Scratch resistant coatings with good appearance and plastic compatibility

Abstract

The present invention relates to a clearcoat system comprising at least a component A) comprising at least one OH-functional polymer a1), and at least one kind of silica nanoparticles a2), and a component B) at least one organic constituent b1) bearing on average 2 or more NCO groups, wherein at least a part of these NCO groups has been reacted with at least one silane prior to incorporation of constituent b1) into component B), and at least one organic constituent b2) bearing on average two or more NCO groups, wherein none of these NCO groups of constituent b2) has been reacted with at least one silane prior to incorporation of constituent b2) into component B), wherein in component B) 0.1 to at most 29.5 mol-% of all originally present NCO groups, based on the total weight of all isocyanate groups of all originally present isocyanate groups containing constituents present in component B) including constituents b1) and b2), have undergone reaction with at least one silane prior to its / their incorporation into component B), a clearcoat composition obtainable by mixing at least components A) and B), a method of coating a substrate making use of said clearcoat composition, a coated substrate obtainable by this method, and to a multilayer coating system comprising at least two coatings layers L1 and L3, wherein layer L3 is obtainable from the clearcoat composition.

Description

[0001] Scratch resistant coatings with good appearance and plastic compatibility

[0002] The present invention relates to a clearcoat system, a clearcoat composition obtainable therefrom, a method of coating a substrate making use of said clearcoat composition, a coated substrate obtainable by this method, and to a multilayer coating system inter alia comprising a coating layer obtainable from applying the clearcoat composition, exhibiting in particular an excellent scratch resistance, appearance, and plastic such as PVC compatibility.

[0003] Background of the invention

[0004] Particularly in the automotive industry, but not limited thereto, not only the coating of metal substrates but also the coating of plastic parts plays a big role. There are high requirements regarding mechanical properties such as scratch resistance related to such coatings, particularly regarding its outermost coating layer, which typically is a clearcoat layer. Scratch resistant clearcoats are important to maintain the gloss of a coating ideally throughout the lifetime of the automobile bearing the coating. However, not only mechanical properties such as a sufficiently high scratch resistance are relevant, but also optical appearance plays a significant role in the coatings industry. Often, however, in particular in case of substrates having a comparably high surface roughness such as substrates bearing an electrodeposition coat, often rather high SW (short wave) values are observed, which are detrimental to a good appearance. Hence, it is desirable to provide not only a high mechanical quality, in particular a high scratch resistance, but also at the same time an excellent appearance of the coatings.

[0005] In addition, in particular in view of the increased use of plastic materials in the automotive industry, nowadays also a good compatibility of the coating, in particular the clearcoat, and plastic materials such as polyvinyl chloride (PVC) is desired, which is, unfortunately, often not fulfilled by conventional coatings and in particular conventional clearcoats. For example, different PVC materials are often used as sealants, e.g., in the interior of an automobile, or for car underbody protection. Such sealants are often applied directly applied onto an electrodeposition coat of the respective part used. Since often even no basecoat layers are additionally present on these parts of the car, a clearcoat layer may be present even in direct contact with the PVC material used. In particular, for such applications it is of great importance that the coating, in particular the clearcoat, shows an excellent compatibility to the PVC materials used, particularly in order to avoid the occurrence of any cracks.

[0006] Thus, there is a need for providing clearcoat compositions, which can be used to prepare clearcoats, which in turn can be used for coating both metal and plastic substrates, e.g., as outermost layer of a multilayer coating system present thereon or even directly onto electrocoated substrates further bearing a sealant layer made of at least one plastic material such as a PVC material, which not only at the same time exhibit both an excellent scratch resistance and appearance, in particular also on comparably rough surfaces, but also show a very good compatibility with plastic materials, in particular to PVC, in order to avoid the occurrence of any cracks. Problem

[0007] It has been therefore an objective underlying the present invention to provide clearcoat compositions, which can be used to prepare clearcoats, which in turn can be used for coating both metal and plastic substrates, e.g., as outermost layer of a multilayer coating system present thereon or even directly onto electrocoated substrates further bearing a sealant layer made of at least one plastic material such as a PVC material, which not only at the same time exhibit both an excellent scratch resistance and appearance, in particular also on comparably rough surfaces, but also show a very good compatibility with plastic materials, in particular to PVC, in order to avoid the occurrence of any cracks.

[0008] Solution

[0009] This objective has been solved by the subject-matter of the claims of the present application as well as by the preferred embodiments thereof disclosed in this specification, i.e., by the subject matter described herein.

[0010] A first subject-matter of the present invention is a clearcoat system comprising at least two components A) and B) and optionally at least one further component C) being different from one another and being separate from each other, wherein component A) comprises at least constituents a1) and a2) and optionally a3), which are different from one another, namely at least one OH-functional polymer as at least one constituent a1), at least one kind of silica nanoparticles, preferably having a median primary particle size in the range of from 5 nm to 1000 nm, as at least one constituent a2), and optionally at least one organic solvent a3), wherein component B) comprises at least constituents b1 ) and b2) and optionally constituent b3), which are different from one another, namely at least one organic constituent b1) bearing on average two or more isocyanate groups, wherein at least a part of these isocyanate groups has been reacted with at least one silane prior to incorporation of constituent b1) into component B), at least one organic constituent b2) being different from organic constituent b1) and bearing on average two or more isocyanate groups, wherein none of the isocyanate groups of constituent b2) has been reacted with at least one silane prior to incorporation of constituent b2) into component B), and optionally at least one organic solvent b3), and wherein optional component C) is a reducer component and comprises at least one organic solvent d), characterized in that in component B) 0.1 to <29.5 mol-% of all originally present isocyanate groups, based on the total molar amount of all originally present isocyanate groups of all isocyanate groups containing constituents present in component B) including constituent b1) and constituent b2), have undergone reaction with at least one silane prior to its / their incorporation into component B).

[0011] A further subject-matter of the present invention is a clearcoat composition obtainable by mixing at least components A) and B) and optionally C) of the inventive clearcoat system with each other.

[0012] A further subject-matter of the present invention is a method of coating a substrate, comprising at least one step of applying to an optionally pre-coated substrate at least one inventive clearcoat composition to form at least one coating film onto the optionally pre-coated substrate and optionally at least one further step of curing the at least one coating film to obtain at least one cured clearcoat layer onto the substrate.

[0013] A further subject-matter of the present invention is a coated substrate, which is obtainable by the inventive method.

[0014] A further subject-matter of the present invention is a multilayer coating system being present on an optionally precoated substrate and comprising at least two coatings layers L1 and L3 and optionally at least one coating layer L2 being different from one another, namely a first coating layer L1 applied over at least a portion of an optionally pre-coated substrate, said layer L1, optionally a second coating layer L2 applied over the first coating layer L1 , said layer L2 being, and a third coating layer L3 applied over the first coating layer L1 or, if present, over the second coating layer L2, said layer L3 being obtainable from the inventive clearcoat composition.

[0015] It has been in particular surprisingly found that an excellent appearance of in particular short wave (SW) values <20 or <15 or < even 10 can be observed for substrates coated with a clearcoat layer, e.g., as outermost layer of a multilayer coating system present on the substrate or wherein the clearcoat layer is present onto a sealant material such as a plastic material, e.g., a PVC material, that in turn is present on an electrocoated substrate, when the clearcoat layer is derived from a clearcoat film, which has been obtained from an inventive clearcoat composition, which in turn has been obtained from an inventive clearcoat system.

[0016] It has been in particular further surprisingly found that at the same time an excellent scratch resistance, in particular both a dry and a wet scratch resistance, can be achieved for substrates coated with a clearcoat layer, e.g., as outermost layer of a multilayer coating system present on the substrate or wherein the clearcoat layer is present onto a sealant material such as a plastic material, e.g., a PVC material, that in turn is present on an electrocoated substrate, when the clearcoat layer is derived from a clearcoat film, which has been obtained from an inventive clearcoat composition, which in turn has been obtained from an inventive clearcoat system.

[0017] Moreover, it has been further surprisingly found that, besides said excellent scratch resistance and appearance, additionally an excellent compatibility to plastic materials such as PVC can be achieved for corresponding substrates coated with a clearcoat layer, e.g., as outermost layer of a multilayer coating system present on the substrate or wherein the clearcoat layer is present onto a sealant material such as a plastic material, e.g., a PVC material, that in turn is present on an electrocoated substrate, when the clearcoat layer is derived from a clearcoat film, which has been obtained from an inventive clearcoat composition, which in turn has been obtained from an inventive clearcoat system. In particular, it has been found in this regard that any occurrence of cracks can be avoided. It has been particularly found in this regard that an excellent compatibility to plastic materials such as PVC is even present, when a clearcoat composition obtainable from the clearcoat system according to the present invention is directly applied onto a plastic material such as a PVC material, e.g., when said plastic material is used as a sealant such as in the interior of an automobile, or for car underbody protection.

[0018] It has been in particular surprisingly found that these technical effects are a result of the silanization degree of the isocyanate containing constituents present in component B) of the clearcoat system, i.e., of the feature that 0.1 to <29.5 mol-% of all originally present isocyanate groups, based on the total molar amount of all originally present isocyanate groups of all isocyanate groups containing constituents present in component B) including constituent b1) and constituent b2), have undergone reaction with at least one silane prior to its / their incorporation into component B), and / or are a result of the presence of constituent a2) in component A) of the clearcoat system. It has been in particular surprisingly found that these technical effects are a result of both aforementioned features, i.e., of a combination thereof. It has been found that a high scratch resistance can be achieved by partial silanization of the isocyanate crosslinkers, i.e., by the presence of constituent b1), and that said excellent scratch resistance can be maintained due to the presence of constituent a2) even at comparably low network densities / low partial silanization degree due to the fact that <29.5 mol-% of all originally present isocyanate groups may have undergone reaction with at least one silane. It has been found that said comparably low partial silanization degree is, however, necessary to also ensure both a good appearance and a good compatibility on PVC materials, even in case of a comparably high surface roughness due to the presence of an electrodeposition coating on the surface when having applied a cathodic dip coating process.

[0019] Detailed description of the invention

[0020] The term "comprising" in the context of the present invention, in particular in connection with the coating system, components A) and B) and optionally C) of the coating system, and the coating composition according to the invention preferably has the meaning "consisting of". In this case, in addition to the mandatory constituents present within components A) and B) and C) or the coating composition, one or more of the further optional constituents mentioned hereinafter contained in each of the components of the coating system or coating composition according to the invention may be contained therein, its components A) and B) and optionally C) or in the coating composition according to the invention. All constituents can be present in each case in their preferred embodiments mentioned hereinafter.

[0021] The proportions and amounts in wt.-% (% by weight) of the constituents present within components A) and B) and C) and of further optionally present constituents in the coating system add up to 100 wt.-%, based in each case on the total weight of the respective component A) or B) or C) of the coating system. The same applies to all constituents present in the coating composition: The proportions and amounts in wt.-% (% by weight) of all constituents present add up to 100 wt.-%, based on the total weight of the clearcoat composition according to the invention.

[0022] Coating system (clearcoat system)

[0023] The inventive coating system is a two- (2K-) or multi-component clearcoat system comprising at least two components A) and B) being different from one another and also being separate from each other. Separate from each other in this context means that, for example, components A) and B) of the coating system can be stored separately until they are mixed with each other in order to prepare an inventive clearcoat composition. When the coating system is a multi-component coating system it preferably contains at least one further optional component C), which is different from components A) and B) and also separate from both A) and B). Component C) preferably is a reducer component used for diluting the to-be-prepared coating composition and thus preferably comprises at least one organic solvent d) and more preferably consists of at least one organic solvent d). In case the coating system is a two-component coating system, however, which is preferred, it preferably consists of components A) and B).

[0024] Upon mixing of at least the two components A) and B) a polyurethane or polyurethane-based coating composition is formed by reaction of the OH-groups of constituent a1) with the isocyanate groups of at least constituents b1) and b2).

[0025] Preferably, both components A) and B) and also optional component C) of the inventive coating system are free or essentially free of water. The same applies to the inventive coating compositions. In the sense of the present invention the term "free of water” preferably means that no water at all is present. In the sense of the present invention the term "essentially free of water” preferably means that essentially no water is present. This means that at least no water is added on purpose to any of the inventively used components A) and B) and optionally C) and to the inventive coating composition. It may, however, not be ruled out that remaining residues of water formed upon preparation of any of the constituents used for preparing the inventively used components A) and B) and optionally C) are present therein. Preferably, the amount of any water present in each of components A) and B) and optionally C) is less than 1 wt.-%, more preferably less than 0.5 wt.-%, even more preferably less than 0.1 wt.- %, still more preferably less than 0.05 wt.-%, yet more preferably less than 0.01 wt.-%, in particular less than 0.005 wt.-% or less than 0.001 wt.-%, in each case based on the total weight of component A) or B) or optionally C).

[0026] Preferably, both components A) and B) and also optional component C) of the coating system are solventborne, i.e. , organic solvent(s)-based. Thus, preferably, the coating system is not a waterborne, i.e. , an aqueous, coating system.

[0027] Preferably, both components A) and B) and optionally C) of the coating system are transparent, i.e., clear. Preferably, of course, also the inventive coating composition is transparent, i.e., clear. In particular, none of components A) and B) and optionally C) of the inventive coating system contains any pigments and / or fillers, in particular any color and / or effect imparting pigments and / or fillers. The same applies, of course, also preferably, to the inventive coating composition.

[0028] Component A)

[0029] Component A), which represents a master batch component, comprises at least constituents a1) and a2), but may additionally comprise further optional constituents.

