Three-coat-one-bake method for preparing multi-layer paint systems

Abstract

The present invention relates to a method for preparing a multi-layer coating system on a substrate, comprising at least the steps of applying a first primer coating composition to a substrate (step (1)), applying a second basecoat composition to the first coating film formed in step (1) before curing the first coating film to form a second coating film (step (2)), applying a third clearcoat composition to the second coating film formed in step (2) before curing the second coating film to form a third coating film (step (3)), and jointly curing the first, second and third coating films (step (4)), wherein one or two of the first, second and third coating compositions contain at least one amino resin (AR) as a crosslinking agent before being used in steps (1), (2) and / or (3) and at least one of the remaining coating compositions does not contain any crosslinking agent but contains at least one crosslinking catalyst (CLC1) before being used in steps (1), (2) and / or (3), a multi-layer coating system on a substrate obtainable by the method of the present invention and the use of an amino resin (AR) as a migratory crosslinking agent.

Description

[0001] The present invention relates to a method for preparing a multi-layer coating system on a substrate, comprising at least the steps of applying a first primer coating composition to a substrate (step (1)), applying a second basecoat composition to the first coating film formed in step (1) before curing the first coating film to form a second coating film (step (2)), applying a third clearcoat composition to the second coating film formed in step (2) before curing the second coating film to form a third coating film (step (3)), and jointly curing the first, second and third coating films (step (4)), wherein one or two of the first, second and third coating compositions contain at least one amino resin (AR) as a crosslinking agent before being used in steps (1), (2) and / or (3) and at least one of the remaining coating compositions does not contain any crosslinking agent but contains at least one crosslinking catalyst (CLC1) before being used in steps (1), (2) and / or (3), a multi-layer coating system on a substrate obtainable by the method of the present invention and the use of an amino resin (AR) as a migratory crosslinking agent. Background of the Invention

[0003] In a typical automotive painting process, at least four layers are applied to the metal surface of a suitable substrate: an electrodeposited coating (e-coat), a primer layer, a basecoat layer, and a clearcoat layer. The e-coat and the primer layer are usually applied to the substrate surface and cured. The basecoat formulation is then applied with a solvent and the solvent is dried in a high temperature process. After the basecoat layer is properly conditioned, the clearcoat is then applied. The coated substrate surface is then passed through an oven at temperatures exceeding 140°C to cure the basecoat and clearcoat.

[0004] Although this conventional method is adequate and commercially used in the automotive industry worldwide, there is still significant room for improvement. For example, any reduction in the energy, materials or time required to prepare these coatings will result in large economic benefits due to the large scale of use. It is particularly beneficial for vehicle manufacturers to reduce the number of high-temperature steps and the process time. It is additionally beneficial to reduce the temperature at which these steps are performed. In addition, it is desirable to develop "lightweight" vehicles. One way to significantly reduce the weight of the vehicle body is to replace heavier metal parts with lighter plastic parts. However, the use of lightweight plastics in conventional methods is a problem because many lightweight plastic substrates physically deform at curing temperatures greater than 130°C. Therefore, a reduction in the curing temperature of basecoats and clearcoats will allow the use of plastics and other heat-sensitive substrates required to reduce vehicle weight. In addition, it is beneficial to use a one-component system that remains stable over a long period of time without decomposing or curing prematurely as is typical for a two-component system, wherein one component contains a curable resin / polymer and the other component contains a crosslinker for the curable resin.

[0005] WO 2018 / 019685 A1 discloses a low-temperature curing composite coating comprising a substrate and two coatings from a solvent-based coating composition applied thereon. Each of these compositions comprises an OH-functional resin, a crosslinking agent and a catalyst. The catalyst present in the first solvent-based basecoat composition catalyzes the crosslinking reaction of the components present in the second solvent-based clearcoat composition and the catalyst present in the second composition catalyzes the crosslinking reaction of the components present in the first composition. Crosslinking occurs only after each catalyst migrates to each adjacent layer. WO 2018 / 019686 A1 relates to a similar low-temperature curing composite coating comprising a substrate and two coatings applied thereto. However, only one coating, i.e., a clearcoat layer, is applied by a solvent-based coating composition as a second composition, while the other coating, i.e., a basecoat layer, is applied by an aqueous coating composition as a first composition. Similarly, US2019 / 031910A1 also relates to a low-temperature curing composite coating comprising a substrate and two coatings applied thereto. The first and second coating compositions disclosed in WO 2018 / 019685 A1, WO 2018 / 01968 A1 and US 2019 / 031910 A1 each require the presence of both a crosslinker and a catalyst.

[0006] WO 2019 / 020324 A1 discloses a double coating on a substrate, comprising a first layer prepared from a polar composition including a non-polar catalyst and a second layer prepared from a non-polar composition including a polar catalyst. The polar and non-polar compositions disclosed in WO 2019 / 020324 A1 require the presence of both a crosslinker and a catalyst.

[0007] There is therefore a need for further improved processes for providing multilayer coatings on substrates to be used in the automotive industry which allow a reduction in energy, material and curing times but nevertheless exhibit good mechanical and optical properties.

[0008] question

[0009] The object of the present invention was therefore to provide a further improved process for providing multilayer coatings on substrates to be used in the automotive industry, which in particular allows a reduction in materials, curing times and temperatures, but wherein the resulting multilayer coated substrates nevertheless exhibit good mechanical and optical properties.

[0010] Solution

[0011] This object is solved by the subject matter of the present application claims and its preferred embodiments disclosed in the present description, namely the subject matter described herein.

[0012] A first subject of the invention is a method for producing a multicoat paint system on a substrate, comprising at least steps (1), (2), (3) and (4), namely:

[0013] (1) applying a first coating composition to an optional precoated substrate and forming a first coating film on the optional precoated substrate, wherein the first coating film is a primer coating film,

[0014] (2) applying a second coating composition to the first coating film on the substrate obtained after step (1) before curing the first coating film to form a second coating film adjacent to the first coating film, wherein the second coating film is a base color coating film,

[0015] (3) applying a third coating composition to the second coating film on the substrate obtained after step (2) before curing the second coating film to form a third coating film adjacent to the second coating film, wherein the third coating film is a clear coat film, and

[0016] (4) jointly curing the first, second and third coating films, wherein the cured third coating film is the outermost layer of the formed multi-layer paint system,

[0017] wherein the first, second and third coating compositions are each different from each other, the first coating composition comprises at least one polymer having a crosslinkable functional group (P1), the second coating composition comprises at least one polymer having a crosslinkable functional group (P2) and the third coating composition comprises at least one polymer having a crosslinkable functional group (P3),

[0018] One or two of the first, second and third coating compositions further independently of each other before being used in step (1), (2) and / or (3) contain at least one amino resin (AR) as a crosslinking agent having crosslinkable functional groups, which can be crosslinked with the crosslinkable functional groups of each of polymer (P1), polymer (P2) and polymer (P3), and at least one of the remaining coating compositions does not contain any crosslinking agent before being used in step (1), (2) and / or (3), but independently of each other before being used in step (1), (2) and / or (3) contains at least one crosslinking catalyst (CLC1), which is suitable for catalyzing the crosslinking reaction between the functional groups of the amino resin (AR) and the functional groups of each of polymer (P1), polymer (P2) and polymer (P3).

[0019] The invention further provides a multicoat paint system on a substrate obtainable by the process according to the invention.

[0020] Another subject of the present invention is the use of an amino resin (AR) having crosslinkable functional groups, said amino resin being present in one or both of a first, a second and a third coating composition, each of which is different from one another, the first coating composition comprising at least one polymer (P1) having crosslinkable functional groups, which can be crosslinked with the crosslinkable functional groups of the amino resin (AR), the second coating composition comprising at least one polymer (P2) having crosslinkable functional groups, which can also be crosslinked with the crosslinkable functional groups of the amino resin (AR), and the third coating composition comprising at least one polymer (P3) having crosslinkable functional groups, which can also be crosslinked with the crosslinkable functional groups of the amino resin (AR), wherein at least one coating composition selected from the first, second and third coating compositions in which the amino resin (AR) is not present does not contain any crosslinking agent, but comprises at least one crosslinking catalyst (CLC1) which is suitable for catalyzing The crosslinking reaction between the functional groups of the amino resin (AR) and the functional groups of each of the polymers (P1), (P2) and (P3) is used to at least partially migrate from one or two coating films obtained from one or two coating compositions selected from the first, second and third coating compositions in which the amino resin is present to at least one coating film obtained from at least one remaining coating composition of the three coating compositions after applying the third coating composition to the second coating film obtained from the second coating composition before curing the coating film obtained from the second coating composition to form a third coating film adjacent to the second coating film, the second coating film being obtained by applying the second coating composition to the first coating film obtained from the first coating composition before curing the first coating film, the second coating film being adjacent to the first coating film, and being used for subsequent crosslinking with the crosslinkable functional groups of each of the polymers (P1), (P2) and (P3), preferably catalyzed by at least a crosslinking catalyst (CLC1).

