Post-rinse pretreatment with aqueous compositions containing alkaline earth metal ions

Abstract

The present invention relates to a method for pre-treating at least one metal surface of a substrate, comprising at least steps 1) and 2), i.e., contacting the at least one surface of the substrate at least partially with an acidic aqueous composition AAC to at least partially form a film on said surface, the acidic aqueous composition contains at least fluorine anions in an amount in the range of 10 to 2000 mg / L and further comprises at least one metal cation (1) selected from the group consisting of Ti, Zr and Hf ions and mixtures thereof, and the membrane obtained after step 1) is AC rinsed with an aqueous composition prior to any optional curing and / or drying of the membrane, the aqueous composition is different from an acidic aqueous composition AAC and contains at least one alkaline earth metal ion (2); a method of applying at least one coating film onto at least one surface of a substrate that has undergone a pretreatment method; a substrate obtainable by these methods; the use of the aqueous composition AC for various purposes; and a kit of parts comprising an acidic aqueous composition AAC and an aqueous composition AC.

Description

[0001] The present invention particularly relates to a method for pretreating at least one surface of a substrate, wherein the surface is at least partially made of at least one metal and / or its alloy, the method using a chemical pretreatment composition containing fluoride anions and a subsequent post - rinsing step; a method for applying at least one coating film, such as an electrodeposited coating film, onto the surface of the substrate that has been pretreated according to the pretreatment method; and a substrate obtainable by one of these methods. Background Art

[0002] Before painting a substrate having a metal surface, i.e., before applying a permanent coating onto its surface, it is nowadays typically subjected to a corrosion - resistant and adhesion - promoting chemical pretreatment by using a suitable chemical pretreatment composition. Generally, an aqueous solution based on metal complex fluorides such as titanium and / or zirconium complex fluorides is used as such a chemical pretreatment composition in order to produce a conversion coating on the metal surface of the substrate. As previously mentioned, such a chemical pretreatment step is carried out before a subsequent coating step, such as an electrodeposition coating step, coating with a primer filler, a base coat and a clear coat or a powder coat. After subjecting the metal surface of the substrate to the chemical pretreatment, it is usually then rinsed with deionized water in a "post - rinsing" step to remove the excess components of the chemical pretreatment composition. It is known to use an alkaline aqueous composition or an aqueous composition containing nitrite instead of deionized water as the post - rinsing composition in order to further improve the corrosion - resistant properties of the conversion - coated surface of the metal substrate, especially to avoid flash rust in the case of substrates made of cold - rolled steel (CRS).

[0003] After the chemical pretreatment, a subsequent coating step is usually carried out as mentioned above. In particular, when a substrate intended for use in the automotive industry has undergone the chemical pretreatment, an electrodeposition coating is usually then applied over its conversion - coated surface to further protect against corrosion. Generally, there are electrodeposition coating material (electrophoretic paint) compositions that can be anodically deposited and cathodically deposited, but the cathodically depositable materials are the most important in industrial coating and especially in automotive coating.

[0004] Due to the chemical pretreatment methods carried out and the parameters used, and further, depending on the type of metal of the metal surface of the substrate used, but particularly depending on the type of the chemical pretreatment composition used and its components, sometimes undesired surface defects / differences in the surface properties of the resulting converted coated substrate are observed. Differences in the surface properties of the substrate may in turn lead to differences in the application process when subsequently applying an electrodeposition coating material composition to its surface. In particular, as a result of the different surface properties of the converted coated substrate, differences in the film build height ("mapping") during its application, too large (too thick) layer thicknesses of the electrodeposition coating, and / or other appearance defects may occur and be observed. This applies in particular to the case where the chemical pretreatment composition used contains fluorides, since the fluorides contained in the conversion coating present on the metal surface may migrate into the applied electrocoating material and negatively affect the film build height and cause mapping and / or cause the above-mentioned appearance defects, especially when the metal surface or at least areas of these surfaces have been in contact with the pretreatment composition for too long a period of time. Different film build heights occurring within one layer of the electrocoating material are undesirable because these differences need to be covered and levelled by a subsequently applied coating material composition (over the electrocoating) such as a primer coating material in order to prevent them from showing through on the surface of the entire automotive coating. Such covering and / or levelling usually requires a cost-intensive post-treatment process, which has to be carried out manually after the electrocoating material has been applied, for example by manual grinding operations. Similarly, the occurrence of the above-mentioned appearance defects is also undesirable, especially since these defects may still be visible even when additional coatings including a topcoat layer have been applied. Too large (too thick) layer thicknesses of the electrodeposition coating are also undesirable because this may result in an unacceptable surface roughness of this layer, which in turn makes it more difficult to apply additional coatings smoothly on top.

[0005] Accordingly, there is a need to provide a chemical pretreatment method using a chemical pretreatment composition containing fluoride anions, which allows for the formation of a uniform film build without the occurrence of mapping and without the occurrence of optical defects during the application of a subsequently to be applied electrodeposition coating material to the chemically pretreated metal surface of the substrate, especially even when at least a part of the surface of the substrate has been in contact with the chemical pretreatment composition for too long a period of time.

[0006] Problem

[0007] Accordingly, an object of the present invention is to provide a chemical pretreatment method using a chemical pretreatment composition containing a fluoride anion, which allows for the formation of a uniform film without unevenness occurring during the application of an electrodeposition coating material to be subsequently applied to the chemically pretreated metal surface of a substrate, and without optical defects occurring, especially even when at least a part of the surface of the substrate has been in contact with the chemical pretreatment composition for an excessive period of time.

[0008] Solution

[0009] This object has been solved by the subject matter of the claims of the present application and by its preferred embodiments disclosed in the present specification, i.e., by the subject matter described herein.

[0010] A first subject of the present invention is a method for pretreating at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy, and the method comprises at least steps 1) and 2), namely,

[0011] 1) bringing the at least one surface of the substrate into contact at least partially with an acidic aqueous composition AAC to form a film at least partially on said surface, the acidic aqueous composition containing at least fluoride anions in an amount preferably in the range of 10 to 2000 mg / L calculated as fluorine, and the acidic aqueous composition further preferably containing at least one metal cation selected from the group consisting of titanium, zirconium, and hafnium ions and mixtures thereof, and

[0012] 2) rinsing the film obtained after step 1) with an aqueous composition AC before any optional curing and / or drying of the film, the aqueous composition being different from the acidic aqueous composition AAC and containing at least one alkaline earth metal ion.