[0030] Preferably, component A) of the coating system has a total solids content, which is >30 wt.-%, preferably >35 wt- %, more preferably >40 wt.-%, even more preferably >45 wt.-%, based on the total weight of component A). The total solids content of component A) of the coating system is preferably in a range of from >35 to 60 wt.-%, more preferably of from 40 to 57.5 wt.-%, even more preferably of from 42.5 to 55 wt.-%, in particular of from 45 to 52.5 wt.-%, based in each case on the total weight of component A). The total solids content, in other words the nonvolatile fraction, is determined in accordance with the method described hereinafter.

[0031] Constituent a1)

[0032] Constituent a1) is at least one OH-functional polymer, which functions as film-forming binder.

[0033] For the purposes of the present invention, the term "binder" is understood in accordance with DIN EN ISO 4618 (German version, date: March 2007) to be the non-volatile constituent of a coating composition, which is responsible for the film formation. Pigments and / or fillers contained therein are thus not subsumed under the term "binder”. Preferably, the at least one OH-functional polymer such as an OH-functional (meth)acrylic copolymer is the main binder of the coating composition. As the main binder in the sense of the present invention, a binder constituent is preferably referred to, when there is no other binder constituent in the coating composition, which is present in a higher proportion based on the total weight of the coating composition.

[0034] The term "polymer" is known to the person skilled in the art and, for the purposes of the present invention, encompasses polyadducts and polymerizates as well as polycondensates. The term "polymer" includes both homopolymers and copolymers. The term (meth)acrylic polymer hence also includes both homopolymers and copolymers in each case, but preferably means copolymers.

[0035] The at least one OH-functional polymer a1) preferably comprises on average two or more OH-groups. Preferably, the at least one OH-functional polymer a1) has an OH number of 30 to 400 mg KOH / g, more particularly between 100 and 300 KOH / g.

[0036] Preferably, the at least one OH-functional polymer a1) has a weight average molecular weight Mw, measured by means of gel permeation chromatography (GPC) against a polystyrene standard, between 800 and 100 000 g / mol, more preferably between 1 000 and 75 000 g / mol, even more preferably between 1 200 and 50 000 g / mol, still more preferably between 1 500 and 25 000 g / mol, yet more preferably between 2 000 and 15 000 g / mol.

[0037] Particularly preferred constituents a1) are selected from the group consisting of polyesters, polyurethanes, poly(meth)acrylates and mixtures thereof. As outlined above these terms include both homopolymers and copolymers in each case.

[0038] Suitable polyesters are described for example in EP-A-0 994 117 and EP-A-1 273 640. Polyurethane polyols are prepared preferably by reaction of polyester polyol prepolymers with suitable di- and / or polyisocyanates and are described for example in EP-A-1 273 640.

[0039] Preferably, the at least one OH-functional polymer a1) is at least one OH-functional (meth)acrylic copolymer and / or at least one OH-functional polyester, more preferably at least one OH-functional (meth)acrylic copolymer. Preferably at least two OH-functional (meth)acrylic copolymers are present as constituent a1) in component (A), which are different from one another. If at least two OH-functional (meth)acrylic copolymers are present as constituent a1) in component (A), they differ from each other preferably in their glass transition temperature.

[0040] Preferably, at least one OH-functional (meth)acrylic copolymer and / or at least one OH-functional polyester, more preferably at least one OH-functional (meth)acrylic copolymer, even more preferably at least two OH-functional (meth)acrylic copolymers being different from one another and optionally additionally at least one OH-functional polyester, is / are present as the at least one OH-functional polymer a1).

[0041] Preferably, the at least one OH-functional polymer a1) has a glass transition temperature, preferably measured by means of DSC measurements in accordance with DIN EN ISO 11357-2 (2019-03), in a range of from -150 to 100°C, more preferably of from -120°C to +80°C. Tgis measured according to the method disclosed in the 'method' section.

[0042] Preferably, in particular when at least one OH-functional (meth)acrylic copolymer is used as part of constituent a1) or as constituent a1) as such, it has a glass transition temperature (Tg) being in a range of from +10 °C to +75 °C, preferably of from +15 °C to +70 °C, more preferably of from +20 °C to +65 °C, still more preferably of from +25 °C to +60 °C, even more preferably of from +30 °C to +55 °C, yet more preferably of from +32 °C or +50 °C, most preferably of from +35 °C to +45 °C or to +40 °C. As mentioned above, if at least two OH-functional (meth)acrylic copolymers are present as constituent a1) in component (A), they differ from each other preferably at least in their glass transition temperature. Preferably, the first (meth)acrylic copolymer has a glass transition temperature as mentioned above in this paragraph and the second (meth)acrylic copolymer has a lower glass transition temperature, more preferably a glass transition temperature (Tg) being in a range of from -70 °C to <+40 °C, preferably of from -50 °C to +35 °C, more preferably of from -25 °C to +30 °C, still more preferably of from -15 °C to +25 °C, even more preferably of from -5 °C to +20 °C, yet more preferably of from 0 °C or +5 °C or +20 °C.

[0043] The term "(meth) acryl" or "(meth) acrylate" or (meth)acrylic” in the context of the present invention in each case comprises the meanings "methacryl" and / or "acryl" "methacrylic" and / or "acrylic" or "methacrylate" and / or "acrylate". Therefore, a "(meth)acrylic copolymer” in general may be formed from only "acrylic monomers”, only "methacrylic monomers” or "acrylic and methacrylic monomers”. However, polymerizable monomers other than acrylic and / or methacrylic monomers as, e.g., styrene and the like may also be contained in a "(meth)acrylic copolymer”. In other words, a (meth)acrylic polymer may consist of only acrylic and / or methacrylic monomer units but does not have to. The notation "(meth)acrylate polymer or copolymer” or "(meth)acrylic polymer or copolymer” is intended to mean that the polymer / copolymer (polymer skeleton / backbone) is formed predominantly, i.e., preferably more than 50% or more than 75% of the monomer units used, from monomers having a (meth)acrylate group. In the preparation of a (meth)acrylic copolymer, preferably more than 50% or 75% of the monomers thus have a (meth)acrylate group. However, the use of further monomers as comonomers such as copolymerizable vinyl monomers, e.g., styrene, for its preparation is not excluded.

[0044] For introduction of OH-functionality, hydroxyl-containing monomers can be used, which include hydroxy alkyl esters of acrylic or methacrylic acid. Non-limiting examples of hydroxyl-functional monomers include hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylates, hydroxybutyl-(meth)acrylates, hydroxyhexyl- (meth)acrylates, propylene glycol mono(meth)acrylate, 2,3-dihydroxypropyl(meth)acrylate, pentaerythritol mono(meth)acrylate, polypropylene glycol mono(meth)acrylates, polyethylene glycol mono(meth)acrylates, reaction products of these with epsilon-caprolactone, and other hydroxyalkyl-(meth)acrylates having branched or linear alkyl groups of up to about 10 carbons, and mixtures of these, where the term "(meth)acrylate” indicates either or both of the methacrylate and acrylate esters. Generally, at least about 5 % by weight hydroxyl-functional monomer is preferably included in the polymer. Hydroxyl groups on a vinyl polymer such as an acrylic polymer can be generated by other means, such as, for example, the ring opening of a glycidyl group, for example from copolymerized glycidyl methacrylate, by an organic acid or an amine.

[0045] Hydroxyl functionality may also be introduced through thio-alcohol compounds, including, without limitation, 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-proanediol, 4-mercapto-1- butanol, and combinations of these. Any of these methods may be used to prepare a useful hydroxyl-functional

[0046] (meth)acrylic polymer.

[0047] Examples of suitable comonomers that may be used include, without limitation, a,p-ethylenically unsaturated monocarboxylic acids containing 3 to 5 carbon atoms such as acrylic, methacrylic, and crotonic acids and the alkyl and cycloalkyl esters, nitriles, and amides of acrylic acid, methacrylic acid, and crotonic acid; a,p-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms and the anhydrides, monoesters, and diesters of those acids; vinyl esters, vinyl ethers, vinyl ketones, and aromatic or heterocyclic aliphatic vinyl compounds. Representative examples of suitable esters of acrylic, methacrylic, and crotonic acids include, without limitation, those esters from reaction with saturated aliphatic alcohols containing 1 to 20 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, hexyl, 2-ethylhexyl, dodecyl, 3,3,5-trimethylhexyl, stearyl, lauryl, cyclohexyl, alkyl-substituted cyclohexyl, alkanol-substituted cyclohexyl, such as 2-tert-butyl and 4-tert-butyl cyclohexyl, 4-cyclohexyl-1 -butyl, 2-tert-butyl cyclohexyl, 4-tert-butyl cyclohexyl, 3, 3, 5, 5, -tetramethyl cyclohexyl, tetrahydrofurfuryl, and isobornyl acrylates, methacrylates, and crotonates; unsaturated dialkanoic acids and anhydrides such as fumaric, maleic, itaconic acids and anhydrides and their mono- and diesters with alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and tert-butanol, like maleic anhydride, maleic acid dimethyl ester and maleic acid monohexyl ester; vinyl acetate, vinyl propionate, vinyl ethyl ether, and vinyl ethyl ketone; styrene, a-methyl styrene, vinyl toluene, 2-vinyl pyrrolidone, and p-tert-butylstyrene.

[0048] The (meth)acrylic copolymer may be prepared using conventional techniques, such as by heating the monomers in the presence of a polymerization initiating agent and optionally a chain transfer agent. The polymerization may be carried out in solution, for example. Typical initiators are organic peroxides such as dialkyl peroxides such as di-t-butyl peroxide, peroxyesters such as t-butyl peroxy 2-ethylhexanoate, and t-butyl peracetate, peroxydicarbonates, diacyl peroxides, hydroperoxides such as t-butyl hydroperoxide, and peroxyketals; azo compounds such as 2,2'azobis(2-methylbutanenitrile) and 1,1'-azobis(cyclohexanecarbonitrile); and combinations of these. Typical chain transfer agents are mercaptans such as octyl mercaptan, n- or tert-dodecyl mercaptan; halogenated compounds, thiosalicylic acid, mercaptoacetic acid, mercaptoethanol and the other thiol alcohols already mentioned, and dimeric alpha-methyl styrene. The polymerization reaction is usually carried out at temperatures from about 20 °C to about 200 °C. The reaction may conveniently be done at the temperature at which the solvent or solvent mixture refluxes, although with proper control a temperature below the reflux may be maintained. The initiator should be chosen to match the temperature at which the reaction is carried out, so that the half-life of the initiator at that temperature should preferably be no more than about thirty minutes. Further details of addition polymerization generally and of polymerization of mixtures including (meth)acrylate monomers is readily available in the polymer art. The solvent or solvent mixture is generally heated to the reaction temperature and the monomers and initiator(s) are added at a controlled rate over a period of time, usually between 2 and 6 hours. A chain transfer agent or additional solvent may be fed in also at a controlled rate during this time. The temperature of the mixture is then maintained for a period of time to complete the reaction. Optionally, additional initiator may be added to ensure complete conversion. The (meth)acrylic copolymers that are especially preferred in accordance with the invention for use as constituent a1) preferably have a weight average molecular weight Mwbetween 1 000 and 35 000 g / mol, more preferably between 1 500 and 30 000 g / mol, even more preferably between 1 500 and 25 000 g / mol, still more preferably between 1 500 and 15 000 or 10 000 g / mol, preferably measured in each case by means of gel permeation chromatography (GPC) against a polystyrene standard. The glass transition temperature of these copolymers is preferably between -100 and 100°C, more particularly between -60 and < 50°C (preferably measured by means of DSC measurements in accordance with DIN EN ISO 11357-2 (2019-03)). These copolymers preferably have an OH number of 60 to 300 mg KOH / g, more particularly between 70 and 250 mg KOH / g, and an acid number of between 0 and 30 mg KOH / g.

[0049] Preferably, the at least one constituent a1), in particular when it is at least one (meth)acrylic polymer, is preferably present in the component A) in an amount in the range of from 5.0 wt.-% to 85.0 wt.-%, based on the total weight of component A). More preferably, the at least one constituent a1) is present in component A) in an amount in the range of from 10.0 wt.-% to 80.0 wt.-%, yet more preferably of from 15.0 wt.-% to 75.0 wt.-%, even more preferably of from 20.0 wt.-% to 70.0 wt.-%, still more preferably of from 25.0 to 65.0 wt.-%, most preferably of from 30.0 to 60.0 wt.-%, in each case based on the total weight of component A).

[0050] Constituent a2)

[0051] At least one kind of silica nanoparticles are present as at least one constituent a2), which preferably have a median primary particle size in the range of from 5 nm to 1000 nm. The median primary particle size is preferably determined via transmission electron microscopy (TEM), more preferably according to ISO 21363:2020 as outlined in the 'method' section.

[0052] More preferably, the at least one kind of silica nanoparticles being present as constituent a2) have a median primary particle size in the range of from 7.5 nm to 750 nm or to 500 nm or to 225 nm, still more preferably of from 10 to 200 nm, even more preferably of from 12.5 to 175 nm, still more preferably of from 15 to 150 or to 100 nm, yet more preferably of from 15 to 75 or to 50 nm or to 35 nm, preferably in each case determined via transmission electron microscopy (TEM), more preferably according to ISO 21363:2020 as outlined in the 'method' section.

[0053] Preferably, the median primary particle size is a number-based (dN,5o%) median primary particle size. Alternatively, and also preferably, the median primary particle size is a volume-based (dv.50%) median primary particle size. The term number-based median particle size (dN,5o%) is a parameter known to a person skilled in the art. The characteristic variable labeled with the lower-case letter “d” is the percentile (50%) of the cumulative distribution curve with the 50% percentile corresponding to the median. The index “N” pertains to the number-based distribution. Similarly, the term volume-based median particle size (dv,5o%) is a parameter known to a person skilled in the art. The characteristic variable labeled with the lower-case letter “d” is the percentile (50%) of the cumulative distribution curve with the 50% percentile corresponding to the median. The index "V” pertains to the volume-based distribution. Preferably, the amount of constituent a2) in component (A) is in a range of from 0.1 to 7.5 wt.-%, more preferably of from 0.2 to 6.0 wt.-%, still more preferably of from 0.3 to 5.0 wt.-%, yet more preferably of from 0.4 to 4.0 wt.-%, even more preferably of from 0.5 to 3.5 wt.-%, based in each case on the total weight of component A).