[0021] It has surprisingly been found that the process of the present invention allows for the crosslinking agent to be dispensed with incorporating each coating composition used and applied in the process of the present invention. Instead, it is only necessary to incorporate at least one amino resin (AR) into one or two, preferably only one, of the three coating compositions used. It has surprisingly been found that the amino resin (AR) can partially migrate from (i) the first coating film into the second and third coating films or (ii) from the second coating film into the first and third coating films or (iii) especially from the third coating film into the first and second coating films after all coating films have been applied via the wet-on-wet-on-wet (3W or three coats and one bake) process of the present invention. Likewise, since at least the at least one coating composition that does not contain any amino resin (AR) contains at least one crosslinking catalyst (CLC1), the crosslinking catalyst (CLC1) can also migrate from the coating film obtained from the coating composition in which it has been included into another coating film after all coating films have been applied via the wet-on-wet-on-wet process of the present invention. Thus, once all coating films have been applied wet-on-wet, the process of the present invention allows for the migration of both the amino resin (AR) and the crosslinking catalyst (CLC1) initially contained in the separate coating films. It is particularly surprising that this is possible even with a three-coat-one-bake (wet-on-wet-on-wet) application method.

[0022] Surprisingly it has been found that the process according to the invention allows a curing step to be carried out at temperatures below 110° C., in particular below 100° C., in a relatively short period of time, such as less than 30 minutes or even less than 25 minutes, in which all applied coating films are cured together. Surprisingly it is possible to effectively cure all applied coating films at such low temperatures, although at least one coating film was applied by using a coating composition which does not contain any crosslinking agent. It is particularly surprising that amino resins (AR) in particular migrate sufficiently to allow such effective curing at these temperatures. It is particularly surprising that this is possible even for a three-coat-one-bake (wet-on-wet-on-wet) application method. DETAILED DESCRIPTION OF THE INVENTION

[0024] For example, the term "comprising" in connection with each of the coating compositions used in the present invention preferably has the meaning of "consisting of..." in the sense of the present invention. For each of the coating compositions used in the present invention, in addition to the essential components present therein, one or more further components indicated below and optionally included in each of the coating compositions used in the present invention may be included therein. All of these components may in each case be present in their preferred embodiments indicated below.

[0025] The term "before its use" in connection with the amino resin (AR) and the crosslinking catalyst (CLC1) and (CLC2) present in any of the coating compositions used according to the invention in a specific step of the method according to the invention preferably means in the sense of the invention that the specific component, i.e. (AR) or (CLC1) or (CLC2) is present as a component in the respective coating composition before the respective coating composition is used in the specific step of the method according to the invention and is also (still) present or still present in any of these respective coating compositions when they are applied in any of the specific steps. However, any of these components can migrate from the coating film obtained by applying the respective coating composition to other coating films applied above and / or already present below.

[0026] Method of the present invention

[0027] The method of the present invention is a method for preparing and providing a multilayer paint system on a substrate, comprising at least steps (1), (2), (3) and (4). However, the method may comprise other additional optional steps.

[0028] Steps of the method (1)

[0029] In the step (1) of the inventive method, the first coating composition is applied to an optional pre-coated substrate and forms a first coating film on the optional pre-coated substrate. The first coating film is a primer coating film. Therefore, the first coating composition is a primer coating composition. The term "primer" is known to those skilled in the art. Primer is usually applied after providing a cured electrodeposition coating to the substrate. In this case, the cured electrodeposition coating film is present below and preferably adjacent to the primer coating film.

[0030] The first coating film formed on the optionally pre-coated substrate is an uncured coating film at this stage.

[0031] The method according to the invention is particularly suitable for coating automobile bodies or parts thereof, including corresponding metal substrates, but also plastic substrates. Therefore, preferred substrates are automobile bodies or parts thereof.

[0032] Suitable metal substrates for use according to the invention are all customary substrates known to the skilled worker. The substrates used according to the invention are preferably metal substrates, more preferably selected from steel, preferably selected from bare steel, cold-rolled steel (CRS), hot-rolled steel, galvanized steel such as hot-dip galvanized steel (HDG), alloy galvanized steel (such as Galvalume, Galvannealed or Galfan) and aluminized steel, aluminum and magnesium, and also Zn / Mg alloys and Zn / Ni alloys. Particularly suitable substrates are body parts or complete bodies of production vehicles.

[0033] The substrate used according to the invention is preferably a substrate pretreated with at least one metal phosphate, such as zinc phosphate. This pretreatment by phosphating, which is usually carried out after cleaning the substrate and before electrodeposition coating of the substrate, is a customary pretreatment step in particular in the automotive industry.

[0034] As mentioned above, the substrate used may be a pre-coated substrate, ie a substrate provided with at least one cured coating film. The substrate used in step (1) may be pre-coated with a cured electrodeposited coating.

[0035] Optional step (1a) of the method

[0036] Preferably, the method of the present invention further comprises a step (1a) performed after step (1) and before step (2). Before applying the second coating composition in step (2), the first coating film obtained after step (1) is dried in step (1a) for a period of preferably 1 to 20 minutes, more preferably 1.5 to 15 minutes, especially 2 to 10 minutes, and most preferably 3 to 6 minutes. Preferably, step (1a) is performed at a temperature not exceeding 40° C., more preferably at a temperature in the range of 18 to 30° C.

[0037] The term "air drying" in the sense of the present invention refers to drying in which at least some solvent and / or water evaporates from the coating film (ie from the formed coating) before the subsequent coating composition is applied and / or curing takes place. Air drying does not carry out curing.

[0038] Step (2) of the method

[0039] In step (2) of the method of the present invention, the second coating composition is applied to the first coating film obtained after step (1) before curing the first coating film on the substrate and forms a second coating film adjacent to the first coating film. Thus, the first and second coating compositions are applied wet-on-wet.

[0040] The second coating film is a basecoat film. Thus, the second coating composition is a basecoat composition. The term "basecoat" is known to those skilled in the art and is used, for example, in Lexikon, paints and printing inks, Georg Thieme Verlag, 1998, 10th edition, definition on page 57. Therefore, basecoat is especially used in automotive painting and general industrial paint coloring to give colored and / or optical effects by using this basecoat as an intermediate coating composition. This is usually applied to metal or plastic substrates, and in the case of metal substrates, applied to the primer layer applied on the electrodeposition coating applied on the metal substrate, or in the case of repair paint applications, applied to an already existing coating, which can also be used as a substrate. In order to protect the basecoat film, especially to prevent environmental influences, at least one additional clearcoat film is applied to it. The term "clearcoat", "varnish" or "clearcoat" is also known to those skilled in the art and represents the transparent outermost layer of the multilayer coating structure applied to the substrate.

[0041] Optional step (2a) of the method

[0042] Preferably, the method of the present invention further comprises a step (2a) performed after step (2) and before step (3). Before applying the third coating composition in step (3), the second coating film obtained after step (2) is dried in step (2a) for a period of preferably 1-20 minutes, more preferably 1.5-15 minutes, especially 2-10 minutes, and most preferably 3-6 minutes. Preferably, step (2a) is performed at a temperature not exceeding 40° C., more preferably at a temperature in the range of 18-30° C.

[0043] Step (3) of the method

[0044] In step (3) of the method of the present invention, the third coating composition is applied to the second coating film before curing the second coating film present on the substrate obtained after step (2) and forms a third coating film adjacent to the second coating film. Therefore, the second and third coating compositions are both applied wet-on-wet. The third coating film is a clear coat film. Therefore, the third coating composition is a clear coat composition. The term "clear coat" is known to those skilled in the art.

[0045] Optional step (3a) of the method

[0046] Preferably, the method of the present invention further comprises a step (3a) performed after step (3) and before step (4). Before performing the curing step (4), the third coating film obtained after step (3) is dried in the step (3a) for preferably 1-20 minutes, more preferably 3-12 minutes, and especially 5-10 minutes. Preferably, step (3a) is performed at a temperature not exceeding 40° C., more preferably at a temperature in the range of 18-30° C.

[0047] Preferably, both step (1a), step (2a) and step (3a) are performed. Preferably, the drying time used in step (3a) exceeds the drying time used in each of step (1a) and step (2a).

[0048] Step (4) of the method

[0049] In step (4) of the method of the invention, the first, second and third coating films are cured together, ie cured simultaneously. The cured third coating film represents the outermost layer of the formed multi-layer paint system obtained after step (4).

[0050] Each resulting cured coating film represents a coating layer. Thus, after performing step (4), first, second and third coating layers are formed on the optionally pre-coated substrate, wherein the third layer is the outermost layer of the formed multi-layer paint system.

[0051] Preferably step (4) is carried out at a substrate temperature of less than 110° C., preferably less than 105° C., especially at a substrate temperature in the range of 80-105° C. or 80-100° C. for a period of 5-45 minutes, preferably 10-35 minutes. The substrate temperature is measured with a thermocouple.

[0052] First, second and third coating compositions and first, second and third coating films obtained therefrom

[0053] The first, second and third coating compositions are each different from each other. The first coating composition comprises at least one polymer having crosslinkable functional groups (P1), the second coating composition comprises at least one polymer having crosslinkable functional groups (P2) and the third coating composition comprises at least one polymer having crosslinkable functional groups (P3).

[0054] One or two, i.e. precisely one or precisely two, preferably only one of the first, second and third coating compositions independently of each other comprises at least one amino resin (AR) as a crosslinking agent before it is used in step (1), (2) and / or (3), and at least one of the remaining coating compositions does not contain any crosslinking agent before it is used in step (1), (2) and / or (3), but independently of each other comprises at least one crosslinking catalyst (CLC1) before it is used in step (1), (2) and / or (3). The at least one amino resin (AR) has functional groups that can be crosslinked with the crosslinkable functional groups of each of the polymers (P1), (P2) and (P3). It is therefore clear that the amino resin (AR) is different from each of the polymers (P1), (P2) and (P3). The at least one crosslinking catalyst (CLC1) is suitable for catalyzing the crosslinking reaction between the functional groups of the amino resin (AR) and the functional groups of each of the polymers (P1), (P2) and (P3).

