Low-cure method for producing a multilayer coating system

Abstract

The invention relates to a method for producing a multilayer coating system on a substrate, wherein a two-pack primer material is applied to a substrate, a basecoat material is applied thereon and a UV-curable solvent-borne clearcoat material is applied thereon, wherein, primer and basecoat material are either solvent-borne or water-borne, and after the application of each coating material a flash-off and / or drying step are carried out at a prescribed temperature for a prescribed duration, followed by UV-radiation curing. The primer material comprises a hydroxy-functional polymer and a polyisocyanate; the basecoat material(s) being selected from the group of physically drying basecoat materials, one-pack basecoat materials and two-pack basecoat materials; and the two-pack clearcoat material comprises a urethane (meth)acrylate having on average 1.5 to 5.5 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g; a (meth)acrylated resin having on average 5.6 to 10 (meth)acrylic functionalities and / or a (meth)acrylated resin having a hydroxy value from 26 to 180 mg KOH / g; and one or more diluents selected from UV reactive monomers, protic and aprotic organic solvents, and an isocyanato (meth)acrylate having on average at least one (meth)acrylic functionality and at least one isocyanate functionality. The invention further related to a multilayer coated substrate and its use and the use of the method in OEM coating.

Description

BASF Coating GmbHDec. 15, 2025LOW-CURE METHOD FOR PRODUCING A MULTILAYER COATING SYSTEMThe invention relates to a method for producing a multilayer coating system on a substrate, a thus produced multilayer coated substrate as well as the use of the multilayer coated substrate as part of a vehicle, particularly and automotive vehicle or part thereof. Further, the invention is related to the use of the method in OEM coating.BACKGROUND ARTIn field of coatings industry, particularly in high-end products like automotive coating, it is desired to provide coating processes allowing to produce coating systems comprising at least three coating layers, namely a primer coat, a basecoat and a clearcoat, which can be cured in short time at low temperature and still providing an excellent adhesion and appearance, particularly in in OEM (original equipment manufacturer) coating lines.The increasing demand in coating processes which save process time and reduce energy consumption requires to rethink the conventionally used coating lines which are based on the use of thermal crosslinking of coating material at comparably high temperatures for relatively long curing times.In current processes there is a need to reduce carbon dioxide emission as well as to save energy. Some techniques which are already establish in some automotive refinish applications have not yet been feasible in automotive OEM multilayer coating systems. This is, e.g., the case for UV curing processes. Particularly the integration of a UV curing step to cure an upper-most clearcoat layer of a multilayer coating, wherein the underlying layers have not yet been fully cured is a powerful challenge considering that A class appearance coating need to result.Consequently, the present invention aims to provide a method for producing a multilayer coating systems comprising at least one primer layer, at least one basecoat layer and at least one clearcoat layer, the process being particularly suitable in OEM coating, such as automotive OEM coating, and which allows the production of such multilayer coating system in short time at low temperature, preferably not exceeding a temperature of 120 °C, or even not exceeding 100 °C, in any of the coating, flashing-off, drying and curing steps. The method should be suitable to provide a multilayer system based on solvent-borne coating materials only, but also a multilayer system based on a combined water-borne / solvent-borne application of coating materials.The multilayer coating systems produced according the method need to possess an excellent interlayer adhesion and adhesion to substrates even after being exposed to humidity (cross-cut adhesion and stone-chip resistance), a good windshield bonding and Tukon hardness, a low tendency for undesired yellowing and a chemical resistance which is comparable with high temperature curing systems, and a long-term durability performance.BASF Coating GmbHDec. 15, 2025Full performance of the multilayer coating, in all relevant aspects, is aimed to be expected within about one to two days after applying and curing the multilayer coating.SUMMARYThe problems addressed herein above are solved by providing a method for producing a multilayer coating system on a substrate, comprising the steps of a. providing a substrate; b. applying a water-borne two-pack primer material or solvent-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min at a temperature in the range of 15 °C to 40 °C to form a primer film; c. applying one or more water-borne basecoat materials, if the two-pack primer is a water-borne two- pack primer material or applying one or more solvent-borne basecoat materials, if the two-pack primer is a solvent-borne primer material, onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 5 min to 20 min at a temperature in the range of 15 °C to 40 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min at a temperature of 60 °C to 95 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min at a temperature in the range of 15 °C to 40 °C to form a clearcoat film; and f. curing the clearcoat film obtained in step e. by UV radiation curing; wherein the two-pack primer material comprises in the A-pack PA one or more hydroxy-functional polymers PA1 ; and in the B-pack PB one or more polyisocyanates PB1 having on average at least 1.5 isocyanate groups; the basecoat material being selected from the group of physically drying basecoat materials, one- pack basecoat materials and two-pack basecoat materials; andBASF Coating GmbHDec. 15, 2025 the two-pack clearcoat material comprises in the A-pack CA one or more urethane (meth)acrylates CA1 each having on average > 1.5 to 5.5 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g; one or more (meth)acrylated resins CA2a each having on average 5.6 to 10 (meth)acrylic functionalities and / or one or more (meth)acrylated resins CA2b having a hydroxy value from 26 to 180 mg KOH / g; and one or more diluents selected from UV reactive monomers CA3, protic organic solvents CA7 and aprotic organic solvents CA8; and in the B-pack CB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality and at least one isocyanate functionality.The above method for producing a multilayer coating system on a substrate, and its preferred embodiments as described herein below, are also referred to as "method(s) according to the invention” or "method(s) of the invention.”The invention further provides a multilayer coated substrate, which is obtainable by the method according to the invention, herein-after also denoted as "multilayer coated substrate according to the invention” or "multilayer coated substrate of the invention.”Yet another object of the present invention is the use of the multilayer coated substrate as a part of a vehicle, such as a vehicle body or part thereof, which herein-after is also referred to as "use according to the invention” or "use of the invention.”A further object of the invention is use of the method according to the invention in original equipment manufacturer (OEM) coating, preferably automotive OEM coating.DETAILED DESCRIPTIONIn the following the method of the invention will be further explained and preferred features and embodiments will be disclosed.First, the method steps of a. providing a substrate;BASF Coating GmbHDec. 