[0054] Preferably, the amount of constituent a2) in the clearcoat composition obtainable from mixing components A) and B) and optionally C) with each other is in a range of from 0.3 to 10.0 wt.-%, more preferably of from 0.4 to 7.5 wt- %, still more preferably of from 0.5 to 5.5 wt.-%, yet more preferably of from 0.6 to 5.0 wt.-%, even more preferably of from 0.7 to 4.0 or to 3.0 wt.-%, based in each case on the total weight of the clearcoat composition.

[0055] Preferably, the silica nanoparticles are surface modified, i.e., have been subjected to a chemical treatment using at least one chemical modification agent such as at least one polysiloxane. In particular, OH-groups being present on the surface of the silica nanoparticles are able to react with suitable reactive groups of the chemical modification agent in order to covalently bind at least part of the chemical modification agent to the surface of the nanoparticles.

[0056] Preferably, the silica nanoparticles have been reacted on their surface with a modification agent with formation of covalent bonds, wherein said agent preferably is a polysiloxane of the following general empirical formula (MA):

[0057] (R1xR23-xSiR3)yR4

[0058] (MA), in which the residues and parameters indicated preferably have the following meanings: x = 0-2, in particular 0, y = 1-10, preferably 2-5,

[0059] R1= monovalent organic radical having 1-18 carbon atoms, in particular 1-3 carbon atoms,

[0060] R2= OH group or hydrolysable group consisting of linear or branched or cyclic alkoxy group having 1-6 carbon atoms, in particular having 1-2 carbon atoms, a halogen atom, in particular a chlorine atom, or a carboxylic acid radical having 1-4 carbon atoms, preferably 2 carbon atoms,

[0061] R3= divalent oxygen or divalent organic radical consisting of preferably linear or branched alkylene radical having 1-8 carbon atoms, alkylene ether, alkylene thioether, alkylene polyether, preferably based on ethylene oxide, propylene oxide or butylene oxide or mixtures of the oxides, arylene polyether, alkylene polyester or an organic aliphatic or aromatic or araliphatic group which in addition to ester and / or ether groups also contain urethane and / or urea groups, wherein R3preferably is a divalent organic radical,

[0062] R4= monovalent or polyvalent organic radical consisting of a polydialkylsiloxane such as a polydimethylsiloxane, preferably having a number average molecular weight of 300 - 5 000 g / mol, the alkyl substituents on the silicon atoms having 1-18, preferably 1-10, carbon atoms. The monovalent or polyvalent organic radical consisting of a polydialkylsiloxane in position R4preferably has 4 to 200 Si-units, the alkyl substituents on the silicon atoms having 1-18, preferably 1-10, carbon atoms. The alkyl substituents on the silicon atoms having 1-18 carbon atoms optionally are partially and, in each case, independently of one another replaced or substituted by one or more of the following modifying groups (G) selected from the following modifying groups (G1) to (G4) listed under (i) to (iv):

[0063] (i) group (G1) containing (poly)ether groups,

[0064] (ii) group (G2) containing polyester groups,

[0065] (iii) group (G3) containing arylalkyl groups, and / or

[0066] (iv) group (G4) containing perfluorinated alkyl groups.

[0067] Preferably, the at least one chemical modification agent is used in an amount of from 0.1 % to 15% by weight, based on the total weight of the surface-modified silica nanoparticles.

[0068] Preferably, the silica nanoparticles, in addition to having been modified with a polysiloxane of the general empirical formula (MA), have been further chemically modified with at least one silane of the general empirical formula (MS1) and / or with at least one silane of the general empirical formula (MS2), namely

[0069] R7(4-x)SiR6x

[0070] (MS1), in which the indices and variables have the following definitions: x = 1-3

[0071] R6= monovalent, linear or branched or cyclic organic radical having 1-18 carbon atoms, preferably 1-6 carbon atoms, more preferably 1-3 carbon atoms

[0072] R7= hydroxyl group or hydrolysable group consisting of linear or branched or cyclic alkoxy group having 1-6 carbon atoms, in particular having 1-2 carbon atoms, a halogen atom, especially chlorine atom, or a carboxylic acid radical having 1-4 carbon atoms, preferably 2 carbon atoms, and / or

[0073] R8(4-x)Si(R9-R10-R11)x

[0074] (MS2),

[0075] X = 1-3

[0076] R8= hydroxyl group or hydrolysable group composed of linear or branched or cyclic alkoxy group having 1-6 carbon atoms, in particular having 1-2 carbon atoms, a halogen atom, especially chlorine atom, or a carboxylic acid radical having 1-4 carbon atoms, preferably 2 carbon atoms, R9= oxygen or divalent organic group, e.g., alkylene radical,

[0077] R10= divalent organic radical having a molar mass in the range 130-5000 daltons, composed of a polyether group consisting preferably of ethylene oxide, propylene oxide, butylene oxide, mixtures of the oxides, aliphatic and / or cycloaliphatic and / or aromatic polyester group containing at least three and / or groups,

[0078] R11= -alkyl, -acetoxy, -O-R12, R12being an alkyl group having 1-18 carbon atoms, or -O-CO-NH-R13, R13being an alkyl group having 1-18 carbon atoms.

[0079] Silica nanoparticles for use as constituent a2) are, e.g., disclosed in EP1690902 B1 and EP2049603 B1 . Further, silica nanoparticles for use as constituent a2) are commercially available, for example in the form of Nanobyk® 3650 and Nanobyk® 3652 from the company Byk Chemie, in the form of products of the Nanopol® series from Evonik Industries and in the form of products from the Modaflow® series from the company Allnex. Nanobyk® 3650 and Nanobyk® 3652, in particular Nanobyk® 3650 are particularly preferred.

[0080] Optional constituent a3)

[0081] Optional constituent a3) is at least one organic solvent, preferably at least one aprotic organic solvent, i.e., solvents not being proton donators and thus being chemically inert towards a reaction with NCO groups. Examples of such organic solvents include heterocyclic, aliphatic, or aromatic hydrocarbons, mono- or polyhydric alcohols, especially methanol and / or ethanol, ethers, esters, ketones, and amides, such as, for example, N-methylpyrrolidone, N- ethylpyrrolidone, dimethylformamide, toluene, xylene, butanol, ethyl glycol, propyl glycol, and butyl glycol and also their acetates, butyl diglycol, diethylene glycol dimethyl ether, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, acetone, isophorone, or mixtures thereof. Component A) may comprise more than one organic solvent as constituent a3). The at least one organic solvent a3) may the identical to or different from the at least one organic solvent b3) and / or d). If more than one organic solvent is used as a3) and / or b3) and / or d) it may be that a3) and b3) and / or d) 3 are both partially identical and partially different.

[0082] Preferably, the amount of constituent a3) in component (A), if present, is in a range of from 10 to 70 wt.-%, more preferably of from 15 to 65 wt.-%, based in each case on the total weight of component A).

[0083] Optional constituent a4)

[0084] Preferably, component A) further comprises at least one urea moiety or moieties containing constituent a4), more preferably as sag control agent (SCA), which is an adduct of at least at least one diisocyanate and / or at least one polyisocyanate and at least one amine, preferably of at least one primary or secondary monoamine.

[0085] Preferably, constituent a4) is present in a crystalline form, e.g., in the form of urea crystals. Preferably, constituent a4) is physically and / or chemically associated with at least one OH-functional polymer as sag control resin or polymer, which may be identical to polymer constituent a1 ) or different therefrom. Preferably, constituent a4) is preferably prepared by adding the at least one diisocyanate and / or the at least one polyisocyanate, preferably the at least one diisocyanate, to a mixture of the at least one primary or secondary amine, in particular monoamine, in the presence of at least one OH-functional polymer, preferably of at least one OH-functional (meth)acrylic copolymer, which can be identical to or different from the at least one OH-functional polymer constituent a1). The OH-functional polymer may function as sag control polymer or resin and as a moderating resin, which is preferably present during the reaction of the isocyanate and the amine. In case the urea formation takes place in the presence of such a polymer, part of the formed urea might not only be physically associated, but also partially chemically associated with the polymer, e.g., by urethan formation as a side reaction between hydroxyl groups of the resin and isocyanate groups of the diisocyanate and / or polyisocyanate.

[0086] Preferably, constituent a4) is present in an amount in the range of from 0.10 to 10.0 wt.-%, more preferably of from 0.10 to 8.0 wt.-%, even more preferably in an amount in the range of from 0.10 to 7.0 wt.-%, yet more preferably of from 0.10 to 5.0 wt.-%, still more preferably of from 0.10 to 4.0 wt.-%, yet more preferably of from 0.10 to 3.0 wt.- %, still more preferably of from 0.10 to 2.0 wt.-%, in particular of from 0.10 to 1.5 wt.-%, most preferably of from 0.10 to 1 .0 wt.-%, in each case based on the total weight of component A).

[0087] Preferably, constituent a4) is present in an amount in the range of from 0.02 to 5.0 wt.-%, based on the total weight of the at least one constituent a1) of component (A), more preferably in an amount in the range of from 0.04 to 4.0 wt.-%, even more preferably of from 0.1 to 3.5 wt.-%, in each case based on the total weight of the at least one constituent a1) of component (A).

[0088] Preferably, urea moiety or moieties containing constituent a4) functions as sag control agent (SCA) as mentioned hereinbefore. Urea moiety or moieties containing constituents a4) for use as constituent a4) are, e.g., disclosed in WO 2013 / 076208 A1 and WO 2012 / 140131 A1. A person skilled in the art is aware that there are so-called transparent sag control agents, which are, e.g., disclosed in WO 2013 / 076208 A1 , and opaque sag control agents, which are, e.g., disclosed in WO 2012 / 140131 A1.

[0089] Preferably, no other starting material besides the at least one diisocyanate and / or polyisocyanate and the at least one amine such as monoamine is used for preparing urea moiety or moieties containing constituent a4). However, as outlined hereinbefore, it is also possible that the adduct a4) is prepared by additionally making use of an OH- functional polymer such as at least part of constituent a1). For example, a constituent a4) may be prepared by reaction of the amine such as monoamine with the diisocyanate and / or polyisocyanate under formation of urea bonds, which still bears NCO-groups. These may then further react with the above mentioned OH-functional polymer. In particular, constituent a4) is prepared by adding the at least one diisocyanate and / or polyisocyanate, preferably the at least one diisocyanate, to a mixture of the at least one amine such as monoamine in the presence of at least one OH-functional polymer, preferably of at least one OH-functional (meth)acrylic copolymer, which can be identical to or different from the at least one OH-functional polymer a1). Thereby an adduct bearing both at least one urea and at least one urethane moiety is formed.

[0090] Preferably, urea moiety or moieties containing constituent a4) does not contain any free NCO-groups, in particular no remaining free NCO-groups due to using the diisocyanate and / or polyisocyanate for its preparation. Alternatively, such NCO-groups may still be present, which will then react with the OH-groups of at least constituent a1) under formation of additionally present urethane bonds within a4).

[0091] Polyisocyanates, which can be used in principle for preparing constituent a4), are organic monomers, oligomers and polymers containing two or more isocyanate groups per molecule. Diisocyanates, which can be used in principle for preparing constituent a4), are organic monomers, oligomers and polymers containing precisely two or isocyanate groups per molecule. The diisocyanates and / or polyisocyanates which can be used are preferably selected from those as disclosed and named hereinafter in connection with constituent b2) contained in the hardener component B). It is also possible to use reaction products as diisocyanates and / or polyisocyanates, which contain isocyanate groups and are in turn the products of reaction of for example, polyols and polyamines and polyisocyanates. The diisocyanates and / or polyisocyanates can be aliphatic including cycloaliphatic or aromatic. Preference is given to using diisocyanates, very specifically aliphatic diisocyanates, more particularly hexamethylene diisocyanate. The following are mentioned as examples of polyisocyanates and / or diisocyanates that can be used: tetramethylene 1 ,4-diisocyanate, hexamethylene 1 ,6-diisocyanate, cyclohexyl 1 ,4-diisocyanate, dicyclohexylmethane 4, 4-diisocy anate, 1 ,5-dimethyl-(2,4-omega-diisocyanatomethyl)benzene, 1 , 5-dimethy l-(2, 4- omega-diisocyanato-ethyl)benzene, 1 ,3,5-trimethyl-(2,4-omega-diisocyanatomethyl)benzene, 1 ,3,5-triethy l-(2,4- omega-diisocyanatomethyl)benzene, the trimer of hexamethylene 1 ,6-diisocyanate, isophorone diisocyanate, 2,4- toluene diisocyanate and / or 2,6-toluene diisocyanate.

[0092] Monoamines, which can be used in principle for preparing constituent a4), are organic monomers, oligomers and polymers containing precisely one amino group per molecule. The amines can be selected from primary amines, secondary amines, diamines, ketamines, aldimines or combinations thereof. The amines are preferably amine monomers. Most preferably, the amines are a primary amines, even more preferred primary monoamines. The amino group is preferably a primary or secondary, more preferably a primary amino group. The monoamine can be aliphatic including cycloaliphatic or aromatic. Examples of primary amines include benzyl amine, ethyl amine, n- propylamine, 2-propylamine, 1-butylamine, 2-butylamine, t-butylamine, n-pentylamine, o-methylbutylamine, a- ethylpropylamine, p-ethylbutylamine, 1 -hexylamine, 2-hexylamine, 3-hexylamine, octylamine, decylamine, laurylamine, stearylamine, cyclohexylamine, and aniline. Most preferred the amine is benzyl amine.