[0055] The term "free of any crosslinking agent" in the sense of the present invention preferably means that no crosslinking agent is present in the respective coating composition before it is used in the process according to the invention. This means that such a crosslinking agent is not intentionally added to any of the coating compositions used according to the invention. However, it may not be excluded that any remaining residues of the crosslinking agent used for the preparation of, for example, certain components present in the composition are (still) present therein. Thus, it is preferred that the amount of any crosslinking agent present in the coating composition "free of any crosslinking agent" is less than 1.0% by weight or less than 0.5% by weight, most preferably less than 0.1% by weight or less than 0.05% by weight or less than 0.01% by weight, in each case based on the total weight of the coating composition.

[0056] Preferably, one or both coating compositions selected from the first, second and third coating compositions which independently of one another comprise the at least one amino resin (AR) as crosslinker before their use in steps (1), (2) and / or (3) do not comprise any crosslinking catalyst at all before their use in steps (1), (2) and / or (3) or independently of one another comprise before their use in steps (1), (2) and / or (3) at least one crosslinking catalyst (CLC2) which is identical to or different from the at least one crosslinking catalyst (CLC1), in an amount, in each case based on the total weight of the respective coating composition, which is less than the amount of the at least one crosslinking catalyst (CLC1) present in the at least one coating composition selected from the first, second and third coating composition which does not contain any crosslinker before its use in steps (1), (2) and / or (3), based on the total weight of the coating composition.

[0057] Preferably, the second and / or third coating composition, independently of one another, comprises the at least one amino resin (AR) as a crosslinker and optionally at least one crosslinking catalyst (CLC2) which is identical to or different from the at least one crosslinking catalyst (CLC1) before its use in step (2) and / or (3), and the first and / or second coating composition - in the case of the second coating composition, with the proviso that it does not contain the at least one amino resin (AR) as a crosslinker - independently of one another, comprises the at least one crosslinking catalyst (CLC1) before its use in step (1) and / or (2).

[0058] In particular, only the third coating composition, before its use in step (3), comprises the at least one amino resin (AR) as a crosslinking agent and optionally at least one crosslinking catalyst (CLC2) which is the same as or different from the at least one crosslinking catalyst (CLC1), and the first and / or second, preferably the first or second coating composition, independently of one another, comprises the at least one crosslinking catalyst (CLC1) before its use in step (1) and / or (2), preferably before its use in step (1) or (2), or only the second coating composition, before its use in step (2), comprises the at least one amino resin (AR) as a crosslinking agent and optionally at least one crosslinking catalyst (CLC2) which is the same as or different from the at least one crosslinking catalyst (CLC1), and the first and / or third, preferably the first or third coating composition, independently of one another, comprises the at least one crosslinking catalyst (CLC1) before its use in step (1) and / or (3), preferably before its use in step (1) or (3).

[0059] However, most preferably only the third coating composition comprises the at least one amino resin (AR) as crosslinking agent and optionally at least one crosslinking catalyst (CLC2) which is the same as or different from the at least one crosslinking catalyst (CLC1) before its use in step (3), and the first and / or second, preferably the first or second coating composition independently of each other, comprises the at least one crosslinking catalyst (CLC1) before its use in step (1) and / or (2), preferably before its use in step (1) or (2).

[0060] In case at least one crosslinking catalyst (CLC2) is present in one or both coating compositions selected from the first, second and third coating compositions comprising the at least one amino resin (AR) as crosslinking agent before its use in steps (1), (2) and / or (3), the relative weight ratio of the at least one crosslinking catalyst (CLC1) present in at least one coating composition selected from the first, second and third coating compositions which does not contain any crosslinking agent before its use in steps (1), (2) and / or (3) to the at least one crosslinking catalyst (CLC2) is at least 5:1, more preferably at least 4:1, still more preferably at least 3:1, in each case based on the total weight of the respective coating composition.

[0061] Preferably, the first coating composition is a 1K (one-component) coating composition. Preferably, the second coating composition is a 1K (one-component) coating composition. Preferably, the third coating composition is a 1K (one-component) coating composition.

[0062] Preferably the first coating composition is a solventborne coating composition, i.e. an organic solvent-based coating composition, or an aqueous coating composition, i.e. an aqueous coating composition, more preferably a solventborne coating composition, the second coating composition is a solventborne or aqueous coating composition and the third coating composition is a solventborne coating composition.

[0063] The term "aqueous" or "aqueous" in connection with any of the coating compositions used in the present invention is preferably understood for the purposes of the present invention to mean that water as solvent and / or as diluent is present as the main component of all solvents and / or diluents present in each of the coating compositions used in the present invention, preferably in an amount of at least 35% by weight, based on the total weight of the electrodeposition coating composition of the present invention. Organic solvents may additionally be present in smaller proportions, preferably in an amount of <20% by weight.

[0064] The coating compositions used according to the invention each preferably comprise—in the case of aqueous compositions—a water proportion of at least 40% by weight, more preferably at least 45% by weight, very preferably at least 50% by weight and more particularly at least 55% by weight, in each case based on the total weight of the coating composition.

[0065] The coating compositions used according to the invention each preferably comprise - in the case of aqueous compositions - a proportion of organic solvent in the range of <20% by weight, more preferably in the range of 0 to <20% by weight, very preferably 0.5-20% by weight or 0.5-17.5% by weight or 0.5-15% by weight or 0.5-10% by weight, in each case based on the total weight of the coating composition. All customary organic solvents known to the person skilled in the art can be used as organic solvents. The term "organic solvent" is known to the person skilled in the art, in particular from Council Directive 1999 / 13 / EC of 11 March 1999. Examples of such organic solvents include heterocyclic, aliphatic or aromatic hydrocarbons, mono- or polyols, in particular methanol and / or ethanol, ethers, esters, ketones and amides, such as N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide, toluene, xylene, butanol, ethylene glycol and butanediol and also their acetates, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetone, isophorone or mixtures thereof.

[0066] The term "solvent" in connection with any of the coating compositions used according to the invention is preferably understood for the purposes of the present invention to mean that an organic solvent as solvent and / or as diluent is present as the main component of all solvents and / or diluents present in each of the coating compositions used according to the invention, preferably in an amount of at least 35% by weight, based on the total weight of the electrodeposition coating composition according to the invention. Water may additionally be present in a smaller proportion, preferably in an amount of <20% by weight.

[0067] The coating compositions used according to the invention each preferably comprise—in the case of solventborne compositions—a proportion of organic solvent of at least 40% by weight, more preferably at least 45% by weight, very preferably at least 50% by weight and in particular at least 55% by weight, in each case based on the total weight of the coating composition. Examples of such organic solvents include heterocyclic, aliphatic or aromatic hydrocarbons, mono- or polyhydric alcohols, in particular methanol and / or ethanol, ethers, esters, ketones and amides, such as N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide, toluene, xylene, butanol, ethylene glycol and butanediol and also the acetates thereof, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetone, isophorone or mixtures thereof.

[0068] The coating compositions used according to the invention each preferably comprise - in the case of solvent-borne compositions - a proportion of water of <20% by weight, more preferably in the range from 0 to <20% by weight, very preferably from 0.5 to 20% by weight or from 0.5 to 17.5% by weight or from 0.5 to 15% by weight or from 0.5 to 10% by weight, in each case based on the total weight of the coating composition.

[0069] The solids content of the coating compositions used according to the invention is preferably in the range from 5 to 45% by weight, more preferably from 5 to 40% by weight, very preferably from 7.5 to 40% by weight, more particularly from 7.5 to 35% by weight, most preferably from 10 to 35% by weight or from 15 to 30% by weight, independently of one another, based in each case on the total weight of the coating composition. The solids content, in other words the non-volatile fraction, is determined as described below.

[0070] The coating compositions used according to the invention can each be used both as OEM coating compositions and for refinish applications, preferably for OEM applications.

[0071] The proportions and amounts of all components present in each of the coating compositions used according to the invention expressed in % by weight add up to 100 % by weight in each case, based on the total weight of the respective coating composition.

[0072] The first coating composition comprises at least one polymer (P1) having a crosslinkable functional group. The second coating composition comprises at least one polymer (P2) having a crosslinkable functional group. The third coating composition comprises at least one polymer (P3) having a crosslinkable functional group.

[0073] The polymers (P1), (P2) and (P3) may be the same or may be different from each other. Each of these polymers is different from the amino resin (AR).

[0074] Polymers (P1), (P2) and (P3) are used as film-forming binders. For the purposes of the present invention, the term "binder" is to be understood as the non-volatile component of the coating composition that is responsible for film formation according to DIN EN ISO 4618 (German version, date: March 2007). Therefore, pigments and / or fillers contained therein are not included under the term "binder". Preferably, the at least one polymer is the main binder of the corresponding coating composition. As main binder in the sense of the present invention, preferably a binder component present in a higher proportion based on the total weight of the coating composition is mentioned when there are no other binder components in the coating composition.

[0075] The term "polymer" is known to the person skilled in the art and for the purposes of the present invention comprises polyadducts and polymers as well as polycondensates. The term "polymer" comprises both homopolymers and copolymers.

