5 to 50 mg / L, most preferably of from 7.5 to 30 mg / L, in each case calculated as metal. It has been found that the presence of copper ions has a positive effect on increasing the Zr coating weight of the chemically pretreated substrate.

[0115] Constituent b3) At least one organosilane and / or at least one hydrolysis and / or condensation product is present as constituent b3). Examples of hydrolysis and / or condensation products of organosilanes that can be formed in the presence of water are organosiloxanes and polyorganosiloxanes. 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.

[0116] Preferably, constituent b4) 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 such as glycidoxy groups, isocyanato groups, mercaptoalkyl groups, succinic anhydride groups, imido groups, imino groups, and / or ureido groups (urea groups).

[0117] Examples of suitable organosilanes are, e.g., aminoalkyltrialkoxysilanes, such as, preferably, 2- aminoethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3- aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane, 4-aminobutyltriethoxysilane, bis(2- ethyltrimethoxysilyljamine, bis(3-propyltrimethoxysilyl)amine, bis(4-butyltrimethoxysilyl)amine, bis(2- ethyltriethoxysilyljamine, bis(3-propyltriethoxysilyl)amine and / or bis(4-butyltriethoxysilyl)amine. Further examples of suitable organosilanes are 1,2-bis(triethoxysilyl)ethane, (3-mercaptopropyl)trimethoxysilane, (3- mercaptopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, (3-glycidyloxypropyl)triethoxysilane, and / or vinyltrimethoxysilane.

[0118] Preferably, at least one aminoalkyltrialkoxysilane and / or at least one hydrolysis and / or condensation product thereof is present as constituent b3).

[0119] Preferably, constituent b3) is present in the composition AC in such an amount that results in a content of Si in a range of from 1 or 5 to 500 mg / L, more preferably of from 7 5 to 250 mg / L, even more preferably of from 10 to 100 mg / L, still more preferably of from 20 to 80 mg / L, most preferably of from 25 to 50 mg / L, in each case calculated as elemental silicon The amount of Si can be measured according to the method described in the ‘methods' section, i.e., by ICP-OES.

[0120] Optional constituent b4)

[0121] Preferably, the aqueous composition AC further comprises as constituent b4) zinc cations, more preferably in an amount in a range of from 0 or 5 to 5000 mg / L, more preferably of from 0 or 10 to 2500 mg / L, even more preferably of from 0 or 25 to 1 000 mg / L, still more preferably of from 0 or 50 to 750 mg / L, yet more preferably of from 0 or 100 to 600 mg / L, in each case calculated as metal. It has been found that the presence of zinc ions has a positive effect on the corrosion resistance. Optional constituent b5)

[0122] Preferably, the aqueous composition AC further comprises as constituent b5) free fluoride anions, preferably in an amount in a range of from 0 or 1 mg / L to 500 mg / L, still more preferably of from 0 or 5 or 400 mg / L, yet more preferably of from 0 or 10 or 300 mg / L, even more preferably of from 0 or 15 to 200 mg / L, still more preferably of from 0 or 20 to 100 mg / L calculated in each case as fluorine. The free fluoride content is determined by means of a fluoride ion sensitive electrode according to the method disclosed in the ‘methods' section.

[0123] Free fluoride anions being present as optional constituent b5) may be generated by adding water-soluble fluorine compounds, e.g., fluorides other than complex fluorides of Zr as well as hydrofluoric acid to the composition.

[0124] Alternatively, free fluoride anions being present as optional constituent b5) may be generated by adding complex fluorides of Zr and / or of other metals such as Ti to the composition. Complex fluorides are coordinated to at least one suitable metal cation such as zirconium in the presence of water. In this case, besides free fluoride anions, the aqueous composition AC preferably further comprises complex fluoride anions as well. Preferably, the total amount of fluorides (being the sum of the amount of free fluoride anions and complex fluorides) in the composition is at least 0.10 g / L, more preferably at least 0.15 g / L.

[0125] Further optional constituents of composition AC

[0126] 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, except of copper and zinc ions, which are present as constituents b1) and b2). 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, iron, calcium, cobalt, magnesium, manganese, molybdenum, niobium, tantalum, yttrium, vanadium, lithium, bismuth, and tin, and mixtures thereof.