15, 2025 b. applying a water-borne two-pack primer material or solvent-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min at a temperature in the range of 15 °C to 40 °C to form a primer film; c. applying one or more water-borne basecoat materials, if the two-pack primer is a water-borne two- pack primer material or applying one or more solvent-borne basecoat materials, if the two-pack primer is a solvent-borne primer material, onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 5 min to 20 min at a temperature in the range of 15 °C to 40 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min at a temperature of 60 °C to 95 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min at a temperature in the range of 15 °C to 40 °C to form a clearcoat film; and f. curing the clearcoat film obtained in step e. by UV radiation curing; will be described in more detail.Thereafter, the two-pack primer material comprising in the A-pack PA one or more hydroxy-functional polymers PA1 ; and in the B-pack PB one or more polyisocyanates PA1 having on average at least 1.5 isocyanate groups; the basecoat material being selected from the group of physically drying basecoat materials, one- pack basecoat materials and two-pack basecoat materials; and the two-pack clearcoat material comprises in the A-pack CA one or more urethane (meth)acrylate CA1 each having on average > 1.5 to 5.5 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g; one or more (meth)acrylated resins CA2a each having on average 5.6 to 10 (meth)acrylic functionalities and / orBASF Coating GmbHDec. 15, 2025 one or more (meth)acrylated resins CA2b having a hydroxy value from 26 to 180 mg KOH / g; and one or more diluents selected from UV reactive monomers CA3, protic organic solvents CA7 and aprotic organic solvents CA8; and in the B-pack CB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality and at least one isocyanate functionality, as used in the method of the invention will be described in further detail.Method for Producing a Multilayer Coating SystemIn the following terms used in view of the method steps are further described.The term "evaporating at least part of the volatile content of the coating material at a temperature in the range of 15 °C to 40 °C” is herein above and below also denoted "flashing off.” This term is therefore understood to mean the evaporation or allowing water and / or organic solvents to evaporate from a coating material applied during the production of a multilayer coating system according to the invention, usually at ambient temperature (herein 15 °C to 40 °C; for a period of 5 min to 20 min). Some of the water and / or organic solvents contained in the applied coating material therefore evaporate during flash-off. Water and / or organic solvents gradually evaporate, resulting in a comparatively smooth coating layer after the flash-off phase, which contains less water and / or solvents than the coating agent applied, but still more than in a fully dried state. It is, for example, no longer flowable, but still soft or sticky, possibly only partially dried. In particular, the coating layer is not yet fully cured.In contrast, the term "drying the coating film at a temperature of 60 °C to 95 °C” is to be understood as "forced- drying”, because it is carried out at a temperature higher than ambient temperature (herein a temperature of 60 °C to 95 °C in a time range from 3 min to 15 min). "Drying” in the above and below meaning is therefore understood as allowing water and / or organic solvents to evaporate from a coating material applied during the production of a multilayer coating system, usually at a temperature higher than the ambient temperature, i.e. a temperature in the range from 60 °C to 95 °C in a time range from 3 min to 15 min. During such drying, the applied coating material loses a further proportion of water and / or organic solvents, preferably up to a fully dried coating layer. Thus, a further part of water and / or organic solvents is removed from the coating, i.e. at least a part of the water and / or solvent, which remained after "flashing off' is evaporated during the drying step. During the drying steps, at least some curing occur of the respective layer occurs. I.e., a proportion of the polymers and crosslinkers, if present, in the respective coating compositions can crosslink or entangle with one another. Drying a primer film and / or basecoat film, as described herein, is to be understood as an at least partially curing of the respective film, preferably a substantially fully cure.BASF Coating GmbHDec. 15, 2025The term "curing of a coating film” or "curing the multilayer coating system”, particularly "fully curing of a coating film” or "fully curing the multilayer coating system” means the conversion of such a film or multilayer coating system into the ready-to-use state, i.e. into a state in which the substrate provided with the respective multilayer coating system can be transported, stored and / or used as intended. A cured coating layer is therefore in particular no longer soft or sticky, but conditioned as a solid coating film which, preferably after a post-curing period of up to a few days, such as 2 or 3 days, does no longer changes its properties such as hardness or adhesion to the substrate significantly even on further exposure to the curing conditions described below.In the method according to the invention a cured multilayer coating system is obtained.Preferably, in any method step a temperature of 120 °C, more preferred 110 °C, even more preferred 100 °C and most preferred 95 °C should not be exceeded.While the method according to the present invention can also be carried out in refinish coating, it is preferably carried out in the original equipment manufacturer coating (OEM), particularly automotive OEM coating.Step a.The substrate as used in step a. is preferably selected from group consisting of metallic substrates, plastic substrates (i.e., polymeric substrates), glass or ceramic. The substrate may be a pre-coated or not precoated substrate. Preferably, the surface of the pre-coated or not precoated substrate comprises isocyanate reactive functional groups, more preferably hydroxyl groups.The term "metallic substrate” encompasses any type of solid metal and alloys thereof. Particularly preferred metallic substrates are bare steel, galvanized steel, zinc, aluminum, magnesium, copper, and alloys of the afore-mentioned metals. Most preferred substrates are steel, like cold rolled steel; galvanized steel, such as hot dip galvanized steel and electrogalvanized steel; and aluminum and its alloys.If the substrate is a metallic substrate, such as an automotive body or part thereof, it is preferred that the substrate is pre-coated, preferably with a conversion coating layer as a pre-treatment, followed by an electrodeposition coating layer.Preferably, if the metallic substrate is coated with a conversion coating layer and an electrodeposition coating layer, a thus coated substrate is also pre-cured.The substrate used can also be a plastic substrate, i.e., a polymeric substrate. Suitable polymers are poly(meth)acrylates including polymethyl(meth)acrylates, polybutyl (meth)acrylates, polyethylene terephthalates,BASF Coating GmbHDec. 15, 2025 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 (aery lonitri le-styrene-acry lie ester copolymers) and ABS (aery lonitri le-butadiene-sty rene 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. The plastic substrate can also be a composite substrate such as a fiber reinforced substrate containing e.g., glass fibers, carbon fibers or polymeric fibers such as polyamide fibers. The plastic substrate can also consist of multiple polymeric layers.If the substrate is a plastic substrate, a glass substrate or ceramic substrate, it may also be a pre-treated and / or pre-coated substrate, which, e.g., bears an adhesion promoting layer.The substrates themselves may be of whatever shape, that is, they may be, for example, simple metal panels or else complex components such as, in particular, automobile bodies and parts thereof.Step b.In step b. a two-pack primer material is applied onto at least part of the substrate. The two-pack primer material can either be water-borne or solvent-borne.Preferably, water-borne two-pack primer materials comprise water as the main part of the volatile content of the primer material, i.e. , the water content in the water-borne two-pack primer material preferably comprises at least 50 wt.-%, more preferred at least 60 wt.-% and even more preferred at least 70 wt.-% or at least 80 wt.