[0093] Other suitable primary amines include alkyl ether amines, such as, for example, 2-aminoethanol alkyl ether, 3- aminopropanol alkyl ether, and 2-ami nopropanol alkyl ether. Examples of secondary amines can include, for example, the N-alkyl derivatives of any of the primary amines listed above wherein alkyl means an alkyl radical having in the range of from 1 to 10 carbon atoms. Examples of diamines can include, aliphatic and cycloaliphatic diamines such as, for example, ethylene diamine, 1 ,2-propylenediamine, 1 ,3-diaminopropane, 1 ,4-butanediamine, neopentanediamine, 4,4-diaminodicyclohexylmethane, isophoronediamine, hexamethylenediamine, 1 ,12- dodecanediamine, piperazine, polyether diamines, polytrimethylene ether diamine or a combination thereof. Examples of preferred monoamines are ethylamine, 1-propyamine, 2-propylamine, 1-butylamine, 2-buty amine, benzylamine and methoxypropylamine. Most preferred are benzylamine or methoxypropylamine.

[0094] Preferably, the at least one amine, more preferably monoamine, is used in an amount for preparing constituent a4) that ensures that all isocyanate groups of the polyisocyanates and / or diisocyanates used are converted to urea groups. In this case the adduct is formed only from making use of the polyisocyanate and / or diisocyanate and the amine such as monoamine.

[0095] Constituent a4) is preferably prepared in the form of a paste containing at least one organic solvent such as at least one organic solvent a3) and also at least one polymer such as an OH-functional polymer such as at least one part of the at least one OH-functional polymer a1). This paste may then be used for preparation of component A). Thus, constituent a4) may be prepared, for example, directly in the presence of at least one polymer such as an OH- functional polymer such as at least one part of the at least one OH-functional polymer a1). In this case, the procedure for preparing the paste, for example, is to add the amine such as monoamine such as methoxypropylamine or benzylamine to a solution or dispersion of at least one polymer such as an OH-functional polymer such as at least one part of the at least one OH-functional polymer a1) in at least one organic solvent or in a mixture of organic solvents such as at least one organic solvent a3), and then to add the polyisocyanate and / or diisocyanate. In such a case there may be also, for example, as already outlined hereinbefore occurring a linking of the polyisocyanate and / or diisocyanate and / or of a precursor of constituent a4) still containing isocyanate groups, with the at least one OH-functional polymer.

[0096] Urea moiety or moieties containing constituent a4) as adduct of a polyisocyanate and / or diisocyanate and methoxypropylamine in the form of mixtures with OH-functional polymers are available, for example, as commercial products of the company Allnex. An example is Setalux® 81753 SS-55. Urea moiety or moieties containing constituent a4) as adduct of a polyisocyanate and / or diisocyanate and benzylamine in the form of mixtures with OH-functional polymers are also available, for example, as commercial products of the company Allnex. An example is Setalux® 91756 VS-60.

[0097] Optional constituent a5)

[0098] Preferably, component A) further comprises at least one melamine resin, more preferably at least one melamine aldehyde resin, even more preferably at least one melamine formaldehyde resin as optional constituent a5). Preferably, the melamine aldehyde resins, more preferably the melamine formaldehyde resins, in each case bear at least one of imino groups, alkykol groups and etherified alkylol groups as functional groups. Examples of alkylol groups are methylol groups.

[0099] At least some of the alkylol groups present in the melamine aldehyde resins may be alkylated through further reaction with at least one alcohol to produce nitrogen-bonded alkoxyalkyl groups (etherified alkylol groups). In particular, the hydroxyl groups in the nitrogen-bonded alkylol groups may be reacted with the alcohol through an etherification reaction to produce nitrogen-bonded alkoxyalkyl groups. The alkoxyalkyl groups are available for a crosslinking reaction with, for example, suitable crosslinkable functional groups such as OH- and / or acid groups. The remaining imino groups present after the aldehyde / melamine reaction are unreactive with the alcohol used for alkylation. As outlined above the alkylol groups of the melamine aldehyde resins may be partially alkylated. By "partially alkylated”, it is meant that a sufficiently low amount of alcohol is reacted with the melamine aldehyde resins to leave some of the alkylol groups in the melamine aldehyde resins, under reaction conditions that should result in incomplete alkylation of the alkylol groups. When the melamine aldehyde resins are partially alkylated, they are typically alkylated with alcohol in amounts sufficient to leave alkylol groups present in the aminoplast in an amount of at least about 2%, more preferably of from about 10% to about 50%, even more preferably of from about 15% to about 40%, in each case based on the total number of reactive sites present in the melamine prior to reaction. Typically, the melamine aldehyde resin is partially alkylated to obtain from about 40 to about 98% of alkoxyalkyl groups, more preferably of from about 50% to about 90%, even more preferably of from about 60% to about 75%, in each case based on the total number of reactive sites present in the melamine prior to reaction.

[0100] Preferably, at least a portion, more preferably only a portion, of the alkylol groups such as methylol groups of the melamine aldehyde resin is etherified by reaction with at least one alcohol. Any monohydric alcohol can be employed for this purpose, including methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, t-butanol, pentanol, hexanol, heptanol, as well as benzyl alcohol and other aromatic alcohols, cyclic alcohols such as cyclohexanol, monoethers of glycols, and halogen-substituted or other substituted alcohols such as 3- chloropropanol and butoxyethanol. In particular, at least a part of the alkylol groups of the melamine aldehyde resin is partially modified with methanol and / or n-butanol and / or iso-butanol.

[0101] Preferably, component A) of the clearcoat system comprises the at least one constituent a5) in an amount in a range of from 0.1 to 20.0 wt.-%, preferably of from 0.5 to 15.0 wt.-%, more preferably of from 1.0 to 10.0 wt.-%, based on the total weight of component A).

[0102] Optional constituent a6)

[0103] Preferably, component A) further comprises at least one catalyst as optional constituent a6).

[0104] Preferably, component A) of the clearcoat system comprises the at least one catalyst a6) in an amount in a range of from 0.01 to 6.00 wt.-%, preferably of from 0.10 to 5.00 wt.-%, more preferably of from 0.40 to 4.00 wt.-%, still more preferably of from 0.50 to 3.00 wt.-%, yet more preferably of from 0.75 to 2.00 wt.-%, most preferably of from 1 .00 to 1 .50 wt.-%, based on the total weight of component A).

[0105] The catalyst a6) can be a catalyst suitable for crosslinking of silane groups, more preferably for the crosslinking of the silane groups and / or Si-functional groups present within constituent b1).

[0106] Examples of constituent a6) are metal complexes with chelate ligands based on zinc or aluminum, such as Lewis acids or the titanates described in WO 05 / 03340 A1 , for example. Other examples include phosphorus-containing, more particularly phosphorus-containing and nitrogen-containing, catalysts for use as catalyst a6). Examples of suitable phosphorus-containing catalysts are substituted phosphonic diesters and diphosphonic diesters, preferably selected from the group consisting of acyclic phosphonic diesters, cyclic phosphonic diesters, acyclic diphosphonic diesters and cyclic diphosphonic diesters. More particularly, however, use as at least one catalyst a6) is made of substituted phosphoric monoesters and phosphoric diesters, preferably selected from the group consisting of acyclic phosphoric diesters and monoesters and cyclic phosphoric diesters and monoesters, which may be in each case amine adducts, e.g., of phosphoric monoesters and diesters. Examples of such amine adducts are corresponding amine-blocked phosphoric esters, and, of these, more particularly, amine-blocked ethylhexyl phosphates and amine-blocked phenyl phosphates, very preferably amine-blocked bis(2-ethylhexyl) phosphate. Examples of amines with which the phosphoric esters are blocked are, in particular, tertiary amines, examples being bicyclic amines, such as diazabicyclooctane (DABCO), diazabicyclononene (DBN), diazabicycloundecene (DBU), dimethyldodecylamine or triethylamine, for example. Particularly preferred for blocking the phosphoric esters is the use of tertiary amines which ensure high activity of the catalyst under the curing conditions. Certain amine-blocked phosphoric acid catalysts are also available commercially (e.g., Nacure types from King Industries such as Nacure® 4167).

[0107] Preferably, however, at least one sulfonic acid such as an unblocked sulfonic acid or a blocked sulfonic acid, more preferably at least one unblocked sulfonic acid, is used as catalyst a6). Examples of unblocked sulfonic acids are para-toluenesulfonic acid (pTSA), methanesulfonic acid (MSA), dodecylbenzene sulfonic acid (DDBSA), dinonylnaphthalene disulfonic acid (DNNDSA), and mixtures thereof. Blocking can be performed by making use of ammonium salts and / or organic amines. Alternatively, blocking may also be performed by making use of epoxides that form p-OH-sulfonates when reversibly reacted with sulfonic acids.

[0108] Optional constituent a7)

[0109] Component (A) may comprise - besides the at least one OH-functional polymer a1) -at least one further polymer as constituent a7), which may also function as binder, and which is different from OH-functional polymer a1), such as a OH-functional polyester.

[0110] Constituent a7) preferably comprises crosslinkable groups, more preferably selected from the group consisting of hydroxyl groups, primary amino groups, secondary amino groups, thiol groups, carboxyl groups and carbamate groups. Preferably, an optionally present constituent a7) has, e.g., carbamate groups. Optional constituent a7) may be, e.g., a carbamate-functional (meth)acrylic copolymer and / or a polyester that may additionally comprise OH- groups. Likewise, e.g., polyethers and / or polyurethanes may also be used as a7).

[0111] Optional constituent a8)

[0112] Component A) can optionally comprise one or more further constituents as a8). Component A) may contain one or more commonly used additives depending on the desired application. For example, it may comprise at least one additive selected from the group consisting of reactive diluents, light stabilizers, antioxidants, deaerators, emulsifiers, slip additives, polymerization inhibitors, plasticizers, initiators for free-radical polymerizations, adhesion promoters, flow control agents, film-forming auxiliaries, flame retardants, corrosion inhibitors, siccatives, biocides, thickeners, wetting agents, levelling agents and / or matting agents. They can be used in the known and customary proportions. Preferably, their content, based on the total weight of the coating composition obtained from mixing components A) and B) and optionally C) is 0.01 to 20.0 wt.-%, more preferably 0.05 to 15.0 wt.-%, particularly preferably 0.1 to 10.0 % by weight, even more 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, in each case based on the total weight of the coating composition.

[0113] Component B)

[0114] Component B), which represents a hardener component, comprises at least constituents b1) and b2) and optionally constituent b3), which are different from one another, but may comprise further optional constituent(s).

[0115] In component B), 0.1 to <29.5mol-% of all originally present isocyanate groups, based on the total molar amount of all originally present isocyanate groups of all isocyanate groups containing constituents present in component B) including constituent b1) and constituent b2), have undergone reaction with at least one silane prior to its / their incorporation into component B). Preferably, in component B), 0.2 to 27.5 mol-%, preferably 0.5 to 25.0 mol-%, more preferably 0.8 to 22.5 mol-%, even more preferably 1.0 to 20.0 mol-%, still more preferably 1.2 to 18.0 mol- %, yet more preferably 1.5 to 16.0 mol-%, still more preferably 2.0 to 15.0 mol-%, even more preferably 2.2 to 14.0 mol-%, still more preferably 2.5 to 12.0 mol-%, yet more most preferably 2.8 to 11 .5 mol-%, and most preferably 3.0 to 11.0 mol-%, of all originally present isocyanate groups, based on the total molar amount of all originally present isocyanate groups of all isocyanate groups containing constituents present in component B) including constituent b1) and constituent b2), have undergone reaction with at least one silane prior to its / their incorporation into component B).

[0116] Preferably, component B) of the coating system has a total solids content, which is >40 wt.-%, more preferably >45 wt.-%, even more preferably >50 wt.-%, still more preferably >55 wt.-%, in each based on the total weight of component B). The total solids content of component B) of the coating system is preferably in a range of from 45 to 100 wt.-%, more preferably of from 50 to <100 wt.-%, even more preferably of from 55 to <100 wt.-%, based in each case on the total weight of component B). The total solids content, in other words the non-volatile fraction, is determined in accordance with the method described hereinafter.

[0117] Constituent b1)

[0118] Constituent b1) is at least one organic constituent b1) bearing on average two or more isocyanate groups, wherein at least a part of these isocyanate groups has been reacted with at least one silane prior to incorporation of constituent b1) into component B).

[0119] Examples of constituents b1) are, e.g., disclosed in WO 2009 / 077181 A1 , WO 2010 / 139375 A1 , WO 2010 / 063332 A1 , WO 2014 / 086530 A1, and WO 2014 / 086529 A1.

[0120] Preferably, constituent b1) bears at least one structural unit of the formula (I)

[0121] -NR-(X-SiR"x(OR')3-x) (I), and / or, preferably and, at least one structural unit of the formula (II)

[0122] -N(X-SiR"x(OR')3-x)n(X'-SiR"y(OR')3-y)m(II), wherein:

[0123] R = hydrogen, alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRagroups, where Ra= alkyl, cycloalkyl, aryl or aralkyl, each R' = independently of one another hydrogen, alkyl or cycloalkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRagroups, each R' preferably = ethyl and / or methyl, each X,X' = independently of one another linear and / or branched alkylene or cycloalkylene radical having 1 to 20 carbon atoms, preferably each X,X' = alkylene radical having 1 to 4 carbon atoms, each R" = independently of one another alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRagroups, each R” preferably = alkyl radical, more particularly having 1 to 6 C atoms, n = parameter of 0 to 2, m = parameter of 0 to 2, m+n = 2, and x, y = parameter of 0 to 2.