[0076] Each polymer (P1), (P2) and (P3) has a crosslinkable functional group, which can be crosslinked with the crosslinkable functional group of the amino resin (AR), i.e., can undergo a crosslinking reaction with the crosslinkable functional group of the amino resin (AR). The crosslinkable groups of polymers (P1), (P2) and (P3) may be identical or different from each other. Any common crosslinkable functional group known to a person skilled in the art may be present. The crosslinkable functional groups of each polymer (P1), (P2) and (P3) are independently selected from primary amino groups, secondary amino groups, hydroxyl groups, thiol groups, carboxyl groups and carbamate groups. Preferably, each polymer (P1), (P2) and (P3) has a functional hydroxyl group (OH group) and / or a carbamate group, in particular a hydroxyl group.

[0077] The polymers (P1), (P2) and (P3) are each preferably independently selected from polyurethanes, polyureas, polyesters, polyamides, polyethers, poly(meth)acrylates and / or copolymers of structural units of said polymers, in particular polyurethane-poly(meth)acrylates and / or polyurethane polyureas, and hybrid polymers thereof. The polymers (P1), (P2) and (P3) are each particularly preferably independently selected from polyurethanes, polyesters, poly(meth)acrylates and / or copolymers of structural units of said polymers. The term "(meth)acryloyl" or "(meth)acrylate" in the context of the present invention in each case includes the meaning "methacrylic acid" and / or "acrylic acid" or "methacrylate" and / or "acrylate".

[0078] Preferred polyurethanes are described, for example, in German patent application DE 199 48 004 A1, page 4, line 19 to page 11, line 29 (polyurethane prepolymer B1), in European patent application EP 0 228 003 A1, page 3, line 24 to page 5, line 40, in European patent application EP 0 634 431 A1, page 3, line 38 to page 8, line 9 and in international patent application WO 92 / 15405, page 2, line 35 to page 10, line 32.

[0079] Preferred polyesters are described, for example, in DE 4009858 A1, column 6, line 53 to column 7, line 61 and column 10, line 24 to column 13, line 3 or in WO 2014 / 033135 A2, page 2, line 24 to page 7, line 10 and page 28, line 13 to page 29, line 13. Likewise preferred polyesters are polyesters having a dendritic structure, such as those described in WO 2008 / 148555 A1. These can be used not only in clearcoats, but also in particular in aqueous basecoats.

[0080] Preferred polyurethane-poly(meth)acrylate copolymers (eg (meth)acrylated polyurethanes)) and their preparation are described, for example, in WO 91 / 15528 A1, page 3, line 21 to page 20, line 33 and DE 4437535 A1, page 2, line 27 to page 6, line 22.

[0081] Preferred poly(meth)acrylates are those which can be prepared by multistage free radical emulsion polymerization of ethylenically unsaturated monomers in water and / or organic solvents. For example, seed-core-shell polymers (SCS polymers) are particularly preferred. Such polymers or aqueous dispersions containing such polymers are known, for example, from WO 2016 / 116299 A1. Particularly preferred seed-core-shell polymers are polymers which can be prepared by the continuous free-radical emulsion polymerization of three preferably different monomer mixtures (A1), (B1) and (C1) of ethylenically unsaturated monomers in water, preferably those having an average particle size of 100 to 500 nm, wherein mixture (A1) contains at least 50% by weight of monomers having a solubility in water at 25° C. of less than 0.5 g / l and the polymer prepared from mixture (A1) has a glass transition temperature of 10 to 65° C., mixture (B1) contains at least one polyunsaturated monomer and the polymer prepared from mixture (B1) has a glass transition temperature of from −35° C. to 15° C. and the polymer prepared from mixture (C1) has a glass transition temperature of from −50° C. to 15° C., and wherein i. mixture (A1) is polymerized first, ii. mixture (B1) is then polymerized in the presence of the polymer formed under i. and iii. mixture (C1) is then polymerized in the presence of the polymer formed under ii. All three mixtures are preferably different from one another.

[0082] Preferred polyurethane-polyurea copolymers are polyurethane-polyurea particles, preferably those with an average particle size of 40 to 2000 nm, which contain, in each case in reacted form, at least one polyurethane prepolymer containing isocyanate groups - containing anionic groups and / or groups that can be converted into anionic groups - and at least one polyamine containing two primary amino groups and one or two secondary amino groups. Such copolymers are preferably used in the form of aqueous dispersions. Such polymers can in principle be prepared, for example, by conventional polyaddition of polyisocyanates with polyols and polyamines.

[0083] Polymers (P1) and (P2) are each especially hydroxy-functional and more preferably have an OH number in the range of 15 to 200 mg KOH / g, more preferably 20 to 150 mg KOH / g. Most preferred are corresponding hydroxy-functional polyurethane-poly(meth)acrylate copolymers, hydroxy-functional polyesters, hydroxy-functional poly(meth)acrylate copolymers and / or hydroxy-functional polyurethane-polyurea copolymers.

[0084] Preferably the at least one polymer (P1 ) is present in the first coating composition in an amount ranging from 10 to 50 wt%, more preferably from 12 to 45 wt%, based on the total weight of the coating composition.

[0085] Preferably the at least one polymer (P2) is present in the second coating composition in an amount ranging from 10 to 50 wt%, more preferably 12 to 45 wt%, based on the total weight of the coating composition.

[0086] Preferably the at least one polymer (P3) is present in the third coating composition in an amount ranging from 10 to 50 wt%, more preferably from 12 to 45 wt%, based on the total weight of the coating composition.

[0087] Amino resin (AR)

[0088] Preferably, the at least one amino resin (AR) used as a crosslinker present in the first or second coating composition is an aminoplast resin, more preferably a melamine resin, even more preferably a melamine formaldehyde resin, especially a hexamethoxymethylmelamine formaldehyde resin. Aminoplast resins are generally based on condensation products of formaldehyde with substances carrying amino and / or amide groups, such as melamine, urea and / or benzoguanamine.

[0089] The at least one amino resin (AR) contains crosslinkable functional groups which can react with the crosslinkable functional groups, such as OH groups, of each of the polymers (P1), (P2) and (P3) when preferably catalyzed at least by the at least one crosslinking catalyst (CLC1).

[0090] Examples of aldehydes suitable for preparing suitable melamine formaldehyde resins include those that result in a C1-C8 alcohol group bonded to a nitrogen atom pendant from the triazene ring of melamine, the C1-C8 alcohol group replacing the nitrogen bonded hydrogen atom. Specific examples of suitable aldehydes include, but are not limited to, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and combinations thereof. Formaldehyde is particularly preferred. Preferably, the at least one melamine resin used as amino resin (AR) is a formaldehyde resin, more preferably a monomeric melamine formaldehyde resin, even more preferably a hexamethoxyalkyl melamine formaldehyde resin, especially a hexamethoxyalkyl melamine formaldehyde resin selected from hexamethoxymethyl melamine formaldehyde resin, hexamethoxybutyl melamine formaldehyde resin, hexamethoxy (methyl and butyl) melamine formaldehyde resin, and mixtures thereof.

[0091] The aldehyde and the melamine are usually reacted in an aldehyde / melamine stoichiometric ratio of 5.4:1 to 6:1, preferably 5.7:1 to 6:1, more preferably 5.9:1 to 6:1. In other words, the reactive sites in the melamine, i.e., the imino groups, may be partially or completely reacted as a result of the reaction of the aldehyde and melamine. Theoretically, an aldehyde / melamine ratio of 5.4:1 should result in a hydroxyalkyl content of about 90% in the resulting product after the reaction of the aldehyde and melamine but before any further reaction, such as reaction with an alcohol in a subsequent etherification, based on the total number of reactive sites present in the melamine prior to the reaction. Likewise, an aldehyde / melamine ratio of 5.7:1 should result in a hydroxyalkyl content of about 95%, an aldehyde / melamine ratio of 5.9:1 should result in a hydroxyalkyl content of about 99% and an aldehyde / melamine ratio of 6:1 should result in a hydroxyalkyl content of about 100%, all before any further reaction, such as reaction with an alcohol and all based on the total number of reactive sites present in the melamine prior to the reaction. Reactive sites from the melamine that are unreacted after the reaction of the aldehyde and melamine remain in the resulting product as imino groups.

[0092] Melamine resins preferably used as amino resins (AR) have an imino content of less than or equal to 10% (corresponding to an aldehyde / melamine ratio of about 5.4:1), more preferably less than about 5% (corresponding to an aldehyde / melamine ratio of about 5.7:1), still more preferably less than about 3%, even more preferably less than about 1% (corresponding to an aldehyde / melamine ratio of about 5.9:1), in each case based on the total number of reactive sites present in the melamine before the reaction. The remaining groups in the melamine resin, if any, are preferably alkoxyalkyl groups.

[0093] The melamine resin used as amino resin (AR) preferably contains hydroxyalkyl groups, more preferably hydroxymethyl and / or other hydroxyalkyl groups such as hydroxybutyl. The preferred hydroxybutyl group is hydroxy-n-butyl. A mixture of hydroxymethyl or hydroxymethyl and hydroxybutyl is also possible. Most preferably, hydroxymethyl.

[0094] At least some of the hydroxyalkyl groups present in the melamine resin used as amino resin (AR) can be alkylated by further reaction with at least one alcohol to produce nitrogen-bonded alkoxyalkyl groups. The hydroxyl groups in the nitrogen-bonded hydroxyalkyl groups can be reacted with alcohols in particular by an etherification reaction to produce nitrogen-bonded alkoxyalkyl groups. The alkoxyalkyl groups can be used for crosslinking reactions with the respective crosslinkable functional groups of polymers (P1), (P2) and (P3), such as OH- and / or urethane groups. The remaining imino groups present in the melamine resin used as amino resin (AR) after the aldehyde / melamine reaction are non-reactive with the alcohol used for alkylation. Some of the remaining imino groups can react with hydroxyl groups in nitrogen-bonded hydroxyalkyl groups from another melamine to form bridging units. However, most of the remaining imino groups remain unreacted.