[0013] Another subject of the present invention is a method for applying at least one coating film to at least one surface of a substrate, the method comprising at least steps 1) and 2) as defined above and below, and further comprising step 3), namely

[0014] 3) applying a coating material composition containing at least one film-forming polymer to the optionally dried and / or optionally cured film, which film is in turn obtainable after having carried out the rinsing step 2) and optionally after having further dried and / or cured the film obtained after the rinsing step 2).

[0015] Preferably, the coating material composition applied in step 3) is an electrodepositable, preferably cathodically electrodepositable, coating material composition, and the at least one film-forming polymer present therein is preferably an electrodepositable, preferably cathodically electrodepositable, polymer.

[0016] Another subject of the present invention is a substrate obtainable by a pretreatment method of the present invention comprising at least steps 1) and 2), or by a method of applying at least one coating film to at least one surface of a substrate of the present invention comprising at least steps 1) and 2), or by the pretreatment method of the present invention and step 3).

[0017] Another subject of the present invention is the aqueous composition AC as defined above and below, for example in connection with step 2) of the pretreatment method of the present invention

[0018] Use for rinsing a film obtainable by applying at least in part an acidic aqueous and fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, to at least one surface of a substrate, wherein said surface is at least in part made of at least one metal and / or its alloy, and wherein the rinsing will be carried out before any optional curing and / or drying of said film

[0019] and / or

[0020] Use for at least partly reducing the fluoride content of a film obtainable by applying at least in part an acidic aqueous and fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, to at least one surface of a substrate, wherein said surface is at least in part made of at least one metal and / or its alloy, said use preferably being achieved by rinsing said film with the aqueous composition AC before any optional curing and / or drying of said film

[0021] and / or

[0022] Use for improving the film formation uniformity and / or for reducing the unevenness of the coating film CF in at least one of its regions, said coating film CF being obtained by applying an electrodeposition coating material composition to a cured or dried film, said cured or dried film being in turn obtainable by applying at least in part an acidic aqueous and fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, to at least one surface of a substrate, wherein said surface is at least in part made of at least one metal and / or its alloy, said use preferably being achieved by rinsing said film with the aqueous composition AC before any optional curing and / or drying of said film and before applying the coating film CF

[0023] Another subject of the present invention is a kit which comprises

[0024] The acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, the acidic aqueous composition contains at least fluoride anions, and

[0025] The aqueous composition AC as defined above and below, for example in connection with step 2) of the pretreatment method of the present invention, the aqueous composition contains at least one alkaline earth metal ion and is different from the acidic aqueous composition AAC.

[0026] It has been particularly surprisingly found that, despite the presence of fluoride anions in the chemical pretreatment composition used in step 1), the pretreatment method of the present invention allows for uniform film formation during the application of the subsequently applied electrodeposition coating material to the chemically pretreated metal surface of the substrate, regardless of the metal substrate material used. It has been unexpectedly found that when the electrodeposition coating material composition is applied to the pretreated surface (which has undergone a rinsing step 2) prior to pretreatment) and during the application of the electrodeposition coating material composition to the pretreated surface, no or at least significantly reduced undesired film formation deviations (non-uniformities) due to the different surface characteristics of the substrate as a result of the chemical pretreatment step 1) are observed. In particular, it has been found that this unexpected technical effect is the result of the specific aqueous composition AC used as the rinsing composition in step 2) and the content of at least one alkaline earth metal ion present therein. It has been found that due to the presence of at least one alkaline earth metal ion in the rinsing composition used in step 2), the amount of fluoride incorporated into the pretreatment film (conversion film) obtained after step 1) can be reduced, and as a result, any negative effects of fluoride anions on the film formation of the electrophoretic coating can be prevented or at least significantly reduced during the application of the electrophoretic coating. In particular, less fluoride migration into the electrophoretic coating film is observed when applying the electrophoretic coating composition (such as by dipping the pretreated substrate into an electrodeposition bath), which results in a decrease in conductivity when a voltage is applied, which in turn advantageously results in a thinner electrodeposited coating.

[0027] Furthermore, it has been found that in addition to the improved uniformity of film formation of the subsequently applied electrodeposition coating material composition, the corrosion protection of the substrate is not negatively affected. Furthermore, it has been found that no negative optical defects (such as the appearance of flow marks) are observed in the layer obtainable from the subsequently applied electrodeposition coating material composition, especially because the local high fluoride concentration in the pretreatment obtained after step 1) is prevented by performing the rinsing step 2). Furthermore, it has been found that other properties of the layer produced by the subsequently applied electrodeposition coating material composition, such as surface roughness, are not negatively affected, and in particular, too high a layer thickness can be avoided.

[0028] Furthermore, it has surprisingly been found that the above unexpected results are particularly observed even when at least a part of the surface of the substrate has been in contact with the chemical pretreatment composition for an extended period of time. Thus, the method of the present invention overcomes the painting defects of channels and unevenness observed in conventional prior art chemical pretreatment methods and allows the formation of a thinner and smoother electrodeposited coating material layer. Detailed Description

[0029] In the context of the present invention, the term "comprising", as related to compositions AC and AAC for example, preferably has the meaning of "consisting of". For example, with regard to compositions AC and AAC, in addition to all the mandatory components present therein, one or more of the additional optional components determined hereinafter may also be included therein. In each case, all components may be present in their preferred embodiments as determined hereinafter.

[0030] The proportions and amounts, in wt.-% (weight percent), of any of the components given hereinafter present in each composition total 100 wt.-%, in each case based on the total weight of the respective composition.

[0031] Pretreatment method

[0032] A first subject of the present invention is a method for pretreating at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy. The method comprises at least steps 1) and 2).

[0033] As used herein, the term "pretreatment" is preferably used according to the term "surface pretreatment" as defined in Lexikon "Lacke und Druckfarben [Varnishes and Inks]" (Publisher: Ulrich Zorll, Editor: Hans-Jürgen P. Adler – Stuttgart; New York: Thieme [Thieme Publishing House], 1998; Term: " [Surface Pretreatment]", page 417). According to DIN 50902:1994-07, on a metal substrate or a substrate having a metal surface, one or more first steps of surface treatment are usually one or more (chemical) cleaning steps (also called "surface preparation steps") carried out with an aqueous or non-aqueous cleaning composition.

