Multilayer coating system obtained from undercoat composition containing block copolymer

Abstract

The invention relates to a multi-layer coating system which is present on a substrate and comprises at least three coatings L1, L2 and L3 which are different from one another, i.e. A first coating L1 which is applied to at least one part of the substrate and contains at least one platelet-like pigment, a second coating L2 which is applied to the first coating L1, and a third coating L3 which is applied to the second coating L2, wherein the second coating layer L2 is formed from a coating composition comprising at least one block copolymer containing a backbone and at least two blocks B1 and B2 and side chains S1 and S2 comprising different polymer moieties M1 and M2, a process for the preparation of said multilayer coating system, a coated substrate obtainable by this process, and a method for the preparation of said multilayer coating system. The invention also relates to the use of a coating composition comprising the block copolymer for improving, in particular for increasing the color of a multilayer coating system according to the invention.

Description

[0001] The present invention relates to a multi-layer coating system which is present on a substrate and comprises at least three mutually different coatings L1, L2 and L3, namely, a first coating L1 containing flaky pigments applied to at least a part of the substrate, a second coating L2 applied on the first coating L1, and a third coating L3 applied on the second coating L2, wherein the second coating L2 is formed from a coating composition containing at least one block copolymer which contains a backbone and at least two blocks B1 and B2 and side chains S1 and S2 containing different polymer parts M1 and M2, a method for preparing the multi-layer coating system, and a coated substrate obtainable by this method Background Art

[0002] In a typical automotive coating process, multiple layers are usually applied to the surface of a suitable substrate such as a metal substrate in the form of a multi-layer coating system: for example, an electrodeposition coating (e-coating), optionally a primer, one or two basecoats, and a topcoat, in particular a clearcoat, as the outermost layer, are applied in this order. Usually, at least the e-coating is applied to the substrate surface and then cured, after which any additional coatings are applied on top. After at least the electrodeposition coating film is applied and cured, and also optionally after the primer is applied, then at least one usually colored (first) basecoat formulation is applied. Usually, a second basecoat is applied on top of the first basecoat film as an additional intermediate coat film. Then, a topcoat such as a clearcoat is usually applied, wherein at least the basecoat and the topcoat are nowadays typically applied using wet-on-wet application. Thereafter, the coated substrate is passed through an oven at a temperature that simultaneously cures at least the one or more basecoats and the topcoat such as the clearcoat. In some cases, the primer coating (if present) is also cured at this stage together with the one or more basecoats and the topcoat, in particular the clearcoat.

[0003] There are quite a number of necessary requirements which must be achieved and / or met by the multi-layer coatings used in the automotive industry due to regulations and also due to the quality standards set by the automotive industry itself. Thus, the multi-layer coatings must exhibit or display many desired characteristics to at least a sufficient extent in order to meet these requirements. For example, it is desirable to avoid optical defects. Furthermore and in particular, it is desirable to achieve excellent color characteristics of the multi-layer coatings.

[0004] Multilayer coatings consisting of at least two coatings are disclosed, for example, in WO 2020 / 160299 A1. The first layer is a photonic crystal film containing pigments and block copolymers. The second layer present on the first layer serves as a top coat and is an optical binder or a UV-curable resin. The block copolymer must be present in the first layer together with at least one pigment. WO 2020 / 160299 A1 aims to provide multilayer coatings with good transparency in the visible spectrum. Coating compositions for preparing colored photonic crystal films are further disclosed in WO 2020 / 180427 A1, but multilayer coatings are not disclosed therein, let alone multilayer coatings prepared by the wet-on-wet technique.

[0005] Since the multilayer coatings known in the prior art do not always exhibit sufficiently good color characteristics, for example, in terms of brightness, but especially in terms of chromaticity, there is a need to provide cured coatings and coating systems that exhibit improved color characteristics and color values compared to the coatings and coating systems known in the prior art, especially with regard to their chromaticity and the achievement of excellent chromaticity values. However, in addition to this, especially for multilayer coatings containing effect pigments that utilize platelet effect pigments in the base coat, it is necessary to improve the color transition characteristics. Furthermore, these cured coatings and coating systems should be prepared in an economically advantageous manner, especially in terms of the shortest possible process time (including the shortest possible curing time), especially when these coatings and coating systems are used in automotive OEM production.

[0006] Problem

[0007] Therefore, the object underlying the present invention is to provide a multilayer coating system that exhibits improved color characteristics and color values compared to the coatings and coating systems known in the prior art, especially in terms of their chromaticity and the achievement of excellent chromaticity values, and at the same time exhibits a unique color transition and can be prepared in an economically advantageous manner, especially in terms of the shortest possible process time (including the shortest possible curing time), especially when these multilayer coating systems are used in automotive OEM production.

[0008] Solution

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

[0010] A first subject matter of the present invention is a multilayer coating system that is present on an optionally pre-coated substrate and comprises at least three mutually different coatings L1, L2, and L3, namely

[0011] a first coating L1 containing at least one platelet pigment applied to at least a part of the optionally pre-coated substrate,

[0012] A second coating L2 applied on the first coating L1, and

[0013] A third top coating L3 applied on the second coating L2,

[0014] characterized in that,

[0015] The second coating L2 is formed from a coating composition comprising at least one block copolymer containing a backbone and at least two different blocks B1 and B2 from each other,

[0016] wherein block B1 comprises at least one side chain S1 attached to the backbone and block B2 comprises at least one side chain S2 different from side chain S1 attached to the backbone, wherein each of the side chains S1 comprises at least one polymer moiety M1 selected from the group consisting of polyester, polyether and poly(meth)acrylate moieties, and each of the side chains S2 comprises at least one polymer moiety M2 different from the polymer moiety M1 and selected from the group consisting of: polyester, poly(meth)acrylate, polyether, polysiloxane and polystyrene moieties.

[0017] A further subject of the present invention is a method for preparing the multi-layer coating system of the present invention, the method comprising at least steps (1), (2), (3) and (4), namely

[0018] (1) Applying a first primer coating composition comprising at least one flaky pigment to at least a part of an optionally pre-coated substrate and forming a first coating film on at least a part of the optionally pre-coated substrate,

[0019] (2) Applying a second primer coating composition comprising at least one block copolymer as defined for the multi-layer coating system and different from the first primer coating composition applied in step (1) to the first coating film present on the substrate obtained after step (1), and forming a second coating film preferably adjacent to the first coating film,

[0020] (3) Applying a coating composition different from the compositions applied in steps (1) and (2) to the second coating film present on the substrate obtained after step (2), and forming a third coating film preferably adjacent to the second coating film, wherein the coating composition is preferably a clear coating composition, and

[0021] (4) Curing together at least the second and third coating films applied in steps (2) and (3) and, optionally, the first coating film if it is not cured before step (2) and the first coating film applied in step (1) to obtain a multi-layer coating system comprising at least the first, second and third coatings L1, L2 and L3.

[0022] Another subject of the present invention is a coated substrate obtainable by the method of the present invention.

[0023] The block copolymer used in the present invention is hereinafter also referred to as a brush block copolymer (BBCP).

[0024] Furthermore, it has been particularly surprisingly found that multilayer coating systems can be produced in an economically advantageous manner, especially with respect to short processing times and short curing times, particularly when these coatings and coating systems are used in automotive OEM production.

[0025] It has been particularly surprisingly found that the above-mentioned advantageous effects are the result of incorporating the block copolymer BBCP into the coating composition and using said coating composition as an intermediate coating composition (second primer composition) in the preparation of the multilayer coating system of the present invention. It has further surprisingly been found that these effects can be particularly advantageously observed when using a specific wet-on-wet application for the preparation of the multilayer coating system, in which the applied coating composition comprising at least one block copolymer BBCP for the preparation of the second coating L2 and the applied coating composition for the preparation of the third coating L3 are co-cured, i.e., cured simultaneously, to obtain the second and third coatings L2 and L3 of the multilayer coating system. Detailed Description

[0026] In the context of the present invention, the term "comprising" in relation to, for example, a coating composition used in the method of the present invention or for the preparation of the multilayer coating system of the present invention preferably has the meaning of "consisting of". For example, with respect to the second primer composition, in addition to all the mandatory components present therein, one or more further components determined hereinafter and optionally included therein may also be included therein. In each case, all components may be present in their preferred embodiments as determined hereinafter.

[0027] The proportion and amount of any component given hereinafter in wt.-% (percent by weight) present in each coating composition total 100 wt.-%, in each case based on the total weight of the respective composition.

[0028] Each coating composition used in steps (1), (2) and (3) of the method according to the invention and / or for preparing coatings L1, L2 and L3 may contain, in addition to the components outlined in more detail below, one or more common additives, depending on the desired application. For example, each coating composition may independently of one another contain at least one additive selected from the group consisting of: reactive diluents, catalysts, light stabilizers, antioxidants, degassing agents, emulsifiers, lubricity promoting additives, polymerization inhibitors, plasticizers, free radical polymerization initiators, adhesion promoters, flow control agents, film forming aids, sag control agents (SCA), flame retardants, corrosion inhibitors, drying agents, thickeners, biocides and / or matting agents. They can be used in known and conventional proportions. Preferably, based on the total weight of each coating composition, their content is from 0.01 to 20.0 wt.-%, more preferably from 0.05 to 15.0 wt.-%, particularly preferably from 0.1% to 10.0% by weight, most preferably from 0.1% to 7.5% by weight, especially from 0.1% to 5.0% by weight and most preferably from 0.1% to 2.5% by weight.

[0029] Each coating composition used in the method according to the invention, in particular in each of steps (1) to (3), and / or for preparing a multi-layer coating system may be water-based (aqueous) or based on organic solvents (solvent-based, non-aqueous).

[0030] For the purposes of the present invention, the term "solvent-based" or "non-aqueous" is preferably to be understood as meaning that if the corresponding coating composition is solvent-based, the organic solvent as solvent and / or diluent is present as the main constituent of all solvents and / or diluents present in the corresponding coating composition (such as in the second primer coating composition applied in step (2)). Preferably, based on the total weight of the coating composition, one or more organic solvents are present in an amount of at least 35 wt.-%. In each case based on the total weight of the coating composition, the solvent-based coating composition preferably contains at least 40 wt.-%, more preferably at least 45 wt.-%, very preferably at least 50 wt.-% of one or more organic solvent fractions. All conventional organic solvents known to the person skilled in the art can be used as the organic solvent. 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 will 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 butylene glycol and also their acetates, butyl diglycol, diethylene glycol dimethyl ether, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetone, isophorone, or mixtures thereof. The solvent-based coating composition preferably contains no or substantially no water. In this context, the term "substantially" preferably means that no water is intentionally added during the preparation of the coating composition.

[0031] For the purposes of the present invention, the term "water-based" or "aqueous" is preferably to be understood as meaning that water is present as the main constituent of all solvents and / or diluents present in the aqueous coating composition (such as in the first primer coating composition applied in step (1) of the process according to the invention). Preferably, based on the total weight of the coating composition, water is present in an amount of at least 35 wt.-%. In each case based on the total weight of the coating composition, the aqueous coating composition preferably comprises at least 40 wt.-%, more preferably at least 45 wt.-%, very preferably at least 50 wt.-% of a water fraction. In each case based on the total weight of the coating composition, one or more organic solvent fractions are preferably <20 wt.-%, more preferably in the range from 0 to <20 wt.-%, very preferably in the range from 0.5 to 20 wt.-% or to 17.5 wt.-% or to 15 wt.-% or to 10 wt.-%.

[0032] Unless otherwise defined in the present invention, polymer-specific terms are used in accordance with the International Union of Pure and Applied Chemistry (IUPAC) Recommendations 2008, published by the Polymer Division of the IUPAC and set forth in the "Compendium of Polymer Terminology and Nomenclature" (RSC Publishing, ISBN: 978-0-85404-491-7).

[0033] Unless otherwise defined in the present invention, coating-specific terms are used in accordance with DIN EN ISO 4618 (German version, date: March 2007).

[0034] Multi-layer coating system of the present invention

[0035] The multi-layer coating system of the present invention is present on an optionally pre-coated substrate and comprises at least three coatings L1, L2 and L3 and is different from each other as defined above.