-%, based on the total weight of the volatile content. However, waterborne two-pack primer material, typically and preferably contain, in addition to water, one or more organic solvents as further part of the volatile content. Such organic solvents are typically polar organic solvents, as will be further described herein below.In contrast to the water-borne two-pack primer material, the solvent-borne two-pack primer material contains organic solvents as the main part of the volatile content of the primer material. Preferably, solvent-borne two-pack primer materials do not intentionally contain water as part of the volatile content, i.e. they are preferable water-free. However, typically small amounts of water are tolerated in solvent-borne two-pack primer materials. Some water may get into the solvent-borne two-pack primer material by use of ingredients, which contain minor amounts of water, such as pigments and fillers or some additives. Preferably, the solvent-borne two-pack primer material contains less than 5 wt.-%, more preferred less than 3 wt.-%, even more preferred less than 2 wt.-%, such as less than 1 wt.-% of water, or more most preferred less than 0.5 wt.-% of water, based on the total weight of the volatile content of the coating material.BASF Coating GmbHDec. 15, 2025The two-pack primer material can be applied by any conventional application technique used in the coatings industry. Generally, but also preferably, in the automotive coatings industry, spraying (pneumatic or electrostatic spray application) is preferred. Thus, the primer material can be feasibly applied via airless spraying, high speed rotation spraying, hot air spraying, etc.After the application of the primer material at least part of the volatile content of the primer material is evaporated.The evaporation time ("flash-off time”) is in the range from 5 min to 20 min, preferably in the range from 7 min to 18 min. Typically, the flash-off time is in the lower range, such as 5 min up to 15 min, more preferred up to 12 min, if the two-pack primer material is solvent-borne and the organic solvents are highly volatile under flash-off conditions. If the two-pack primer material is water-borne, the flash-off time is preferably in the range from 5 min to 20 min, such as in the range from 7 min to 18 min.The temperature at which the flash-off takes place is in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C, more preferably in the range from 20 °C to 25 °C ("ambient temperature range”).In step b. a primer film is formed which preferably has a dry film thickness, determined according to the method as described in the experimental section of the present invention, in the range from 5 m to 30 pm, more preferred in the range from 10 pm to 25 pm and even more preferred in the range of 15 pm to 20 pm.During step b. the primer film may partially cure, i.e. partial crosslinking between the hydroxy-functional binder material(s) contained in the A-pack of the primer material and the crosslinking agent of the B-pack may occur. However, after step b. the primer material forming the primer film is not fully cured.Step c.In step c. one or more basecoat materials comprising water and / or organic solvents as volatile content, are applied onto at least part of the preferably not fully cured primer film formed in step b, whereas the basecoat material(s) differ from the primer material. If the primer material is water-borne, the basecoat material(s) is / are also waterborne, and if the primer material is solvent-borne, the basecoat material(s) is / are also solvent-borne.The basecoat material can be applied by any conventional application technique used in the coatings industry. Generally, but also preferably, in the automotive coatings industry, spraying (pneumatic or electrostatic spray application) is preferred. Thus, the basecoat material can be feasibly applied via airless spraying, high speed rotation spraying, hot air spraying, etc.BASF Coating GmbHDec. 15, 2025It is possible that more than one basecoat film is formed, such as two or more basecoat films, one on top of the other. If two basecoat films are applied, they may be denominated "first and second basecoat film,” or "basecoat film and midcoat film” or "groundcoat film and midcoat film.” In the following only the terms "basecoat material,” "basecoat film” and "basecoat layer” are used, although they encompass the "groundcoat / midcoat” terminology.After the application of the basecoat material at least part of the volatile content of the basecoat material is evaporated.The evaporation time ("flash-off time”) is in the range from 1 min to 10 min, preferably in the range from 3 min to 8 min. Typically, the flash-off time is in the lower range, such as 1 min to 8 min, more preferred 2 to 7 min, if the basecoat material is solvent-borne and the organic solvents are highly volatile under flash-off conditions. If the basecoat material is water-borne, the flash-off time is preferably in the range from 3 min to 10 min, such as in the range from 4 min to 9 min.The temperature at which the flash-off takes place is in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C, more preferably in the range from 20 to 25 °C ("ambient temperature range”).If two or more basecoat films are applied, the flash-off period between the application of the basecoat materials can be shorter, preferably in the range from 1 min to 5 min.In step c. one or more basecoat film(s) is / are formed which preferably has / have a combined dry film thickness, determined according to the method as described in the experimental section of the present invention, in the range from 5 pm to 50 pm, more preferred in the range from 8 pm to 40 pm and even more preferred in the range of 15 pm to 30 pm or 8 pm to 15 pm. Particularly for dark basecoat films, such as black basecoat films, a range from 8 pm to 15 pm, such as 8 pm to 12 pm is preferred.During step c. the basecoat film may partially cure. However, after step c. the basecoat material(s) forming the basecoat film(s) is / are preferably not fully cured.Step d.In step d., following step c., the primer film and basecoat film(s) are dried in a time range from 3 to 15 min, preferably 5 to 10 min at a temperature of 60 °C to 95 °C, preferably 65 °C to 90 °C ("forced drying”).Generally, it is preferred to dry the primer film and basecoat film(s) for a time in the upper part of the time range, preferably in the range of 6 min to 15 min, more preferably 8 min to 12 min and / or at a temperature in the upper temperature range, preferably 70 °C to 95 °C, more preferable 75 °C to 90 °C, if the primer material and basecoatBASF Coating GmbHDec. 15, 2025 material(s) are water-borne coating material(s). Generally, it is preferred to dry the primer film and basecoat film(s) for a time in the lower part of the time range, preferably in the range of 3 min to 10 min, more preferably 5 min to 8 min and / or at a temperature in the lower temperature range, preferably 60 °C to 90 °C, more preferably 65 °C min to 90 °C, if the primer material and basecoat material(s) are solvent-borne coating materials.Step e.After step d. a solvent-borne, UV radiation curable, two-pack clearcoat material is applied onto at least part of the basecoat film obtained in step c. (and step d., respectively).The solvent-borne, UV radiation curable, two-pack clearcoat material is preferably applied by spraying (pneumatic or electrostatic spray application). The clearcoat material can be feasibly applied via airless spray, high speed rotation, hot air spray, etc.The solvent-borne, UV radiation curable, two-pack clearcoat material can be applied by any conventional application technique used in the coatings industry. Generally, but also preferably, in the automotive coatings industry, spraying (pneumatic or electrostatic spray application) is preferred. Thus, the solvent-borne, UV radiation curable, two-pack clearcoat material can be feasibly applied via airless spraying, high speed rotation spraying, hot air spraying, etc.After the application of the solvent-borne, UV radiation curable, two-pack clearcoat material, at least part of the organic solvents comprised in the volatile content is evaporated in time ("flash-off time”) in the range from 1 min to 15 min, preferably 3 min to 12 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a clearcoat film.In step e. a clearcoat film is formed which preferably has a dry film thickness, determined according to the method as described in the experimental section of the present invention, in the range from 25 pm to 80 pm, more preferred in the range from 35 pm to 70 pm and even more preferred in the range of 45 pm to 60 pm.The clearcoat film thus obtained in step e. may optionally be dried in a time range from 1 min to 20 min, at a temperature in the range from 40 °C to 80 °C, preferably 40 °C to 60 °C.Step f.UV curing can be accomplished by any conventional UV lamp, such as mercury-based lamps or preferably by use of LED (light emitting diodes) based light sources.BASF Coating GmbHDec. 