[0127] 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.

[0128] Optionally, the aqueous composition AC further comprises at least one kind of metal cations selected from titanium and hafnium cations.

[0129] 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-butyl ether and mixtures thereof. Methanol and ethanol can be, e g., present as reaction products of the organosilane hydrolysis and can, e.g., have been performed during such a synthesis from constituent b3) .

[0130] 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 and / or at least one organic acid having at least one carboxylic acid group 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 Zr cations being present in the composition as b1 ).

[0131] The aqueous composition may further comprise at least one of the following constituents: one or more waxes, one or more wetting agents and one or more defoamers and / or rheology additives.

[0132] Optionally, the aqueous composition AC may comprise at least one water-soluble polymer 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.

[0133] Optional step 2a)

[0134] According to optional step 2a) at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC in step 2) is rinsed at least once with water.

[0135] As outlined hereinbefore the term "rinsing'' preferably means, in accordance with the general understanding of this term, a removal of excessive parts of the aqueous composition AC, which was been contacted with the surface in step 2) directly preceding the optional rinsing step. Tap water and / or deionized water can be used for rinsing in optional step 2a). As outlined hereinbefore, optional step 2a) can be performed more than once. It is hence possible, e.g., to perform a rinsing in step 2a) once with tap water followed by rinsing with deionized water or vice versa.

[0136] Preferably, optional step 2a) is carried out. More preferably, in optional step 2a) the rinsing is performed at least twice, even more preferably at least once with tap water and at least once with deionized water, preferably in this sequence.

[0137] Optional step 3) According to optional step 3) curing or drying of at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC obtained in step 2) or that has been rinsed according to optional step 2a) is performed.

[0138] Optional step 3) is performed in order to obtain a cured or dried coating layer. Preferably, by performing the optional step 3) of drying or curing, more preferably of drying, the first coating film CF1 such as a first conversion coating film obtained after step 1) and the second coating film CF2 such as a second conversion coating obtained after step 2) are dried or cured, preferably dried. As a result dried or cured, preferably dried, coating layers CL1 (from coating film CF1) and CL2 (from coating film CF2) are obtained.

[0139] 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) and 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) and step

[0140] 2), although in such a case preferably prior to that step 3) is carried out.

[0141] 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. Once a film is dried, the resulting product can be regarded as a layer

[0142] 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 pirn. Preferably, the obtained cured or dried coating layer obtained after step

[0143] 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, in particular of from 80 to 150 nm.

[0144] Chemically pretreated substrate

[0145] A further subject-matter of the present invention is a chemically pretreated substrate being obtainable by the inventive of method of chemical pretreatment.

[0146] 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. Preferably, when optional step 3) has been performed, the chemically pretreated substrate comprises a cured or dried coating layer obtained after step 3), which has a dry film thickness below 0.5 m.

[0147] Preferably, when optional step 3) has been performed, the chemically pretreated substrate comprises a cured or dried coating layer obtained after step 3), which has a coating weight of Zr, calculated as metal, in a range of from 10 to 300 mg / m2, more preferably of from 30 to 100 mg / m2, and of Si, calculated as element, in a range of from 1 to 10 mg / m2, more preferably of from 1 to 4 mg / m2, determined in each case via XRF measurements.

[0148] Preferably, when optional step 3) has been performed, the chemically pretreated substrate comprises a cured or dried coating layer obtained after step 3), which has a coating weight ratio of elements Zr to Si in a range of from 1 :1 to 150: 1 , more preferably of from 10:1 to 90:1, determined via XRF measurements.

[0149] Coating method

[0150] 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 as defined hereinbefore and hereinafter, the method of coating comprising at least step 4), namely

[0151] 4) applying at least one coating material composition, preferably comprising at least one film-forming polymer and / or resin, onto at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC in step 2) or that has been rinsed according to optional step 2a) of the inventive method of chemical pretreatment, optionally, but preferably, after having performed drying or curing step 3) of the inventive method of chemical pretreatment.

[0152] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, and the substrate obtainable therefrom, are also preferred embodiments of the inventive coating method.

[0153] The coating material composition used in step 4) is different from each of compositions AC and PRC.