[0034] The term "chemical pretreatment" is used according to EN ISO 4618:2006 (E / F / D) (Term: 2.41 "chemical pretreatment", which represents any chemical process applied to the surface before the application of the coating material). According to this standard, treatments that can be included, for example, under the term "conversion treatment" (such as chromating and phosphating) belong to chemical pretreatment and are thus distinguished from the (subsequent) coating step in which the coating material, i.e., a coating composition such as a powder coating composition, an electrodeposition coating composition, an aqueous or non-aqueous liquid coating material, is applied. In addition to conversion treatments (such as chromating and phosphating), chemical surface pretreatment can generally also be achieved with passivating compositions and film-forming compositions (including aqueous compositions containing fluoride anions such as composition AAC which is compulsorily used as the chemical pretreatment composition in step 1).

[0035] According to the above internationally valid definition of "pretreatment" of a metal substrate, the pretreatment method according to the present invention preferably covers a surface preparation cleaning step in addition to the chemical pretreatment step 1) and the rinsing step 2).

[0036] Preferably, the pretreatment method does not include any step involving any treatment with chromium ions such as Cr(VI) ions and / or Cr(III) ions. Preferably, the chemical pretreatment step 1) is the only chemical pretreatment step of the pretreatment method. Therefore, preferably, no other chemical pretreatment compositions other than composition AAC are used.

[0037] Substrate

[0038] The substrate has at least one surface, and the at least one surface is at least partially made of at least one metal and / or its alloy. Therefore, the substrate has at least one metal surface.

[0039] Preferably, the at least one surface of the substrate is at least partially made of at least one metal and / or its alloy, more preferably at least partially made of steel, aluminum, aluminum alloy, and zinc alloy. The steel is preferably steel selected from the group consisting of: bare steel, cold-rolled steel (CRS), hot-rolled steel, galvanized steel such as hot-dip galvanized steel (HDG), alloy galvanized steel, and aluminized steel (such as or ), the aluminum alloy includes aluminum-magnesium alloy, aluminum-magnesium-silicon alloy, aluminum-copper alloy, aluminum-zinc alloy, and aluminum-zinc-copper alloy, and the zinc alloy such as Zn / Mg alloy, Zn / Ni alloy, and Zn / Mg / Al alloy.

[0040] Preferably, not only at least one surface of the substrate is metallic, but the substrate itself is metallic. The term "metal substrate" covers, according to the general understanding of the term, any substrate having a surface comprising one or more pure metals and / or their alloys. If the substrate comprises regions of different metals, such a substrate is herein denoted as a "multi-metal substrate", which is a subclass of the metal substrates.

[0041] Preferably, the substrate used is a conductive substrate, which is commonly used and known to the person skilled in the art. The substrate can have all kinds of geometric structures and shapes, such as coils and sheets, as well as parts such as automotive parts, including vehicle parts such as wheel parts, which in turn also include electric vehicle parts such as battery housings and other workpieces. Particularly suitable substrates are parts for the production of a body or the entire body of a vehicle.

[0042] Optional steps carried out before step 1)

[0043] Before step 1), one or more of the following optional steps can be carried out in the following order:

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

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

[0046] Step C-1): Contacting the surface of the substrate with an aqueous composition comprising at least one inorganic acid, said aqueous composition being different from compositions AC and AAC, or alternatively contacting it with an aqueous alkaline composition or a pH-neutral aqueous composition, each of these compositions also being different from composition AC, 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) can be carried out in one step, which is preferred. Preferably, both steps A-1) and B-1) are carried out.

[0049] Optional step C-1) is preferably used to remove oxides, undesired alloy components, surface layers, brushing dust, etc. from the surface of the substrate, and thus to activate the surface for the subsequent conversion treatment in step 1).

[0050] Preferably, at least one inorganic acid of the composition in step C-1) is sulfuric acid and / or nitric acid, more preferably sulfuric acid.

[0051] The rinsing step D-1) and the optional rinsing as part of step A-1) are preferably carried out by using deionized water or tap water. Preferably, step D-1) is carried out by using deionized water.

[0052] Step 1) and composition AAC

[0053] According to step 1) of the pretreatment method, at least one surface of the substrate is at least partially contacted with the acidic aqueous composition AAC to at least partially form a film on the surface, and the acidic aqueous composition contains at least fluoride anions. The acidic aqueous composition AAC represents a chemical pretreatment composition. By carrying out step 1), a conversion film is formed on the surface of the substrate that has been contacted with the acidic aqueous composition AAC.

[0054] The term "at least partially" preferably means in some cases, according to the general understanding of the term, it may be desirable or sufficient for the entire surface of the substrate not to be in contact with the chemical pretreatment composition AAC. If only a part of the metal surface is in contact with the corresponding composition, it is typically the same part for all steps of the method. However, it is generally desirable for the entire surface of the metal substrate to be in contact with the corresponding composition.

[0055] The "contact" according to step 1) can be a spraying, dipping or roll coating step. The composition AAC can also be applied by flooding the surface or even manually by wiping or brushing. Spraying, dipping or roll coating is preferred.

[0056] The treatment time, i.e., the time period during which the surface is in contact with the acidic aqueous composition AAC in step 1), is preferably 15 seconds to 20 minutes, more preferably 30 seconds to 10 minutes and most preferably 45 seconds to 5 minutes, such as for example 1 to 3 minutes.

[0057] The temperature of the acidic aqueous composition AAC used in step 1) is preferably 5 °C to 50 °C, more preferably 15 °C to 45 °C and most preferably 25 °C to 40 °C.

[0058] The acidic aqueous composition AAC can be used as a dip coating bath. However, it can also be applied by almost any conventional coating procedure as outlined above in connection with step 1), such as for example spraying, roll coating, brushing, wiping, etc. Spraying and dipping are preferred.

[0059] The acidic aqueous composition AAC used in step 1) preferably does not contain any chromium ions such as Cr(VI) cations and / or Cr(III) cations. The acidic aqueous composition AAC used in step 1) preferably does not contain any phosphonate anions and / or phosphate anions.