[0095] As mentioned above, the hydroxyalkyl groups of the melamine resin used as aminoplast (AR) may be partially alkylated. "Partially alkylated" means that a sufficiently low amount of alcohol reacts with the melamine resin under reaction conditions that should result in incomplete alkylation of the hydroxyalkyl groups, leaving some hydroxyalkyl groups in the melamine resin. When the melamine resin is partially alkylated, it is usually alkylated with alcohol in an amount sufficient to leave the hydroxyalkyl groups present in the aminoplast in an amount of at least about 7%, more preferably about 10-50%, even more preferably about 15-40%, in each case based on the total number of reactive sites present in the melamine before the reaction. The melamine resin is usually partially alkylated to obtain about 40-93%, more preferably about 50-90%, even more preferably about 60-75% of alkoxyalkyl groups, in each case based on the total number of reactive sites present in the melamine before the reaction. Thus, when partially alkylated, the melamine resin is typically alkylated with at least one alcohol in a stoichiometric ratio of hydroxyl groups in the alcohol to hydroxyalkyl groups in the melamine resin of about 0.5:1.0 to 0.93:1.0, more preferably about 0.60:1.0 to 0.9:1.0, even more preferably about 0.6:1 to 0.85:1.0.

[0096] Preferably, at least a portion, more preferably only a portion, of the hydroxyalkyl groups, such as hydroxymethyl groups, of the melamine resin are etherified by reaction with at least one alcohol. Any monohydric alcohol can be used for this purpose, including methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, pentanol, hexanol, heptanol as well as benzyl alcohol and other aromatic alcohols, cyclic alcohols such as cyclohexanol, monoethers of diols and halogen-substituted or other substituted alcohols such as 3-chloropropanol and butoxyethanol. The melamine resin used as amino resin (AR) is in particular partially etherified with methanol and / or butanol, most preferably methanol and / or n-butanol.

[0097] Melamine resins preferably used as amino resins (AR) are melamine-aldehyde resins, especially melamine-formaldehyde resins, which carry hydroxyalkyl groups, preferably hydroxymethyl and / or hydroxybutyl groups as crosslinkable functional groups, preferably in an amount of at least 90%, based on the total number of reaction sites present in the melamine before the reaction with the aldehyde, and preferably have an imino content of equal to or less than 10%, more preferably equal to or less than 5%, still more preferably equal to or less than 3%, in particular equal to or less than 1%, in each case based on the total number of reaction sites present in the melamine before the reaction with the aldehyde.

[0098] Particularly preferably, at least one hydroxymethyl group (-CH2OH) and / or at least one group of the general formula -CH2OR 1 Alkoxymethyl—where R 1As the melamine resin, melamine formaldehyde resins having an alkyl chain of 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and combinations thereof are used. Hexamethoxymethylmelamine (HMMM) and / or hexamethoxybutylmelamine (HMBM) are most preferred, and (HMMM) is particularly preferred. Melamine resins containing a combination of methoxybutyl and methoxymethyl groups are also suitable as melamine resins.

[0099] The hydroxyalkyl and alkoxyalkyl groups of the melamine resin (e.g. the CH2OCH3 ether groups of HMMM) are particularly reactive towards OH groups and / or carbamate groups of, for example, polymers (P1), (P2) and (P3), such as OH-functional and / or carbamate-functional polymers, in particular when catalyzed at least by the at least one crosslinking catalyst (CLC1), such as a strong acid catalyst, such as the unblocked sulfonic acid used as the crosslinking catalyst (CLC1).

[0100] Preferably, the at least one amino resin (AR) used as a crosslinking agent has a maximum number average molecular weight of 1500 g / mol. Preferably, the at least one amino resin (AR) used as a crosslinking agent has a number average molecular weight in the range of 200-1500 g / mol, more preferably 250-1000 g / mol, especially 300-700 g / mol. The number average molecular weight is determined according to the method disclosed in the 'Methods' section.

[0101] Preferably, the at least one amino resin (AR) is present in one or both, preferably one, of the first, second and third coating compositions in an amount in the range of 10-40% by weight, more preferably 12-35% by weight, based in each case on the total weight of the respective coating composition.

[0102] Crosslinking catalysts (CLC1) and (CLC2)

[0103] Preferably, the at least one crosslinking catalyst (CLC1) is present in at least one of the first, second and third coating compositions in an amount in the range of 5-40% by weight, more preferably 7.5-35% by weight, in each case based on the total solids content of the respective coating composition.

[0104] The crosslinking catalysts (CLC1) and (CLC2) may be the same as or may be different from each other.

[0105] Preferably, the at least one crosslinking catalyst (CLC1) is a sulfonic acid such as an unblocked sulfonic acid. It is also preferred that the at least one crosslinking catalyst (CLC2) - if present - is a sulfonic acid such as an unblocked sulfonic acid.

[0106] The crosslinking catalyst (CLC1) - and preferably also the crosslinking catalyst (CLC2) - is suitable for catalyzing the crosslinking reaction between the functional groups of the amino resin (AR), such as hydroxyalkyl and alkoxymethyl groups, and the functional groups of each of the polymers (P1), (P2) and (P3), such as the OH groups of these polymers.

[0107] Examples of unblocked sulfonic acids are p-toluenesulfonic acid (pTSA), methanesulfonic acid (MSA), dodecylbenzenesulfonic acid (DDBSA), dinonylnaphthalene disulfonic acid (DNNDSA) and mixtures thereof. DDBSA is particularly preferred, both as crosslinking catalyst (CLC1) and as crosslinking catalyst (CLC2).

[0108] If the at least one crosslinking catalyst (CLC2) is present in one or both of the first, second and third coating compositions additionally containing the at least one amino resin (AR), it is present in an amount in the range of 1 to 10% by weight, more preferably 1.5 to 5% by weight, in each case based on the total solids content of the respective coating composition.

[0109] Other optional components of the coating composition

[0110] At least the first coating composition preferably comprises at least one pigment and / or filler. Preferably the second coating composition also comprises at least one pigment and / or filler. Preferably the third coating composition does not contain any pigment.

[0111] The term "pigment" is known to the skilled person, for example, by DIN 55943 (date: October 2001). "Pigments" in the sense of the present invention preferably relate to components in the form of powders or flakes which are substantially, preferably completely insoluble in the medium surrounding them, such as one of the coating compositions used according to the invention. Pigments are preferably colorants and / or substances which can be used as pigments due to their magnetic, electric and / or electromagnetic properties. Pigments differ from "fillers" preferably in their refractive index, which is ≥1.7 for pigments. The term "filler" is known to the skilled person, for example, by DIN 55943 (date: October 2001). "Fillers" for the purposes of the present invention are preferably components which are substantially, preferably completely insoluble in the application medium, such as one of the coating compositions used according to the invention and which are used in particular to increase the volume. "Fillers" in the sense of the present invention preferably differ from "pigments" in their refractive index, which is <1.7 for fillers.

[0112] Any conventional fillers known to the skilled worker may be used. Examples of suitable fillers are kaolin, dolomite, calcite, chalk, calcium sulfate, barium sulfate, graphite, silicates such as magnesium silicate, especially the corresponding phyllosilicates such as hectorite, bentonite, montmorillonite, talc and / or mica, silicon dioxide, especially fumed silicon dioxide, hydroxides such as aluminum hydroxide or magnesium hydroxide, or organic fillers such as textile fibers, cellulose fibers, polyethylene fibers or polymer powders; for further details see Lexikon Lacke und Druckfarben, Georg Thieme Verlag, 1998, pp. 250 ff., “Filling”.

[0113] Any conventional pigment known to the skilled person can be used. Examples of suitable pigments are inorganic and organic coloring pigments. Examples of suitable inorganic coloring pigments are white pigments such as zinc white, zinc sulfide or lithopone; black pigments such as carbon black, iron manganese black or spinel black; color pigments such as chromium oxide, hydrated chromium oxide green, cobalt green or ultramarine green, cobalt blue, ultramarine blue or manganese blue, ultramarine violet or cobalt violet and manganese violet, iron oxide red, cadmium sulfoselenide, molybdenum chrome red or ultramarine red; iron oxide brown, mixed brown, spinel phase and corundum phase or chrome orange; or iron oxide yellow, titanium nickel yellow, titanium chrome yellow, cadmium sulfide, cadmium sulfide zinc, chrome yellow or bismuth vanadate. Other inorganic coloring pigments are silicon dioxide, aluminum oxide, hydrated aluminum oxide, especially boehmite, titanium dioxide, zirconium dioxide, cerium dioxide and mixtures thereof. Examples of suitable organic color pigments are monoazo pigments, disazo pigments, anthraquinone pigments, benzimidazole pigments, quinacridone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, dioxadiazole ... Azine pigment, indanthrone pigment, isoindoline pigment, isoindolinone pigment, azomethine pigment, thioindigo pigment, metal complex pigment, pyrene pigment, perylene pigment, phthalocyanine pigment or aniline black.

[0114] If one or more pigments and / or fillers are present in any of the coating compositions, in particular in one of the first and second coating compositions, their proportion in the coating composition is preferably in the range of 1.0 to 40.0% by weight, preferably 2.0 to 35.0% by weight, particularly preferably 5.0 to 30.0% by weight, in each case based on the total weight of the coating composition. In the case of the third coating composition, the amount is preferably lower, in particular the proportion is in the range of 0 to 6% by weight, based on the total weight of the coating composition.