[0124] The respective preferred alkoxy radicals (OR1) may be identical or different, but what is decisive for the structure of the radicals is the extent to which they influence the reactivity of the hydrolysable silane groups. Preferably R' is an alkyl radical, more particularly having 1 to 6 carbon atoms. Particularly preferred are radicals R' which increase the reactivity of the silane groups, i.e., represent good leaving groups. Accordingly, a methoxy radical is preferred over an ethoxy radical, which in turn is preferred over a propoxy radical. With particular preference, therefore, R' = ethyl and / or methyl, more particularly methyl. The reactivity of organofunctional silanes may also be influenced considerably, furthermore, by the lengths of the spacers X, X' between silane functionality and organic functional group which serves for reaction with the constituent to be modified. Examples thereof that may be mentioned include the "alpha” silanes, which are obtainable from the company Wacker, and in which there is a methylene group, instead of the propylene group present in the case of "gamma” silanes, between Si atom and functional group.

[0125] In constituent b1) preferably, between 10 and 80 mol-%, preferably between 15 and 70 mol-%, more preferably between 20 and 50 mol-% and still more preferably between 25 and 40 mol-% of the isocyanate groups originally present have undergone reaction with the at least one silane, preferably to form structural units (I) and / or (II), more preferably to form structural units (I) and (II).

[0126] Moreover, preference is given to constituent b1), in which the total amount of structural units (I) is between 2 and 90 mol-%, more preferably between 3 and 70 mol-%, based in each case on the entirety of the structural units (I) plus (II), and the total amount of structural units (II) is between 98 and 10 mol-%, more preferably between 97 and 30 mol-%, based in each case on the entirety of the structural units (I) plus (II).

[0127] The at least one organic constituent b1) bearing on average two or more NCO-groups, which serves - before reaction with at the least one silane - as the parent structure for the constituent b1) represent at this stage before reaction with the at least one silane a di- and / or polyisocyanate. Preferably, said at least one di- and / or polyisocyanate is an aromatic, aliphatic, cycloaliphatic and / or heterocyclic di- and / or polyisocyanate, in particular an aliphatic alicyclic and / or cyclic di- and / or polyisocyanate.

[0128] Preferably, the at least one organic constituent b1) present in component B) has an aliphatic or cycloaliphatic structure and / or a parent structure that is derived from an aliphatic or cycloaliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation. Trimers, i.e., isocyanurates, of IPDI (isophorone diisocyanate) and / or HDI (hexamethylene diisocyanate) are particularly preferred.

[0129] Preferably, the at least one organic constituent b1) has a cycloaliphatic parent structure and / or a parent structure, it is derived from a cycloaliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, wherein constituent b1) has at least one structural unit of the formula (I) and / or (II). Alternatively, or additionally, the at least one organic constituent b1) preferably has an acyclic aliphatic parent structure and / or a parent structure that is derived from an acyclic aliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, wherein constituent b1) has at least one structural unit of the formula (I) and / or (II). Most preferably, the at least one organic constituent b1) has an acyclic aliphatic parent structure and / or a parent structure that is derived from an acyclic aliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, wherein constituent b1) has at least one structural unit of the formula (I) and / or (II). Trimers, i.e. , isocyanurates, are particularly preferred.

[0130] The acyclic aliphatic polyisocyanates serving as parent structures are preferably substituted or unsubstituted aliphatic polyisocyanates that are known per se. 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 aforementioned polyisocyanates.

[0131] Additionally preferred polyisocyanate parent structures are the polyisocyanates derived from such an acyclic aliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, more particularly the biuret dimer and / or the allophanate dimer and / or the isocyanurate trimer. The polyisocyanate parent structures may also be polyisocyanate prepolymers having urethane structural units which are obtained by reaction of polyols with a stoichiometric excess of aforementioned acyclic aliphatic polyisocyanates. Polyisocyanate prepolymers of this kind are described for example in US-A- 4,598, 131. Particularly preferred polyisocyanate parent structures are hexamethylene diisocyanate and / or its biuret dimer and / or allophanate dimer and / or isocyanurate trimer and / or its uretdione, and also mixtures of the stated polyisocyanate parent structures. Especially preferred polyisocyanate parent structures are hexamethylene diisocyanate and / or its isocyanurate trimer, optionally together with its uretdione.

[0132] The cycloaliphatic polyisocyanates used as parent structures are preferably substituted or unsubstituted cycloaliphatic polyisocyanates which are known per se. Examples of preferred polyisocyanates are isophorone diisocyanate, cyclobutane 1 ,3-diisocyanate, cyclohexane 1 ,3-diisocyanate, cyclohexane 1 ,4-diisocyanate, methylcyclohexyl diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2,6-diisocyanate, hexahydrophenylene 1 ,3-diisocyanate, hexahydrophenylene 1 ,4-diisocyanate, perhydrodiphenylmethane 2,4'- diisocyanate, 4,4’-methylendicyclohexyl diisocyanate (e.g. Desmodur ® W from Bayer AG) and mixtures of the aforementioned polyisocyanates. Additionally preferred polyisocyanate parent structures are the polyisocyanates derived from such a cycloaliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, more particularly the biuret dimer and / or the allophanate dimer and / or the isocyanurate trimer. The polyisocyanate parent structures may be ppolyisocyanate prepolymers having urethane structural units which are obtained by reaction of polyols with a stoichiometric excess of aforementioned cycloaliphatic polyisocyanates. Such polyisocyanate prepolymers are described for example in US-A-4,598, 131 . Particularly preferred cycloaliphatic polyisocyanates are isophorone diisocyanate and 4,4'- methylenedicyclohexyl diisocyanate and / or the biuret dimers thereof and / or the allophanate dimers thereof and / or the isocyanurate trimers thereof. The at least one silane used for reaction with at least one organic constituent b1) bearing on average two or more NCO-groups prior to incorporation of b1) into the (B) component is preferably at least one compound of the formula (la)

[0133] H-NR-(X-SiR"x(OR')3-x) (la), and / or at least one compound of the formula (Ila) HN(X-SiR"x(OR')3-x)n(X'-SiR"y(OR')3-y)m (Ha), where the substituents have the definitions stated above including the preferred definitions.

[0134] Preferred compounds (la) are aminoalkyltrialkoxysilanes, such as, preferably, 2-aminoethyltrimethoxysilane, 2- aminoethyltriethoxysilane, 3-aminopropyltrimethoxy-silane, 3-aminopropyltriethoxysilane, 4-amino- butyltrimethoxysilane, 4-aminobutyltriethoxysilane. Particularly preferred compounds (la) are N-(2- (trimethoxysilyl)ethyl)alkylamines, N-(3-(trimethoxysilyl)propyl)alkylamines, N-(4-(trimethoxysilyl)butyl)alkylamines, N-(2-(triethoxysilyl)ethyl)alkylamines, N-(3-(triethoxysilyl)propyl)alkylamines and / or N-(4- (triethoxysilyl)butyl)alkylamines. Especially preferred is N-(3-(trimethoxysilyl)propyl)butylamine. Aminosilanes of these kinds are available for example under the brand name DYNASYLAN® from DEGUSSA or Silquest® from OSI.

[0135] Preferred compounds (Ila) are bis(2-ethyltrimethoxysilyl)amine, bis(3-propyltrimethoxysilyl)amine, bis(4- butyltrimethoxysilyl)amine, bis(2-ethyltriethoxysilyl)amine, bis(3-propyltriethoxysilyl)amine and / or bis(4- buty Itriethoxysily l)amine. Especially preferred is bis(3-propy Itrimethoxysily l)ami ne. Aminosilanes of these kinds are available for example under the brand name DYNASYLAN® from DEGUSSA or Silquest® from Momentive.

[0136] Constituent b2)

[0137] Organic constituent b2) is different from organic constituent b1) and bears on average two or more isocyanate groups, wherein none of the isocyanate groups of constituent b2) has been reacted with at least one silane prior to incorporation of constituent b2) into component B). Thus, the at least one organic constituent b2) bearing on average two or more NCO-groups does not contain any silane modified NCO-groups.

[0138] Preferably, the at least one organic constituent b2) is present in component B), more preferably in an amount that exceeds the amount of constituent b1), preferably both by weight and in the sense of a molar amount.

[0139] Preferably, the at least one organic constituent b2) optionally present in component B) has an aliphatic or cycloaliphatic structure and / or a parent structure that is derived from an aliphatic or cycloaliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation. Trimers, i.e., isocyanurates, of IPDI (isophorone diisocyanate) and / or HDI (hexamethylene diisocyanate) are particularly preferred.

[0140] Suitable aliphatic polyisocyanates are preferably substituted or unsubstituted aliphatic polyisocyanates such as 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 aforementioned polyisocyanates. Suitable polyisocyanate parent structures may be polyisocyanate prepolymers having urethane structural units which are obtained by reaction of polyols with a stoichiometric excess of aforementioned aliphatic polyisocyanates. Particularly preferred polyisocyanate parent structures are hexamethylene diisocyanate and / or its biuret dimer and / or allophanate dimer and / or isocyanurate trimer and / or its uretdione, and also mixtures of the stated polyisocyanate parent structures. Especially preferred polyisocyanate parent structures are hexamethylene diisocyanate and / or its isocyanurate trimer, optionally together with its uretdione.

[0141] Suitable cycloaliphatic polyisocyanates are preferably substituted or unsubstituted cycloaliphatic polyisocyanates such as isophorone diisocyanate, cyclobutane 1 ,3-diisocyanate, cyclohexane 1 ,3-diisocyanate, cyclohexane 1 ,4- diisocyanate, methylcyclohexyl diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2,6- diisocyanate, hexahydrophenylene 1 ,3-diisocyanate, hexahydrophenylene 1 ,4-diisocyanate, perhydrodiphenylmethane 2,4'-diisocyanate and 4,4'-methylendicyclohexyl diisocyanate and mixtures of the aforementioned polyisocyanates. Suitable polyisocyanate parent structures may be polyisocyanates derived from a cycloaliphatic polyisocyanate by trimerization, dimerization, urethane formation, biuret formation, uretdione formation and / or allophanate formation, more particularly the biuret dimer and / or the allophanate dimer and / or the isocyanurate trimer. The polyisocyanate parent structures may be polyisocyanate prepolymers having urethane structural units which are obtained by reaction of polyols with a stoichiometric excess of aforementioned cycloaliphatic polyisocyanates. Particularly preferred cycloaliphatic polyisocyanates are isophorone diisocyanate and 4,4'-methy lenedicyclohexy I diisocyanate and / or the biuret dimers thereof and / or the allophanate dimers thereof and / or the isocyanurate trimers thereof.

[0142] Optional constituent b3)

[0143] Optional constituent b3) is at least one organic solvent. Examples of such organic solvents include the ones already mentioned hereinbefore in connection with constituent a3). Component B) may comprise more than one organic solvent b3). The at least one organic solvent b3) may the identical to or different from the at least one organic solvent a3) and / or d). If more than one organic solvent is used as a3) and / or b3) it may be that a3) and b3) are both partially identical and partially different.

[0144] Preferably, the amount of constituent b3) in component B), if present, is in the range of from 5 to 50 wt.-%, more preferably of from 7.5 to 40 wt.-%, even more preferably of from 10 to 20 wt.-%, based in each case on the total weight of component B). Optional component (0)

[0145] Optional component C) is a reducer component and comprises at least one organic solvent d) and preferably consists of at least one organic solvent d). Examples of such organic solvents include the ones already mentioned hereinbefore in connection with constituents a3) and b3). Component C) may comprise more than one organic solvent d). The at least one organic solvent d) may the identical to or different from the at least one organic solvent a3) and / or b3). If more than one organic solvent is used as a3) and / or b3) and / or d) it may be that a3) and / or b3) and / or d) are both partially identical and partially different.

[0146] Coating composition

[0147] A further subject-matter of the present invention is a clearcoat composition obtainable by mixing components A) and B) and optionally C) of the coating system with each other.

[0148] All preferred embodiments described above herein in connection with the inventive coating system and the preferred embodiments thereof, are also preferred embodiments of the inventive coating composition.

[0149] The preparation of the coating composition can be carried out using customary and known preparation and mixing methods and mixing units, or using conventional dissolvers and / or stirrers.

[0150] Preferably, the clearcoat composition is a solventborne, i.e., an organic solvent(s) based, coating composition, preferably due to the presence of constituents a3) and / or b3) and optionally d). The term "solventborne” in connection with the coating composition is understood preferably for the purposes of the present invention to mean that the aforementioned organic solvent(s), as solvent and / or as diluent, is / are present as the main constituent(s) of all solvents and / or diluents present therein, preferably in an amount of at least 35 wt.-%, based on the total weight of the coating composition. Thus, preferably, the coating composition is not a waterborne, i.e., an aqueous, coating composition.

[0151] The coating composition preferably includes an organic solvent(s) fraction of at most 65 wt.-%, more preferably of at most 60 wt.-%, even more preferably of at most 55 wt.-%, still more preferably of at most 50 wt.-%, yet more preferably of at most 48 wt.-%, in particular of at most 45 wt.-% or of at most 40 wt.-% or of at most 35 wt.-%, based in each case on the total weight of the coating composition. All conventional organic solvents known to those skilled in the art can be used as organic solvents, i.e., as constituents a3) and b3) and optionally d ). The term "organic solvent" is known to those skilled in the art, in particular from Council Directive 1999 / 13 / EC of 11 March 1999. Examples of the organic solvents which can be used have been mentioned hereinbefore in connection with constituents a3) and b3) and d). Preferably, the coating composition has a total solids content, which is >35 wt.-%, more preferably >40 wt.-%, even more preferably >45 wt.-%, still more preferably >50 wt.-%, based in each case on the total weight of the coating composition. The total solids content of the coating composition is preferably in a range of from >35 to 75 wt.-%, more preferably of from >40 to 70 wt.-%, even more preferably of from >45 to 65 wt.-%, still more preferably of from >48 to 60 wt.-%, based in each case on the total weight of the coating composition. The total solids content, in other words the non-volatile fraction, is determined in accordance with the method described hereinafter.