[0036] Preferably, at least the second and third coatings L2 and L3 are positioned adjacent to each other. More preferably, the first coating L1 and the second coating L2 are also positioned adjacent to each other. Most preferably, the first, second and third coatings L1, L2 and L3 are positioned adjacent to each other, and the coatings L1 and L2 are at least partially transparent to visible light.

[0037] Preferably, the multi-layer coating system can be obtained by a method according to which at least the applied coating composition for preparing the second coating L2 containing the at least one block copolymer BBCP and the applied coating composition for preparing the third coating L3 are co-cured to obtain the second and third coatings L2 and L3 of the multi-layer coating system.

[0038] Curing is preferably selected from chemical curing (such as chemical crosslinking, radiation curing), and / or physical drying (non-chemical curing), in each case at room temperature or at elevated temperature, more preferably selected from chemical curing (such as chemical crosslinking), and / or physical drying (non-chemical curing), in each case at room temperature or at elevated temperature, in each case preferably where the lowest curing temperature applied for curing is 80 °C.

[0039] Substrate

[0040] The multi-layer coating system of the present invention is particularly suitable as a coating for an automotive body or a part thereof (including the corresponding metal substrate, and also including a plastic substrate, such as a polymer substrate). Accordingly, a preferred substrate is an automotive body or a part thereof.

[0041] Suitable metal substrates for use in accordance with the present invention are all substrates commonly used and known to those skilled in the art. The substrate used in accordance with the present invention is preferably a metal substrate, more preferably selected from the group consisting of: steel, preferably steel selected from the group consisting of bare steel, cold rolled steel (CRS), hot rolled steel, galvanized steel (such as hot dip galvanized steel (HDG)), alloy galvanized steel (such as Galvalume, Galvannealed or Galfan) and aluminized steel; aluminum and magnesium, as well as Zn / Mg alloys and Zn / Ni alloys. Particularly suitable substrates are parts for the production of a vehicle body or the entire vehicle body of an automobile.

[0042] Preferably, thermoplastic and thermosetting polymers are used as plastic substrates. Suitable polymers are poly(meth)acrylates (including poly(methyl)methacrylate, poly(methyl)butyl acrylate), polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polyvinyl chloride, polyesters (including polycarbonate and polyvinyl acetate), polyamides, polyolefins (such as polyethylene, polypropylene, polystyrene and also polybutadiene), polyacrylonitrile, polyacetals, acrylonitrile - ethylene - propylene - diene - styrene copolymer (A - EPDM), ASA (acrylonitrile - styrene - acrylate copolymer) and ABS (acrylonitrile - butadiene - styrene copolymer), polyetherimide, phenolic resin, urea resin, melamine resin, alkyd resin, epoxy resin, polyurethane (including TPU), polyether ketone, polyphenylene sulfide, polyethers, polyvinyl alcohol, and mixtures thereof. Polycarbonate and poly(meth)acrylates are particularly preferred.

[0043] The substrate used in accordance with the present invention is preferably a metal substrate pretreated with at least one conversion coating composition (such as a composition containing metal phosphate, like a composition containing zinc phosphate) and / or pretreated with oxalate. This pretreatment using phosphating is usually carried out after the substrate is cleaned and before the substrate is electro-deposition coated, and it is a pretreatment step commonly used especially in the automotive industry.

[0044] As outlined above, the substrate used can be a pre-coated substrate, i.e., a substrate with at least one cured coating film. The substrate can be pre-coated with a cured electrodeposition coating. For example, the substrate can additionally or alternatively be provided with at least one cured or uncured primer coating film as at least one additional pre-coat. The term "primer" is known to those skilled in the art. Typically, the primer is applied after the substrate already has a cured electrodeposition coating. In the presence of a cured primer coating film, the cured electrodeposition coating film is present below the cured primer coating film and preferably adjacent to the cured primer coating film. The curing of the primer preferably can be carried out at a temperature in the range of 40 °C to 140 °C, and particularly can include a "low-temperature baking" step at a temperature in the range of 80 °C to 100 °C. As outlined above, substrates with an uncured primer coating film can also be used, particularly metal substrates with a cured electrodeposition coating film on which the uncured primer coating film is present. Thus, the primer composition can be applied to the optionally pre-coated substrate and a primer coating film can be formed on the optionally pre-coated substrate. Then, an optional curing step for the primer coating film is possible. Then, the coating composition for forming the first coating L1 can subsequently be applied before or after the primer coating film is cured, optionally and preferably after a flash-off period (such as a flash-off period of 1 to 20 minutes at a temperature preferably not exceeding 40 °C, such as at a temperature in the range of 18 °C to 30 °C).

[0045] Coating L1 and first primer composition for forming said layer

[0046] The first coating L1 containing at least one flaky pigment is applied to at least a part of the optionally pre-coated substrate. Thus, the first coating L1 is present on at least a part of the surface of the optionally pre-coated substrate.

[0047] Preferably, the first coating L1 is capable of at least partially reflecting, but also and even more preferably additionally at least partially absorbing those wavelengths not reflected by the second layer L2.

[0048] The first coating L1 is formed from a colored coating composition containing at least one flaky pigment and preferably also at least one non-flaky, preferably absorptive pigment. Such a coating composition is also referred to herein as the first primer coating composition. This composition is the composition used in step (1) of the method of the present invention.

[0049] The first primer coating composition is preferably an aqueous (i.e., water-based) coating composition or a solvent-based primer coating composition. In particular, it is a solvent-based primer coating composition. The first primer coating composition can be a 1K (one-component) or 2K (two-component) composition. Preferably, it is a 1K composition.

[0050] The term "priming layer" is known in the art and is used, for example, in Lexikon, paints and printing inks, Georg Thieme Verlag, 1998, 10th edition, page 57. Basecoats are therefore used in particular in the tinting of automotive paints and industrial paints in general in order to provide tinting and / or optical effects by using the basecoat as an intermediate coating composition.

[0051] pigment

[0052] The first basecoat composition is colored. The term "pigment" is known to the skilled person, for example from DIN 55943 (date: October 2001). In the sense of the present invention, "pigment" preferably refers to a colorant and / or optical effect providing component in particulate form (such as in powder or flaky form), which is substantially, preferably completely insoluble in the medium around them, such as, for example, insoluble in one of the coating compositions used in the present invention. The difference between pigments and "fillers" is preferably their refractive index, the refractive index of the pigment being ≥1.7. The term "filler" is known to the skilled person, for example from DIN 55943 (date: October 2001). Pigments can be inorganic or organic.

[0053] Flake Pigments

[0054] The first basecoat composition contains at least one flake pigment. The term "flake pigment" as used in the coating field refers to flake metallic effect pigments as well as so-called flake special effect pigments. These special effect pigments are typically grouped into pearlescent pigments and interference pigments.

[0055] As used herein, the flake-shaped pigments preferably have a number average flake thickness h in the range of 30 nm to 1 μm. 50 , and a median flake diameter D preferably in the range of 5 μm to 40 μm 50 , and therefore the aspect ratio D 50 / h 50 Preferably in the range of about 5:1 to about 1300:1. 50 is the volume-based median particle size as measured using a laser diffraction particle analyzer such as the Malvern Mastersizer 3000 (available from Malvern Panalytical, Ltd., UK), and h 50 is the average particle thickness. The average thickness h 50 The value is formed in which 50% of the flake-shaped pigments have a specified thickness or less in a cumulative frequency distribution (also called a cumulative pass curve), in which at least 100 particles of pigment are measured, for example 100 particles of pigment.50 The value can be determined by preparing a cured coating containing the pigment. It is important to ensure the most favorable possible orientation of these flakes in the applied medium. Thereafter, the cured coating is partially abraded and its cross-section is observed by electron microscopy (SEM or TEM, both being equivalent for the purposes of the present invention). Only the particles showing the favorable orientation are counted.

[0056] In the case of flaky metallic effect pigments, flakes from a single metal or its alloy can be used. Such metallic effect pigments are typically aluminum flakes, zinc - copper flakes, copper flakes, nickel flakes or steel flakes, with aluminum and copper flakes being most preferred, and aluminum flakes being particularly preferred. Typical flake shapes are the so-called silver dollar and cornflake shapes, especially for aluminum pigments. Very thin metallic effect pigments are for example PVD pigments (i.e., physical vapor deposition pigments). The flaky metallic effect pigments can be surface-modified, i.e., modified or coated with inorganic or organic compounds. Such modification can be oxidation of the pigment surface, or application of a metal oxide coating or an organic coating with for example silanes or organic colorants.

[0057] Among the flaky special effect pigments, coated flakes selected particularly from mica, silica, alumina, glass and borosilicates can be used. The coatings of the flakes of the above types can be non-absorbing coatings such as those containing TiO 2 (rutile), TiO 2 (anatase), ZrO 2 , SnO 2 and SiO 2 or coatings consisting of them; or selectively absorbing coatings such as FeOOH, Fe 2 O 3 , Cr 2 O 3 , TiO 2-x , TiO x N y , KFe[Fe(CN) 6 or colorant coatings.

[0058] Further flaky special effect pigments are for example substrate-free flaky pearlescent pigments such as natural pearl essence, basic lead carbonate, bismuth oxychloride, iron oxide mica and titanium dioxide flakes.

[0059] An aqueous or non-aqueous pigment paste containing at least one flaky pigment is preferably used for preparing the first primer coating composition, depending on whether the first primer coating composition is solvent-based or aqueous.

[0060] The amount of the flaky effect pigment for use in the coating composition according to the invention can vary widely and is determined on the one hand by the opacity of the effect pigment and the intensity of the optical effect to be achieved. Preferably, the first primer coating composition according to the invention comprises 0.5 to 12.5 wt.-%, more preferably 1.0 to 10.0 wt.-%, and most preferably 2.0 to 6.0 wt.-% of one or more flaky pigments, based on the total weight of the coating composition.

[0061] Non-flaky pigment

[0062] Preferably, the first primer coating composition further comprises at least one non-flaky pigment that absorbs visible light (wavelength 380 to 750 nm), more preferably at least one black and / or colored pigment, and most preferably at least one black pigment, in particular at least one inorganic black pigment and / or at least one organic black pigment.

[0063] If at least one organic black pigment is present in the first primer coating composition, it is preferably at least one perylene black pigment, such as Pigment Black 31 or Pigment Black 32. The most preferred black organic pigment is perylene black P.B. 32. If at least one inorganic black pigment is present in the first primer coating composition, it is preferably at least one carbon black pigment.

[0064] An aqueous or non-aqueous pigment paste comprising at least one pigment is preferably used for preparing the first primer coating composition, depending on whether the first primer coating composition is solvent-based or aqueous.

[0065] Preferably, then, at least one non-flaky pigment preferably present in the first primer coating composition is included therein in an amount in the range of 0.1 to 25.0 wt.-%, more preferably 0.3 to 10.0 wt.-%, and even more preferably 0.5 to 7.5 wt.-%, based on the total solids content of the first primer coating composition.

[0066] Binder

[0067] The first primer coating composition preferably further comprises at least one binder, more preferably at least one polymer (a1) as the binder, in addition to at least one flaky pigment.

[0068] For the purposes of the present invention, the term "binder" is understood, in accordance with DIN EN ISO 4618 (German version, date: March 2007), as the non-volatile component of a coating composition which is responsible for film formation. The term includes crosslinking agents and additives, if these represent non-volatile components. Thus, pigments and / or fillers included therein are not included under the term "binder". Preferably, the at least one polymer (a1) is the main binder of the coating composition. As the main binder in the present invention, when no other binder components are present in the coating composition, preference is given to mentioning the binder component present in a higher proportion based on the total weight of the coating composition.

[0069] The term "polymer" is known to the person skilled in the art and, for the purposes of the present invention, encompasses addition polymers and polymerizates as well as condensation polymers. The term "polymer" includes both homopolymers and copolymers.

[0070] Preferably, the first primer coating composition does not contain the copolymer BBCP as present in the coating composition for forming the coating L2. Thus, preferably, the first primer coating composition does not contain any polymer which is the copolymer BBCP.

[0071] The at least one polymer used as component (a1) can be self-crosslinking or non-self-crosslinking. Suitable polymers which can be used are known, for example, from EP 0 228 003 A1, DE 44 38 504 A1, EP 0 593 454 B1, DE 199 48004A1, EP 0 787 159 B1, DE 40 09858A1, DE 44 37 535 A1, WO 92 / 15405A1 and WO 2005 / 021168 A1.