15, 2025One important parameter is the amount of radiant power impinging on a unit surface area from all forward angles, which is the irradiance measured in (W / cm2). The irradiance arriving at the surface depends on the distance from the lamp. Irradiance values may be given by the manufacturers for selected distances, however, often without characterization of the wavelength range. Thus, they are better measured with radiometry for the actual UV system.Another important parameter is the energy density, which is the radiant energy arriving at the surface per unit area, the time integral of irradiance, usually expressed in J / cm2. Other terms for the energy density are "light dose” or "radiant exposure.”Acceptable energy densities for curing are, e.g., achieved using a lamp (H-Lamp) with a comparable irradiance of 9 W / cm2for a total energy density of UVA / B / C light preferably totaling 0.5 J / cm2to 12 J / cm2, more preferably 1.0 J / cm2to 10 J / cm2, or even further preferred from 1.5 J / cm2to 8 J / cm2, such as 1.5 J / cm2to 6 J / cm2.Preferred UV curing systems are electrodeless, microwave-powered broadband UV lamp (such as Light Hammer 6 Mark I irradiator and the housing / conveyor system DRS 10 / 12 from Heraeus Noblelight). These lamps have the benefit of a high-power class (12 to 16 W / m) while also being able to maintain this level of power over the lifetime of the lamp. Furthermore, these lamps do not have a significant "warm-up” time and reach full power shortly after being turned on.In the method according to the present invention a combination of UV-A, UV-B, and UV-C light is preferred for optimal physical performance. For example, the removal of UV-C light from the system may deteriorate the physical performance, such as scratch resistance, chemical resistance, and solvent resistance. Several classes of UV bulbs exist which can give the necessary output in these regions, e.g., H-bulbs (Hg bulb), or D-bulbs (Hg-Fe doped bulbs) are being used in step f. of the method according to the invention.Curing is preferably performed using a conveyor driven system to deliver uniform light across the clearcoat film to be cured. The conveyor speed can vary in a wide range and is preferably at a speed of 1 m / s to 15 m / s, more preferably 2 m / s to 10 m / s, even more preferred in the range from 4 m / s to 8 m / s such as 6 m / s.Coating Materials used in the Method of the InventionIn the following terms used in view of the coating materials are further described.As is known to one of skill in the art, coating materials can in principle be cured physically and / or chemically, depending on the components they contain, such as binders and crosslinking agents.BASF Coating GmbHDec. 15, 2025In the case of chemical curing, thermal-chemical curing and UV-radiation-chemical curing come into consideration, whereby also combinations or the afore-mentioned curing mechanism are possible, as e.g., in "dual cure” coating materials.A coating material can be self-crosslinking and / or externally crosslinking, for example if it is thermo-chemically curable. With the statement that a coating material crosslinks itself and / or is externally crosslinked, it is to be understood in the context of the present invention that this coating material contains polymers as binders and, if appropriate, crosslinking agents which can crosslink with said polymers. The underlying mechanisms and the binders and crosslinking agents (film-forming components) that can be used are described herein below.In the context of the present invention, the term "physically curable" or the term "physical curing" means the formation of a cured coating layer by releasing solvent from polymer solutions or polymer dispersions, the curing being achieved by entanglement of polymer chains. Such coating compositions are generally formulated as one- pack coating material.The term "one-pack coating material” means a coating material, which, in its ready-to-use formulation will not or only negligibly cure, i.e., it is storage stable.In contrast thereto, the term "two-pack coating material” means a coating material which at least comprises an A- pack and a B-pack, which are stored separately, because upon mixing a curing process starts. Neither the A-pack nor the B-pack are typically apt to form a cured durable coating layer. Besides the A-pack and B-pack, a so called "two-pack coating material” may also comprise further packs, such as a C-pack etc., while this is typically not preferred.In the context of the present invention, "thermochemically curable" or the term "thermochemical curing" means the crosslinking of a coating film initiated by chemical reaction of reactive functional groups (formation of a cured coating film), the energetic activation of this chemical reaction by thermal energy is possible. Different functional groups that are complementary to one another can react with one another ("complementary functional groups”) and / or the formation of the hardened layer is based on the reaction of autoreactive groups, i.e. functional groups that react with one another with groups of their own kind. Examples of suitable complementary reactive functional groups and autoreactive functional groups are, for example, described in German patent application DE 199 30 665 A1 , page 7, line 28, to page 9, line 24.This crosslinking can be a self-crosslinking and / or an external crosslinking. If, for example, the complementary reactive functional groups are already present in an organic polymer used as a binder, for example a polyester, a polyurethane or a poly(meth)acrylate, then there is self-crosslinking. External crosslinking occurs, for example, when a (first) organic polymer containing certain functional groups, e.g. hydroxyl groups, with a crosslinking agentBASF Coating GmbHDec. 15, 2025 known per se, e.g., a polyisocyanate and / or a melamine resin. The crosslinking agent thus contains reactive functional groups which are complementary to the reactive functional groups present in the (first) organic polymer used as binder.Particularly in the case of external crosslinking, the known one-pack and two-pack coating materials, in particular two-pack coating materials, come into consideration.In thermo-chemically curable one-pack coating materials, the components to be crosslinked, for example organic polymers as binders and crosslinking agents, are present side by side, i.e. in one component, i.e. one pack. The prerequisite for this is that the components to be crosslinked only react effectively with one another at elevated temperatures of, herein temperatures in range up to 95 °C, i.e. undergo curing reactions. Otherwise, the components to be crosslinked would have to be stored separately from one another and only mixed together shortly before application to a substrate in order to avoid premature at least partial thermal-chemical curing (compare two- pack coating materials). Hydroxy-functional polyesters and / or polyurethanes with melamine resins and / or blocked polyisocyanates as crosslinking agents may be mentioned as an example of a combination.In thermal-chemically curable two-pack coating materials, the components to be crosslinked, for example the organic polymers as binders and the crosslinking agent, are present separately from one another in at least two components (at least