[0152] The clearcoat compositions of the invention are employed in particular in the technologically and esthetically particularly demanding field of automotive OEM finishing and also of automotive refinish.

[0153] The term "clear coat”, "clearcoat” or "clear coating” is known to a person skilled in the art and preferably represents a substantially transparent or transparent outermost layer preferably of a multilayer coating structure applied to a substrate.

[0154] Preferably, the clearcoat composition is obtainable by mixing components A) and B) in a weight ratio (component A) / component B)) in the range of from 6:1 to 1 :3. More preferably, mixing is performed in a weight ratio in the range of from 5: 1 to 1 :2, even more preferably in a weight ratio in the range of from 4: 1 to 1 : 1 .5, in particular in a weight ratio in the range of from 3.5: 1 to 1 :1.2, most preferred in a weight ratio in the range of from 3:1 to 1 :1.

[0155] Preferably, the clearcoat composition does not comprise more than 5 wt.-% of pigments and / or fillers, based on its total weight, since otherwise the transparency or desired clarity of the clearcoat coating layer produced from the composition could be affected. More preferably, the clearcoat composition is free of any pigments and / or fillers, in particular of any effect pigments.

[0156] Method of coating

[0157] A further subject-matter of the present invention is a method of coating a substrate, comprising at least one step of applying to an optionally pre-coated substrate the inventive clearcoat composition, preferably via spray application, to form at least one coating film onto the optionally pre-coated substrate, and optionally comprising at least one further step of curing the at least one coating film to obtain at least one cured coating layer onto the substrate.

[0158] All preferred embodiments described hereinabove in connection with the inventive coating system and clearcoat composition are also preferred embodiments with regard to the aforementioned inventive method.

[0159] The pre-coated substrate can be a substrate that already bears a coating system on at least one of its surfaces, e.g., an electrodeposition coat, onto which at least one of a primer, filler and basecoat material has been applied. The pre-coated substrate can also be a substrate that bears on at least one of its surfaces, e.g., an electrodeposition coat, and, further at least one sealant material on top of the electrodeposition coat, such as a sealant material, which is a plastic material, e.g., a PVC material.

[0160] Preferably, the inventive method is a method of preparing a multilayer coating system onto an optionally pre-coated substrate comprising at least steps 1), 3), and 4), and optionally 2), namely

[0161] 1) applying a first coating composition to an optionally pre-coated substrate and forming a first coating film on the optionally pre-coated substrate,

[0162] 2) optionally applying a second coating composition to the first coating film present on the substrate obtained after step 1) prior to curing the first coating film and forming a second coating film adjacent to the first coating film,

[0163] 3) applying a third coating composition to the first coating film present on the substrate obtained after step 1) prior to curing the first coating film and forming a third coating film adjacent to the first coating film in case optional step 2) is not performed or applying a third coating composition to the second coating film present on the substrate obtained after step 2) prior to curing the second coating film and forming a third coating film adjacent to the second coating film in case optional step 2) is performed, wherein the third coating composition is an inventive clearcoat composition as defined hereinbefore and hereinafter, and

[0164] 4) jointly curing the first and third and optionally second coating films, the cured third coating film being the outermost layer of the formed multilayer coating system, to obtain cured first, optionally second, and third coating layers.

[0165] Examples of coating compositions that are applied as first coating composition are primer and basecoat compositions. Examples of coating compositions that are applied as second coating composition are basecoat compositions. The term "primer” is known to a person skilled in the art. A primer typically is applied after the substrate has been provided with a cured electrodeposition coating layer in case of metallic substrates. In this case, the cured electrodeposition coating film is present underneath and preferably adjacent to the primer coating film. This is an example of a pre-coated substrate. In case of non-metallic substrates such as plastic substrates including fiber reinforced plastic substrates the primer coating film typically represents the first coating film applied onto their surfaces. The term "basecoat” is known to a person skilled in the art as well and, for example, defined in Rdmpp Lexikon, paints and printing inks, Georg Thieme Verlag, 1998, 10th edition, page 57. A basecoat is therefore in particular used in automotive painting and general industrial paint coloring in order to give a coloring and / or an optical effect by using the basecoat as an intermediate coating composition. This is generally applied to a metal or plastic substrate, in each case being optionally pre-coated. In order to protect a basecoat film in particular against environmental influences, at least one additional clearcoat film is applied to it. The term "clear coat”, "clearcoat” or "clear coating” is also known to a person skilled in the art and represents a transparent outermost layer of a multilayer coating structure applied to a substrate.

[0166] Any type of basecoat and primer composition can be used, e.g., a 1 K- or 2K-basecoat or primer composition, preferably a 1 K-composition, which may be solventborne or aqueous and may contain coloring and / or effect pigments. Preferably, the basecoat or primer composition comprises at least one film-forming binder, preferably at least one polymer, more preferably at least one polymer, which has functional groups that are reactive towards NCO-groups. Optionally, the basecoat or primer composition may include at least one crosslinking agent, preferably selected from melamine formaldehyde resins and / or preferably blocked polyisocyanates, in particular in case the at least film-forming binder is an externally crosslinking polymer.

[0167] Preferably, at least step 3), more preferably also step 1) and optional step 2) is performed via a spray application.

[0168] The first, optionally second, and third coating film formed on the optionally pre-coated substrate by performing step 1), optional step 2), and step 3) are at this stage each an uncured coating film. Thus, both the first and the optionally second and the third coating compositions are applied wet-on-wet.

[0169] The method of the invention is particularly suitable for the coating of automotive vehicle bodies or parts thereof including respective metallic substrates, but also plastic substrates such as polymeric substrates. Consequently, the preferred substrates are automotive vehicle bodies or parts thereof.

[0170] Suitability as metallic substrates used in accordance with the invention are all substrates used customarily and known to the skilled person. The substrates used in accordance with the invention are preferably metallic substrates, 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, for example, Galvalume, Galvannealed or Galfan) and aluminized steel, aluminum and magnesium, and also Zn / Mg alloys and Zn / Ni alloys. Particularly suitable substrates are parts of vehicle bodies or complete bodies of automobiles for production.

[0171] The substrate used in accordance with the invention is preferably a metallic substrate pretreated with at least one metal phosphate such as zinc phosphate and / or pretreated with at least one an oxalate. A pretreatment of this kind by means of phosphating or oxalating, which takes place normally after the substrate has been cleaned and before the substrate is electrodeposition-coated, is in particular a pretreatment step that is customary in the automobile industry. The metallic substrate may further comprise a cured electrodeposition coating layer as pre-coat.

[0172] Preferably, thermoplastic polymers are used as plastic substrates. Suitable polymers are poly(meth)acrylates including polymethyl(meth)acrylates, polybutyl (meth)acrylates, polyethylene terephthalates, polybutylene terephthalates, polyvinylidene fluorides, polyvinyl chlorides, polyesters, including polycarbonates and polyvinyl acetate, polyamides, polyolefins such as polyethylene, polypropylene, polystyrene, and also polybutadiene, polyacrylonitrile, polyacetal, polyacrylonitrile-ethylene-propylene-diene-styrene copolymers (A-EPDM), ASA (acrylonitrile-styrene-acrylic ester copolymers) and ABS (acrylonitrile-butadiene-styrene copolymers), polyetherimides, phenolic resins, urea resins, melamine resins, alkyd resins, epoxy resins, polyurethanes, including TPU, polyetherketones, polyphenylene sulfides, polyethers, polyvinyl alcohols, and mixtures thereof. Polycarbonates and poly(meth)acrylates are especially preferred. Further, fiber reinforced plastic substrates are used. Glass and / or carbon fibers can be in particular used for reinforcement, most preferably carbon fibers.

[0173] As outlined above the substrate used may be a pre-coated substrate, i.e., a substrate bearing at least one cured coating film. The substrate used in step 1) can be pre-coated with a cured electrodeposition coating layer. As outlined hereinbefore, a sealant material may be present on said cured electrodeposition coating layer such as a plastic material, e.g., a PVC material. The substrate can, e.g., be provided also with at least one cured primer coating film as at least one additional pre-coat. The term "primer” is known to a person skilled in the art. A primer typically is applied after the substrate has been provided with a cured electrodeposition coating layer. In case a cured primer coating film is also present, the cured electrodeposition coating film is present underneath and preferably adjacent to the cured primer coating film.

[0174] Preferably, the inventive method further comprises a step 1a), which is carried out after step 1) and before optional step 2). In said step 1a) the first coating film obtained after step 1) is flashed-off before applying the second coating material composition in optional step 2) preferably for a period of 1 to 20 minutes, more preferably for a period of 2 to 15 minutes, in particular for a period of 5 to 10 minutes. Preferably, step 1 a) is performed at a temperature not exceeding 40°C, more preferably at a temperature in the range of from 18 to 30°C.

[0175] Preferably, the inventive method further comprises a step 2a), which is carried out after step 2) and before step 3). In said step 2a) the second coating film obtained after step 2) is flashed-off before applying the third coating material composition in step 3) preferably for a period of 1 to 20 minutes, more preferably for a period of 2 to 15 minutes, in particular for a period of 5 to 10 minutes. Preferably, step 2a) is performed at a temperature not exceeding 40°C, more preferably at a temperature in the range of from 18 to 30°C.

[0176] Preferably, the inventive method further comprises a step 3a), which is carried out after step 3) and before step 4). In said step 3a) the third coating film obtained after step (3) is flashed-off before performing curing step 4) preferably for a period of 1 to 20 minutes, more preferably for a period of 2 to 15 minutes, in particular for a period of 5 to 10 minutes. Preferably, step 3a) is performed at a temperature not exceeding 40°C, more preferably at a temperature in the range of from 18 to 30°C. The term "flashing off” in the sense of the present invention preferably means a drying, wherein at least some and / or some amounts of the organic solvents are evaporated from the coating film, before the next coating composition is applied and / or a curing is carried out. No curing is performed by the flashing-off.

[0177] In step 4) of the inventive method the first and third coating films and optionally also the second coating film are jointly cured, i.e., are cured together simultaneously. The cured third coating film represents the outermost layer of the formed multilayer coating system obtained after step 4).

[0178] Each resulting cured coating film represents a coating layer. Thus, after performing step 4) a first and third and optionally also second coating layer are formed on the optionally pre-coated substrate, with the third layer being the outermost layer of the formed multilayer coating system.

[0179] Preferably, step 4) is performed at a temperature in a range of from 80 to 180 °C, more preferably in a range of from 100 to 170 °C, even more preferably in a range of from 120 to 160 °C, still more preferably in a range of from 130 to 150 °C, in each case for a period of 5 to 45 minutes, preferably for a period of 10 to 40 minutes, in particular for a period of 12.5 to 35 minutes, most preferably for a period of 15 to 30 minutes.

[0180] Preferably, the cured first coating film (layer L1), preferably obtained after having performed step 4) of the inventive method of preparing a multilayer coating system, has a dry film thickness in a range of from 10 to 35 pm. Preferably, the cured second film (layer L2), if present, preferably obtained after having performed step 4) of the inventive method of preparing a multilayer coating system, has a dry film thickness in a range of from 10 to 35 pm. Preferably, the cured clearcoat film (layer L3), preferably obtained after having performed step 4) of the inventive method of preparing a multilayer coating system, has a dry film thickness in a range of from 30 to 80 pm, more preferably of from 30 to 70 pm.

[0181] Coated substrate

[0182] A further subject-matter of the present invention is a coated substrate, which is obtainable by the inventive method.

[0183] All preferred embodiments described hereinabove in connection with the inventive coating system and clearcoat composition and method are also preferred embodiments with regard to the aforementioned inventive coated substrate.

[0184] Multilayer coating system

[0185] A further subject-matter of the present invention is a multilayer coating system being present on an optionally precoated substrate and comprising at least two coatings layers L1 and L3 and optionally at least one coating layer L2 being different from one another, namely a first coating layer L1 applied over at least a portion of an optionally pre-coated substrate, said layer L1 being preferably obtainable from the first coating composition applied in step 1) of the inventive method, optionally a second coating layer L2 applied over the first coating layer L1 , said layer L2 being preferably obtainable from the second coating composition applied in optional step 2) of the inventive method, and a third coating layer L3 applied over the first coating layer L1 or, if present, over the second coating layer L2, said layer L3 being obtainable from the inventive clearcoat composition.

[0186] All preferred embodiments described hereinabove in connection with the inventive coating system, clearcoat composition, method and coated substrate are also preferred embodiments with regard to the aforementioned inventive multilayer coating system.

[0187] Preferably, the at least two coatings layers L1 and L3 as well as optionally present layer L2 are being positioned adjacently to each other. Preferably, the third coating layer L3 is the outermost coating layer of the multilayer coating system.

[0188] Preferably, the multilayer coating system is obtainable by the inventive method of preparing a multilayer coating system, which has been described in detail hereinbefore.

[0189] Preferably, the multilayer coating system displays SW (short wave) values <20, more preferably <15, even more preferably < 10, the values being determined via the method disclosed in the specification.

[0190] METHODS

[0191] 1. Dry scratch resistance (Crockmeter test)

[0192] Dry scratch resistance was assessed with a Crockmeter according to DIN EN ISO 21546-2021-02 (10 double strokes; 9 m paper grain 3M 281 Q wetordry). The evaluation of tests was performed by conducting gloss measurements on the unstressed and stressed samples at a geometry of 20° with a commercially available reflectometer, with the percentage of residual gloss in view of initial gloss being expressed as test result.