[0072] The at least one polymer used as component (a1) is preferably selected from the group consisting of polyurethanes, polyureas, polyesters, polyamides, polyethers, poly(meth)acrylates and / or copolymers of the structural units of said polymers, in particular polyurethane-poly(meth)acrylates and / or polyurethane polyureas. The at least one polymer used as component (a1) is particularly preferably selected from the group consisting of polyurethanes, polyesters, poly(meth)acrylates and / or copolymers of the structural units of said polymers. In the context of the present invention, the term "(meth)acryloyl" or "(meth)acrylate" includes in each case the meanings "methacrylic" and / or "acrylic" or "methacrylate" and / or "acrylate".

[0073] Preferred polyurethanes are described, for example, on page 4, line 19 to page 11, line 29 of German patent application DE 199 48 004 A1 (polyurethane prepolymer B1), in Example D of German patent application DE 4437535 A1, on page 7, line 55 to page 8, line 23, on page 3, line 24 to page 5, line 40 of European patent application EP 0 228 003 A1, on page 3, line 38 to page 8, line 9 of European patent application EP 0634 431 A1, on page 6, line 24 to line 41 and lines 45 to 47 of European patent EP 0574417 B2, on page 9, line 11 to line 28 of European patent EP 0521928 B1, and on page 2, line 35 to page 10, line 32 of international patent application WO 92 / 15405.

[0074] Preferred polyethers are described, for example, in WO 2017 / 097642 A1 and WO 2017 / 121683 A1.

[0075] Preferred poly(meth)acrylates are described, for example, on page 12, line 41 to page 13, line 4 of EP 0569907 B1, or on page 7, lines 10 to 21 and page 8, lines 3 to 16 of EP 0589340 B1.

[0076] Preferred polyesters are described, for example, in column 6, line 53 to column 7, line 61 and column 10, line 24 to column 13, line 3 of the described DE 4009858 A1, on page 16, line 50 to page 17, line 6 of EP 2421924 B1, or on page 2, line 24 to page 7, line 10 and page 28, line 13 to page 29, line 13 of WO2014 / 033135A2. Also preferred polyesters are polyesters having a dendritic or star structure, as described, for example, in WO 2008 / 148555 A1.

[0077] Preferred polyurethane - poly(meth)acrylate copolymers (for example, (meth)acrylated polyurethanes) and their preparation are described, for example, on page 3, line 21 to page 20, line 33 of the described WO 91 / 15528A1 and on page 2, line 27 to page 6, line 22 of DE 4437535 A1.

[0078] Preferred (meth)acrylic acid copolymers are OH-functional. Hydroxyl-containing monomers include hydroxyalkyl esters of acrylic or methacrylic acid, which can be used to prepare the copolymers. Non-limiting examples of hydroxyl-functional monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxyhexyl (meth)acrylate, propylene glycol mono(meth)acrylate, 2,3-dihydroxypropyl (meth)acrylate, pentaerythritol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, reaction products of these with ε-caprolactone, and other hydroxyalkyl (meth)acrylates having a branched or straight-chain alkyl group of up to about 10 carbons and mixtures thereof. Hydroxyl groups on vinyl polymers such as (meth)acrylic acid polymers can be generated by other means, such as by ring-opening of glycidyl groups (e.g., from copolymerized glycidyl methacrylate) with organic acids or amines. Hydroxyl functional groups can also be introduced by thiol compounds, including but not limited to 3-mercapto-1-propanol, 3-mercapto-2-butanol, 11-mercapto-1-undecanol, 1-mercapto-2-propanol, 2-mercaptoethanol, 6-mercapto-1-hexanol, 2-mercaptobenzyl alcohol, 3-mercapto-1,2-propanediol, 4-mercapto-1-butanol, and combinations thereof. Any of these methods can be used to prepare useful hydroxyl-functional (meth)acrylic polymers. Examples of suitable comonomers that can be used include but are not limited to α,β-ethylenically unsaturated monocarboxylic acids containing 3 to 5 carbon atoms, such as acrylic acid, methacrylic acid, and crotonic acid, and alkyl and cycloalkyl esters, nitriles, and amides of acrylic acid, methacrylic acid, and crotonic acid; α,β-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms and anhydrides, monoesters, and diesters of these acids; vinyl esters, vinyl ethers, vinyl ketones, and aromatic or heterocyclic aliphatic vinyl compounds.Representative examples of suitable esters of acrylic acid, methacrylic acid, and crotonic acid include, but are not limited to, esters resulting from the reaction with saturated fatty alcohols containing 1 to 20 carbon atoms, such as methyl esters, ethyl esters, propyl esters, isopropyl esters, n-butyl esters, isobutyl esters, tert-butyl esters, hexyl esters, 2-ethylhexyl esters, dodecyl esters, 3,3,5-trimethylhexyl esters, stearyl esters, lauryl esters, cyclohexyl esters, alkyl-substituted cyclohexyl esters, alkanol-substituted cyclohexyl esters, such as 2-tert-butyl and 4-tert-butyl cyclohexyl esters, 4-cyclohexyl-1-butyl esters, 2-tert-butyl cyclohexyl esters, 4-tert-butyl cyclohexyl esters, 3,3,5,5,-tetramethyl cyclohexyl esters, tetrahydrofurfuryl esters, and isobornyl esters; unsaturated diacids and acid anhydrides, such as fumaric acid, maleic acid, itaconic acid, and acid anhydrides, and their mono- and diesters with alcohols (such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and tert-butanol), such as maleic anhydride, dimethyl maleate, and monohexyl maleate; vinyl acetate, vinyl propionate, vinyl ethyl ether, and vinyl ethyl ketone; styrene, α-methylstyrene, vinyltoluene, 2-vinylpyrrolidone, and p-tert-butylstyrene. (Meth)acrylic acid copolymers can be prepared using conventional techniques, such as by heating monomers in the presence of a polymerization initiator and optionally a chain transfer agent.

[0079] Suitable poly(meth)acrylates are also those that can be prepared by multistage free radical emulsion polymerization of ethylenically unsaturated monomers in water and / or organic solvents. Examples of seed-core-shell polymers (SCS polymers) obtained in this way are disclosed in WO 2016 / 116299A1.

[0080] Preferred polyurethane-polyurea copolymers are polyurethane-polyurea particles, preferably those having a Z-average particle size of 40 to 2000 nm, each polyurethane-polyurea particle being in a reactive form and containing at least one isocyanate group-containing polyurethane prepolymer, the polyurethane prepolymer containing anions 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. Preferably, such copolymers are used in the form of an aqueous dispersion. Such polymers can in principle be prepared by conventional addition polymerization of, for example, polyisocyanates with polyols and polyamines.

[0081] The polymer used as component (a1) preferably has reactive functional groups capable of undergoing a crosslinking reaction. Any common crosslinkable reactive functional groups known to those skilled in the art can be present. Preferably, the polymer used as component (a1) has at least one functional reactive group selected from the group consisting of primary amino groups, secondary amino groups, hydroxyl groups, thiol groups, carboxyl groups, and urethane groups. Preferably, the polymer used as component (a1) has functional hydroxyl groups and / or urethane groups.

[0082] Preferably, the polymer used as component (a1) is hydroxy-functional and more preferably has an OH value in the range of 15 to 400 mg KOH / g, more preferably 20 to 250 mg KOH / g.

[0083] Particularly preferably, the polymer used as component (a1) is a hydroxy-functional polyurethane-poly(meth)acrylate copolymer, a hydroxy-functional polyester, and / or a hydroxy-functional polyurethane-polyurea copolymer.

[0084] Furthermore, the first primer composition may contain at least one crosslinker known per se. The crosslinker is included in the film-forming non-volatile components of the coating composition and thus falls within the general definition of "binder". Therefore, the crosslinker is classified under component (a1).

[0085] All conventional crosslinkers can be used. This includes melamine resins, preferably melamine aldehyde resins, more preferably melamine formaldehyde resins, blocked polyisocyanates, polyisocyanates having free (unblocked) isocyanate groups, crosslinkers having amino groups such as secondary amino groups and / or primary amino groups, and crosslinkers having epoxy groups and / or hydrazide groups, and crosslinkers having carbodiimide groups, provided that the functional groups of the specific crosslinker are suitable for reacting with the crosslinkable functional groups of the film-forming polymer used as the binder in the crosslinking reaction. For example, a crosslinker having blocked or free isocyanate groups can be reacted with a film-forming polymer having crosslinkable OH-groups and / or amino groups at elevated temperatures (in the case of 1K formulations) and at ambient temperature (in the case of 2K formulations).

[0086] If a crosslinker is present, it is preferably at least one aminoplast resin and / or at least one blocked or free polyisocyanate, preferably an aminoplast resin. Among the aminoplast resins, melamine resins such as melamine formaldehyde resins are particularly preferred. Preferably, the melamine aldehyde resins, preferably melamine formaldehyde resins, each carry at least one of imino groups, alkanol groups, and etherified alkanol groups as functional groups reactive towards the functional groups of the binder to be crosslinked. Examples of alkanol groups are hydroxymethyl.

[0087] The solids content of the first primer composition

[0088] Preferably, the total solids content of the first primer composition is in the range of 10 to 65 wt.-%, more preferably 15 to 60 wt.-%, even more preferably 20 to 50 wt.-%, particularly 25 to 45 wt.-% in each case based on the total weight of the first primer composition. The method for measuring the solids content (non-volatile content) is described in the'methods' section below.

[0089] Coating L2 and second primer composition for forming said layer

[0090] The second coating L2 is applied onto the first coating L1. Thus, the second coating L2 is preferably located above the coating L1. The second coating L2 is formed from a coating composition comprising at least one block copolymer BBCP. This coating composition is also referred to herein as the second primer coating composition and is the composition used in step (2) of the method of the present invention.

[0091] The second primer coating composition can be an aqueous (i.e., water-based) coating composition. The second primer coating composition can alternatively be a solvent-based primer coating composition. In particular, it is preferably a solvent-based primer coating composition. The primer coating composition can be a 1K (one-component) or 2K (two-component) composition. Preferably, it is a 1K composition.

[0092] Preferably, the second primer coating composition does not contain pigments. Preferably, the second primer coating composition does not contain fillers, and most preferably does not contain both pigments and fillers. However, alternatively, the coating composition comprising at least one block copolymer BBCP is a colored coating composition.

[0093] Most preferably, the second primer coating composition is a solvent-based coating composition that preferably does not contain pigments.

[0094] Preferably, the total solids content of the second primer coating composition is in the range of 15 to 70 wt.-%, more preferably 20 to 65 wt.-%, even more preferably 25 to 60 wt.-%, particularly 30 to 55 wt.-% in each case based on the total weight of the second primer coating composition. The method for measuring the solids content (non-volatile content) is described in the 'Method' section below.

[0095] Block copolymer

[0096] The second primer coating composition must comprise at least one block copolymer BBCP. As already outlined above, the block copolymer used in the present invention is also referred to as copolymer BBCP hereinbelow and above.

[0097] Preferably, at least one copolymer BBCP is present in the coating composition in an amount in the range of 10 to 100 wt.-%, more preferably 15 to 100 wt.-%, even more preferably 20 to 95 wt.-% in each case based on the total solids content of the coating composition used for preparing the second coating L2.

[0098] At least one block copolymer BBCP contains a backbone and at least two different blocks B1 and B2 from each other. Block B1 contains at least one side chain S1 attached to the backbone, and block B2 contains at least one side chain S2 different from side chain S1 attached to the backbone. Since each of side chains S1 and S2 is attached to the backbone of the copolymer BBCP used in the present invention and the copolymer must be a block copolymer comprising the at least two blocks B1 and B2, where block B1 further contains the above-mentioned side chain S1 and block B2 further contains the above-mentioned side chain S2, it is obvious that at least the part of the backbone of the copolymer used in the present invention attached to side chain S1 is also part of block B1, and at least the part of the backbone of the copolymer used in the present invention attached to side chain S2 is also part of block B2. Further, it is obvious that the part of block B1 that does not constitute at least one side chain S1 but is attached to side chain S1 constitutes part of the copolymer backbone, and the part of block B2 that does not constitute at least one side chain S2 but is attached to side chain S2 also constitutes part of the copolymer backbone. Each of side chains S1 contains at least one polymer part M1 selected from the group consisting of polyester, polyether, and poly(meth)acrylate moieties, and each of side chains S2 contains at least one polymer part M2 different from polymer part M1 and selected from the group consisting of: polyester, poly(meth)acrylate, polyether, polysiloxane, and polystyrene moieties. Side chains S1 and S2 are preferably covalently attached to the backbone of block copolymer BBCP. The backbone (main chain) of copolymer BBCP preferably contains ethylenically unsaturated carbon-carbon double bonds, but does not necessarily contain them.