[0154] The coating material composition applied in step 4) 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 coating composition subsequently to form a multilayer coating system, which is conventionally used, e.g., in the automotive industry. 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.

[0155] Preferably, the at least one coating material composition is applied in step 4) onto the present dried or cured, more preferably dried, coating layers, which in turn are obtainable from drying or curing, preferably from drying, the coating films formed by having performed steps 1) and 2), wherein drying or curing, preferably drying, of these films in turn preferably is performed according to optional step 3) of the inventive method of chemical pretreatment.

[0156] Coated substrate

[0157] A further subject-matter of the present invention is a coated substrate being obtainable by the inventive coating method.

[0158] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, and the inventive coating method, and in each case preferred embodiments thereof, are also preferred embodiments of the inventive coated substrate.

[0159] Kit-of-parts

[0160] A further subject-matter of the present invention is a kit-of-parts comprising, preferably consisting of, an inventively used aqueous pre-rinse composition PRC as defined hereinbefore and hereinafter, which comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely zirconium cations as constituent a1), and copper cations as constituent a2), or a concentrate of said aqueous pre-rinse composition PRC, and an inventively used aqueous composition AC as defined hereinbefore and hereinafter, which is different from aqueous pre-rinse composition PRC and which comprises, besides water, at least constituents b1), b2) and b3), which are different from one of another, namely zirconium cations as constituent b1 ), copper cations as constituent b2), and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent b3), or a concentrate of said aqueous composition AC.

[0161] The term 'kit-of-parts' herein means, in accordance with common usage of this term, that it comprises at least two spatially separate constituents, which are functionally unitary through purposeful use. In the present case these at least two spatially separate constituents are the compositions PRC and AC or, in each case, concentrates thereof.

[0162] All preferred embodiments described above herein in connection with the inventive chemical pretreatment method, the substrate obtainable therefrom, the inventive coating method, and the inventive coated substrate, and in each case preferred embodiments thereof, are also preferred embodiments of the inventive kit-of-parts. Concentrates allow to produce the compositions PRC and AC in each case independently of one another by diluting the concentrate with water and if applicable by adjusting the pH value. The concentrate typically contains the constituents of the compositions PRC and AC to be produced in the desired proportions, but at a higher concentration. Preferably, the concentrate is diluted with water and / or an aqueous solution in the ratio of 1 :5,000 to 1: 10, more preferred 1 :1,000 to 1 :10, most preferred in the ratio of 1:300 to 1 :10 and even more preferred 1 :150 to 1 :50.

[0163] METHODS

[0164] 1. Solid content

[0165] The solid content (non-volatile content) was determined via DIN EN ISO 3251 :2019:09 at 105 °C for 60 min.

[0166] 2. ICP-OES

[0167] The amounts of certain elements in a sample under analysis, such as of zirconium, titanium, hafnium etc., was determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885 (date: September 1 , 2009). A sample was subjected to thermal excitation in an argon plasma generated by a high-frequency field, and the light emitted due to electron transitions became visible as a spectral line of the corresponding wavelength and was 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 were carried out as a function of the particular sample under analysis. These calibrations could be used to determine concentrations of unknown solutions such as the concentration of the amount of titanium, zirconium, and hafnium.

[0168] 3. XRF (X-ray fluorescence spectroscopy)

[0169] XRF (X-ray fluorescence spectroscopy) was used for determining the coating weight in mg / m2of certain (tracer) element(s) such as Ti, Zr, Cu and / or Si in a layer such as the conversion layer resulting from applying the chemical pretreatment composition to a substrate. XRF analyses were performed on the following instruments: Panalytical Axios max or Malvern Panalytical Zetium. There was one calibration per substrate for the particular element required. The calibrations were based on the data of the ICP measurements (the surface of the panels used for calibration was detached and measured by ICP; ICP uses standards traceable to NIST). The samples were circular blanks with a diameter of 4 cm.

[0170] 4. Free fluoride content determination

[0171] The free fluoride content was determined by means of a fluoride ion selective electrode (Thermo Scientific Orion 9609BNWP). The electrode was calibrated using two master solutions with known fluoride concentrations (20 and 200 ppm). The calibration process resulted in the building of a calibration curve. Then the fluoride content was determined by using of the curve. The device used for determining the free fluoride content was “Orion 4-Star1' or "Orion Star A324".