[0115] The coating composition used in the present invention can contain one or more conventional additives depending on the required application. For example, each coating composition can include at least one additive selected from reactive diluent, light stabilizer, antioxidant, degasser, emulsifier, slip additive, inhibitor, plasticizer, radical polymerization initiator, adhesion promoter, flow control agent, film-forming aid, sag control agent (SCA), flame retardant, corrosion inhibitor, siccator, biocide and / or matting agent. They can be used in known common ratios. Preferably, its content is 0.01-20.0 wt %, more preferably 0.05-15.0 wt %, particularly preferably 0.1-10.0 wt %, most preferably 0.1-7.5 wt %, especially 0.1-5.0 wt %, most preferably 0.1-2.5 wt % based on the gross weight of the coating composition.

[0116] The coating compositions used according to the invention may each optionally contain at least one thickener. Examples of such thickeners are inorganic thickeners, for example metal silicates such as phyllosilicates, and organic thickeners, for example poly(meth)acrylic acid thickeners and / or (meth)acrylic acid (meth)acrylate copolymer thickeners, polyurethane thickeners and polymer waxes. Such organic thickeners are included in the polymers (P1) and (P2) used as binders. The metal silicates are preferably selected from smectites. Smectites are particularly preferably selected from montmorillonites and hectorites. Montmorillonites and hectorites are especially selected from aluminum magnesium silicates and sodium-magnesium and sodium-magnesium fluoride-lithium phyllosilicates. These inorganic phyllosilicates are sold, for example, under the trademark SULFATE®. Thickeners based on poly(meth)acrylic acid and (meth)acrylic acid (meth)acrylate copolymer thickeners are optionally crosslinked and / or neutralized with a suitable base. Examples of such thickeners are "alkali swellable emulsions" (ASE) and their hydrophobically modified variants "hydrophobically modified alkali swellable emulsions" (HASE). Preferably, these thickeners are anionic. Corresponding products such as AS 1130 is commercially available. Polyurethane-based thickeners (e.g. polyurethane associative thickeners) are optionally crosslinked and / or neutralized with a suitable base. Corresponding products such as PU 1250 is commercially available. Examples of suitable polymer waxes are optionally modified polymer waxes based on ethylene-vinyl acetate copolymers. Corresponding products are available, for example, under the names 8421 purchased from the market.

[0117] If at least one thickener is present in any of the coating compositions, it is preferably present in an amount of up to 10% by weight, more preferably up to 7.5% by weight, most preferably up to 5% by weight, in particular up to 3% by weight, most preferably not more than 2% by weight, in each case based on the total weight of the coating composition. The minimum amount of thickener is preferably 0.1% by weight, based in each case on the total weight of the coating composition.

[0118] The preparation of each of the coating compositions can be carried out using customary and known preparation and mixing methods and mixing units or using customary dissolvers and / or stirrers.

[0119] Multi-coat paint system according to the invention

[0120] The present invention further provides a multicoat paint system on a substrate obtainable by the process according to the invention.

[0121] All preferred embodiments described above for the process according to the invention are also preferred embodiments for the multicoat paint system according to the invention on the substrate described above.

[0122] Use of the present invention

[0123] Another subject of the present invention is the use of an amino resin (AR) having crosslinkable functional groups, said amino resin being present in one or both of a first, a second and a third coating composition, each of which is different from one another, the first coating composition comprising at least one polymer (P1) having crosslinkable functional groups, which can be crosslinked with the crosslinkable functional groups of the amino resin (AR), the second coating composition comprising at least one polymer (P2) having crosslinkable functional groups, which can also be crosslinked with the crosslinkable functional groups of the amino resin (AR), and the third coating composition comprising at least one polymer (P3) having crosslinkable functional groups, which can also be crosslinked with the crosslinkable functional groups of the amino resin (AR), wherein at least one coating composition selected from the first, second and third coating compositions in which the amino resin (AR) is not present does not contain any crosslinking agent, but comprises at least one crosslinking catalyst (CLC1) which is suitable for catalyzing The crosslinking reaction between the functional groups of the amino resin (AR) and the functional groups of each of the polymers (P1), (P2) and (P3) is used to at least partially migrate from one or two coating films obtained from one or two coating compositions selected from the first, second and third coating compositions in which the amino resin is present to at least one coating film obtained from at least one remaining coating composition of the three coating compositions after applying the third coating composition to the second coating film obtained from the second coating composition before curing the coating film obtained from the second coating composition to form a third coating film adjacent to the second coating film, the second coating film being obtained by applying the second coating composition to the first coating film obtained from the first coating composition before curing the first coating film, the second coating film being adjacent to the first coating film, and being used for subsequent crosslinking with the crosslinkable functional groups of each of the polymers (P1), (P2) and (P3), preferably catalyzed by at least a crosslinking catalyst (CLC1).

[0124] All preferred embodiments described above for the method according to the invention and the multicoat coating system according to the invention on a substrate are also preferred embodiments for the above-described use according to the invention.

[0125] method

[0126] 1. Non-volatile fraction

[0127] The non-volatile fraction (solids or solids content) is determined in accordance with DIN EN ISO 3251 (date: June 2008). This involves weighing 1 g of sample into an aluminum dish that has been dried beforehand and drying the dish with the sample in a drying cabinet at 130° C. for 60 minutes, cooling it in a desiccator and then reweighing it. The residue relative to the total amount of sample used corresponds to the non-volatile fraction.

[0128] 2. Number average molecular weight (M n )

[0129] In order to determine the average molecular weight (M) of the polymer by gel permeation chromatography (GPC), w 、M n and M p ), the completely dissolved polymer sample is fractionated on a porous column stationary phase. Tetrahydrofuran (THF) is used as the elution solvent. The stationary phase is a combination of Waters Styragel HR 5, HR 4, HR 3 and HR 2 columns. 5 mg of sample is added to 1.5 mL of elution solvent and filtered through a 0.5 μm filter. After filtration, 100 μl of polymer sample solution is injected into the column at a flow rate of 1.0 ml / min. Separation is performed based on the size of the polymer coils formed in the elution solvent. The molecular weight distribution, number average molecular weight M of the polymer sample n , weight average molecular weight M w and the highest peak molecular weight M p The polydispersity index (PDI) is calculated by means of a chromatography software using a calibration curve generated by a polymer standard validation kit including a series of unbranched polystyrene standards with different molecular weights, purchased from Polymer Standards Service. w / M n Sure.

[0130] 3. MEK friction test

[0131] The MEK rub test was performed according to ASTM D5402.

[0132] 4. Tukon Hardness

[0133] To evaluate the Tukon microhardness of the coated substrate, a Wolpert Wilson Tukon 2100 device was used. The coated substrate was placed on a table under the Tukon indenter of the instrument. The indenter used a pyramidal diamond tip that applied a 25g load to the surface of the coated substrate for 18 ± 0.5 seconds. The instrument also had a microscope with a filamentary micrometer eyepiece. After the indentation was completed, the microscope was used to measure the indentation length. The instrument calculated the Knoop hardness value (KHN) by the following equation:

[0134]

[0135] in:

[0136] 0.025 = load applied to the pressure head, kg

[0137] L = diagonal length of the indentation, mm, and

[0138] C p = pressure head constant = 7.028 × 10 (-2)

[0139] 5. Adhesion

[0140] Adhesion was measured according to ASTM D3359.

[0141] 5. Anti-chipping

[0142] Chip resistance was measured according to SAE J400.

[0143] 6. Layer thickness

[0144] Dry film thickness is determined in accordance with ASTM D4138 - Standard Practice for Measuring Dry Film Thickness of Protective Coating Systems by Cross-Section Destruction. Example

[0145] The following examples further illustrate the present invention but should not be construed as limiting its scope.

[0146] 1. Used as a primer for a first coating composition

[0147] 1.1 A gray primer composition PC1 used as a first coating composition was prepared by mixing the ingredients listed in Table 1.1 in this order. The primer composition PC1 did not contain any crosslinking agent, especially no amino resin, and also did not contain any crosslinking catalyst. PC1 had a total solid content of 59.8% by weight based on its total weight.

[0148] Table 1.1: Primer composition PC1

[0149]

[0150] The branched polyester resin had an acid number of 30 mg KOH / g. The resin was used in the form of a dispersion having a solids content of 73% by weight.

[0151] Emulsion Microgel 1 is a branched acrylic microgel emulsion with an acid value of 10 mg KOH / g available from BASF Corp. The emulsion had a solids content of 31 wt%.

[0152] Acrylic resin 1 is an ε-caprolactone-modified acrylic resin having an OH number of 73 mg KOH / g and a weight average molecular weight of 11100 g / mol, available from BASF Corp. The resin was used in the form of a dispersion having a solid content of 75% by weight.

[0153] 1.2 A number of other primer compositions for use as first coating composition were prepared by mixing primer composition PC1 with different crosslinking catalysts. An overview is given in Table 1.2.

[0154] Table 1.2: Primer compositions PC2, PC3 and PC4

[0155] Element PC2 PC3 PC4 PC1 250 parts by weight 250 parts by weight 250 parts by weight C1 14.07 parts by weight - - C2 - 29.30 parts by weight - C3 - - 28.96 parts by weight

[0156] A commercially available sulfonic acid crosslinking catalyst (dodecylbenzenesulfonic acid (DDBSA) in isopropanol) was used. 1270 was used as crosslinking catalyst C1. A solution of p-toluenesulfonic acid (pTSA) in n-butanol (17.8 wt. % pTSA) was used as crosslinking catalyst C2. A solution of methanesulfonic acid (MSA) in n-butanol (10 wt. % MSA) was used as crosslinking catalyst C3.