[0099] Copolymer BBCP can preferably be obtained by ring-opening metathesis polymerization (ROMP) using a cyclic ethylenically unsaturated monomer, preferably a cyclic olefin monomer. ROMP is a specific olefin metathesis chain-growth polymerization. The driving force of this reaction is the relief of ring strain in the cyclic olefin (such as norbornene or cyclopentene monomer).

[0100] Preferably, the backbone of copolymer BBCP contains olefinic carbon-carbon double bonds, more preferably arranged in a regular and / or repeating pattern, and even more preferably arranged in such a way that each of the structural units described below is covalently linked to another structural unit via a carbon-carbon double bond. These double bonds are preferably formed during ROMP. If copolymer BBCP is obtained in this way (i.e., by ROMP), the carbon-carbon double bonds present in the backbone formed thereafter can optionally be hydrogenated to saturated carbon bonds, such as an alkylidene moiety.

[0101] Those skilled in the art know the methods for preparing copolymer BBCP, especially such copolymers prepared via ROMP: Copolymer BBCP itself is known and is disclosed, for example, in WO 2020 / 160299 A1, WO 2020 / 180427 A1, and B.R. et al., in PNAS [Proceedings of the National Academy of Sciences of the United States of America] 2012, 109(36), pp. 14332 - 14336. The preparation of the copolymer BBCP is also described in these references and, in the case of the cited journal articles, also in their supporting information.

[0102] The block copolymer BBCP is preferably a linear block copolymer. The block copolymer BBCP preferably has a block - like sequence of copolymerized structural units that are at least partially derived from suitable ethylenically unsaturated monomers, preferably cyclic olefins. Preferably, (meth)acrylic monomers are not used to prepare the block copolymer BBCP.

[0103] The block copolymer BBCP contains at least two blocks and is thus at least a diblock copolymer, more preferably a linear diblock copolymer. However, the copolymer BBCP can contain one or more additional blocks and can also be, for example, a triblock copolymer.

[0104] A block copolymer is a copolymer obtained by adding at least two different ethylenically unsaturated monomers, a mixture of two different ethylenically unsaturated monomers, or adding an ethylenically unsaturated monomer and a mixture of ethylenically unsaturated monomers at different times in the practice of controlled polymerization, where an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers is initially charged at the start of the reaction. When adding an additional ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers or adding ethylenically unsaturated monomers in portions, the ethylenically unsaturated monomer added at the start of the polymerization may have completely reacted or may still be partially unpolymerized. As a result of such polymerization, the block copolymer can have at least one transition in its structural units along the polymer chain (polymer backbone), which marks the boundary between the individual blocks. Suitable block copolymer structures are, for example, AB diblock copolymers, ABA triblock copolymers, or ABC triblock copolymers. The block copolymers preferably used according to the invention contain blocks with a minimum number of two structural units each.

[0105] Preferably, the block copolymer BBCP is of the A - B, A - B - A, B - A - B, A - B - C, and / or A - C - B type, where the A, B, and C blocks represent structural units of different compositions, where the blocks A, B, and C differ in the respective composition of their structural units, and / or where the amounts of structural units in two adjacent blocks differ from each other by more than 5% by weight in each case. However, the most preferred is the AB diblock copolymer.

[0106] Preferably, the number - average molecular weight (M n)In the range of 450 to 6000 kDa, more preferably in the range of 500 to 2500 kDa, even more preferably in the range of 550 to 2000 kDa, still more preferably in the range of 600 to 1500 kDa, particularly in the range of 650 to 1000 kDa.

[0107] For measuring the number-average molecular weight (M n ) and for measuring the weight-average molecular weight (M w ) and the polydispersity index (PDI) are described in the 'Methods' section below.

[0108] As mentioned above, each of the side chains S1 contains at least one polymer moiety M1 selected from the group consisting of polyester, polyether, and poly(meth)acrylate moieties, and each of the side chains S2 contains at least one polymer moiety M2 different from the polymer moiety M1 and selected from the group consisting of: polyester, poly(meth)acrylate, polyether, polysiloxane, and polystyrene moieties.

[0109] Preferably, after the copolymer BBCP has been polymerized in a polymer-analogous reaction, side chains are not introduced into the copolymer. Instead, the side chains are preferably introduced into suitable monomers for the polymerization reaction to prepare the copolymer BBCP. Since these monomers carry the above polymer moieties, the corresponding monomers represent macromonomers.

[0110] Preferably, cyclic olefins, more preferably norbornene or cyclopentene monomers, are used to prepare the copolymer BBCP. Polymer moieties such as M1 and M2 can be introduced into such monomers, for example, by using norbornene or cyclopentene monomers having at least one functional group (such as a carboxylic acid group and / or a hydroxyl group).

[0111] Examples of suitable norbornene monomers are For example, (B) can be used as an initiator alcohol for the polymerization, such as the tin-catalyzed polymerization of lactide (such as racemic lactide), to produce a poly(lactide) macromonomer having both OH-functional end groups and being functionalized with norbornene at its other end. The poly(lactide) unit represents an example of a polyester moiety as the polymer moiety M1. The norbornene moiety can then be used in ROMP to prepare the copolymer BBCP. The preparation of such macromonomers is described, for example, in B.R. et al., in the Supporting Information of PNAS [Proceedings of the National Academy of Sciences of the United States of America] 2012, 109(36), pages 14332 - 14336. The monomer (A) can also be used to prepare suitable macromonomers suitable for ROMP. For example, a polymer having terminal OH - groups, such as polystyrene, can be prepared. The terminal OH - groups of the formed precursor can then be converted into ester bonds via reaction with (A) to produce a suitable macromonomer with a polystyrene moiety as the polymer moiety M2. The preparation of such macromonomers is described, for example, in Example 2 of WO 2020 / 180427 A1.

[0112] Preferably, each of the side chains S1 of the first block B1 of the copolymer BBCP contains at least one polymer moiety M1 containing at least one, preferably terminal, hydroxyl group, where the polymer moiety M1 is preferably selected from the group consisting of preferably aliphatic polyester moieties and preferably aliphatic polyether moieties, particularly representing a polylactide moiety, and further preferably, each of the side chains S2 of the second block B2 of the copolymer BBCP contains at least one polymer moiety M2 free of both hydroxyl and carboxylic acid groups, where the polymer moiety M2 is preferably selected from the group consisting of polyether, polysiloxane, and polystyrene moieties, particularly representing a polystyrene moiety.

[0113] Preferably, the first block B1 of the copolymer BBCP contains at least one structural unit SU1a and optionally at least one structural unit SU1b, where the structural unit SU1a is represented by at least one of the partial structures PS1a - 1 and PS1a - 2, and where the optionally present structural unit SU1b is represented by the partial structure PS1b, and all the structural units present in the first block are preferably randomly arranged within the first block B1 of the copolymer BBCP

[0114]

[0115] wherein independently of each other

[0116] the parameter x is in the range from 1 to 1000, preferably from 1 to 750, more preferably from 2 to 500, even more preferably from 3 to 300,

[0117] the parameter a is in the range from 0 to 1000, preferably from 1 to 750, more preferably from 2 to 500, even more preferably from 3 to 300,

[0118] the relative ratio of the parameter x:a is in the range from 1:0 to 1:3, preferably from 2:1 to 1:2,

[0119] Mx, J 1 and G independently of each other represent CH 2 or C=O,

[0120] Q represents a divalent alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl or heteroaryl residue,

[0121] Rx represents a side chain S1 containing a polymer part M1, preferably represents C 2 -C 6 -alkylene-O-[C(=O)-C 2 -C 6 -alkylene-O] n -H, where the parameter n ranges from 1 to 500, preferably from 1 to 300, and

[0122] R 1 represents C 1 -C 6 -alkyl residue, preferably an unbranched C 1 -C 6 -alkyl residue.

[0123] Preferably, the second block B2 of the copolymer BBCP contains at least one structural unit SU2a and optionally at least one structural unit SU2b, where the structural unit SU2a is represented by at least one of the partial structures PS2a-1 and PS2a-2, and where the optionally present structural unit SU2b is represented by the partial structure PS2b, and all the structural units present in the second block are preferably randomly arranged within the second block B2 of the copolymer BBCP

[0124]

[0125] where independently of each other

[0126] the parameter y ranges from 1 to 1000, preferably from 1 to 750, more preferably from 2 to 500, even more preferably from 3 to 300,

[0127] the parameter b ranges from 0 to 1000, preferably from 1 to 750, more preferably from 2 to 500, even more preferably from 3 to 300,

[0128] the relative ratio of the parameter y:b ranges from 1:0 to 1:3, preferably from 2:1 to 1:2,

[0129] My, J 2 and G independently of each other represent CH 2 or C=O,

[0130] Q represents a divalent alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl or heteroaryl residue,

[0131] Ry represents a side chain S2 containing a polymer part M2, preferably represents C 1 -C 8-alkylene-Z-T, where Z represents C(=O)-O or a divalent N-containing heterocyclic residue, and T represents C bonded to the polystyrene moiety 1 -C 4 -alkylene residue, and

[0132] R 2 represents C 1 -C 6 -alkyl residue, preferably branched C 1 -C 6 -alkyl residue.

[0133] Preferably, parameters a and b are each independently 1 - 300, 5 - 50, 50 - 100, 100 - 150, 150 - 200, 200 - 250, 250 - 300, 300 - 400, 400 - 500, 500 - 600, 600 - 700, 700 - 800, 800 - 900, or 900 - 1000. Preferably, x and y are each independently 1 - 300, 5 - 50, 50 - 100, 100 - 150, 150 - 200, 200 - 250, 250 - 300, 300 - 400, 400 - 500, 500 - 600, 600 - 700, 700 - 800, 800 - 900, or 900 - 1000. Preferably, the ratio of x:a is 1:0.5 to 1:1, 1:1.5, 1:2, or up to 1:2.5. Preferably, the ratio of y:b is 1:0.5 to 1:1, 1:1.5, 1:2, or up to 1:2.5.

[0134] Preferably, a + x + b + y is in the range of 100 to 500, more preferably 120 to 480, even more preferably 140 to 400, still more preferably 160 to 350, particularly 180 to 300.