[0172] 5. pH measurements pH measurements were done using the device “WTW pH 330 i” with the following pH electrode: “SI Analytics Blueline 28 pH". The calibration was done with three buffer solutions (traceable to SRM from NIST and PTB) with the following pH values: 4, 7, 10.

[0173] 6. VDA 621-415 corrosion test, delamination, and stone chip resistance A cyclic corrosion test according to VDA 621-415 was performed for 10 weeks for steel substrates. The coated substrates were then investigated for their level of delamination in mm according to DIN EN ISO 4628-8:2013-03. In addition, stone chip resistance measured according to DIN EN ISO 20567-1 :2017:07, method C, was investigated, in each case after having performed the cyclic corrosion test. The smaller the score in the stone chip test, the better the resistance.

[0174] 7. CASS corrosion test, delamination, and stone chip resistance

[0175] A cyclic corrosion test according to DIN EN ISO 9227 CASS:2017-07 (copper-accelerated acetic acid-salt spray test) was performed for 10 weeks for aluminum substrates. The coated substrates were then investigated for their level of delamination in mm according to DIN EN ISO 20567-1 :2017: 07.

[0176] EXAMPLES

[0177] The following examples further illustrate the invention but are not to be construed as limiting its scope.

[0178] 1. Pre-rinse compositions (as composition PRC)

[0179] A pre-rinse bath was first filled up with fully demineralized water to about 80 wt.-% of the required intended amount. Then, a number of commercially available products (all from Chemetall GmbH) were added to the bath, with stirring, namely Oxsilan® additive 9936, Gardobond® additive H 7107, Oxsilan® additive 9901 , and Gardobond® additive H 7269. After that, the bath was filled up with deionized water to a level of 100 wt.-%. The pH of the bath was adjusted to about 4.8 using sodium carbonate and nitric acid. The chemical pretreatment bath obtained in this manner contained about 100 ppm zirconium ions, about 400 ppm zinc ions, about 12 ppm copper ions, in each case calculated as metal, and had a free fluoride content of about 30 to 35 ppm, calculated as F. The resulting bath PRC1 was aged for at least 12 hours to obtain a chemical equilibrium before being used.

[0180] 2. Chemical pretreatment compositions (as composition AC)

[0181] A chemical pretreatment bath was first filled up with fully demineralized water to about 80 wt.-% of the required intended amount. Then, a number of commercially available products (all from Chemetall GmbH) were added to the bath, with stirring, namely Oxsilan® additive 9936, Gardobond® additive H 7107, Oxsilan® 9810 / 3, Oxsilan® additive 9901, and Gardobond® additive H 7269. After that, the bath was filled up with deionized water to a level of 100 wt.-%. The pH of the bath was adjusted to about 4.8 using sodium carbonate and nitric acid. The chemical pretreatment bath obtained in this manner contained about 100 ppm zirconium ions, about 400 ppm zinc ions, about 12 ppm copper ions, in each case calculated as metal, had a free fluoride content of about 30 to 35 ppm, calculated as F, and a silicon content of about 30 ppm, calculated as element. The Si content originated from the presence of organosilanes and / or hydrolysis and / or condensation products thereof being present in Oxsilan® 9810 / 3. The resulting bath CPC1 was aged for at least 12 hours to obtain a chemical equilibrium before being used

[0182] 3. Pretreatment including chemical pretreatment method

[0183] 3.1 Steel substrates (CRS and HDG panels) or aluminum panels (AA6014S) were used (each 10.5 x 19 cm)). Each of the substrates was cleaned via spraying by making use of a commercially alkaline cleaner having a temperature of about 55 °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).

[0184] 3.2 A pre-rinse contacting step was then carried out, wherein the overall surface of each of the substrates was contacted with the pre-rinse composition PRC1 described hereinbefore in section 1. for 30 seconds by spray rinsing at about 35 °C. For a comparative run, pre-rinse contacting step was not performed.