[0060] In the context of the present invention, the term "aqueous" with respect to the composition AAC used in the present invention preferably means that the composition AAC 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 the total content of organic and inorganic solvents including water. Thus, the composition AAC may contain at least one organic solvent in addition to water, however, in an amount lower than the amount of water present.

[0061] Preferably, the acidic aqueous composition AAC 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.

[0062] The acidic aqueous composition AAC preferably has a pH value in the range from 0.5 to 6.5. Preferably, the pH value is measured at room temperature (23 °C). The pH value of the acidic aqueous composition is more preferably in the range from 1.0 to 6.0, still more preferably in the range from 2.0 or 3.0 to 5.5. If desired, the pH can preferably be adjusted by using nitric acid, ammonia water and / or sodium carbonate.

[0063] The total amount of all components (component / constituent) present in the composition AAC amounts to 100 wt.-%. The composition AAC can be a dispersion or a solution. Preferably, it is a solution.

[0064] Preferably, the acidic aqueous composition AAC contains fluoride anions in an amount in the range from 10 to 2000 mg / L, more preferably from 15 to 1500 mg / L, even more preferably from 20 to 1000 mg / L, still more preferably from 25 to 500 mg / L, yet more preferably from 25 to 500 mg / L, in each case calculated as fluorine. As will be outlined below, preferably, complexes formed by complexing fluorides such as zirconium, titanium and / or hafnium with fluoride ions (for example by coordinating fluoride anions to zirconium, titanium and / or hafnium cations in the presence of water) are present in the composition AAC. Alternatively, the fluoride anions can be generated by adding other water-soluble fluorine compounds such as fluorides (other than the complexing fluorides of Ti, Zr and / or Hf) and hydrofluoric acid to the composition. The free fluoride content is determined by a fluoride ion-sensitive electrode according to the method disclosed in the'method' section.

[0065] Preferably, the acidic aqueous composition AAC contains at least one metal cation selected from the group consisting of titanium, zirconium and hafnium ions and mixtures thereof, more preferably selected from the group consisting of titanium and zirconium ions and mixtures thereof, even more preferably selected from zirconium ions.

[0066] Preferably, the acidic aqueous composition AAC comprises at least one organosilane, preferably in an amount of 5 to 1000 mg / L, more preferably 5 to 500 mg / L. Examples are, for example, (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-glycidoxypropyl)trimethoxysilane and / or (3-glycidoxypropyl)triethoxysilane, and / or vinyltrimethoxysilane. The organosilane preferably exists in its hydrolyzed form.

[0067] Preferably, the acidic aqueous composition AAC comprises at least one metal cation selected from the group consisting of titanium, zirconium and hafnium ions and mixtures thereof, in an amount in the range of 5 to 2000 mg / L, more preferably 7.5 to 1500 mg / L, even more preferably 10 to 1000 mg / L, still more preferably 15 to 500 mg / L, yet more preferably 20 to 300 mg / L, in each case calculated as the metal. Preferably, a precursor metal compound is used to generate the at least one metal cation. Preferably, the precursor metal compound is water-soluble. The solubility is determined at a temperature of 20 °C and atmospheric pressure (1.013 bar). Particularly preferred zirconium compounds, titanium compounds and / or hafnium compounds are the complex fluorides of these metals. The term "complex fluoride" includes monoprotated and polyprotated forms as well as deprotonated forms. Mixtures of such complex fluorides can also be used. In the context of the present invention, a complex fluoride is a complex formed by zirconium, titanium and / or hafnium with fluoride ions in the composition (e.g., by coordinating fluoride anions to zirconium, titanium and / or hafnium cations in the presence of water). The content of the at least one metal cation can be monitored and determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy). The method is described below in the 'Method' section.

[0068] Optionally, the composition AAC can comprise additional components, such as other metal cations (other than Zr, Ti and / or Hf), and / or at least one water-soluble polymer such as a water-soluble polymer having at least one functional group selected from acid groups, hydroxyl groups and mixtures thereof. The solubility is determined at a temperature of 20 °C and atmospheric pressure (1.013 bar). Preferably, the at least one water-soluble polymer is a homopolymer or copolymer obtainable by the polymerization of at least one ethylenically unsaturated monomer, wherein at least a part of the monomers bears at least one functional group selected from acid groups, hydroxyl groups and mixtures thereof; more preferably a homopolymer or copolymer obtainable by the polymerization of at least one vinyl monomer and / or (meth)acrylic monomer, wherein at least a part of the monomers bears at least one functional group selected from acid groups, hydroxyl groups and mixtures thereof.

[0069] Preferably, the conversion layer formed after drying or curing, preferably drying, the film obtainable after step 1) (and after rinsing step 2)) has the following coating weights determined by XRF (X-ray fluorescence spectrometry):

[0070] 0.5 to 500 mg / m 2 , more preferably 1 to 400 mg / m 2 , even more preferably 3 to 350 mg / m 2 , still more preferably 5 to 300 mg / m 2 of zirconium, titanium and / or hafnium ions, preferably zirconium and / or titanium, especially zirconium, each calculated as metal.

[0071] Step 2) and composition AC

[0072] According to step 2) of the pretreatment method, the film obtained after step 1) is rinsed with an aqueous composition AC before any optional curing and / or drying of the film, the aqueous composition being different from the acidic aqueous composition AAC and containing at least one alkaline earth metal ion.

[0073] The aqueous composition AC used in rinsing step 2) preferably represents a "rinsing composition". This term preferably defines such a composition according to the general understanding of this term, which removes the excess of the composition that has come into contact with the metal surface in the step directly before the rinsing step, in which the rinsing composition is used - in this case, the rinsing composition comes into contact with the composition AAC in step 1).

[0074] Preferably, the at least one alkaline earth metal ion is present in the aqueous composition AC in an amount in the range of 5 to 2000 ppm, more preferably 5 to 1500 ppm, still more preferably 5 to 1000 ppm, even more preferably 10 to 1000 ppm, still more preferably 15 to 800 ppm, yet more preferably 20 to 750 ppm, still more preferably 25 to 600 ppm, even more preferably 35 to 500 ppm, yet more preferably 45 to 400 ppm, still more preferably 50 to 300 or 250 ppm, in each case calculated as alkaline earth metal. ICP-OES can also be used to determine this amount.