[0135] The term "alkyl" refers to a branched or unbranched hydrocarbon having, for example, 1 to 20 carbon atoms, and typically 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms; or within the range of 1 to 20 carbon atoms (such as 2 to 6, 3 to 6, 2 to 8, or 3 to 8 carbon atoms). Examples include, but are not limited to, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl (isobutyl), 2-butyl (sec-butyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 3-methyl-3-pentyl, 2-methyl-3-pentyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, hexyl, octyl, decyl, and dodecyl. The alkyl can be unsubstituted or substituted. The term "heteroalkyl" is preferably understood to be an alkyl having at least one heteroatom selected from nitrogen, sulfur, oxygen, and / or at least one heteroatom-containing group as defined above. The term "cycloalkyl" preferably refers to a cyclic alkyl having 3 to 10 carbon atoms, for example, having a single ring or multiple fused rings. By way of example, cycloalkyl includes monocyclic structures such as cyclopropyl, cyclobutyl, cyclopentyl, cyclooctyl, or polycyclic structures such as adamantyl. The cycloalkyl can be unsubstituted or substituted. The cycloalkyl can be monovalent or divalent and can optionally be substituted as described for alkyl. The cycloalkyl can optionally contain one or more sites of unsaturation, for example, the cycloalkyl can contain one or more carbon-carbon double bonds. The term "heterocycloalkyl" preferably refers to a saturated or partially saturated monocyclic, bicyclic, or polycyclic ring containing at least one heteroatom selected from nitrogen, sulfur, oxygen, preferably 1 to 3 heteroatoms, in at least one ring. Each ring is preferably 3 to 10 membered, more preferably 4 to 7 membered. Examples of suitable heterocycloalkyl include pyrrolidinyl, tetrahydrofuranyl, tetrahydrothiophenyl, piperidinyl, piperazinyl, tetrahydropyranyl, morpholinyl, 1,3-diazepanyl, 1,4-diazepanyl, 1,4-oxazepanyl, and 1,4-oxathiepanyl. The group can be a terminal group or a bridging group. The term "aryl" preferably refers to an aromatic hydrocarbon group. The aryl can have 6 to 30 carbon atoms, for example, about 6 to 10 carbon atoms. Alternatively, the aryl can have 6 to 60 carbon atoms, 6 to 120 carbon atoms, or 6 to 240 carbon atoms. The aryl can have a single ring (e.g., phenyl) or multiple fused rings (fused rings), where at least one ring is aromatic (e.g., naphthyl, dihydrophenanthryl, fluorenyl, or anthryl). Typical aryls include, but are not limited to, groups derived from benzene, naphthalene, anthracene, and biphenyl. The aryl can be unsubstituted or optionally substituted.The term "heteroaryl" preferably refers to a monocyclic, bicyclic or tricyclic system containing one, two or three aromatic rings and containing at least one nitrogen, oxygen or sulfur atom and / or heteroatom-containing group in the aromatic ring. The heteroaryl may be unsubstituted or substituted by, for example, one or more, and particularly one to three substituents. Typical heteroaryls also contain 2-20 carbon atoms in the ring skeleton in addition to one or more heteroatoms. Examples of heteroaryls include, but are not limited to, 2H-pyrrolyl, 3H-indolyl, 4H-quinolizinyl, acridinyl, benzo[b]thienyl, benzothiazolyl, b-carbolinyl, carbazolyl, chromenyl, cinnolinyl, dibenzo[b,d]furanyl, furazanyl, furyl, imidazolyl, imidizolyl, indazolyl, indolizinyl, indolyl, isobenzofuranyl, isoindolyl, isoquinolyl, isothiazolyl, isoxazolyl, naphthyridinyl, oxazolyl, peridinyl, phenanthridinyl, phenanthrolinyl, phenarsazinyl, phenazinyl, phenothiazinyl, phenoxathiinyl, phenoxazinyl, phthalazinyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolyl, pyridazinyl, pyridyl, pyrimidinyl, pyrrolyl, quinazolinyl, quinolinyl, quinoxalinyl, thiadiazolyl, thianthrenyl, thiazolyl, thienyl, triazolyl, tetrazolyl and xanthenyl. Preferably, "heteroaryl" denotes a monocyclic aromatic ring containing five or six ring atoms, these ring atoms containing carbon and 1, 2, 3 or 4 heteroatoms independently selected from non-peroxide oxygen, sulfur and N(Z), where Z is absent or is H, O, alkyl, aryl or (C. 1 -C 6 ) alkylaryl. The heteroaryl may also denote an ortho-fused bicyclic heterocycle having about eight to ten ring atoms derived therefrom, particularly a benzo derivative or a derivative derived by fusing propylene, trimethylene or tetramethylene diyl thereto. As used herein, the term "substituted" or "substituent" preferably means that one or more (e.g., 1-20, or 1-10, or 1, 2, 3, 4 or 5, or 1, 2 or 3, or 1 or 2) hydrogens on the group indicated in the expression "substituted" (or "substituent") are replaced by an option from the indicated group or a suitable group known to those skilled in the art, provided that the normal valence of the indicated atom is not exceeded and the substitution results in a stable compound. Suitable indicated groups include, for example, alkyl, alkenyl, alkynyl, alkoxy, halo, haloalkyl, hydroxy, hydroxyalkyl, aryl, heteroaryl, heterocyclic, cycloalkyl, alkanoyl, alkoxycarbonyl, amino, alkylamino, dialkylamino, trifluoromethylthio, difluoromethyl, acylamino, nitro, trifluoromethyl, trifluoromethoxy, carboxyl, carboxyalkyl, keto, thio, alkylthio, alkanesulfinyl, alkylsulfonyl, and cyano. Additionally, non-limiting examples of substituents that can be bonded to a substituted carbon (or other) atom include F, Cl, Br, I, OR', OC(=O)N(R') 2 , CN, CF3 , OCF 3 , R’, O, S, C(=0), methylenedioxy, ethylenedioxy, N(R') 2 , SR’, SOR', SO 2 R', SO 2 N(R’) 2 , SO 3 R', C(=O)R’, C(=O)C(=O)R', C(=O)CH 2 C(=O)R', C(=S)R’, C(=O)OR’, OC(=O)R’, C(=O)N(R') 2 , OC(=O)N(R') 2 , C(=S)N(R’) 2 , (CH 2 ) 0-2 NHC(=O)R', N(R')N(R')C(=O)R', N(R')N(R’)C(=O)OR’, N(R’)N(R’)CON(R’) 2 , N(R’)SO 2 R’, N(R')SO 2 N(R’) 2 , N(R')C(=O)OR', N(R')C(=O)R', N(R’)C(S)R’, N(R’)C(=O)N(R') 2 , N(R')C(S)N(R') 2 , N(COR’)COR’, N(OR’)R’, C(=NH)N(R') 2 , C(=O)N(OR’)R', or C(=NOR’)R’, where R’ can be hydrogen or a carbon-based moiety.

[0136] Since the backbone of the copolymer BBCP preferably contains ethylenically unsaturated carbon-carbon double bonds, the structural units present in each block are preferably covalently linked in such a way that each unit is connected to another unit via a carbon-carbon double bond. In the case where the copolymer BBCP is linear, it further preferably contains two end groups, which is preferred. Each of these end groups is covalently bonded to a structural unit. The end groups of the copolymer (i.e., the initiator end or the terminus) are preferably low molecular weight moieties (e.g., below 500 Da) such as H, OH, COOH, CH 2 OH, CN, NH 2 , or a hydrocarbon such as an alkyl (e.g., butyl or 2-cyanopropan-2-yl moieties at the initiator end and the terminus), an alkene or an alkyne, or a moiety resulting from an elimination reaction at the first and / or last repeating unit in the copolymer.

[0137] Preferably, the block copolymer BBCP is a brush block copolymer. The brush block copolymer comprises a main chain (backbone) having straight-chain, unbranched side chains. Brushes are typically characterized by a high density of graft chains. Thereby, the limited space results in strong extension of the side chains.

[0138] Preferably, the first block B1 of the copolymer BBCP comprises at least one structural unit SU1a represented by at least the partial structure PS1a-1, and further comprises at least one structural unit SU1b represented by the partial structure PS1b, and the second block B2 of the copolymer BBCP comprises at least one structural unit SU2a represented by at least the partial structure PS2a-1, and further comprises at least one structural unit SU2b represented by the partial structure PS1b,

[0139] wherein independently of each other

[0140] the parameter x is in the range from 2 to 500, preferably from 3 to 300,

[0141] the parameter a is in the range from 2 to 500, preferably from 3 to 300,

[0142] the relative ratio of the parameter x:a is in the range from 2:1 to 1:2, preferably from 1.5:1 to 1:1.5,

[0143] the parameter y is in the range from 2 to 500, preferably from 3 to 300,

[0144] the parameter b is in the range from 2 to 500, preferably from 3 to 300,

[0145] the relative ratio of the parameter y:b is in the range from 2:1 to 1:2, preferably from 1.5:1 to 1:1.5, and the remaining residues and variables have one or more of the meanings defined above.

[0146] Preferably, the coating composition comprising at least one block copolymer BBCP for preparing the second coating L2 further comprises at least one preferably straight-chain homopolymer, more preferably at least one selected from polyester, poly(meth)acrylate, polyether, polysiloxane and polystyrene homopolymers, still more preferably selected from polystyrene, polyether and polyester homopolymers and mixtures thereof, even more preferably selected from polystyrene and aliphatic polyesters such as polylactide homopolymers and mixtures thereof, wherein the number-average molecular weight (M n ) is preferably higher than the number-average molecular weight (M n) at least 100 times lower, preferably at least 150 times lower, more preferably at least 175 times lower, and wherein preferably, the relative weight ratio of BBCP copolymer solids to at least one homopolymer solid in the coating composition is in the range of 99:1 to 5:95, more preferably 95:5 to 10:90, even more preferably 90:10 to 15:85, still more preferably 85:15 to 20:80, yet more preferably 75:25 to 25:75, particularly 60:40 to 30:70. Methods for measuring the number-average molecular weight (M n ) and for measuring the weight-average molecular weight (M w ) and the polydispersity index (PDI) are described in the 'Methods' section below.

[0147] Methods for preparing such homopolymers are disclosed, for example, in WO 2020 / 160299 A1 (pages 25 / 26, Example 1) and WO 2020 / 180427 A1 (pages 25 / 26, Example 1).

[0148] Preferably, at least one homopolymer is present in the second primer coating composition in an amount in the range of 0 to 90 wt.-%, preferably 20 to 80 wt.-%, more preferably 40 to 60 wt.-%, particularly 30 to 70 wt.-% in each case based on the total solids content of the second primer coating composition.

[0149] Preferably, the relative weight ratio of BBCP copolymer solids to the at least one homopolymer solid in the second primer coating composition is in the range of 99:1 to 5:95, preferably 95:5 to 10:90, more preferably 90:10 to 15:85, even more preferably 85:15 to 20:80, yet more preferably 75:25 to 25:75, particularly 60:40 to 30:70.

[0150] Preferably, in addition to the copolymer BBCP and in addition to at least one homopolymer as defined above (if such a homopolymer is present), the coating composition comprising at least one block copolymer BBCP for preparing the second coating L2 further comprises at least one additional resin, more preferably at least one polymeric resin, wherein the relative weight ratio of BBCP copolymer solids to the solids of at least one additional resin in the coating composition is preferably in the range of 5:95 to 100:0, more preferably 10:90 to 100:0, even more preferably 15:85 to 95:5, still more preferably 20:80 to 90:10, yet more preferably 25:75 to 85:15, particularly 30:70 to 80:20, most preferably 40:60 to 80:20.

[0151] Preferably, in addition to the copolymer BBCP and in addition to at least one homopolymer as defined above (if such a homopolymer is present), a coating composition comprising at least one block copolymer BBCP for preparing the second coating L2, wherein the relative weight ratio of the sum of the BBCP copolymer solids and the homopolymer solids (if present) in the topcoat composition to the solids of at least one additional resin is preferably in the range of 40:60 to 100:0, more preferably 45:55 to 100:0, even more preferably 50:50 to 95:5, still more preferably 55:45 to 90:10, yet more preferably 60:40 to 85:15.

[0152] Binder

[0153] In addition to the copolymer BBCP and in addition to at least one homopolymer present, at least one additional resin, preferably at least one polymeric resin, optionally present in the second primer composition preferably acts as at least one binder (b1). The same binder comprising the crosslinker (i.e., crosslinking agent) described above in connection with component (a1) and below in connection with component (c1) can also be used as component (b1). The optionally present at least one polymeric component (b1) is of course different from the copolymer BBCP and the above-mentioned homopolymer.

[0154] Coating L3 and coating composition for forming said layer

[0155] The third coating L3 is applied on the second coating L2. Thus, the third coating L3 is preferably located above the coating L2 and in direct contact with the layer L2.

[0156] Preferably, the third coating L3 is a transparent coating formed from a coating composition which is a transparent coating composition, preferably a solvent-based transparent coating composition, wherein the third coating L3 is preferably the outermost coating of a multilayer coating system. This coating composition is also referred to herein as the topcoat composition and is the composition used in step (3) of the process of the present invention.

[0157] The topcoat composition can be an aqueous (i.e., water-based) coating composition. It can alternatively be a solvent-based primer composition. In particular, it is in fact a solvent-based transparent coating composition. The topcoat composition can be a 1K (one-component) or 2K (two-component) composition.

[0158] Preferably, the total solids content of the topcoat composition is in the range of 10 to 65 wt.-%, more preferably 15 to 60 wt.-%, even more preferably 20 to 50 wt.-%, particularly 25 to 45 wt.-% in each case based on the total weight of the topcoat composition.

[0159] The topcoat composition preferably comprises at least one binder, more preferably at least one polymer (c1) as the binder. The same binder including the crosslinking agent described above in connection with components (a1) and (b1) can also be used as component (c1).