[0185] 3.3 A contacting step was then carried out, wherein the overall surface of each of the substrates was contacted with the chemical pretreatment composition CPC1 described hereinbefore in section 2. for 75 seconds (in case pre- rinsing with PRC1 had been performed) or for 180 seconds (in case no pre-rinsing with PRC1 had been performed) by immersion or spraying at about 35 °C in order to form a conversion coating film onto the surface of each of the substrates. Following said contacting step, rinsing with deionized water was performed (for 30 seconds at ambient temperature).

[0186] 3.4 Then, a drying step was performed by warm air drying for about 10 minutes in an oven at 110 °C air temperature. 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 object temperature for 15 minutes. The dry layer thickness of the ED coat was 18.5 to 22.2 m. Afterwards, further commercially available coating compositions were applied in order to obtain a multilayer coating onto the ED coating, i.e., in this sequence, a filler (Hydro-filler from PPG Hemmelrath), a basecoat (Hydro-basecoat from NPAC Nippon Paint) and a clearcoat (2K clearcoat from Axalta Coating Systems). The overall dry layer thickness of all coatings applied on the substrates, after baking, was about 87 to 104 pm.

[0187] 4. Investigation of the properties of the substrates

[0188] 4.1 The substrates obtained, after the method described hereinbefore in section 3. had been performed, were then investigated according to the methods described in the 'methods’ section. The results for substrate CRS are shown in Table 1a.

[0189] Table 1a

[0190] = average value of 5 trials

[0191] As it is evident from the results of Table 1a performing of a pre-rinse with PRC1 prior to the chemical pretreatment with CPC1 leads to a significant improved delamination and to improved stone chipping results. The results for substrate HDG are shown in Table 1 b

[0192] Table 1b

[0193] = average value of 5 trials

[0194] The results for substrate AA6014S are shown in Table 1c.

[0195] Table 1c * = average value of 5 trials

[0196] 4.2 In Table 2 the Zr / Si-ratios (determined after measuring the coating weight of the respective elements in mg / m2by XRF according to the method described in the 'methods' section) on CRS are shown. Table 2 As it is evident from Table 2 the relatively high Zr / Si-ratio determined for the experimental run, in which a pre-rinse with PRC1 prior to chemical pretreatment with CPC1 had been performed, correlates with the significantly better

[0197] 5 delamination and stone chipping results as shown in Table 1a.

Claims

CLAIMS1 . A method of chemical pretreatment of a metallic surface of a substrate comprising at least steps 1) and 2) and optionally one or more of steps 1a), 2a) and 3), namely1) contacting at least one metallic surface of at least one substrate at least in portion with an aqueous pre-rinse composition PRC, which comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely zirconium cations as constituent a1), and copper cations as constituent a2),1a) optionally rinsing at least the pre-rinsed portion of the metallic surface of the substrate obtained after step 1) at least once with water,2) contacting at least the pre-rinsed portion of the metallic surface of the substrate obtained after step 1) or after optional step 1 a) at least in portion with an aqueous composition AC, which is different from aqueous pre-rinse composition PRC and which comprises, besides water, at least constituents b1), b2) and b3), which are different from one of another, namely zirconium cations as constituent b1), copper cations as constituent b2), and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent b3),2a) optionally rinsing at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC in step 2) at least once with water, and3) optionally curing or drying at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC obtained in step 2) or that has been rinsed according to optional step 2a).

2. The method according to claim 1 , characterized in that optional rinsing step 1 a) is not performed.

3. The method according to claim 1 or 2, characterized in that the duration of contacting step 2) exceeds the duration of contacting step 1), preferably in that the duration of contacting step 2) is at least twice as long as the duration of contacting step 1).

4. The method according to one or more of the preceding claims, characterized in that each of the aqueous pre-rinse composition PRC and the aqueous composition AC, independently of one another, comprises zirconium cations in an amount in a range of from 1 or 5 to 2 000 mg / L, more preferably of from 7.5 to 1 500 mg / L, even more preferably of from 10 to 1 000 mg / L, still more preferably of from 12.5 to 750 mg / L,yet more preferably of from 15 to 500 mg / L, even more preferably of from 20 to 250 mg / L, most preferably of from 50 to 150 mg / L, in each case calculated as metal.