two packs; A-pack and B-pack) which are only combined shortly before application. This form is chosen when the components to be crosslinked react effectively with one another even at ambient temperatures or only slightly elevated temperatures. Examples of combinations that may be mentioned are hydroxy-functional polyesters and / or hydroxy-functional polyurethanes and / or hydroxy-functional poly(meth)acrylates with free polyisocyanates as crosslinking agents.It is also possible for an organic polymer as a binder to have both self-crosslinking and externally crosslinking functional groups and then to combine it with crosslinking agents.In the context of the present invention, "UV-radiation-curable" means "chemical curing by UV-radiation". Curing by UV radiation is usually initiated by free radical or cationic photoinitiators. Typical UV-curable functional groups are carbon-carbon double bonds, herein preferably (meth)acrylic group, with free-radical photoinitiators generally being used here. The UV curing is also based on a chemical crosslinking. The term "UV radiation curable coating material” as used herein refers to a coating material which cures upon irradiation with UV light, herein most preferred is UV light emitted in all UV wavelength regions of the spectrum, i.e., in the UV-A, UV-B and UV-C region of the spectrum.Of course, during the curing of a coating material characterized as chemically curable, physical curing, i.e. an entanglement of polymer chains, will always occur. The physical hardening can even make up the predominant part. Nevertheless, such a coating agent is referred to as chemically curable if it contains at least a proportion ofBASF Coating GmbHDec. 15, 2025 film-forming components that are chemically curable. In some cases, even the presence of crosslinking agents such as aminoplast resins, like melamine resins, does not necessarily mean that such resin participates in thermochemical curing, since it is known that the presence of such crosslinking agent may act flexibilizing, particularly in physically curing coating materials.The term "resin” as used herein has the well-established meaning known to one of skill in the art of coatings. This term encompasses oligomers and polymers likewise.The term "(meth)acrylic” or "(meth)acrylate” as used herein encompasses acrylic and methacrylic, as well as acrylate and methacrylate, respectively.It follows from the above that, depending on the type of coating material and the components contained therein as well as the temperature, curing is brought about by different mechanisms, which may also necessitate different conditions during curing.The multilayer coating systems of the present invention is a very low temperature curable system, which is curable at a temperature < 95 °C, preferably < 90 °C, such as in the range from 60 °C to 95 °C, preferably 65 °C to 90 °C. That means that in no step of the method according to the invention it is necessary to cure any film formed in any step at a temperature above 95 °C. Thus, "low-temperature” curable in the meaning of the present inventionTwo-Pack Primer Coating MaterialThe primer coating material (often termed: "primer”, "surfacer” or "primer surfacer”) provides the bond between the substrate (preferably a metallic electrodeposition coated substrate) and the basecoat.In the present invention the primer coating material is a two-pack primer coating material. The primer coating material can either be water-borne or solvent-borne. The primer coating material is water-borne, if the subsequent basecoat film is formed by a water-borne basecoat material, and the primer coating material is solvent-borne, if the subsequent basecoat film is formed by a solvent-borne basecoat material.The two-pack primer material (i.e., A-pack plus B-pack) in general preferably has a solids content in the range from 20 wt.-% to 80 wt.-%, more preferably in the range from 25 wt.-% to 75 wt.-%, even more preferred 30 wt.-% to 70 wt.-%, and most preferred 35 wt.-% to 65 wt.-%. For solvent-borne two-pack primer material the solids content is more preferably in the range from 35 wt.-% to 80 wt.-%, even more preferably in the range from 40 wt.-% to 75 wt.- %, most preferred 45 wt.-% to 70 wt.-%, and most preferably in the range from 40 wt.-% to 70 wt.-% For waterborne two-pack primer material the solids content is more preferably in the range from 20 wt.-% to 60 wt.-%, evenBASF Coating GmbHDec. 15, 2025 more preferably in the range from 25 wt.-% to 55 wt.-%, and most preferred 30 wt.-% to 50 wt.-%. The solids content is determined as described in the experimental part of the specification.A-Pack of the Primer Coating Material PAHydroxy functional Polymer PA1The A-pack comprises at least one hydroxy functional polymer PA1 , preferably selected from the group consisting of polyurethanes, polyesters, poly(meth)acrylates, polyester-polyurethanes, polyether-polyesters, and chlorinated polyolefins which are modified with an acrylic resin, and any copolymers thereof. The hydroxy functional polymers may optionally be in form of microgel emulsions, particularly, if the polymer is a hydroxy functional (meth)acrylic polymer.Most preferred hydroxy functional polymers are selected from the group comprising or consisting of polyesters, polyurethanes, polyester-polyurethanes, and poly(meth)acrylates.Those hydroxy functional polymers PA1 which are used in water-borne primer coating materials preferably possess carboxylic acid functional groups which are at least partially neutralized and / or they possess polyethylene oxide chains. Both means serve do enhance the compatibility of the hydroxy functional polymers PA1 with water and protic solvents contained in the water-borne primer coating material.In case of hydroxy functional polymers comprising urethane groups, such as polyurethanes or polyesterpolyurethane there might however be no need for carboxylic acid functional groups which are at least partially neutralized and / or polyethylene oxide chains to enhance the compatibility with water, because NH groups interact with water and may stabilize the hydroxyl functional polymer PA1 in a water-borne primer coating composition.The hydroxyl number (i.e., hydroxyl value) of the hydroxy functional polymers PA1 in general are preferably in the range from 5 to 300 mg KOH / g, more preferred in the range from 10 to 250 mg KOH / g. For water-borne two-pack primer materials the hydroxyl number of the hydroxy functional polymers PA1 is even more preferred in the range from 5 to 200 mg KOH / g, more preferred 10 to 250 mg KOH / g, and for solvent-borne two-pack primer materials the hydroxyl number of the hydroxy functional polymers PA1 is even more preferred in the range from 10 to 300 mg KOH / g, more preferred 15 to 250 mg KOH / g.The weight-average molecular weight (Mw) of the hydroxy functional polymers PA1 in solvent-borne primers is preferably in the range from 1000 to 20000 g / mol, more preferred in the range from 1500 to 17000 g / mol, even more preferred in the range from 2000 to 15000 g / mol.BASF Coating GmbHDec. 15, 2025For water-borne two-pack primer materials the Mwof the hydroxy functional polymers PA1 is even more preferred in the range from 10,000 to 80,000 g / mol, more preferred 20,000 to 50,000 g / mol.Pigments PA2 and / or Fillers PA2The A-pack of the primer coating material further contains one or more pigments PA2 and / or one or more fillers PA2.According to EN ISO 4618:2006, a “pigment” is a coloring material, generally in the form of fine particles, which is practically insoluble in the medium and which is used because of its optical, protective, and / or decorative properties. Herein it is not distinguished between fillers and pigments. A “filler” (also denoted as “extender” in the aforementioned standard) is material in granular or powder form, insoluble in the medium and used to modify or influence certain physical properties. Typically, the terms “pigment” and “filler / extender” are only distinguished by the refractive index, which is less than 1 .7 for fillers / extenders. Thus, both, pigments and fillers are subsumed under “PA2.”The pigments and fillers are preferably selected from the group comprising or consisting of titanium dioxide, barium sulfate, talc, silicon dioxide, feldspar, and carbon blacks. They are typically introduced into the A-pack of the primer coating material in form of pigment pastes or filler pastes. Such piments pastes and filler pastes typically contain grinding resins, selected from the same groups of resins as described for the hydroxy functional polymers PA1 , and the pastes may further comprise wetting and dispersion agents for wetting and dispersing the pigments and / or fillers. However, such wetting and dispersing additives may also be added separately as coating additive PA4 as described below.Diluents PA3By definition, water-borne primer coating materials comprise at least water as a diluent PA3, while solvent-borne primer coating materials comprise at least one organic solvent as a diluent PA3, preferably an organic solvent mix.While water-borne primer coating materials preferably further comprise one or more organic solvents as cosolvents, the solvent-borne primer coating materials are preferably water-free, preferably having a water content of less than 5 wt.