[0193] 2. Wet scratch resistance (AMTEC)

[0194] Wet scratch resistance was assessed in an Amtec-Kistler Carwash test according to DIN EN ISO 20566, utilizing a polyethylene brush drum that was rotated over the surface of the samples. As the samples move beneath the brush, the brush rotates the bristles against the direction of sample movement. A quartz dispersion (1.5 g silica per liter of water) was sprayed during the test to simulate dirt and other abrasive particles. The samples were exposed to 10 cycles in the test apparatus to simulate carwash scratching. The initial gloss and residual gloss were measured at a geometry of 20° with a commercially available reflectometer before and after Amtec-Kistler test, respectively, with the percentage of residual gloss in view of initial gloss being expressed as test result.

[0195] 3. PVC compatibility testing

[0196] Clearcoats applied on PVC beads present on bonder plates obtained as disclosed in the experimental section were visually examined for cracks in the clearcoat. The number of cracks observed were given, e.g., 0 = zero cracks, 1 = one crack, etc.

[0197] 5. Solids content

[0198] The solids content (non-volatile fraction) was determined by drying approximately 1 g of the respective sample at a temperature of 130 °C for 60 min according to DIN EN ISO 3251 :2018-07, whereby the solid content resembles the residual amount of the respective sample in percent by weight.

[0199] 6. Hydroxyl value

[0200] The hydroxyl value indicates the quantity of KOH in mg that is equivalent to the amount of acetic acid bound in the acetylation of 1 g of sample. The hydroxyl value is based on the solids content of the sample. For the determination, if not indicated otherwise, the sample was boiled with acetic anhydride-pyridine and the resultant acid was titrated with potassium hydroxide solution (DIN EN ISO 4629-2:2016-12).

[0201] 7. Acid number

[0202] The acid number was determined according to DIN EN ISO 2114 (date: June 2002), using "method A”. The acid number corresponds to the mass of potassium hydroxide in mg required to neutralize 1 g of sample under the conditions specified in DIN EN ISO 2114. The acid number reported corresponds here to the total acid number as specified in the DIN standard and is based on the solids content.

[0203] 8. Viscosity

[0204] The viscosity was determined according to DIN EN ISO 2884-1.

[0205] 9. Weight-average molecular weight Mwand number-average molecular weight Mn

[0206] To determine polymer molecular weights by GPC, fully dissolved polymer samples were fractionated on a porous column stationary phase. A 0.1 mol / l acetic acid solution in tetrahydofuran (THF) was used as the eluent solvent. The stationary phase was a combination of Waters Styragel® HR 5, HR 4, HR 3, and HR 2 columns. Five milligrams of sample are added to 1.5 mL of eluent solvent and filtered through a 0.5 pm filter. After filtering, 100 pl of the polymer sample solution is injected into the column at a flow rate of 1 .0 mL / min. Separation takes place according to the size of the polymer coils which form in the eluent solvent. Small molecules diffuse into the pores of the column material more frequently and are therefore retarded more than large molecules. Thus, large molecules are eluted earlier than small molecules. The molecular weight distribution, the number-average Mnand weight-average Mwand the polydispersity Mw / Mnof the polymer samples are calculated with the aid of chromatography software utilizing a calibration curve generated with the EasyValid validation kit which includes a series of unbranched-polystyrene standards of varied molecular weights available from Polymer Standards Service.

[0207] 10. Glass transition temperature Tg

[0208] The glass transition temperature is measured by means of DSC measurements in accordance with DIN EN ISO 11357-2 (2019-03).

[0209] 11. Appearance

[0210] Appearance is determined by measuring short wave (SW) values of the coatings to be investigated via BYK wave scan meter 2.

[0211] 12. Median primary particle size

[0212] The median primary particle size is determined by transmission electron microscopy (TEM) according to ISO 21363:2020. EXAMPLES

[0213] The following examples further illustrate the invention but are not to be construed as limiting its scope. If not indicated otherwise, “%” values are weight percentage values and "part” or "parts” are parts by weight (pbw).

[0214] 1. Preparation of 2K clearcoat compositions C1-C6 (comparative) and 2K clearcoat compositions 11 to I3 (inventive)

[0215] 1.1 Preparation of master batch constituents

[0216] 1.1.1 Hydroxy-functional poly(meth)acrylate P1 (used as sag control agent resin)

[0217] 636.45 g of solvent naphtha 160 / 180 were initially charged to a nitrogen-flushed 5L steel vessel fitted with monomer feed, initiator feed, thermometer, oil heating and reflux condenser, and heated to the polymerization temperature of 160°C. Then a mixture A comprising 93.75 g solvent naphtha 160 / 180 and 39.4 g di-tert-butyl peroxide was added with stirring at a rate such that the addition of the mixture A was finished after 4.75 h. 15 min after the commencement of the addition of the mixture A, a monomer mixture B comprising 554.6 g n-butyl acrylate, 636.5 g styrene, 323.2 g hydroxyethyl acrylate, and 16.3 g acrylic acid was added to the reaction mixture at a rate such that the addition of the mixture B was finished after 4 h. Upon conclusion of the additions, the reaction mixture was maintained at 160°C for another 2 h. After cooling to 60°C the reaction product was filtered through a 5 pm GAF- Bag filter and allowed to cool to room temperature. The resulting hydroxy-functional poly(meth)acrylate precursor had a solids content of 62 wt.-% + / - 1 wt.-% in solvent Naphtha 160 / 180 (60 min, 130° C; circulating-air oven), a Brookfield CAP03 23°C, 5000 1 Is viscosity of 912 mPa*s, an acid number of 8.8 mg KOH / g of resin, and a hydroxyl number of 105 mg KOH / g (calculated), in each case based on the solids content, and a weight-average molecular weight Mwof about 10,000 g / mol. A Tgof about +17 °C was measured for the resin.

[0218] 446.7 g of the hydroxy-functional poly(meth)acrylate precursor having the aforementioned solids content of 62 wt- % + / - 1 wt.-% obtained in this manner and 18.3 g n-butyl acetate were weight into a 1 Kg stirring vessel of a lab dissolver (Dispermat CV-2, VMA-Getzmann GmbH) having a diameter of 11.0 cm equipped with a toothed, stainless steel dissolver disk with a diameter of 40 mm (VMA-Getzmann GmbH) and stirred for 30 min. A pre-mixed and homogenized mixture of 16.8 g n-butyl acetate (BASF SE, Ludwigshafen) and 7.9 g hexamethylene diisocyanate (Basonate H1 100, available from BASF SE, Ludwigshafen) were metered into the stirring vessel at a uniform rate so as not to exceed 40°C, forming a hexamethylene diisocyanate adduct with benzylamine in the presence of the polymerization product and n-butyl acetate. The resulting product, the hydroxy-functional poly(meth)acrylate P1 , had a solids content of 59 wt.-% + / - 1 wt.-% in Solvent Naphtha 160 / 180 (60 min, 130° C; circulating-air oven) and a dynamic (10 1 / s, CC39, 23°C) viscosity of 1700 mPA*s. The hydroxyl value, weightaverage molecular weight (Mw), and glass transition temperature Tgremained at the values given for the hydroxyfunctional poly(meth)acrylate precursor. 1.1.2 Hydroxy-functional poly(meth)acrylate P2

[0219] 736.7 g of solvent naphtha 160 / 180 were initially charged to a nitrogen-flushed 5L steel vessel fitted with monomer feed, initiator feed, thermometer, oil heating and reflux condenser, and heated to the polymerization temperature of 155°C under pressure of 2.5 bar. Then a mixture A comprising 78.4 g solvent naphtha 160 / 180 and 45.7 g di- tert-butyl peroxide was added with stirring at a rate such that the addition of the mixture A was finished after 4.75 h. 15 min after the commencement of the addition of the mixture A, a monomer mixture B comprising 156.7 g n- butyl methacrylate, 261.2 g styrene, 287.3 g hydroxyethyl methacrylate, 352.6 g hydroxypropyl methacrylate, 235.1 g cyclohexyl methacrylate, and 13.1 g acrylic acid was added to the reaction mixture at a rate such that the addition of the mixture B was finished after 4 h. Upon conclusion of the additions, the reaction mixture was maintained at 155°C under pressure of 2.5 bar for another 2 h. After cooling to 60°C the reaction product was filtered through a 5 pm GAF-Bag filter and allowed to cool to room temperature. The resulting product had a solids content of 54% + / - 1 in solvent Naphtha 160 / 180 (60 min, 130° C; circulating-air oven), a weight-average molecular weight (Mw) of about 3800 g / mol, a viscosity of 828 mPa*s, an acid number of 9.8 mg KOH / g of resin, and a hydroxyl number of 200 mg KOH / g (calculated), in each case based on the solids content. A Tgof about +37 °C was measured for the resin.

[0220] 1.1.3 Polyester P3

[0221] 685.0 g of hexahydrophthalic anhydride, 364.8 g isononanoic acid, 266.2 g neopentyl glycol and 400.7 g trimethylolpropane were reacted in an azeotropic distillation at a maximum temperature of 220°C with a column head temperature not exceeding 100°C and 17.2 g xylene charged to a water separator. The course of the reaction was followed by monitoring the volume of the condensate and its acid number. Upon reaching a calculated acid number the xylene fraction was removed and the reaction mixture stirred at 220°C until an acid number of 7-11 mg KOH / g was obtained. After cooling to 160°C solvent napthta 160 / 180 was added to set a target solid content of 60 wt.-% + / - 1 wt.-%. The resulting polyester resin had a solids content of 59.6 wt.-% + / - 1 wt.-% in solvent Naphtha 160 / 180 (60 min, 130° C; circulating-air oven), a weight-average molecular weight (Mw) of about 3000 g / mol, a viscosity of 340 mPa*s, an acid number of 9.6 mg KOH / g of resin, and a hydroxyl number of 158 mg KOH / g, in each case based on the solids content.

[0222] 1.2 Preparation of master batches MB1, MB2 and MB3

[0223] Master batches MB1 , MB2, and MB3 used as "A'-components have been prepared by mixing the constituents listed in Table 1.in this order, "pbw” means parts by weight. MB1 is a comparatively used master batch, whereas MB2 and MB3 are inventively used master batches. Table 1 - "A”-components MB1 , MB2 and MB3

[0224] UV absorber and HALS were commercially available products. The melamine crosslinker was a commercially available n-butylated imino groups containing melamine crosslinker. Polyester P4 was a commercially available saturated polyester resin modified with a sag control agent (SCA). Nanobyk® 3562 are commercially available silica nanoparticles. Commercially available catalysts have been used as catalysts.

[0225] 1.3 Preparation of hardener components HO, H1, H2 and H3

[0226] In a reaction vessel, hexamethyl 1 ,6-diisocyanate (HDI) trimer (Desmodur® N3300) and butyl acetate were introduced. With reflux cooling, nitrogen blanketing and stirring, a mixture of N-[3-(trimethoxysilyl)propyl]butylamine (Dynasylan® 1189) and Bis[3-trimethoxysilylpropyl]amine (Dynasylan® 1124) was added dropwise at a rate such that a temperature of 50-60° C was not exceeded. The reaction mixture was stirred until the NCO content, determined by means of titration, had reached the theoretically calculated NCO content by weight. To the intermediate hardener constituent obtained in this manner in the first step, hexamethyl 1 ,6-diisocyanate (HDI) trimer (Desmodur® N3300), isophorone diisocyanate (IPDI) trimer (Desmodur® Z4470, 70 wt.-% solid content in solvent naphtha) and butyl acetate were added in a subsequent second step.

[0227] Hardener components H1 and H2 used as "B”-components have been prepared in this manner by mixing the constituents listed in Table 2 in this order, "pbw” means parts by weight. Hardener component H3 has also been prepared in this manner except of the fact that no HDI trimer had been used in the second step. Hardener component HO has also been prepared in this manner except of the fact that no HDI trimer had been used in the second step and that no silanization was performed in the first step. HO and H3 are comparatively used hardener components, whereas H1 and H2 are inventively used hardener components.

[0228] Table 2 - "B”-components HO, H1 , H2 and H3

[0229] 1> Amount of NCO-groups (based on the NCO groups originally present in the HDI) present in silanized form within the intermediate organic constituent (silanization degree of the intermediate polyisocyanate constituent).

[0230] 2> Amount of NCO-groups in total in the hardener component (based on all NCO-groups originally present in HDI and IPDI) present in silanized form within the polyisocyanate mixture prepared in this manner (silanization degree of all polyisocyanates in total being present in the hardener component).

[0231] 1.4 Preparation of clearcoat compositions

[0232] Each of the "A” components MB1 , MB2 and MB3 was mixed with a “B” component B1 in a weight ratio as indicated in Table 3 by means of a dissolver for 10 minutes. In this manner clearcoat compositions 01 to C6 (all comparative) and compositions 11 to I3 (all inventive) were obtained. Table 3 - Clearcoat compositions prepared from MB1 to MB3 and HO to H3

[0233] 2. Preparation of multilayer coating systems and investigation of properties thereof

[0234] 2.1 Two commercially available bonder metal sheets used as substrates S1 and S2 were coated with a commercially available electrodeposition coating composition and, after baking, were mounted vertically and coated first with a commercially available basecoat and then with one of coating compositions C1 to C6 or I to I3 (dry film thickness 40 ± 1 pm) using pneumatic application, followed by curing in a convection oven for 20 minutes at 140 °C with the coated substrate remaining in vertical position. Prior to application of one of coating compositions C1 to C6 or I to I3 and also prior to application of the electrocoat, the surface roughness Raof both substrates S1 and S2 was determined. S1 had a rougher surface (Ra-0.5-0.6) than S2 (Ra-0.2-0.3), whereby the mean roughness value Rais the arithmetic mean of all profile values in the roughness profile.