[0160] Preferably, the topcoat composition comprises at least one polymer (c1) having on average two or more OH-groups and / or amino groups and / or urethane groups, more preferably OH-groups and / or urethane groups. Preferably, the at least one preferably at least OH- and / or urethane-functional polymer (c1) has a weight-average molecular weight M measured by gel permeation chromatography (GPC) against polystyrene standards, preferably between 800 and 100,000 g / mol, more particularly between 1000 and 75,000 g / mol. w 。

[0161] If the topcoat composition is formulated as a 2K coating composition, it preferably contains (as at least one additional polymer (c1) present therein) at least one polyisocyanate having free NCO-groups as the crosslinking agent. If the topcoat composition is formulated as a 1K coating composition, it preferably contains (as at least one additional polymer (c1) present therein) at least one polyisocyanate having blocked NCO-groups and / or at least one melamine formaldehyde resin as the crosslinking agent.

[0162] Suitable component (c1) used as a crosslinking agent is an organic component having on average two or more NCO-groups. At least one organic component used as a crosslinking agent preferably has an alicyclic structure and / or a parent structure derived from an alicyclic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation. Alternatively or additionally, at least one organic component used as a crosslinking agent preferably has an acyclic aliphatic structure and / or a parent structure derived from an acyclic aliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation. The acyclic aliphatic polyisocyanate - optionally serving as the parent structure - is preferably a known substituted or unsubstituted aliphatic polyisocyanate. Examples are tetramethylene 1,4-diisocyanate, hexamethylene 1,6-diisocyanate, 2,2,4-trimethylhexane 1,6-diisocyanate, ethylene diisocyanate, dodecane 1,12-diisocyanate and mixtures of the above polyisocyanates. The alicyclic polyisocyanate - optionally serving as the parent structure - is preferably a known substituted or unsubstituted alicyclic polyisocyanate. Examples of preferred polyisocyanates are isophorone diisocyanate, cyclobutane 1,3-diisocyanate, cyclohexane 1,3-diisocyanate, cyclohexane 1,4-diisocyanate, methylcyclohexyl diisocyanate, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2,6-diisocyanate, hexahydro-phenylene 1,3-diisocyanate, hexahydro-phenylene 1,4-diisocyanate, perhydrodiphenylmethane 2,4'-diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate) (e.g., W) and mixtures of the above polyisocyanates. The above-mentioned organic components having on average two or more NCO-groups can also be partially silanized. Such silanized crosslinking agents are disclosed, for example, in WO 2010 / 063332 A1, WO2010 / 139375 A1 and WO 2009 / 077181 A1.

[0163] Especially in the case where the topcoat composition is formulated as a 1K coating composition, a suitable component (c1) used as a crosslinking agent is a melamine formaldehyde resin. The same melamine formaldehyde resins as already discussed above in connection with component (a1) can be used.

[0164] Preferably, the topcoat composition 3) does not contain a copolymer (BBCP) as present in the second primer composition.

[0165] The topcoat composition can be uncolored. However, even when the topcoat composition is formulated as a clearcoat composition, it can alternatively contain coloring and / or effect pigments, preferably coloring pigments, in an amount that does not interfere with the desired transparency of the cured clearcoat. For example, the clearcoat composition can contain at least one coloring pigment in each case up to 7.5 wt.-%, preferably up to 5.0 wt.-%, more preferably up to 2.5 wt.-%, still more preferably up to 1.5 wt.-%, based on the total solids content of the clearcoat composition. This also applies to fillers optionally present within the clearcoat composition. However, preferably, the clearcoat composition is free of pigments and / or fillers.

[0166] In Figure 1 illustrated is a multilayer coating system of the present invention comprising layers L1, L2, and L3, which is located on top of a substrate S precoated with a primer P.

[0167] Method of the present invention

[0168] The method of the present invention is a method for preparing the multilayer coating system of the present invention on an optionally precoated substrate, which method comprises at least steps (1), (2), (3), and (4).

[0169] The method of the present invention is applicable to both automotive OEM and refinish applications, and is particularly applicable to automotive OEM applications.

[0170] Preferably, each of steps (1) to (3) is carried out by spray application.

[0171] At least the second and third coating films, but optionally also the first coating film, at this stage - after carrying out the corresponding one or more steps - are preferably each an uncured coating film. Thus, the coating composition applied at least in step (3) is preferably applied wet-on-wet to the second coating film obtained after carrying out step (2). If only the resulting second and third coating films are cured together, the first coating film applied in step (1) is cured before carrying out step (2). However, alternatively, the coating composition applied in step (2) is also preferably applied wet-on-wet to the first coating film obtained after carrying out step (1). In this case, when carrying out step (2), the first coating film is still an uncured coating film. If the resulting first, second, and third coating films are cured together in step (4), the method of the present invention is a wet-on-wet-on-wet method.

[0172] Step (1)

[0173] According to step (1), a first primer coating composition comprising at least one flaky pigment is applied to at least a part of an optionally pre-coated substrate and a first coating film is formed on at least a part of the optionally pre-coated substrate. The primer coating composition for step (1) of the method of the present invention is also referred to as the "first primer coating composition".

[0174] Optional step (1a)

[0175] Preferably, the method of the present invention further comprises step (1a), which is carried out after step (1) and before step (2). In said step (1a), before applying the second primer coating composition in step (2), the first coating film obtained after step (1) is flash dried, preferably for a period of 1 to 20 minutes, more preferably for a period of 2 to 15 minutes, particularly for a period of 5 to 10 minutes. Preferably, step (1a) is carried out at a temperature not exceeding 80°C, more preferably at a temperature in the range of 30°C to 60°C.

[0176] In the context of the present invention, the term "flash drying" preferably means at least partially "drying", wherein at least some of the solvents (water and / or one or more organic solvents) are evaporated from the coating film before applying the next coating composition and / or carrying out curing. Preferably, curing is not carried out by flash drying or at least not completely cured.

[0177] Optional step (1b)

[0178] Preferably, the method of the present invention further comprises step (1b), which is carried out after step (1) or step (1a) and before step (2). In said step (1b), before applying the second primer coating composition in step (2), the first coating film obtained after step (1) or (1a) is cured. The same curing conditions as outlined in detail below in connection with step (4) can be used / applied.

[0179] Preferably, step (1a) and / or (1b) is carried out. More preferably, at least step (1b) is carried out such that the second primer coating composition applied in step (2) is applied to the cured first coating film.

[0180] Step (2)

[0181] According to step (2), a second primer coating composition comprising at least one block copolymer BBCP and different from the primer coating composition applied in step (1) is applied to the first coating film present on the substrate obtained after step (1) and a second coating film is formed, preferably adjacent to the first coating film.

[0182] Step (2) can be carried out before curing the first coating film obtained after step (1). Alternatively and preferably, step (2) is carried out after curing the first coating film obtained after step (1), i.e., after at least carrying out the optional step (1b).

[0183] Optional step (2a)

[0184] Preferably, the method of the present invention further comprises step (2a), which is carried out after step (2) and before step (3). In said step (2a), before applying the topcoat composition in step (3), the second coating film obtained after step (2) is flash-evaporated, preferably for a period of 1 to 20 minutes, more preferably for a period of 2 to 15 minutes, particularly for a period of 5 to 10 minutes. Preferably, step (2a) is carried out at a temperature not exceeding 40 °C, more preferably in the temperature range of 18 °C to 30 °C.

[0185] Step (3)

[0186] According to step (3), a coating composition different from the compositions applied in steps (1) and (2) is applied to the second coating film present on the substrate obtained after step (2), and a third coating film is formed, preferably adjacent to the second coating film, wherein said coating composition is a topcoat composition and preferably a transparent coating composition.

[0187] Preferably, the third coating film obtained after step (3) is the outermost film of the formed multilayer coating system.

[0188] Optional step (3a)

[0189] Preferably, the method of the present invention further comprises step (3a), which is carried out after step (3) and before step (4). In said step (3a), before carrying out the curing step (4), the third coating film obtained after step (3) is flash-evaporated, preferably for a period of 1 to 20 minutes, more preferably for a period of 2 to 15 minutes, particularly for a period of 5 to 10 minutes. Preferably, step (3a) is carried out at a temperature not exceeding 40 °C, more preferably in the temperature range of 18 °C to 30 °C.

[0190] Step (4)

[0191] According to step (4), the at least second and third coating films applied in steps (2) and (3), and optionally also the first coating film, while the first coating film applied in step (1) is uncured before performing step (2), are co-cured, i.e., cured simultaneously, to obtain a multi-layer coating system comprising at least the first, second, and third coatings L1, L2, and L3. Each resulting cured coating film represents a coating.

[0192] Preferably, step (4) is carried out at a temperature below 180 °C, preferably below 160 °C, more preferably below 150 °C, particularly at a temperature in the range of 15 °C to <180 °C or 15 °C to <160 °C for a period of 5 to 45 minutes, preferably 20 to 45 minutes, particularly 25 to 35 minutes. However, preferably, the minimum curing temperature applied in step (4) is at least 80 °C. In this case, the curing according to step (4) is preferably carried out at a temperature in the range of 80 °C to <180 °C or 80 °C to <160 °C.

[0193] Preferably, the curing according to step (4) is selected from chemical curing (such as chemical crosslinking, radiation curing), and / or physical drying (non-chemical curing), in each case at room temperature or at elevated temperature, more preferably selected from chemical curing (such as chemical crosslinking), and / or physical drying (non-chemical curing), in each case at room temperature or at elevated temperature, in each case preferably where the minimum curing temperature applied in step (4) is at least 80 °C.

[0194] Coated substrate of the present invention

[0195] Another subject of the present invention is a coated substrate obtainable by the method of the present invention.

[0196] All preferred embodiments described above in connection with the method of the present invention and the multi-layer coating system of the present invention are also preferred embodiments with respect to the above-described coated substrate of the present invention.

[0197] Method

[0198] 1. Determination of non-volatile content

[0199] The amount of the solid content (non-volatile matter, solid fraction), including the total solid content, is determined by DIN EN ISO 3251:2019-09 at 110 °C for 60 min.

[0200] 2. M n , M w and measurement of PDI

[0201] Polymer molecular weight (number-average molecular weight (M n ) and weight-average molecular weight (M W)) and molecular weight distribution (PDI; polydispersity index) were determined by gel permeation chromatography (GPC) using a combination of differential refractive index (dRI) and two light scattering (LS) detectors. The use of LS detectors enables the analysis of the absolute molecular weight of polymer samples. The solvent for all samples was tetrahydrofuran (THF) with an elution rate of 1.0 mL / min. The polymer samples were completely dissolved in HPLC grade THF at a concentration ranging from 2.5 - 7.5 mg / mL, passed through a 0.5 μm syringe filter, and injected via an autosampler. The porous column stationary phase consisted of two Malvern T600 monolithic columns with an exclusion limit of 20,000,000 Da for poly(styrene). The molecular weight and PDI were determined by OMNISEC software.

[0202] 3. Determination of L*, a*, b*, C* and h values

[0203] Color data for the three - layer coatings were determined by using a Byk Mac i instrument (from Byk Gardner GmbH, Germany). The illumination was D65 illumination (observer angle 10°). The multi - angle (viewing angles: - 15°, + 15°, + 25°, + 45°, + 75°, + 110°) measurement geometry is shown in Figure 2 The 110° angle is also referred to as the "flop angle".

[0204] Using the above - mentioned instrument, the L*, a*, and b* values of the two - layer and three - layer coatings were determined. C* was calculated using the following equation: C*=(a 2 +b 2 ) 0.5 and h = arctan(b / a).

[0205] The CIELAB formula defines a color space characterized by an a* axis ranging from green to red, a b* axis extending from blue to yellow, and a luminance axis L* perpendicular to the other two axes. Negative values of b* mean the color is slightly blue, while positive values of b* represent more slightly yellowish colors. High values of L* (i.e., luminance) represent lighter colors, while low values of L* represent darker colors.

[0206] 4. Determination of dry layer thickness of the coating

[0207] The dry - layer thickness of the coatings of the present invention was determined by using an Elcometer such as the Fischer Dualscope FMP20C.

[0208] Examples

[0209] The following examples further illustrate the present invention but should not be construed as limiting its scope. 'Pbw' means parts by weight. If not otherwise defined, 'parts' means 'parts by weight', and if not otherwise indicated, all 'percentage' values are in 'wt-%'.