[0075] Preferably, the at least one alkaline earth metal ion present in the aqueous composition AC is selected from beryllium cations, magnesium cations, calcium cations, strontium cations, barium cations and mixtures thereof, more preferably from magnesium cations, calcium cations and mixtures thereof, most preferably from magnesium cations.

[0076] Preferably, the aqueous composition AC is obtainable by dissolving at least one alkaline earth metal salt in water. Various suitable salts can be used. Exemplary salts are salts selected from alkaline earth metal nitrates, sulfates, acetates, and mixtures thereof. In the case of using an acetate, preferably the pH value of the aqueous composition AC is adjusted by using at least one pH-adjusting compound or salt.

[0077] Preferably, the aqueous composition AC is free or substantially free of fluoride anions.

[0078] Preferably, the aqueous composition AC comprises water in an amount of at least 80 wt.-%, more preferably at least 85 wt.-%, still more preferably at least 90 wt.-%, even more preferably at least 95 wt.-%, still more preferably at least 98 wt.-%, and yet more preferably at least 99 wt.-%, in each case based on the total weight of the composition AC.

[0079] Preferably, the aqueous composition AC has a temperature in the range from 15 °C to 55 °C, more preferably from 17 °C to 50 °C.

[0080] Optional step 2a)

[0081] Optionally, an additional rinsing step can be carried out after step 2), according to which the film obtainable after step 2) is rinsed with water, preferably with deionized water.

[0082] Optional step 2b)

[0083] Optional step 2b) is a step in which the film obtained after step 2) or optionally after step 2a) is dried and / or cured, preferably dried.

[0084] When, for example, a powder coating composition is applied as the coating material composition in step 3) outlined below, drying and / or curing can be carried out. However, step 2b) is only optional, and thus, further method steps such as step 3) can be carried out without drying and / or curing the film obtained after the rinsing step 2). In particular, the coating material composition such as an electrocoating material composition in step 3) outlined below can be applied to the wet film obtained after the rinsing step 2).

[0085] The drying or curing step 2b) can preferably be carried out, if required, at a temperature in the range of, for example, 15 °C to 100 °C, more preferably at a temperature in the range of 18 °C to 95 °C, and in particular at a temperature in the range of 20 °C to 90 °C. In the context of the present invention, "drying" means physical drying by evaporation of water, which is initially present, in particular, in one or more of the compositions used, while "curing" further includes a chemical reaction between at least two components initially present in the one or more compositions and / or a chemical reaction between at least one component initially present in the one or more compositions and suitable functional groups present on the metal surface or in the conversion film, for example, in the case where a water-soluble polymer is present in composition AAC.

[0086] Method of applying at least one coating film

[0087] Another subject of the present invention is a method for applying at least one coating film to at least one surface of a substrate, the method comprising at least steps 1) and 2) as defined above and below, and further comprising step 3), namely

[0088] 3) applying a coating material composition comprising at least one film-forming polymer to a film which is optionally dried and / or optionally cured, preferably optionally dried, and which is in turn obtainable after having carried out the rinsing step 2), optionally after having further dried and / or cured the film obtained after the rinsing step 2).

[0089] All preferred embodiments described above in connection with the pretreatment method and its preferred embodiments are also preferred embodiments of the method for applying at least one coating film to at least one surface of a substrate.

[0090] Preferably, the coating material composition applied in step 3) is an electrodepositable, preferably cathodically electrodepositable, coating material composition, and the at least one film-forming polymer present therein is preferably an electrodepositable, preferably cathodically electrodepositable, polymer. Of course, the substrate used is preferably a conductive substrate. Preferably, the coating material composition applied in step 3), such as an electrodepositable, preferably cathodically electrodepositable, coating material composition, is applied to the wet film obtained after having carried out the rinsing step 2).

[0091] Electrodeposition coating (electrophoretic coating) material compositions are coating materials comprising a polymer as a binder, which coating materials comprise optionally crosslinking agents, pigments and / or fillers, and often additives. Usually, there are anodically electrodepositable and cathodically electrodepositable electrophoretic coating materials. Preferred cathodically electrodepositable materials are disclosed, for example, in EP 1 041 125 A1, DE 19703 869 A1 and WO 91 / 09917 A2.

[0092] Preferably, the electrodeposition coating (electrophoretic coating) material composition used is aqueous.

[0093] Any polymer is suitable as the cathode - deposit - able polymer as long as it is cathode - deposit - able. Preferred are poly(meth)acrylates, (meth)acrylate copolymers, and epoxide polymers. Most preferred is the epoxide - amine adduct. The epoxide - amine adduct for the purposes of the present invention is the reaction product of at least one epoxy resin and at least one amine. The epoxy resins used are more particularly those based on bisphenol A and / or its derivatives. The amines reacting with the epoxy resins are primary and / or secondary amines or their salts and / or salts of tertiary amines. The at least one epoxide - amine adduct used is preferably a cationic, epoxy - based, and amine - modified resin.

[0094] At least one cross - linker may be present in the electrodeposition coating material composition, which is selected from the group consisting of blocked polyisocyanates, free polyisocyanates, amino resins, and mixtures thereof.

[0095] The term "blocked polyisocyanate" is known to those skilled in the art. The blocked polyisocyanates that can be used are polyisocyanates having at least two isocyanate groups (diisocyanates in the case of exactly two isocyanate groups), but preferably having more than two, for example 3 to 5 isocyanate groups, where the isocyanate groups have reacted such that the resulting blocked polyisocyanate is stable at room temperature (i.e., at a temperature of 18 °C to 23 °C), especially towards hydroxyl and amino groups such as primary and / or secondary amino groups, but at elevated temperatures, such as for example at ≥80 °C, ≥110 °C, ≥130 °C, ≥140 °C, ≥150 °C, ≥160 °C, ≥170 °C, or ≥180 °C, conversion occurs and carbamate and / or urea bonds are formed.

[0096] Amino resins (aminoplast resins) are likewise known to those skilled in the art. The amino resins used are preferably melamine resins, more particularly melamine - formaldehyde resins, which are likewise known to those skilled in the art. However, it is preferred not to use amino resins such as melamine - formaldehyde resins as cross - linkers.