-%, more preferred less than 3 wt.-%, even more preferred less than 1 wt.-% based on the total weight of diluents PA3.BASF Coating GmbHDec. 15, 2025Preferred organic solvents can be protic organic solvents or aprotic organic solvents. Both types of solvents which can also be used in the basecoat material are herein described as CA7 and CA8 further below.Coating Additives PA4The A-pack of the primer coating material preferably contains one or more additives from the group comprising or consisting of the already mentioned pigments wetting and dispersion agents, defoaming and deaerating additives, surfactants and substrate wetting additives, neutralizing and pH adjustment agents, and rheology additives.Catalysts PA5While catalysts PA5 are often subsumed under the term "coatings additives,” herein they are dealt with separately. Amongst the catalyst, those are preferred which are selected from blocked or non-blocked acid catalysts, organometal catalysts, such as organotin catalysts, and non-tin containing but metal containing catalysts. Particularly preferred are amine-blocked sulfonic acids and amine-blocked phosphoric acid catalyst, including the partially amine-blocked acids; and non-blocked sulfonic acid catalysts and phosphoric acid catalysts.The non-blocked sulfonic acids are preferably alkylaromatic sulfonic acids, more preferred alkylbenzene sulfonic acids, even more preferred Ci-C2o-alkylbenzene sulfonic acids, such as methylbenzene sulfonic acid (such as paratoluene sulfonic acid) and dodecylbenzene sulfonic acid. The alkyl of the alkylbenzene can be linear or branched.The amine-blocked sulfonic acids are preferably amine-blocked alkylaromatic sulfonic acids, more preferred amine- blocked alkylbenzene sulfonic acids, even more preferred amine-blocked Ci-C2o-alkylbenzene sulfonic acids, such as amine-blocked methylbenzene sulfonic acid (such as amine-blocked para-toluene sulfonic acid) and amine- blocked dodecyl benzene sulfonic acid. The alkyl of the alkylbenzene can be linear or branched. Such amine- blocked sulfonic acids and their manufacture are, e.g., described in US 4,812,506 A. The amine with which the sulfonic acids are blocked are preferably selected from the group of amino alcohols, primary amines, secondary amines, and tertiary amines. Examples for suitable amines are 2-amino-2-methyl-1-propanol (AMP), diethylmethanol amine, methyl diethanol amine, ethyl diethanol amine, dimethylethanol amine, diisopropyl amine, diisopropanol amine, tris-ethylhexyl amine, triethyl amine, and trihexyl amine.The non-blocked phosphoric acid catalyst is preferably selected from organophosphoric acids, more preferably from alky l-phosphate esters, and aromatic-phosphate esters, even more preferably it is selected from a monoester or diester of phosphoric acid, and most preferred an monoalkylester, dialkylester, monoarylester or diarylester of phosphoric acid or a mixture of two or more of the afore-mentioned esters, and particularly a monophenyl phosphoric acid, a diphenyl phosphoric acid or a mixture thereof, also known as phenyl acid phosphate.BASF Coating GmbHDec. 15, 2025The amine-blocked phosphoric acid is preferably selected from amine-blocked organophosphoric acids, more preferably from amine blocked alky l-phosphate esters, and amine-blocked aromatic-phosphate esters, even more preferably it is selected from an amine-blocked monoester or diester of phosphoric acid, and most preferred an amine-blocked monoalkylester, dialkylester, monoarylester or diarylester of phosphoric acid or a mixture of two or more of the afore-mentioned esters, and particularly preferred an amine-blocked monophenyl phosphoric acid, a diphenyl phosphoric acid or a mixture thereof, also known as phenyl acid phosphate. The amine with which the phosphoric acids are blocked are defined as the amines used for blocking the sulfonic acids.Organotin catalysts are, e.g., dibutyl tin dilaurate or dioctyl tin dilaurate.From the environmental view, it is preferred that one or more catalysts are used which are tin-free, preferably, if catalysts are used, it is preferred that all catalysts are tin-free. Suitable metal comprising, but tin-free catalysts are selected from zinc, zirconium, bismuth, and potassium compounds, particularly the carboxylates of the aforementioned metals.It is particularly preferred that the water-borne two-pack primer material is free of metal containing catalysts or even more preferred of catalysts at all. If metal containing catalysts are present in the water-borne two-pack primer material, the catalysts are preferably the afore-mentioned tin-free catalysts.It is particularly preferred that the solvent-borne two-pack primer material comprises one or more of the following catalysts, namely amine-neutralized sulfonic acid catalysts, amine-neutralized phosphate acid catalysts, sulfonic acid catalysts, phosphate acid catalysts, and metal comprising catalysts, or mixture thereof.B-Pack of the Primer Coating Material PBPolyisocyanates PB1The B-pack of the two-pack primer coating material comprises at least one, preferably one or two, or two or more, preferably one polyisocyanates PA1 , having at least 1.5 free isocyanato groups, and which preferably comprises one or more moieties selected from the group consisting of urethane moieties, allophanate moieties, biuret moieties, uretdione moieties, iminooxadiazindione moieties and isocyanurate moieties.The term "polyisocyanate” as used herein encompasses all isocyanates having 1 .5 or more free isocyanate groups, preferably 2 or more free isocyanate groups, such as up to 5, preferably up to 4, more preferred up to 3 free isocyanate groups.BASF Coating GmbHDec. 15, 2025Aliphatic or aromatic polyisocyanates may be used in the B-pack of the primer coating material, preferably aliphatic polyisocyanates, even more preferred only aliphatic polyisocyanates are used in the B-pack of the primer coating material. The term "aliphatic” as used herein and defined by IUPAC includes acyclic or cyclic, saturated or unsaturated carbon containing compounds or residues, excluding aromatic compounds or residues.Particularly preferred are oligomerization products of diisocyanates, such as dimerization, trimerization and tetramerization products of diisocyanates. Most preferred are oligomerization product of diisocyanates, wherein the oligomerization products comprise one or more moieties selected from urethane moieties, allophanate moieties, biuret moieties, uretdione moieties, iminooxadiazindione moieties and isocyanurate moieties, particularly preferred isocyanurate moieties.Suitable aromatic diisocyanates for such oligomerization are aromatic diisocyanates having a divalent hydrocarbon residue between two isocyanate groups, the divalent hydrocarbon residue being aromatic and containing 6 to 20, more preferred 7 to 16, even more preferred 7 to 14 carbon atoms.Suitable aliphatic diisocyanates, for such oligomerization, which are preferred herein, are preferably saturated aliphatic diisocyanates having a divalent hydrocarbon residue between the two isocyanate groups, the divalent