[0210] Preparation of the copolymer used in the present invention

[0211] Under an inert atmosphere, norbornene-functionalized poly(lactide) macromonomer (PLA-MM) (29.14 mmol, having an M of 3.26 kDa) in dichloromethane and d,x-DME (dimethyl 5-norbornene-2,3-dicarboxylate, where d = endo and x = exo) were added in equimolar amounts to a 2000 mL container. PLA-MM was pre-prepared by tin-catalyzed ring-opening polymerization of lactide using a norbornenol initiator, thereby producing an OH-functional and norbornene-functionalized poly(lactide) macromonomer PLA-MM. PLA-MM was prepared in a general manner as described in the supporting information of B.R. n et al., PNAS [Proceedings of the National Academy of Sciences of the United States of America] 2012, 109(36), pp. 14332-14336. Then, a bis-bipyridine ruthenium catalyst was rapidly added to the mixture of PLA-MM and d,x-DME to initiate copolymerization, with the aim of PLA -r-DME 100 -r-DME 100 . "r" means that the two monomer units PLA and DME are randomly arranged. The mixture was stirred at room temperature for 45 minutes (first block mixture). In a separate container, under an inert atmosphere, norbornene-functionalized polystyrene macromonomer (PS-MM; having an M of 3.83 kDa) was prepared in dichloromethane n) and a solution of d,x-DIPE (diisopropyl 5-norbornene-2,3-dicarboxylate, where d = endo and x = exo) (second block mixture). PS-MM was prepared beforehand in a general manner described in Example 2 of WO 2020 / 180427 A1 in two steps: The OH-functionalized polymerization precursor of PS-MM was prepared by polymerizing styrene in toluene with sec-butyllithium as the initiator. After chain termination by adding propylene oxide and then methanol, quenching was carried out. Then, the terminal OH-groups of the formed precursor were converted into ester bonds via reaction with norbornene carboxylic acid to produce PS-MM. The solution of PS-MM and d,-DIPE was rapidly added to the first block reaction mixture. The two monomer units PS and DIPE are randomly arranged within the formed second block of the copolymer. The resulting mixture was stirred at room temperature for another 4 h and then quenched by adding ethyl vinyl ether. Then, a functionalized silica absorbent was used to scavenge the quenched catalyst, and it was stirred for about 4 h. The mixture was filtered, and the solution was concentrated under reduced pressure. A solid copolymer was obtained after removing the solvent. It was dried in a vacuum oven at 75 °C for 4 hours to remove residual solvent. The obtained product (BBCP1) was used in this form.

[0212] BBCP1 has a number-average molecular weight (M n ) of 788.3 kDa and a weight-average molecular weight (M w ) of 865.7 kDa. Thus, the polydispersity index (PDI) is 1.10.

[0213] Preparation of the coating composition

[0214] To illustrate the unique color characteristics of the brush block copolymer and to give a non-limiting example of the color space possibilities achievable with the brush block copolymer, three different colors were produced by laminating a second primer layer containing the brush block copolymer on three different first primer layers (given as A, B, and C) made of conventional pigments and effect pigments. The combination of a metallic or pearlescent effect coating laminated with the brush block copolymer layer produced unique and aesthetically pleasing colors.

[0215] First primer composition according to the present invention

[0216] The first primer coating compositions A, B, and C used as in the present invention (step lamination of the present invention) are waterborne one-component compositions, each containing a combination of the following flaky interference pigments and carbon black pigment paste:

[0217] · Flaky titanium dioxide-coated silica effect pigment (Colorstream T20-04 WNT LapisSunlight); or

[0218] · Aluminum pigments coated with sheet-like organic blue pigments (Friend Color D462 BL); or

[0219] · Non-fluorinated mica effect pigments coated with sheet-like titanium dioxide (Pyrisma T81-23 SW Liquid Blue)

[0220] The exact composition is shown in Table 2.

[0221] Second primer composition according to the present invention

[0222] To produce the colors of the present invention, the first primer compositions A, B, and C are each coated with a second primer composition D containing a brush block copolymer.

[0223] The second primer composition is obtained by preparing a solution of 1.50 g of BBCP1, 0.75 g of polystyrene homopolymer (PS-HP), 0.75 g of poly(lactide) homopolymer (PLA-HP), and 7 g of n-butyl acetate. The relative weight ratio of BBCP1 solids to the combined solids of PS-HP and PLA-HP in BC3 is 50:50.

[0224] Third coating composition (transparent coating) according to the present invention

[0225] As a transparent coating, a commercial high-solid transparent coating (R10CG392D; from BASF Corp. USA) is used.

[0226] Comparative second primer composition

[0227] To illustrate the unique color space obtained by the above lamination, a separate set of control experiments was conducted, in which the first primer compositions A, B, and C of the present invention were coated with a second primer composition E of the present invention containing conventional pigments (see Table 4) to attempt to match the color space as closely as possible.

[0228] In this scheme, (A + D), (B + D), and (C + D) each plus the transparent coating of the present invention are compared with the comparative colors produced by (A + E), (B + E), and (C + E) each plus the transparent coating of the present invention.

[0229] Additional comparative examples

[0230] In addition, another set of control experiments was carried out, thereby attempting to match the color space of the present invention by using various combinations of conventional pigments and effect pigments. Comparative compositions F, G, and H (see Table 3) are waterborne one-component compositions, each of which contains a combination of flaky effect pigments and non-flaky organic and inorganic pigments, the latter being incorporated into the composition in the form of a pigment paste, as described in Table 1.

[0231] Coating compositions F, G, and H represent an attempt to match the color characteristics of three multilayer coating compositions of the present invention, which are derived from using the first primer coating compositions A, B, and C of the present invention laminated with the second primer coating composition D of the present invention.

[0232] Coating compositions F, G, and H are non-covering compositions applied over a black primer and respectively attempt to match the colors of (A + D), (B + D), and (C + D). In this scheme, (A + D), (B + D), and (C + D) are respectively compared with the comparative colors produced by (black primer + F), (black primer + G), and (black primer + H). The composition of the black primer is not particularly limited, and several grades can be used. The lightness value L* of the black primer used in the examples is 8.

[0233] In all additional comparative examples, a transparent coating of the present invention is also applied as the topcoat.

[0234] The components of compositions A, B, C, E, F, G, and H are shown in Tables 1 to 4.

[0235] Application of multilayer coating (two-layer and three-layer coating) films

[0236] The first primer coating compositions A, B, C of the present invention and the comparative primer coating compositions F, G, and H are applied to the baked primer layer by pneumatic manual application to form a primer coating with a dry layer thickness of approximately 20 μm (primer coating L1, i.e., L1(A), L1(B), and L1(C) respectively formed by primer coating compositions A, B, and C) and a coating with a thickness of approximately 18 μm (coatings F and G respectively formed by primer coating compositions F and G) and a coating with a thickness of approximately 14 μm (coating H formed by coating composition H).

[0237] In a set of examples, on top of the primer coats L1(A), L1(B), and L1(C), after a flash-off of 1 to 3 minutes, it is applied pneumatically by hand in a wet-on-wet manner, and a second primer coat composition D is applied on top of the primer coats L1(A), L1(B), and L1(C) respectively to form layer L2(D). After a flash-off of 1 to 3 minutes, a second primer coat composition E that is not of the present invention is applied by pneumatic hand application to form a second primer coat E. The dry film thickness of the second primer coat L2(D) of the present invention is about 12 μm, and the dry film thickness of the second primer coat E that is not of the present invention is 5 μm.

[0238] In another set of examples, there is no second primer coat applied on top of the first primer coats F, G, and H that are not of the present invention.

[0239] Subsequently, after a heat (63 °C) flash-off of 3 to 5 minutes, a one-component clear coat composition is applied pneumatically by hand. The clear coat is a one-component polyurethane paint (applied to a dry film thickness of about 40 - 55 μm).

[0240] The panel thus coated is flash-off for 5 to 10 minutes and then cured at 130 °C for 25 minutes.

[0241] Table 1 - Pigment pastes PP1 to PP9

[0242]

[0243]

[0244] 1 Acrylic dispersant resin A: Prepared according to lines 41 on page 12 to line 4 on page 13 of EP 0569907 B1.

[0245] 2 Acrylic dispersant resin B: Prepared according to lines 10 - 21 on page 7 and lines 3 - 16 on page 8 of EP 0589340 B1.

[0246] 3 PU dispersion C: Prepared according to lines 24 - 41 and lines 45 - 47 on page 6 of EP 0574417 B2.

[0247] 4 PU dispersion D: Prepared according to lines 11 - 28 on page 9 of EP 0521928 B1.

[0248]

[0249]

[0250]

[0251] Result

[0252] Three-layer coating ([L1(A)] - [L2(D) or E] - [transparent coating]) and

[0253] Two-layer coating ([F] - [transparent coating])

[0254] In Tables 5-1 and 5-2, three multilayer coatings were compared. The first was of the present invention and utilized the first primer composition A to form the first primer coat L1(A), and subsequently the second primer composition D of the present invention containing a brush block copolymer to form the second primer coat L2(D), and subsequently a transparent coating composition to form the layer L3. The second multilayer coating not of the present invention utilized the first primer composition A to form the first primer coat L1(A), and subsequently a second primer composition E not of the present invention colored with a non-flaky organic pigment paste to form the second primer coat, and subsequently a transparent coating composition to form the top coat. The third multilayer coating utilized only one primer composition F to form a primer coat, and subsequently a transparent coating composition to form the top coat. The data in Tables 5-1 and 5-2 show the innovative color space of the multilayer compositions of the present invention compared to compositions not of the present invention.

[0255] Table 5-1

[0256]

[0257] In the near off-specular range (-15° to +15° angle), there are significant differences in the color positions of the multilayer coatings of the present invention, which cannot be achieved using conventional traditional pigments, whether laminated with a colored primer composition or composition F.

[0258] Table 5-2

[0259]

[0260] Three-layer coating ([L1(B)] - [L2(D) or E] - [transparent coating]) and

[0261] Two-layer coating ([G] - [transparent coating])

[0262] In Tables 6-1 and 6-2, three multi-layer coatings are compared. The first is of the present invention and uses the first primer composition B to form the first primer coat L1(B), then uses the second primer composition D of the present invention containing a brush block copolymer to form the second primer coat L2(D), and then uses a transparent coating composition to form layer L3. The second multi-layer coating not of the present invention uses the first primer composition B to form the first primer coat L1(B), then uses the second primer composition E not of the present invention colored with a non-flaky organic pigment paste to form the second primer coat, and then uses a transparent coating composition to form the top coat. The third multi-layer coating uses only one primer composition G to form a primer coat and then uses a transparent coating composition to form the top coat. The data in Tables 6-1 and 6-2 show the innovative color space of the multi-layer composition of the present invention compared to the compositions not of the present invention.

[0263] Table 6-1

[0264]

[0265]

[0266] In the near off-specular range (-15° to +15° angle), there are significant differences in the color positions of the multi-layer coatings of the present invention, which cannot be achieved using conventional traditional pigments, whether laminated with a colored primer composition or composition G.

[0267] Table 6-2

[0268]

[0269] Three-layer coating ([L1(C)] - [L2(D) or E] - [transparent coating]) and

[0270] Two-layer coating ([H] - [transparent coating])

[0271] In Tables 7-1 and 7-2, three multi-layer coatings are compared. The first is of the present invention and uses the first primer composition C to form the first primer coat L1(C), then uses the second primer composition D of the present invention containing a brush block copolymer to form the second primer coat L2(D), and then uses a transparent coating composition to form layer L3. The second multi-layer coating not of the present invention uses the first primer composition B to form the first primer coat L1(C), then uses the second primer composition E not of the present invention colored with a non-flaky organic pigment paste to form the second primer coat, and then uses a transparent coating composition to form the top coat. The third multi-layer coating uses only one primer composition H to form a primer coat and then uses a transparent coating composition to form the top coat. The data in Tables 7-1 and 7-2 show the innovative color space of the multi-layer composition of the present invention compared to the compositions not of the present invention.

[0272] Table 7-1

[0273]

[0274] In the near-deviation mirror range (-15° to +15° angle), there are significant differences in the color position of the multi-layer coating of the present invention, which cannot be achieved using conventional traditional pigments, whether laminated with a colored undercoat composition or composition H.