[0157] 1.3 A primer composition PC5 for comparison of the first coating composition was prepared by mixing the ingredients listed in Table 1.3 in this order. The primer composition PC5 contained two amino resins ( 755 and 747) as a crosslinking agent. Additionally, PC5 contains a crosslinking catalyst, namely a blocked sulfonic acid catalyst (amine blocked dodecylbenzenesulfonic acid (DDBSA).

[0158] Table 1.3: Primer composition PC5

[0159]

[0160] Emulsion microgel 1, acrylic resin 1 and branched polyester resin have been described for PC1.

[0161] 2. Basecoat for use as a secondary coating composition

[0162] 2.1 A black basecoat composition BC1 was prepared by mixing the ingredients listed in Table 2.1 in this order. BC1 did not contain any crosslinking agent, in particular no amino resin, and also did not contain any crosslinking catalyst.

[0163] Table 2.1: Basecoat composition BC1

[0164]

[0165]

[0166] Emulsion Microgel 1 and Acrylic Resin 1 have been described above with respect to PC1.

[0167] Emulsion Microgel 2 is a branched acrylic microgel emulsion with an acid value of 13.5 mg KOH / g available from BASF Corp. The emulsion had a solids content of 31.3 wt%.

[0168] 2.2 A number of further basecoat compositions for use as second coating compositions were prepared by mixing basecoat composition BC1 with different crosslinking catalysts. An overview is given in Table 2.2.

[0169] Table 2.2: Basecoat compositions BC2, BC3 and BC4

[0170] Element BC2 BC3 BC4 BC1 250 parts by weight 250 parts by weight 250 parts by weight C1 24.45 parts by weight - - C2 - 50.88 parts by weight - C3 - - 50.36 parts by weight

[0171] A commercially available sulfonic acid crosslinking catalyst (dodecylbenzenesulfonic acid (DDBSA) in isopropanol) was used. 1270 was used as crosslinking catalyst C1. A solution of p-toluenesulfonic acid (pTSA) in n-butanol (17.8 wt. % pTSA) was used as crosslinking catalyst C2. A solution of methanesulfonic acid (MSA) in n-butanol (10 wt. % MSA) was used as crosslinking catalyst C3.

[0172] 2.3 A basecoat composition BC5 for comparison with the second coating composition was prepared by mixing the ingredients listed in Table 2.3 in this order. BC5 contains two amino resins ( 755 and 764) as a crosslinking agent. Additionally, BC5 contains a crosslinking catalyst, namely a blocked sulfonic acid catalyst (amine-blocked dodecylbenzenesulfonic acid (DDBSA).

[0173] Table 2.3: Basecoat composition BC5

[0174]

[0175]

[0176] Acrylic resin 1 and latex microgel 1 have been described for PC1.

[0177] The polyester resin (star) is a branched aliphatic star polyester resin having an OH number of 115 mg KOH / g and a weight average molecular weight of 2000 g / mol available from BASF Corp. The resin is used in the form of a dispersion having a solids content of 80% by weight.

[0178] 3. Clearcoat for use as a third coating composition

[0179] 3.1 Solvent-based varnish composition CC1

[0180] The varnish composition CC1 was prepared by mixing the ingredients listed in Table 3.1 in this order. CC1 contained an amino resin ( 747) as a crosslinking agent. CC1 had a total solid content of 57.9 wt % based on its total weight.

[0181] Table 3.1: Clearcoat CC1

[0182]

[0183]

[0184] The urethane acrylic resin was purchased from BASF Corp. and had an OH number of 0 mg KOH / g and a weight average molecular weight of 4000 g / mol. The urethane equivalent weight was 438 g / mol. The resin was used in the form of a dispersion having a solids content of 70% by weight.

[0185] The resin blend may be composed of 2 mmol methyl carbamate and 1 mmol C 36 C 36 The diurethane was used in the form of a dispersion with a solid content of 60% by weight. The carbamate equivalent weight was 344 g / mol. The IPDI / HPC reactive intermediate, which can be obtained from 1 mol of IPDI trimer and 3 mol of hydroxypropyl carbamate, present in the resin blend was used in the form of a dispersion with a solid content of 38.5% by weight. The carbamate equivalent weight was 374 g / mol. The resin blend used had a total solid content of 55% by weight.

[0186] The IPDI / HPC reactive intermediate present in CC1 has itself been described for this resin blend.

[0187] Acrylic resin 2 was purchased from BASF Corp. and was a GMA-acrylic resin, an epoxy resin having a weight average molecular weight of 27400 g / mol. The epoxy equivalent weight was 430 g / mol. The resin was used in the form of a dispersion having a solid content of 60% by weight.

[0188] The thermosetting acrylic resin was purchased from BASF Corp. and was an OH-functional acrylic resin having an OH number of 182 mg KOH / g and a weight average molecular weight of 4600 g / mol. The resin was used in the form of a dispersion having a solids content of 67.5% by weight.

[0189] LP R 23429 is a commercially available rheology additive from BYK Chemie GmbH.

[0190] 3.2 Solvent-based varnish composition CC2 (for comparison)

[0191] The varnish composition CC2 was prepared by mixing the ingredients listed in Table 3.2 in this order. CC2 contained an amino resin ( 747) as a crosslinking agent. Additionally, CC2 contains two crosslinking catalysts, namely a blocked sulfonic acid catalyst (amine blocked dodecylbenzenesulfonic acid (DDBSA) and 1270.

[0192] Table 3.2: Varnish CC2

[0193]

[0194] Urethane acrylic resin, resin blend (50 wt% C 36 Diurethane / 50 wt% IPDI / HPC reactive intermediate), IPDI / HPC reactive intermediate, acrylic resin 2 and thermosetting acrylic resin have been described for CC1.

[0195] 4. Preparation of multi-layer paint systems

[0196] 4.1 A number of multicoat paint systems are obtained by using the above-described primer, basecoat and clearcoat compositions.

[0197] Multicoat coating systems IE1-IE3 using primer compositions containing crosslinking catalysts:

[0198] The multi-layer paint system IE1 was prepared by using the primer composition PC2, the basecoat composition BC1 and the clearcoat composition CC1. The multi-layer paint system IE2 was prepared by using the primer composition PC3, the basecoat composition BC1 and the clearcoat composition CC1. The multi-layer paint system IE3 was prepared by using the primer composition PC4, the basecoat composition BC1 and the clearcoat composition CC1.

[0199] Multicoat paint systems IE4-IE6 using basecoat compositions containing a crosslinking catalyst:

[0200] A multi-layer paint system IE4 was prepared by using a primer composition PC1, a basecoat composition BC2 and a clearcoat composition CC1. A multi-layer paint system IE5 was prepared by using a primer composition PC1, a basecoat composition BC3 and a clearcoat composition CC1. A multi-layer paint system IE6 was prepared by using a primer composition PC1, a basecoat composition BC4 and a clearcoat composition CC1.

[0201] Multi-layer paint system IE7 (comparison)

[0202] A multicoat coating system IE7 was prepared by using the primer composition PC5, the basecoat composition BC5 and the clearcoat composition CC2.

[0203] 4.2 Cold rolled steel test panels with a size of 4" x 12" were used as substrates. 958 zinc phosphate pretreatment solution pretreatment and use Each panel was electrocoated with a 0.7-0.8 mil thick layer of BASF 800 electrocoat and bake at 350°F (176.7°C) substrate temperature for 20 minutes. Spray one of PC2-PC5 on each panel and let dry at ambient conditions for 4 minutes. Spray one of BC1-BC5 on the primed panel and let dry at ambient conditions for 4 minutes. Then apply CC1 or CC2 and let dry at ambient conditions for 10 minutes. After CC is dried, bake each panel at 210°F (98.9°C) for 20 minutes.

[0204] The dry film thickness of each basecoat after curing was 0.6 mil (15.24 μm) and the dry film thickness of each clearcoat CC1 after curing was 1.8 mil (45.72 μm). The dry film thickness of each primer coat after curing was 0.8 mil (20.32 μm).

[0205] Before applying CC1 or CC2 to the substrate, it was diluted to 105 cP with n-butyl acetate.

[0206] 5. Properties of substrates coated with multi-coat paint systems

[0207] A number of properties measured and / or determined according to the methods defined in the "Methods" section are summarized in Table 5.1.

[0208] Table 5.1 - Properties of multi-coat paint systems IE1-IE6

[0209] Initial adhesion Anti-chipping IE1 5B Ok IE2 5B Ok IE3 5B Ok IE4 5B Ok IE5 5B Ok IE6 5B Ok

[0210] With respect to the multicoat paint system IE7, after preparation and after baking at 210°F (98.9°C) for 20 minutes as described in item 4.2, as in the case of IE1-IE6, it was noted that the multicoat paint system IE7 present on the resulting panels was tacky (uncured) and not suitable for testing according to the same procedure that had been successfully performed for IE1-IE6. In contrast to IE7, any of IE1-IE6 showed excellent curing (not tacky) when baked at 210°F (98.9°C) for 20 minutes. Therefore, in the case of IE7, adequate curing could not be achieved under these conditions.