[0097] The electrodeposition coating material composition is preferably a one - component (1K) coating composition. For this reason, the electrodeposition coating composition preferably does not contain free polyisocyanates.

[0098] The electrodeposition coating material composition may contain at least one pigment and / or filler. The term "filler" is known to the person skilled in the art, for example from DIN 55943 (date: October 2001). For the purposes of the present invention, a "filler" is preferably a component that is substantially, preferably completely insoluble in the application medium (such as an electrodeposition coating material composition) and is particularly used to increase volume. In the sense of the present invention, a "filler" preferably differs from a "pigment" in its refractive index, the refractive index of the filler being < 1.7. All conventional fillers and pigments can be used.

[0099] Step 3) is preferably carried out by: immersing the substrate with the dried or cured, preferably dried film (which film is in turn obtainable by drying or curing the film obtainable after the rinsing step 2)) obtained after step 2) into an electrodeposition coating bath containing the electrodeposition coating material composition, connecting the substrate as the cathode, depositing a coating film CF obtained from the electrodeposition coating material composition on the substrate using direct current, removing the coated substrate from the electrodeposition coating bath, and baking the coating film CF deposited on the substrate. The applied voltage is preferably in the range of 50 to 500 volts. The electrodeposition coating bath preferably has a bath temperature in the range of 20 °C to 45 °C.

[0100] Substrate obtainable by the pretreatment method or the method of applying at least one coating film

[0101] Another subject of the present invention is a substrate obtainable by the pretreatment method of the present invention comprising at least steps 1) and 2) or by the method of applying at least one coating film to at least one surface of a substrate of the present invention comprising at least steps 1) and 2) or by the pretreatment method of the present invention and step 3).

[0102] All the preferred embodiments described above in connection with the pretreatment method and the method of applying at least one coating film to at least one surface of a substrate and their preferred embodiments are also preferred embodiments of the substrate of the present invention.

[0103] Use of the aqueous composition AC

[0104] Another subject of the present invention is the aqueous composition AC as defined above and below, for example in connection with step 2) of the pretreatment method of the present invention

[0105] Use for rinsing a film obtainable by at least partially applying an acidic aqueous composition containing fluorine anions, preferably an acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, to at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy, and wherein the rinsing will be carried out before any optional curing and / or drying of the film

[0106] and / or

[0107] Use for at least partially reducing the fluoride content of a film obtainable by at least partially applying an acidic aqueous fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, to at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy, said use preferably being effected by rinsing the film with the aqueous composition AC before any optional curing and / or drying of the film.

[0108] and / or

[0109] Use for improving the film-forming uniformity and / or for reducing the unevenness of a coated film CF in at least one of its regions, said coated film CF being obtainable by applying an electrodeposition coating material composition to a cured or dried film, which cured or dried film is in turn obtainable by at least partially applying an acidic aqueous fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, to at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy, said use preferably being effected by rinsing the film with the aqueous composition AC before any optional curing and / or drying of the film and before applying the coated film CF.

[0110] All preferred embodiments described above in connection with the pretreatment method and the method of applying at least one coated film to at least one surface of a substrate, as well as the substrate of the present invention and its preferred embodiments, are also preferred embodiments of the use of the present invention.

[0111] Kit

[0112] Another subject of the present invention is a kit which preferably consists of the following:

[0113] An acidic aqueous composition AAC as defined above and below, for example in connection with step 1) of the pretreatment method of the present invention, said acidic aqueous composition containing at least fluoride anions, and

[0114] An aqueous composition AC as defined above and below, for example in connection with step 2) of the pretreatment method of the present invention, said aqueous composition containing at least one alkaline earth metal ion and being different from the acidic aqueous composition AAC.

[0115] In accordance with common usage, the term 'kit' herein means that it contains at least two spatially separated components which are functionally unified by a purposeful use.

[0116] All of the preferred embodiments described above in connection with the pretreatment method and the method of applying at least one coating film to at least one surface of a substrate and the substrate and use of the present invention and its preferred embodiments are also preferred embodiments of the kit of the present invention.

[0117] Method

[0118] 1. Determination of free fluoride content

[0119] The free fluoride content is determined by a fluoride ion selective electrode. At least three mother solutions with known fluoride concentrations are used to calibrate the electrode. The calibration process results in the establishment of a calibration curve. Then the fluoride content is determined by using this curve.

[0120] 2. ICP-OES

[0121] The amounts of certain elements (such as zirconium, titanium, hafnium, etc.) in the analyzed sample are determined by inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885 (date: September 1, 2009). The sample is subjected to thermal excitation in an argon plasma generated by a high-frequency field, and the light emitted due to electronic transitions becomes visible as spectral lines of the corresponding wavelengths and is analyzed using an optical system. There is a linear relationship between the intensity of the emitted light and the concentration of the element in question. Before implementation, calibration measurements are carried out using known elemental standards (reference standards) according to the specific sample to be analyzed. These calibrations can be used to determine the concentration of unknown solutions, such as the concentrations of the amounts of titanium, zirconium, and hafnium.

[0122] 3. Coating weight

[0123] XRF (X-ray fluorescence spectrometry) is used to determine the coating weight (in mg / m 2 2) of a certain element in a layer (such as a conversion layer produced by applying a chemical pretreatment composition to a substrate).

[0124] 4. Coating thickness

[0125] The paint thickness (dry film layer thickness) of the electrodeposited coating is measured (in μm) according to DIN EN ISO 2178:2016-11 by using the MP20E-S tool from Fischer. Each measured value represents the average of 5 measurements. By measuring the dry film layer thickness, film formation and differences in film formation (non-uniformity) can be determined.

[0126] Examples

[0127] The following examples further illustrate the present invention, but should not be construed as limiting its scope.

[0128] 1. Products and materials used

[0129] A commercially available product (Chemetall GmbH) was used as the chemical pretreatment composition (CPC), namely product 9835, which is an acidic aqueous composition particularly containing fluoride anions and zirconium ions.