[0275] Table 7-2

[0276]

Claims

1. A multi-layer coating system which is present on an optionally pre-coated substrate and comprises at least three mutually different coatings L1, L2 and L3, namely a first coating L1 containing at least one flaky pigment, applied to at least a part of the optionally pre-coated substrate, a second coating L2 applied on the first coating L1, and a third top coating L3 applied on the second coating L2, characterized in that the second coating L2 is formed from a coating composition containing at least one block copolymer, the block copolymer containing a backbone and at least two mutually different blocks B1 and B2, wherein block B1 contains at least one side chain S1 attached to the backbone and block B2 contains at least one side chain S2 different from side chain S1 attached to the backbone, wherein each of the side chains S1 contains at least one polymer moiety M1 selected from the group consisting of polyester, polyether and poly(meth)acrylate moieties, and each of the side chains S2 contains at least one polymer moiety M2 different from polymer moiety M1 and selected from the group consisting of: polyester, poly(meth)acrylate, polyether, polysiloxane and polystyrene moieties.

2. The multi-layer coating system according to claim 1, characterized in that the at least one flaky pigment is selected from the group consisting of metallic effect pigments and special effect pigments.

3. The multi-layer coating system according to claim 3, characterized in that the metallic effect pigments are selected from the group consisting of coated and uncoated metals and alloys; and characterized in that the special effect pigments are selected from the group consisting of pearlescent pigments and interference pigments.

4. The multi-layer coating system according to claim 2 or 3, characterized in that the metallic effect pigments are surface-modified or un-surface-modified and are selected from the group consisting of aluminum flakes, zinc-copper flakes, copper flakes, nickel flakes or steel flakes; and characterized in that These special effect pigments are selected from the group consisting of: flakes selected from the group consisting of mica, silica, alumina, glass, and borosilicate, said flakes being coated with one or more of rutile, anatase, ZrO 2 、SnO 2 、SiO 2 、FeOOH、Fe 2 O 3 、Cr 2 O 3 、TiO 2-x 、TiO x N y 、KFe[Fe(CN) 6 and a colorant coating; and flakes selected from the group consisting of substrate-free pearlescent pigments such as natural pearl essence, basic lead carbonate, bismuth oxychloride, iron oxide mica and titanium dioxide flakes.

5. The multi-layer coating system according to any one or more of the preceding claims, characterized in that These flaky pigments have a number-average flake thickness h in the range of 30 nm to 1 μm 50 , a median flake diameter D in the range of 5 μm to 40 μm 50 , and an average aspect ratio D 50 / h 50 in the range of about 5:1 to about 1300:1, where D 50 is the volume-based median particle size as determined by laser diffraction spectrometry, and h 50 is the average particle thickness as determined by electron microscopy.

6. The multi-layer coating system according to any one of the preceding claims, characterized in that it further contains non-flaky visible light absorbing pigments, preferably organic or inorganic black pigments.

7. The multi-layer coating system according to claim 1 or 2, characterized in that the at least one flaky pigment contained in the first coating L1 is capable of reflecting at least those wavelengths not reflected by the second layer L2.

8. The multi-layer coating system according to one or more of the preceding claims, characterized in that the third coating L3 is formed from a coating composition which is a transparent coating composition, preferably a solvent-based transparent coating composition, wherein the third coating L3 is preferably the outermost coating of the multi-layer coating system.

9. The multi-layer coating system according to one or more of the preceding claims, characterized in that At least the first, second, and third coatings L1, L2, and L3 are positioned adjacent to each other, and are characterized in that coatings L2 and L3 are at least partially transparent to visible light.

10. The multilayer coating system according to one or more of the preceding claims, characterized in that, the multilayer coating system can be obtained by a method according to which at least the applied coating composition for preparing the second coating L2 containing the at least one block copolymer and the applied coating composition for preparing the third coating L3 are co-cured to obtain the second and third coatings L2 and L3 of the multilayer coating system, wherein the curing is preferably selected from chemical curing such as chemical crosslinking, radiation curing, and / or physical drying (non-chemical curing), in each case at room temperature or at elevated temperature, more preferably selected from chemical curing such as chemical crosslinking and / or physical drying (non-chemical curing), in each case at room temperature or at elevated temperature, and in each case preferably wherein the minimum curing temperature for curing applied is 80 °C.

11. The multilayer coating system according to one or more of the preceding claims, characterized in that, the backbone of the copolymer contains ethylenically unsaturated carbon-carbon double bonds, preferably characterized in that, the copolymer can be obtained by ring-opening metathesis polymerization (ROMP) using cyclic ethylenically unsaturated monomers, preferably cyclic olefin monomers.

12. The multilayer coating system according to one or more of the preceding claims, characterized in that, each of the side chains S1 of the first block B1 of the copolymer contains at least one polymer moiety M1 containing at least one preferably terminal hydroxyl group, wherein the polymer moiety M1 is preferably selected from the group consisting of preferably aliphatic polyester moieties and preferably aliphatic polyether moieties, particularly representing a polylactide moiety, and characterized in that, each of the side chains S2 of the second block B2 of the copolymer contains at least one polymer moiety M2 free of both hydroxyl and carboxylic acid groups, wherein the polymer moiety M2 is preferably selected from the group consisting of polyether, polysiloxane, and polystyrene moieties, particularly representing a polystyrene moiety.

13. The multilayer coating system according to one or more of the preceding claims, characterized in that, The at least one copolymer has a number average molecular weight (M n ) in the range of 450 to 6000 kDa, more preferably in the range of 500 to 2500 kDa, even more preferably in the range of 550 to 2000 kDa, still more preferably in the range of 600 to 1500 kDa, particularly in the range of 650 to 1000 kDa.

14. The multilayer coating system according to one or more of the preceding claims, characterized in that, the first block B1 of the copolymer contains at least one structural unit SU1a and optionally at least one structural unit SU1b, wherein the structural unit SU1a is represented by at least one of the partial structures PS1a-1 and PS1a-2, and wherein the optionally present structural unit SU1b is represented by the partial structure PS1b, wherein all the present structural units are preferably randomly arranged within the first block B1 of the copolymer wherein independently of each other the parameter x is in the range from 1 to 1000, preferably from 1 to 750, more preferably from 2 to 500, even more preferably from 3 to 300, the parameter a is in the range from 0 to 1000, preferably from 1 to 750, more preferably from 2 to 500, even more preferably from 3 to 300, The relative ratio of parameter x:a is in the range of 1:0 to 1:3, preferably 2:1 to 1:2, Mx, J 1 and G each independently represents CH 2 or C=O, Q represents a divalent alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl or heteroaryl residue, Rx represents a side chain S1 containing a polymer moiety M1, preferably represents C 2 -C 6 -alkylene-O-[C(=O)-C 2 -C 6 -alkylene-O] n -H, where the parameter n ranges from 1 to 500, preferably from 1 to 300, and R 1 represents C 1 -C 6 -alkyl residue, preferably unbranched C 1 -C 6 -alkyl residue, and is characterized in that the second block B2 of the copolymer comprises at least one structural unit SU2a and optionally at least one structural unit SU2b, wherein the structural unit SU2a is represented by at least one of the partial structures PS2a-1 and PS2a-2, and wherein the optionally present structural unit SU2b is represented by the partial structure PS2b, and wherein all the present structural units are preferably randomly arranged within the second block B2 of the copolymer wherein independently of each other parameter y is in the range of 1 to 1000, preferably 1 to 750, more preferably 2 to 500, even more preferably 3 to 300, parameter b is in the range of 0 to 1000, preferably 1 to 750, more preferably 2 to 500, even more preferably 3 to 300, the relative ratio of parameter y:b is in the range of 1:0 to 1:3, preferably 2:1 to 1:2, My, J 2 and G each independently represents CH 2 or C=O, Q represents a divalent alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl or heteroaryl residue, Ry represents a side chain S2 containing a polymer moiety M2, preferably represents C 1 -C 8 -alkylene-Z-T, where Z represents C(=O)-O or a divalent N-containing heterocyclic residue, and T represents C bonded to the polystyrene moiety 1 -C 4 -alkylene residue, and R 2 represents C 1 -C 6 -alkyl residue, preferably branched C 1 -C 6 -alkyl residue, preferably characterized in that the first block B1 of the copolymer comprises at least one structural unit SU1a represented by at least the partial structure PS1a-1, and further comprises at least one structural unit SU1b represented by the partial structure PS1b, and is characterized in that, the second block B2 of the copolymer comprises at least one structural unit SU2a represented by at least the partial structure PS2a-1, and further comprises at least one structural unit SU2b represented by the partial structure PS1b, wherein independently of each other parameter x is in the range of 2 to 500, preferably 3 to 300, parameter a is in the range of 2 to 500, preferably 3 to 300, the relative ratio of parameter x:a is in the range of 2:1 to 1:2, preferably 1.5:1 to 1:1.5, parameter y is in the range of 2 to 500, preferably 3 to 300, parameter b is in the range of 2 to 500, preferably 3 to 300, the relative ratio of parameter y:b is in the range of 2:1 to 1:2, preferably 1.5:1 to 1:1.5, and the remaining residues and variables have the meanings as defined above in this claim.

15. The multilayer coating system according to one or more of the preceding claims, characterized in that, the at least one copolymer is present in the coating composition for preparing the second coating L2 in an amount in the range of 10 to 100 wt.-%, preferably 15 to 100 wt.-%, more preferably 20 to 95 wt.-% in each case based on the total solids content of the coating composition.

16. The multilayer coating system according to one or more of the preceding claims, characterized in that, The coating composition for preparing the second coating L2, which comprises at least one block copolymer, further comprises at least one homopolymer, preferably at least one homopolymer selected from the group consisting of polyester, poly(meth)acrylate, polyether, polysiloxane, and polystyrene homopolymers, more preferably selected from polystyrene, polyether, and polyester homopolymers and mixtures thereof, even more preferably selected from polystyrene and aliphatic polyesters such as polylactide homopolymers and mixtures thereof, wherein the at least one homopolymer preferably has a number-average molecular weight (M n ) that is at least 100 times lower, preferably at least 150 times lower, more preferably at least 175 times lower than the number-average molecular weight (M n ) of the at least one copolymer, and wherein preferably, the relative weight ratio of the copolymer solids to the solids of the at least one homopolymer in the coating composition is in the range of 99:1 to 5:95, more preferably 95:5 to 10:90, even more preferably 90:10 to 15:85, still more preferably 85:15 to 20:80, yet more preferably 75:25 to 25:75, particularly 60:40 to 30:

70.

17. The multilayer coating system according to one or more of the preceding claims, characterized in that, The coating composition comprising the at least one block copolymer for preparing the second coating L2 comprises at least one additional resin, preferably at least one polymeric resin, in addition to the copolymer and, if such a homopolymer is present, in addition to the at least one homopolymer as defined in claim 13, wherein the relative weight ratio of the copolymer solids to the solids of the at least one additional resin in the coating composition is preferably in the range of 5:95 to 100:0, more preferably 10:90 to 100:0, even more preferably 15:85 to 95:5, still more preferably 20:80 to 90:10, yet more preferably 25:75 to 85:15, particularly 30:70 to 80:20, most preferably 40:60 to 80:

20.

18. A method for preparing a multi-layer coating system according to one or more of the preceding claims, the method comprising at least steps (1), (2), (3) and (4), namely (1) applying a colored primer coating composition to at least a part of an optionally pre-coated substrate and forming a first coating film on at least a part of the optionally pre-coated substrate, (2) applying a second primer coating composition comprising at least one block copolymer and different from the primer coating composition applied in step (1) to the first coating film present on the substrate obtained after step (1), and forming a second coating film preferably adjacent to the first coating film, (3) applying a coating composition different from the compositions applied in steps (1) and (2) to the second coating film present on the substrate obtained after step (2), and forming a third coating film preferably adjacent to the second coating film, wherein the coating composition is preferably a clear coating composition, and (4) co-curing at least the second and third coating films applied in steps (2) and (3) and, optionally, also the first coating film if the first coating film applied in step (1) is not cured before performing step (2), to obtain a multi-layer coating system comprising at least the first, second and third coatings L1, L2 and L3.

19. A coated substrate obtainable by the method according to claim 18.

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