Claims

1. A method for preparing a multilayer paint system on a substrate, comprising at least steps (1), (2), (3) and (4), namely: (1) applying a first coating composition to an optional precoated substrate and forming a first coating film on the optional precoated substrate, wherein the first coating film is a primer coating film, (2) applying a second coating composition to the first coating film obtained after step (1) before curing the first coating film on the substrate to form a second coating film adjacent to the first coating film, wherein the second coating film is a base color coating film, (3) applying a third coating composition to the second coating film obtained after step (2) and existing on the substrate before curing the second coating film to form a third coating film adjacent to the second coating film, wherein the third coating film is a clear coat film, and (4) jointly curing the first, second and third coating films, wherein the cured third coating film is the outermost layer of the formed multi-layer paint system, wherein the first, second and third coating compositions are each different from each other, the first coating composition comprises at least one polymer P1 having crosslinkable functional groups, the second coating composition comprises at least one polymer P2 having crosslinkable functional groups and the third coating composition comprises at least one polymer P3 having crosslinkable functional groups, One or two of the first, second and third coating compositions further independently of each other contain at least one amino resin as a crosslinking agent having crosslinkable functional groups before being used in step (1), (2) and / or (3), which can be crosslinked with the crosslinkable functional groups of each of polymer P1, polymer P2 and polymer P3, and at least one of the remaining coating compositions does not contain any crosslinking agent before being used in step (1), (2) and / or (3), but independently of each other contains at least one crosslinking catalyst CLC1 before being used in step (1), (2) and / or (3), which is suitable for catalyzing the crosslinking reaction between the functional groups of the amino resin and the functional groups of each of polymer P1, polymer P2 and polymer P3.

2. The method according to claim 1, characterized in that It comprises another step (1a) and / or another step (2a) and / or another step (3a), wherein step (1a) is performed after step (1) and before step (2), step (2a) is performed after step (2) and before step (3), and step (3a) is performed after step (3) and before step (4), namely: (1a) drying the first coating film obtained after step (1) for 1 to 20 minutes before applying the second coating composition in step (2), and / or (2a) drying the second coating film obtained after step (2) for 1 to 20 minutes before applying the third coating composition in step (3), and / or (3a) Drying the third coating film obtained after step (3) for 1 to 20 minutes before performing the curing step (4).

3. The method according to claim 1, characterized in that The one or two coating compositions selected from the first, second and third coating compositions which independently of one another comprise the at least one amino resin as a crosslinker before their use in steps (1), (2) and / or (3) do not comprise any crosslinking catalyst at all before their use in steps (1), (2) and / or (3) or independently of one another comprise at least one crosslinking catalyst CLC2 which is identical to or different from the at least one crosslinking catalyst CLC1 before their use in steps (1), (2) and / or (3), the amount of which, in each case based on the total weight of the respective coating composition, is less than the amount of the at least one crosslinking catalyst CLC1 present in the at least one coating composition selected from the first, second and third coating compositions which does not contain any crosslinker before their use in steps (1), (2) and / or (3), based on the total weight of the coating composition.

4. The method according to claim 2, characterized in that The one or two coating compositions selected from the first, second and third coating compositions which independently of one another comprise the at least one amino resin as a crosslinker before their use in steps (1), (2) and / or (3) do not comprise any crosslinking catalyst at all before their use in steps (1), (2) and / or (3) or independently of one another comprise at least one crosslinking catalyst CLC2 which is identical to or different from the at least one crosslinking catalyst CLC1 before their use in steps (1), (2) and / or (3), the amount of which, in each case based on the total weight of the respective coating composition, is less than the amount of the at least one crosslinking catalyst CLC1 present in the at least one coating composition selected from the first, second and third coating compositions which does not contain any crosslinker before their use in steps (1), (2) and / or (3), based on the total weight of the coating composition.

5. The method according to any one of claims 1 to 4, characterized in that The second and / or third coating composition independently of one another comprises, before its use in step (2) and / or (3), the at least one amino resin as a crosslinking agent and optionally at least one crosslinking catalyst CLC2 which is identical to or different from the at least one crosslinking catalyst CLC1, and the first and / or second coating composition - in the case of the second coating composition, with the proviso that it does not contain the at least one amino resin as a crosslinking agent - independently of one another comprises, before its use in step (1) and / or (2), the at least one crosslinking catalyst CLC1.

6. The method according to any one of claims 1 to 4, characterized in that Only the third coating composition contains the at least one amino resin as a crosslinking agent and optionally at least one crosslinking catalyst CLC2 that is the same as or different from the at least one crosslinking catalyst CLC1 before it is used in step (3), and the first and / or second coating composition independently of each other contains the at least one crosslinking catalyst CLC1 before it is used in steps (1) and / or (2), or only the second coating composition contains the at least one amino resin as a crosslinking agent and optionally at least one crosslinking catalyst CLC2 that is the same as or different from the at least one crosslinking catalyst CLC1 before it is used in step (2), and the first and / or third coating composition independently of each other contains the at least one crosslinking catalyst CLC1 before it is used in steps (1) and / or (3).

7. The method according to claim 5, characterized in that Only the third coating composition contains the at least one amino resin as a crosslinking agent and optionally at least one crosslinking catalyst CLC2 that is the same as or different from the at least one crosslinking catalyst CLC1 before it is used in step (3), and the first and / or second coating composition independently of each other contains the at least one crosslinking catalyst CLC1 before it is used in steps (1) and / or (2), or only the second coating composition contains the at least one amino resin as a crosslinking agent and optionally at least one crosslinking catalyst CLC2 that is the same as or different from the at least one crosslinking catalyst CLC1 before it is used in step (2), and the first and / or third coating composition independently of each other contains the at least one crosslinking catalyst CLC1 before it is used in steps (1) and / or (3).

8. The method according to any one of claims 1 to 4, characterized in that The first coating composition is a solvent-borne or water-borne coating composition, the second coating composition is a solvent-borne or water-borne coating composition and the third coating composition is a solvent-borne coating composition.

9. The method according to claim 8, characterized in that The first coating composition is a solvent-borne coating composition.

10. The method according to any one of claims 1 to 4, characterized in that The at least one amino resin present and used as a crosslinking agent is an aminoplast resin.

11. The method according to claim 10, characterized in that The aminoplast resin is melamine formaldehyde resin.

12. The method according to claim 11, characterized in that The melamine formaldehyde resin is hexamethoxymethyl melamine formaldehyde resin.

13. The method according to any one of claims 1 to 4, characterized in that The at least one amino resin used as a crosslinking agent has a maximum number average molecular weight of 1500 g / mol.

14. The method according to claim 13, characterized in that The at least one amino resin used as a crosslinking agent has a number average molecular weight in the range of 300-700 g / mol.

15. The method according to any one of claims 1 to 4, characterized in that The at least one amino resin is present in one or both of the first, second and third coating compositions in an amount in the range from 10 to 40% by weight, in each case based on the respective total weight of the respective coating composition.

16. The method according to claim 15, characterized in that The at least one amino resin is present in one of the first, second and third coating compositions in an amount in the range from 12 to 35% by weight, based in each case on the respective total weight of the respective coating composition.

17. The method according to any one of claims 1 to 4, characterized in that Step (4) is performed at a temperature less than 110° C. for a period of 5 to 45 minutes.

18. The method according to claim 17, characterized in that Step (4) is carried out at a temperature less than 105°C.

19. The method according to claim 18, characterized in that Step (4) is performed for 10-35 minutes.

20. The method according to any one of claims 1 to 4, characterized in that The at least one crosslinking catalyst CLC1 is an unblocked sulfonic acid.

21. The method according to any one of claims 1 to 4, characterized in that The at least one crosslinking catalyst CLC1 is present in the at least one of the first, second and third coating compositions in an amount in the range from 5 to 40% by weight, in each case based on the total solids content of the respective coating composition.

22. The method according to any one of claims 1 to 4, characterized in that The polymers P1 and P2 each have a hydroxyl group as a crosslinkable functional group.

23. A multi-coat paint system on a substrate obtainable by a process according to any one of claims 1 to 22.

24. Use of amino resins having crosslinkable functional groups, the amino resin is present in one or both of the first, second and third coating compositions, each of which is different from the other, the first coating composition comprising at least one polymer P1 having crosslinkable functional groups which can be crosslinked with the crosslinkable functional groups of the amino resin, the second coating composition comprising at least one polymer P2 having crosslinkable functional groups which can also be crosslinked with the crosslinkable functional groups of the amino resin, and the third coating composition comprising at least one polymer P3 having crosslinkable functional groups which can also be crosslinked with the crosslinkable functional groups of the amino resin, wherein the at least one coating composition selected from the first, second and third coating compositions in which the amino resin is not present does not contain any crosslinking agent but comprises at least one crosslinking catalyst CLC1 which is suitable for catalyzing the crosslinking reaction between the functional groups of the amino resin and the functional groups of each of the polymers P1, P2 and P3, for at least partially migrating from one or two coating films obtained from one or two coating compositions selected from the first, second and third coating compositions in which the amino resin is present to at least one coating film obtained from at least one remaining coating composition of the three coating compositions after applying the third coating composition to the second coating film obtained from the second coating composition before curing the coating film obtained from the second coating composition to form a third coating film adjacent to the second coating film, wherein the second coating film is obtained by applying the second coating composition to the first coating film before curing the first coating film obtained from the first coating composition, the second coating film being adjacent to the first coating film, and is used for subsequent crosslinking with the crosslinkable functional groups of each of polymer P1, polymer P2 and polymer P3.

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