[0130] Different aqueous post-rinse compositions (comparative and those used in the present invention) were used, namely

[0131] PRC1 (comparative): deionized water;

[0132] PRC2 (comparative): an aqueous alkaline composition (deionized water, to which NaOH was added until a pH value of 10 was reached);

[0133] PRC3 (comparative): an aqueous composition containing sodium nitrite (50 ppm, calculated as NO2); and

[0134] PRC4a to PRC4d

[0135] (all of the present invention): an aqueous composition containing magnesium nitrate; PRC4a: 20 ppm, calculated as Mg; PRC4b: 100 ppm, calculated as Mg; PRC4c: 200 ppm, calculated as Mg; PRC4d: 980 ppm, calculated as Mg.

[0136] 2. Method (pretreatment step, post-rinse and electrocoating)

[0137] A hot-dip galvanized steel substrate (HDG substrate) was provided in the form of a metal panel.

[0138] The substrate was cleaned by using a commercially available alkaline cleaner having a pH value of about 10.5 (applied by spraying or dipping for about 1.5 minutes at 55 °C). Then, it was rinsed with tap water and subsequently rinsed with deionized water (30 seconds each time).

[0139] Two different methods were carried out for the subsequent contacting step:

[0140] Method 1:

[0141] Perform the contact step, in which the entire surface of the substrate is brought into contact with the chemical pretreatment composition CPC described above in item 1. by immersion for 3 minutes. Thereafter, 50% of the surface area of each substrate is brought into further contact with the composition CPC by immersion for another 3 minutes. Thus, 50% of the surface area of each substrate is brought into contact with the composition CPC for a total of 6 minutes to simulate a longer treatment time, and the corresponding surface area obtained is hereinafter referred to as the "flow channel area".

[0142] Method 2:

[0143] Perform the contact step, in which the entire surface of the substrate is brought into contact with the chemical pretreatment composition CPC described above in item 1. by immersion for 3 minutes. Subsequently, the composition CPC is allowed to flow again on a part of the surface area of the substrate using a dropping funnel for 3 minutes. The corresponding surface area obtained with a contact time of 6 min is hereinafter referred to as the "flow channel area".

[0144] The "flow channel area" of the surface is the area that has been brought into contact with the composition CPC for a longer time than planned in an uncontrolled manner so that undesired unevenness can be observed in these areas. The remaining surface area of each substrate is brought into contact with the composition CPC for a total of only 3 minutes, and the corresponding surface area obtained is hereinafter referred to as the "non-flow channel area".

[0145] In each case, the composition (CPC) has been heated to 30 °C before application.

[0146] After the contact step according to Method 1 or 2, a post-rinsing step is carried out at ambient temperature (18 °C to 25 °C) by using one of the compositions PRC1, PRC2, PRC3, PRC4a, PRC4b, PRC4c or PRC4d for 1 minute. In this way, the entire surface of all substrates is post-rinsed.

[0147] After the post-rinsing step, a final rinse is carried out with deionized water (for 30 seconds).

[0148] Next, a drying step is carried out via blowing.

[0149] Finally, each of the obtained substrates is coated with a commercial electrodeposition coating composition, i.e., a commercially available product 800. Electrodeposition coating is carried out at a bath temperature of 31 °C - 33 °C with a deposition voltage of 180 - 260 V (voltage ramp: 4 s, 30 s or 60 s) over a period of 2 minutes. Subsequently, the substrates are baked at 175 °C (substrate temperature) for 25 minutes.

[0150] 3. Study of the properties of the coated substrate

[0151] 3.1 Determine the total amount of F present in the layer formed by applying the chemical pretreatment composition CPC in the form of the quotient of the total coating weight of Zr (resulting from the zirconium cations present in the CPC) (in mg / m 2 calculated) and the total amount of F (resulting from the fluoride anions present in the CPC) (in mg / m 2 calculated) (hereinafter also referred to as the "Zr / F-ratio"). A higher Zr / F-ratio indicates a higher or more effective reduction / removal of F from the layer, which is desirable. In Tables 1a and 1b shown below, the resulting Zr / F-ratios determined for the two methods 1 and 2 described above in item 2 are summarized.

[0152] Table 1a (contact step via Method 1):

[0153]

[0154] Table 1b (contact step via Method 2):

[0155]

[0156] As is evident from Tables 1a and 1b, after chemical pretreatment with the fluoride anion-containing composition CPC, post-rinsing with one of PRC4a to PRC4d results in a reduction in the amount of F in the chemical pretreatment layer.

[0157] 3.2 In addition, the paint thickness (dry layer thickness) (in μm) of the electrodeposited coating has also been determined according to the method defined in the 'Method' section and is given in Tables 1c and 1d. The effect of the type of post-rinsing composition used on the paint thickness of the "flow channel area" of the surface has been studied. The results are shown in Tables 1c and 1d. The corresponding paint thicknesses of the "non-flow channel area" of the surface of the same panel are also given in Tables 1c and 1d. It can be seen that the post-rinsing treatment has only a minor effect on the thickness of the electrodeposited coating obtained in the "non-flow channel area", while having a significant effect on the thickness of the electrodeposited coating obtained in the "flow channel area". This ultimately results in leveling the difference in the thickness of the electrodeposited coating between the "non-flow channel area" and the "flow channel area", which is desirable.

[0158] Table 1c (contact step via Method 1):

[0159]

[0160]

[0161] Table 1d (contact step via Method 2):

[0162]

[0163] As is clearly seen from Tables 1c and 1d, after chemical pretreatment with the fluorine-containing anion composition CPC, post-rinsing with one of PRC4a to PRC4d significantly reduces the paint thickness of the electrodeposition coating in the "flow channel area". A paint thickness difference (difference in film formation and thus undesirable unevenness) between the "flow channel area" and the "non-flow channel area" exceeding 1.5 μm (as observed when using one of PRC1 to PRC3 instead) is unacceptable because it can be visually detected even after applying the topcoat layer (which is to be applied subsequently after applying the electrodeposition coating and optionally additional layers such as the primer coat), and furthermore, an additional grinding operation is required after applying the electrodeposition coating in order to achieve a uniform and even film formation. As outlined above, post-rinsing with deionized water (PRC1) or using a conventional post-rinsing composition (such as the NaOH-containing composition (PRC2) or the sodium nitrite-containing composition (PRC3)) is ineffective in this regard, as is also clearly seen from Tables 1c and 1d.