[0235] Dry and wet scratch resistance as well as appearance (SW values) were measured according to the methods disclosed in the ‘method section’. The results are summarized in Table 4 (average values measured for coatings present on S1 and S2 are given). The indication of C1 to C6 and 11 to I3 in each case means a multilayer coating system comprising a clearcoat layer derived from one of C1 to C6 and 11 to I3.

[0236] 2.2 For determination of PVC compatibility, substrates S1 and S2 coated with a commercially available electrodeposition coating composition as mentioned above were provided with 5 mm thick beads of a commercially available PVC seam sealing material. Subsequently, the substrates were air dried for 40 min and then baked for 20 min and 160 C°. Afterwards, the resulting substrates were mounted vertically and directly coated with one of coating compositions C1 to C6 or I to I3 (dry film thickness 40 ± 1 pm) using pneumatic application, without applying a basecoat prior to that, followed by curing in a convection oven for 20 minutes at 140 °C with the coated substrate remaining in vertical position.

[0237] The PVC material on the substrates obtained in this way were examined for cracks in the clearcoats applied on top of them according to the method disclosed in the ‘method section’. The results are summarized in Table 5 for substrate S1. The indication of C1 to C6 and 11 to I3 in each case means a multilayer coating system comprising a clearcoat layer derived from one of C1 to C6 and 11 to I3. 2.3 Results and discussion

[0238] Table 4

[0239] Table 5

[0240] The dry and wet scratch resistance tests initially showed excellent results for comparative example C6 having a high silanization degree of about 30 mol-% and no silica nanoparticles present, with values of 91 % and 85%, respectively. A decrease in dry and wet scratch resistance can be observed with decreasing silanization degree for comparative examples C4 and C5 also not containing any silica nanoparticles. On the other hand, comparative examples C1 to 03 having a silanization degree of 0 mol-% show the lowest dry and wet scratch resistances with values in the range from 45 to 62 and 58 to 68, respectively. Also, in view of comparative examples 01 to 03, an increase of the dry and wet scratch performance can be observed by adding silica nanoparticles (01 vs. 02) and by increasing the silica nanoparticles content (02 vs. 03). Overall, the effect of silanization overweighs the effect of adding silica nanoparticles in terms of dry and wet scratch resistance when (comparing 01 to 03 vs. 04 to 06).

[0241] However, comparative example 06, although showing the best scratch resistance results, was shown to exhibit the worst short-wave (SW) values, and, further, resembles the only sample with cracks in the PVC test as shown in Table 5).

[0242] A combination of a modest silanization degree of about 3 mol-% with 1.5 wt.-% silica nanoparticles originally present in the master batch used as shown in inventive example 11 results in outperforming comparative example 02 also containing 1.5 wt.-% silica nanoparticles originally present in the master batch, but no silanization of the hardener being present and, further, results in outperforming of comparative example 04 not containing any silica nanoparticles, but having the same silanization degree of 3 mol-%, in each case as far as dry and wet scratch resistance is concerned. Compared to inventive example 11 , by increasing the Si-nanoparticle content to about 3 wt.-% originally present in the master batch used, in inventive example I2 wet and dry scratch resistance was shown to be even further improved, outperforming in terms of wet and dry scratch resistance almost all comparative examples (but comparative example 06). A further increase of the silanization degree from about 3 mol-% (inventive example 11) to about 11 mol-% (inventive example I3), with both samples having a silica nanoparticles content of about 1 .5 wt.- % originally present in the master batch, shows a further improved top wet and dry scratch resistance with still acceptable short-wave values.

[0243] In summary, inventive examples 11 to I3 have very good dry and wet scratch resistances with an increase of performance with increasing silanization degree and good or at least still acceptable short-wave values, the combination not being available without combination of silica nanoparticles and a certain silanization degree. At the same time excellent PVC compatibility is observed.

[0244] 2.4 In summary, it is evident from Tables 4 and 5 that the higher the degree of silanization of the polyisocyanate hardener used, the higher the SW values, especially when using substrate S1 having a comparably high roughness (comparative example 06). The degree of silanization is advantageous for both the wet and dry scratch resistance, which, without silica nanoparticles being present, however, only has a positive effect at higher weight percentages. However, if the wet and dry scratch resistance is only achieved via the degree of silanization of the polyisocyanate constituent used (comparative example 06), cracks are obtained on the PVC material suitable for use for, e.g., car underbody protection, besides an insufficient appearance (SW values). Only the combination of silica nanoparticles and using a partially silanized polyisocyanate hardener component (inventive examples 11 to I3) results in both a high wet and dry scratch resistance and low SW values and an excellent PVC compatibility without cracks.

Claims

CLAIMS1. A clearcoat system comprising at least two components A) and B) and optionally at least one further component C) being different from one another and being separate from each other, wherein component A) comprises at least constituents a1) and a2) and optionally a3), which are different from one another, namely at least one OH-functional polymer as at least one constituent a1), at least one kind of silica nanoparticles as at least one constituent a2), and optionally at least one organic solvent a3), wherein component B) comprises at least constituents b1) and b2) and optionally constituent b3), which are different from one another, namely at least one organic constituent b1) bearing on average two or more isocyanate groups, wherein at least a part of these isocyanate groups has been reacted with at least one silane prior to incorporation of constituent b1) into component B), at least one organic constituent b2) being different from organic constituent b1) and bearing on average two or more isocyanate groups, wherein none of the isocyanate groups of constituent b2) has been reacted with at least one silane prior to incorporation of constituent b2) into component B), and optionally at least one organic solvent b3), and wherein optional component C) is a reducer component and comprises at least one organic solvent d), characterized in that in component B) 0.1 to <29.5 mol-% of all originally present isocyanate groups, based on the total molar amount of all originally present isocyanate groups of all isocyanate groups containing constituents present in component B) including constituent b1) and constituent b2), have undergone reaction with at least one silane prior to its / their incorporation into component B).

2. The clearcoat system according to claim 1 , characterized in that in component B) 0.2 to 27.5 mol-%, preferably 0.5 to 25.0 mol-%, more preferably 0.8 to 22.5 mol-%, even more preferably 1.0 to 20.0 mol-%, still more preferably 1.2 to 18.0 mol-%, yet more preferably 1.5 to 16.0 mol-%, still more preferably 2.0 to 15.0 mol-%, even more preferably 2.2 to 14.0 mol-%, still more preferably 2.5 to 12.0 mol-%, yet more most preferably 2.8 to 11 .5 mol-%, and most preferably 3.0 to 11.0 mol-%, of all isocyanate groups, based on the total molar amount of all isocyanate groups of all isocyanate groups containing constituents presenttherein including constituent b1) and constituent b2), have undergone reaction with at least one silane prior to its / their incorporation into component B).

3. The clearcoat system according to claim 1 or 2, characterized in that the at least one organic constituent b2) is present in component B) in an amount that exceeds the amount of constituent b1).

4. The clearcoat system according to one or more of the preceding claims, characterized in that the at least one constituent b1) bears at least one structural unit of the formula (I)-NR-(X-SIR"X(OR')3-X) (I), and / or, preferably and, at least one structural unit of the formula (II)-N(X-SiR"x(OR')3-x)n(X'-SiR"y(OR')3-y)m (II), wherein:R = hydrogen, alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRagroups, where Ra= alkyl, cycloalkyl, aryl or aralkyl, each R' = independently of one another hydrogen, alkyl or cycloalkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRagroups, preferably wherein each R' = ethyl and / or methyl, each X,X' = independently of one another linear and / or branched alkylene or cycloalkylene radical having 1 to 20 carbon atoms, preferably wherein each X,X' = alkylene radical having 1 to 4 carbon atoms, each R" = independently of one another alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRagroups, preferably wherein each R” = alkyl radical, more particularly having 1 to 6 C atoms, n = parameter of 0 to 2, m = parameter of 0 to 2, m+n = 2, and x, y = parameter of 0 to 2.

5. The clearcoat system according to one or more of the preceding claims, characterized in that the at least one kind of silica nanoparticles being present as constituent a2) have a median primary particle size in the range of from 5 or from 7.5 nm to 1000 nm or to 750 nm or to 500 nm or to 225 nm, preferably of from 10 to 200 nm, more preferably of from 12.5 to 175 nm, still more preferably of from 15 to 150 or to 100 nm, yet more preferably of from 15 to 75 or to 50 nm or to 35 nm, preferably in each case determined via transmission electron microscopy (TEM).

6. The clearcoat system according to one or more of the preceding claims, characterized in that the amount of constituent a2) in component (A) is in a range of from 0.1 to 5.0 wt.-%, preferably of from 0.2 to 4.0 wt.- %, more preferably of from 0.3 to 3.0 wt.-%, yet more preferably of from 0.4 to 2.5 wt.-%, even morepreferably of from 0.5 to 2.0 wt.-%, based in each case on the total weight of component A), and / or in that the amount of constituent a2) in the clearcoat composition obtainable from mixing components A) and B) and optionally C) with each other is in a range of from 0.3 to 10.0 wt.-%, preferably of from 0.4 to 7.5 wt.- %, more preferably of from 0.5 to 6.5 wt.-%, yet more preferably of from 0.6 to 5.5 wt.-%, even more preferably of from 0.7 to 5.0 or to 4.5 wt.-%, based in each case on the total weight of the clearcoat composition.

7. The clearcoat system according to one or more of the preceding claims, characterized in that component A) further comprises at least one urea moiety or moieties containing constituent a4), preferably as sag control agent (SCA), which is an adduct of at least at least one diisocyanate and / or at least one polyisocyanate and at least one preferably primary or secondary amine, preferably monoamine, wherein constituent a4) preferably is present in a crystalline form, wherein constituent a4) preferably is physically and / or chemically associated with at least one OH-functional polymer as sag control polymer, which may be identical to polymer constituent a1) or different therefrom, and wherein constituent a4) is preferably prepared by adding the at least one diisocyanate and / or the at least one polyisocyanate, preferably the at least one diisocyanate, to a mixture of the at least one primary or secondary amine, preferably monoamine, in the presence of at least one OH-functional polymer, preferably of at least one OH-functional (meth)acrylic copolymer, which can be identical to or different from the at least one OH-functional polymer constituent a1).

8. The clearcoat system according to one or more of the preceding claims, characterized in that at least one OH-functional (meth)acrylic copolymer and / or at least one OH-functional polyester, preferably at least one OH-functional (meth)acrylic copolymer, more preferably at least two OH-functional (meth)acrylic copolymers being different from one another and optionally additionally at least one OH-functional polyester, is / are present as the at least one OH-functional polymer a1).

9. The clearcoat system according to one or more of the preceding claims, characterized in that component A) further comprises at least one melamine resin, preferably at least one melamine aldehyde resin, more preferably at least one melamine formaldehyde resin, as constituent a5) and / or at least one catalyst as constituent a6), which is preferably selected from unblocked sulfonic acids and blocked sulfonic acids, more preferably from unblocked sulfonic acids.

10. A clearcoat composition obtainable by mixing at least components A) and B) and optionally C) of the clearcoat system according to one or more of claims 1 to 9 with each other, wherein the clearcoat composition preferably is a solventborne clearcoat composition.

11. The clearcoat composition according to claim 10, characterized in that it is obtainable by mixing components A) and B) in a weight ratio (component A) / component B)) in a range of from 6:1 to 1 :3, more preferably in a range of from 5:1 to 1 :2, still more preferably in a range of from 4:1 to 1 :1.5, yet morepreferably in a weight ratio in a range of from 3.5: 1 to 1 : 1.2, still more preferably in a range of from 3:1 to 1 : 1.

12. A method of coating a substrate, comprising at least one step of applying to an optionally pre-coated substrate at least one clearcoat composition according to claim 10 or 11 to form at least one coating film onto the optionally pre-coated substrate and optionally at least one further step of curing the at least one coating film to obtain at least one cured clearcoat layer onto the substrate.

13. The method according to claim 12, characterized in that it is a method of preparing a multilayer coating system onto an optionally pre-coated substrate comprising at least steps 1), 3), and 4), and optionally 2), namely1) applying a first coating composition to an optionally pre-coated substrate and forming a first coating film on the optionally pre-coated substrate,2) optionally applying a second coating composition to the first coating film present on the substrate obtained after step 1) prior to curing the first coating film and forming a second coating film adjacent to the first coating film,3) applying a third coating composition to the first coating film present on the substrate obtained after step 1) prior to curing the first coating film and forming a third coating film adjacent to the first coating film in case optional step 2) is not performed or applying a third coating composition to the second coating film present on the substrate obtained after step 2) prior to curing the second coating film and forming a third coating film adjacent to the second coating film in case optional step 2) is performed, wherein the third coating composition is a clearcoat composition according to claim 10 or 11, and4) jointly curing the first and third and optionally second coating films, the cured third coating film being the outermost layer of the formed multilayer coating system, to obtain cured first, optionally second, and third coating layers.

14. A coated substrate, which is obtainable by the method according to claim 12 or 13.

15. A multilayer coating system being present on an optionally pre-coated substrate and comprising at least two coatings layers L1 and L3 and optionally at least one coating layer L2 being different from one another, namelya first coating layer L1 applied over at least a portion of an optionally pre-coated substrate, said layer L1 being preferably obtainable from the first coating composition applied in step 1) of claim 13, optionally a second coating layer L2 applied over the first coating layer L1, said layer L2 being preferably obtainable from the second coating composition applied in optional step 2) of claim 13, and a third coating layer L3 applied over the first coating layer L1 or, if present, over the second coating layer L2, said layer L3 being obtainable from the clearcoat composition according to claim 10 or 11 .

Images