hydrocarbon residue containing 4 to 20, more preferred 4 to 16, even more preferred 4 to 12 and most preferred 6 to 10 carbon atoms.Examples of customary aliphatic diisocyanates are acyclic diisocyanates, such as tetramethylene diisocyanate, 1 ,6-hexamethylene diisocyanate (1,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysindiisocyanate, tetramethylxylylene diisocyanate, trimethylhexane diisocyanate or tetramethylhexane diisocyanate; cycloaliphatic diisocyanates such as 1 ,4-, 1 ,3- or 1 ,2-diisocyanatocyclohexane, 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl) cyclohexane (isophorone diisocyanate), 1 , 3- or 1 ,4- bis(isocyanatomethyl) cyclohexane or 2,4- or 2, 6-diisocyanato-1 -methylcyclohexane. Most preferred are 1 ,3- bis(isocyanatomethyl) cyclohexane, di(isocyanatocyclohexyl)methane, 1 ,6-hexamethylene diisocyanate and isophorone diisocyanate, amongst which isophorone diisocyanate and 1 ,6-hexamethylene diisocyanate, particularly the latter one is even more preferred.Of course, mixtures of diisocyanates, such as the afore-mentioned diisocyanates, preferably the afore-mentioned aliphatic diisocyanates may also be used.Dimerization, trimerization or tetramerisation products of the afore-mentioned diisocyanates preferably contain one or more moieties selected from urethane moieties, allophanate moieties, biuret moieties, uretdione moieties, urethane moieties, iminooxadiazindione moieties and isocyanurate moieties. Some of the moieties, such asBASF Coating GmbHDec. 15, 2025 allophanate groups and urethane groups may be formed by oligomerization of the diisocyanates in the presence of hydroxyl functional compounds or water in case of biuret groups.It is possible and particularly preferred, that the polyisocyanates PB1 are partially silylated with monosilanes and / or bissilanes containing one or more, preferably 2 or 3 hydrolysable silane groups. A partially silylated polyisocyanates PB1 , is still a polyisocyanate PB1 under the definition of the present invention, thus still having at least 1.5 free isocyanato groups on average after silylation.As an example, if the polyisocyanate is an HDI isocyanurate trimer having exactly 3 NCO groups, on average 1.5 of those free NCO groups may be consumed by silylation. Furthermore, if there is a low degree of silylation, e.g. 11 mole-% of the NCO groups of an HDI isocyanurate trimer are reacted with a monoamino silane to form a polyisocyanates PB1 , it is evident that on average 2 of 3 HDI isocyanurate trimers are unsilylated and on average in only every third HDI isocyanurate trimer one NCO groups is silylated. Thus, in such cases, mixtures of unsilylated polyisocyanates PB1 and silylated polyisocyanates PB1 are formed, such mixtures are herein also denoted as "partially silylated polyisocyanates PB1”.Preferably 0 to 30 mole-%, more preferred 2 to 25 mole-%, even more preferred 5 to 20 mole-% and most preferred 8 to 15 mole-% of the free isocyanato groups present in the "starting” polyisocyanates PB1 are preferably reacted with a monoamino silane, the monoamino silane being at least one of a bissilane of formula (Sbis) and a monosilane of formula (Smono):R1SiR3m(OR5)3.mH-NR2SiR4n(OR6)3-n (Sbis), whereinR1and R2are independently from each other selected from linear, branched, and cyclic alkylene groups having 1 to 10 carbon atoms,R3and R4are independently from each other selected from linear, branched, and cyclic alkyl groups having 1 to 10 carbon atoms,R5and R6are independently selected from alkyl residues containing 1 to 3 carbon atoms, and n and m are independently of each other 0, 1 or 2;R1°H-lR7SiR8x(OR9)3.x (Smono)whereinBASF Coating GmbHDec. 15, 2025R7is selected from linear, branched, and cyclic alkylene groups having 1 to 10 carbon atoms,R8is selected from linear, branched, and cyclic alkyl groups having 1 to 10 carbon atoms,R9is selected from alkyl residues containing 1 to 3 carbon atoms,R10is selected from H and linear, branched, and cyclic alkyl groups having 1 to 10 carbon atoms and x being 0, 1 or 2.If there is a partial silylation of free isocyanate groups of the polyisocyanates PB1 , the adhesion of the primer coating material tends to be improved. However, if more than 30 mole-% of the free isocyanato groups present in the polyisocyanates PB1 are reacted with one or more silanes of formulae (Smono) and (Sbis), the appearance and flexibility may deteriorate.As already defined above, R1and R2are independently from each other selected from linear, branched and cyclic alkylene groups having 1 to 10 carbon atoms. Preferably the number of carbon atoms in R1and R2is 2 to 8, even more preferred 3 to 6 and most preferred 3, 4 and 5. Most preferably, R1and R2are linear alkylene groups having 3, 4 or 5, most preferably 3 carbon atoms, such as in (CH2)3 groups.R3and R4are independently from each other selected from linear, branched and cyclic alkyl groups having 1 to 10 carbon atoms. Preferably the number of carbon atoms is 1 to 6, even more preferred 1 to 4 and most preferred 1 , 2 or 3. Preferably R3and R4are selected from linear or branched alkyl groups.R5and R6are independently selected from alkyl residues containing 1 to 3 carbon atoms, preferably 1 or 2 and most preferred 1. The alkyl groups can be linear or branched. Preferably the alkyl groups are selected from methyl, ethyl, n-propyl and i-propyl, even more preferred from methyl and ethyl, most preferred R5and R6are methyl.Residues OR5and OR6participate in the crosslinking reaction with the hydroxy-functional polymers comprised in the A-pack of the primer coating material, as well as in water- or moisture-induced self-crosslinking reactions as explained in more detail in the next paragraph. Generally, it can be stated that the reactivity of residues OR5and OR6in the crosslinking reactions decreases with an increasing number of carbon atoms in the residues R5and R6. Thus, methyl groups are more reactive than ethyl groups, and ethyl groups are more reactive than propyl groups.The values for n and m are independently of each other 0, 1 or 2, preferably 0 or 1 and most preferred 0. The values for n and m determine the numbers of alkoxy groups bound to the silane. If m = 0, formula (II) contains an Si(OR5)3 group and if n = 0, formula (II) contains an Si(OR6)3 group. Preferably, at least one of n and m is 0. Even more preferred n and m are 0.BASF Coating GmbHDec. 15, 2025In the crosslinking reaction between the hydroxy groups of, e.g., a hydroxy-functional polymer selected from the group consisting of poly(meth)acrylic polymers, polyesters, polyurethanes and polyethers and the crosslinking agents (X) the following reaction occurs: Si-OR5 / 6+ HO-Polymer -> Si-O-Polymer + HO-R5 / 6. This reaction is accompanied in the presence of liquid water or moisture from the air, by a hydrolytic silane self-crosslinking reaction, which can be depicted as follows: 2 Si-OR5 / 6+ H2O -> Si-O-Si + 2 HO-R5 / 6.The more Si-OR5 / 6groups (i.e., Si-OR5groups or Si-OR6groups) are present in the crosslinking agent, the higher the crosslinking density with, e.g., a hydroxy functional polymer and the higher the self-crosslinking density, compared to compositions which are identical, except for having a higher value of the sum of n+m. Since preferably a high crosslinking density is desired n and m should be 0 or 1 , more preferably n+m should be 0 or 1 , most preferably n+m should be 0.As already defined above, R7is selected from linear, branched and cyclic alkylene groups having 1 to 10, preferably 2 to 8, more preferred 3 to 6 and even more preferred 3, 4 or 5 carbon atoms and most preferred 3 carbon atoms, such as in (CH2)3 groups. Groups R8are selected independently from each other from linear, branched and cyclic alkyl groups having 1 to 10, preferably 1 to 6, more preferred 1 to 4 and most preferred 1 , 2 or 3 carbon atoms. Groups R9are independently selected from alkyl groups containing 1 to 3, more preferred 1 or 2 and most preferred 1 carbon atoms. Group R10is H or preferably an alkyl group containing 1 to 10, preferably 2 to 8, more preferred 4 to 6, and most preferred 4 carbon atoms. The value of x being 0, 1 or 2, preferably 0 or 1 , most preferred 0.The considerations regarding the structure-reactivity relationships between the residues R1, R2, R3, R4, R5and R6and the reactivities of these residues themselves within groups R1SiR3m(OR5)3-mand R2SiR4n(OR6)3-nas well as the corresponding values for n and m, are likewise valid for the residues R7, R8and R9and the value of x in groups R7SiR8x(OR9)3-x.Preferably the weight ratio of monosilanes to bissilanes is in the range from 1 :40 to 1 :5, more preferred from 1 :30 to 1 :10, even more preferred 1 :25 to 1 : 12 and most preferred in the range from 1 :20 to 1 : 15.Basecoat MaterialThe basecoat material used in the method of the present invention is not particularly limited except for the proviso that it is solvent-borne, if the primer coating material is solvent-borne, and water-borne, if the primer coating material is water-borne.The basecoat material should preferably be a curable basecoat material which cures at a temperature below 120 °C, more preferably below 110 °C, even more preferably below 100 °C and even more preferred below 95 °C, whereas the term "curable basecoat material” includes physically drying basecoat materials, thermally curing 1 KBASF Coating GmbHDec. 