5. The method according to one or more of the preceding claims, characterized in that each of the aqueous pre-rinse composition PRC and the aqueous composition AC, independently of one another, comprises copper cations in an amount in a range of from 1 to 1 000 mg / L, more preferably of from 1 to 500 mg / L, even more preferably of from 1.5 to 250 mg / L, still more preferably of from 2 to 150 mg / L, yet more preferably of from 2.5 to 100 mg / L, even more preferably of from 5 to 50 mg / L, most preferably of from 7.5 to 30 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 pre-rinse composition PRC further comprises as constituent a3) zinc cations, 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 mg / L, still more preferably of from 50 to 750 mg / L, yet more preferably of from 100 to 600 mg / L, in each case calculated as metal, and / or in that the aqueous composition AC further comprises as constituent b4) zinc cations, 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 mg / L, still more preferably of from 50 to 750 mg / L, yet more preferably of from 100 to 600 mg / L, in each case calculated as metal.7 The method according to one or more of the preceding claims, characterized in that the aqueous pre-rinse composition PRC further comprises as constituent a4) free fluoride anions, preferably 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, still more preferably of from 20 to 100 mg / L calculated in each case fluorine, and / or in that the aqueous composition AC further comprises as constituent b5) free fluoride anions, preferably 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, still more preferably of from 20 to 100 mg / L calculated in each case fluorine.

8. The method according to one or more of the preceding claims, characterized in that constituent b3) is present in the composition AC in such an amount that results in a content of Si in a range of from 1 or 5to 500 mg / L, preferably of from 7.5 to 250 mg / L, more preferably of from 10 to 100 mg / L, still more preferably of from 20 to 80 mg / L, most preferably of from 25 to 50 mg / L, in each case calculated as elemental silicon.

9. The method according to one or more of the preceding claims, characterized in that the aqueous pre-rinse composition PRC used in step 1) is free or essentially free of any organosilanes and / or hydrolysis and / or condensation products thereof.

10. The method according to one or more of the preceding claims, characterized in that the aqueous pre-rinse composition PRC is an aqueous acidic 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 and / or in that the aqueous composition AC is an aqueous acidic 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.

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 kind of steel, at least one kind of steel alloys, at least one kind of aluminum, at least one kind of aluminum alloys, at least one kind of zinc, at least one kind of zinc alloys including zinc magnesium alloys, and / or mixtures thereof, preferably is made at least partially of at least one kind of steel and / or at least one kind of steel alloys.

12. 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, the method of coating comprising at least step 4), namely4) applying at least one coating material composition, preferably comprising at least one film-forming polymer and / or resin, onto at least the portion of the metallic surface of the substrate that has been contacted with the aqueous composition AC in step 2) or that has been rinsed according to optional step 2a) as defined in claim 1, optionally after having performed drying or curing step 3) as defined in claim 1 .

13. 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 12.

14. The substrate according to claim 13, which is a chemically pretreated substrate being obtainable by the method according to one or more of claims 1 to 11, characterized in that the chemically pretreated substrate when optional step 3) has been performed has a cured or dried coating layer obtained after step 3), which has a dry film thickness below 0.5 pim, and / or has a cured or dried coating layer obtained after step 3), which has a coating weight of Zr, calculated as metal, in a range of from 10 to 300 mg / m2, more preferably of from 30 to 100 mg / m2, and of Si, calculated as element, in a range of from 1 to 10 mg / m2, more preferably of from 1 to 4 mg / m2, determined in each case via XRF measurements, and / or has a cured or dried coating layer obtained after step 3), which has a coating weight ratio of elements Zr to Si in a range of from 1 :1 to 150: 1 , more preferably of from 10: 1 to 90:1 , determined via XRF measurements.

15. A kit-of-parts comprising an aqueous pre-rinse composition PRC as defined in one or more of claims 1, 4 to 7, 9, and 10, which comprises, besides water, at least constituents a1) and a2), which are different from one of another, namely zirconium cations as constituent a1), and copper cations as constituent a2), or a concentrate of said aqueous pre-rinse composition PRC, and an aqueous composition AC as defined in one or more of claims 1 and 4 to 8, and 10, which is different from aqueous pre-rinse composition PRC and which comprises, besides water, at least constituents b1), b2) and b3), which are different from one of another, namely zirconium cations as constituent b1), copper cations as constituent b2), and at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent b3), or a concentrate of said aqueous composition AC.