Claims

1. A method for pretreating at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy, the method comprising at least steps 1) and 2), that is, 1) bringing at least one surface of the substrate into contact at least partially with an acidic aqueous composition AAC to form a film at least partially on said surface, the acidic aqueous composition containing at least an amount of fluoride anions in the range of 10 to 2000 mg / L calculated as fluorine, and further containing at least one metal cation selected from the group consisting of titanium, zirconium and hafnium ions and mixtures thereof, and 2) rinsing the film obtained after step 1) with an aqueous composition AC before any optional curing and / or optional drying of the film, the aqueous composition being different from the acidic aqueous composition AAC and containing at least one alkaline earth metal ion.

2. The method according to claim 1, wherein The at least one alkaline earth metal ion is present in the aqueous composition AC in an amount in the range of 5 to 2000 ppm, preferably 5 to 1500 ppm, more preferably 5 to 1000 ppm, even more preferably 10 to 1000 ppm, still more preferably 15 to 800 ppm, yet more preferably 20 to 750 ppm, still more preferably 25 to 600 ppm, even more preferably 35 to 500 ppm, yet more preferably 45 to 400 ppm, still more preferably 50 to 300 or 250 ppm, in each case calculated as alkaline earth metal.

3. The method according to claim 1 or 2, characterized in that, The at least one alkaline earth metal ion present in the aqueous composition AC is selected from beryllium cations, magnesium cations, calcium cations, strontium cations, barium cations and mixtures thereof, preferably selected from beryllium cations, magnesium cations, strontium cations, barium cations and mixtures thereof, even more preferably selected from magnesium cations, calcium cations and mixtures thereof, and most preferably selected from magnesium cations.

4. The method according to one or more of the preceding claims, characterized in that, The aqueous composition AC is obtainable by dissolving at least one alkaline earth metal salt in water, wherein said salt is preferably selected from alkaline earth metal nitrates, sulfates, acetates and mixtures thereof.

5. The method according to one or more of the preceding claims, characterized in that The aqueous composition AC contains water in an amount of at least 80 wt.-%, preferably at least 85 wt.-%, more preferably at least 90 wt.-%, even more preferably at least 95 wt.-%, still more preferably at least 98 wt.-%, yet more preferably at least 99 wt.-%, in each case based on the total weight of the composition AC.

6. The method according to one or more of the preceding claims, characterized in that, The acidic aqueous composition AAC contains fluoride anions in an amount in the range of 15 to 1500 mg / L, preferably 20 to 1000 mg / L, still more preferably 25 to 500 mg / L, yet more preferably 25 to 500 mg / L, in each case calculated as fluorine.

7. The method according to one or more of the preceding claims, characterized in that The acidic aqueous composition AAC contains at least one metal cation selected from the group consisting of titanium and zirconium ions and mixtures thereof, preferably selected from zirconium ions.

8. The method according to one or more of the preceding claims, characterized in that, The acidic aqueous composition AAC comprises at least one metal cation selected from the group consisting of titanium, zirconium and hafnium ions and mixtures thereof, in an amount in the range of from 5 to 2000 mg / L, preferably from 7.5 to 1500 mg / L, more preferably from 10 to 1000 mg / L, still more preferably from 15 to 500 mg / L, yet more preferably from 20 to 300 mg / L, in each case calculated as metal.

9. The method according to one or more of the preceding claims, characterized in that, The acidic aqueous composition AAC has a pH value in the range of from 0.5 to 6.5, preferably from 1.0 to 6.0, more preferably from 2.0 or 3.0 to 5.

5.

10. The method according to one or more of the preceding claims, characterized in that, The rinsing step 2) is carried out for a period of time in the range of from 10 seconds to 5 minutes, preferably from 20 seconds to 4.5 minutes, more preferably from 30 seconds to 4 minutes.

11. A method of applying at least one coating film to at least one surface of a substrate, the method comprising at least steps 1) and 2) as defined in one or more of claims 1 to 10, and further comprising step 3), namely 3) applying a coating material composition comprising at least one film-forming polymer to the optionally dried and / or optionally cured film, which film is in turn obtainable after having carried out the rinsing step 2) and optionally after having further dried and / or cured the film obtained after the rinsing step 2).

12. The method according to claim 11, wherein The coating material composition is an electrodepositable, preferably cathodically electrodepositable coating material composition, wherein the at least one film-forming polymer present therein is preferably an electrodepositable, more preferably cathodically electrodepositable polymer.

13. A substrate obtainable by the pretreatment method according to one or more of claims 1 to 10 or by the method according to claim 11 or 12.

14. An aqueous composition AC as defined in one or more of claims 1 to 5 for use in rinsing a film obtainable by applying an acidic aqueous and fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined in one or more of claims 1 and 6 to 9, at least in part to at least one surface of a substrate, wherein said surface is at least in part made of at least one metal and / or its alloy, and wherein the rinsing is carried out before any optional curing and / or drying of the film, and / or for use in at least partially reducing the fluoride content of a film obtainable by applying an acidic aqueous and fluoride anion-containing composition, preferably an acidic aqueous composition AAC as defined in one or more of claims 1 and 6 to 9, at least in part to at least one surface of a substrate, wherein said surface is at least in part made of at least one metal and / or its alloy, said use being preferably achieved by rinsing the film with the aqueous composition AC before any optional curing and / or drying of the film, and / or Use for improving the uniformity of film formation and / or for reducing the unevenness of a coated film CF in at least one of its regions, said coated film CF being obtained by applying an electrodeposition coating material composition onto a cured or dried film, which cured or dried film is in turn obtainable by applying an acidic aqueous and fluoride anion-containing composition, preferably by applying at least partially an acidic aqueous composition AAC as defined in one or more of claims 1 and 6 to 9 onto at least one surface of a substrate, wherein said surface is at least partially made of at least one metal and / or its alloy, said use being preferably achieved by rinsing said film with the aqueous composition AC before any optional curing and / or drying of said film and before applying the coated film CF.

15. A kit, comprising an acidic aqueous composition AAC as defined in one or more of claims 1 and 6 to 9, said acidic aqueous composition containing at least fluoride anions, and an aqueous composition AC as defined in one or more of claims 1 to 5, said aqueous composition containing at least one alkaline earth metal ion and being different from the acidic aqueous composition AAC.

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