15, 2025 basecoat materials (1-pack materials) and thermally curing 2K basecoat materials (2-pack materials), or combinations thereof.Preferably, the basecoat material is physically drying and / or a 1-pack basecoat material.The basecoat material preferably has a solids content in the range from 15 wt.-% to 80 wt.-%, more preferably in the range from 20 wt.-% to 75 wt.-%. For solvent-borne basecoats the solids content is more preferably in the range from 30 wt.-% to 80 wt.-%, even more preferably in the range from 35 wt.-% to 75 wt.-%, and most preferably in the range from 40 wt.-% to 70 wt.-% For water-borne basecoats the solids content is more preferably in the range from 15 wt.-% to 60 wt.-%, even more preferably in the range from 20 wt.-% to 50 wt.-%. The solids content is determined as described in the experimental part of the specification. If the solids content is lower than 15 wt.- %, depending on the solvents used in the basecoat composition, flash-off and / or drying times might tend to increase.The basecoat material preferably comprises at least one hydroxy functional polymer B1 , preferably selected from the group consisting of polyurethanes, polyesters, polyethers, poly(meth)acrylates, polyester-polyurethanes, epoxy-modified acrylic resins, polyether-polyesters, and any copolymers thereof; optionally at least one crosslinking agent B2 possessing groups which are reactive with the hydroxy functional polymer, preferably selected from melamine formaldehyde resins and blocked polyisocyanates; optionally, but preferably one or more pigments B3 and / or one or more fillers B3; one or more diluents B4 selected from water and organic solvents; optionally one or more coating additives B5 and one or more catalysts B6 preferably selected from blocked or non-blocked acid catalysts and organotin catalysts.Hydroxy Functional Polymer B1The hydroxy functional polymers B1 are preferable defined in the same way as the hydroxy functional polymers PA1 . Thus, all specifications for the hydroxy functional polymers PA1 apply for hydroxy functional polymers B1 .Preferably at least one hydroxy functional polymer B1 is the same as used as PA1 in the primer material.Crosslinking Agents B2Since the basecoat material can be a physically drying basecoat material crosslinking agents are not always necessary. Preferred crosslinking agents are melamine-formaldehyde resins and blocked polyisocyanates.The main structural element of melamine-formaldehyde resins is melamine having the following structure:BASF Coating GmbHDec. 15, 2025A monomeric melamine-formaldehyde resin can be depicted by the following formula:If only one of the two R groups bound to a nitrogen is R = CH2-OH or CH2-O-alkyl and the other R = H, a group NHR with R = CH2-OH or CH2-O-alkyl is formed, which is called an imino group. In the present invention it is preferred, preferably in the solvent-borne basecoat material, that practically no imino groups are present, or only a very low number. Further, it is preferred that the methylol groups (CH2-OH) are alkylated, thus groups R = CH2-O- alkyl are formed, e.g., alkyl being methyl or butyl, such as n-butyl or iso-butyl. Butyl groups and mixtures of butyl groups with methyl groups are preferred if the crosslinking agent is used in a solvent-borne basecoat material. Methyl groups are preferred if the crosslinking agent is used in a water-borne basecoat material.Blocked polyisocyanates can also be used as crosslinking agents. They are prepared from polyisocyanates which are defined in the same way as polyisocyanates PB1 of the B-pack of the primer coating material, and all preferred embodiments thereof, but without silylation. In blocked polyisocyanates all free isocyanato groups are reacted with a blocking agent having preferably a low crosslinking temperature. Preferred blocking agents for blocking the polyisocyanates are dimethyl pyrazole, esters of malonic acid, or esters of other CH-acidic compounds like esters of acetoacetic acid.Pigments B3 and / or Fillers B3In basecoat materials the same pigments and fillers can be contained as in the primer coating material. Thus, the same applies as for pigments PA2 and fillers PA2. However, since the basecoat layer is just coated with a clearcoat, any color impression or (metallic) effect impression is mainly cause by the pigments used in the basecoat material. The pigments may be inorganic pigments or organic pigments and may preferably be selected from the group of color pigments and effect pigments, such as pearlescent pigments and metal effect pigments, such as aluminum pigments. The color pigments may have any color including black and white.BASF Coating GmbHDec. 15, 2025Diluents B4By definition, water-borne basecoat materials comprise at least water as a diluent B4, while solvent-borne primer coating materials comprise at least one organic solvent as a diluent B4, preferably an organic solvent mix.While water-borne primer coating materials preferably further comprise one or more organic solvents as cosolvents, the solvent-borne primer coating materials are preferably water-free, preferably having a water content of less than 5 wt.-%, more preferred less than 3 wt.-%, even more preferred less than 1 wt.-% based on the total weight of diluents PA3.Preferred organic solvents can be protic organic solvents or aprotic organic solvents. Both types of solvents which can also be used in the basecoat material are herein described as CA7 and CA8 further below.Coating Additives B5The basecoat material preferably contains one or more additives from the group comprising or consisting of the already mentioned pigments wetting and dispersion agents, defoaming and deaerating additives, surfactants and substrate wetting additives, neutralizing and pH adjustment agents, and rheology additives.Catalysts B6The catalysts B6 are defined in the same way as catalysts PA5. Therefore, it is fully referred to catalysts PA5 in the A-pack of the primer coating material.It is particularly preferred that the water-borne basecoat material is free of metal containing catalysts or even more preferred free of catalysts at all. If metal containing catalysts are present in the water-borne two-pack primer material, the catalysts are preferably the afore-mentioned tin-free catalysts. In physically drying water-borne basecoat material, it is preferred that they do not contain catalysts.It is particularly preferred that the solvent-borne basecoat material comprises one or more of the following catalysts, namely amine-neutralized sulfonic acid catalysts, amine-neutralized phosphate acid catalysts, sulfonic acid catalysts, phosphate acid catalysts, and metal comprising catalysts, or mixture thereof.BASF Coating GmbHDec. 15, 2025UV Radiation Curable, Two-Pack Solventborne Clearcoat MaterialThe UV radiation curable, two-pack solvent-borne clearcoat material comprises at least an A-pack and a B-pack, if further packs are comprised the two-pack solvent-borne clearcoat material is still considered to be a "two-pack” coating material. Preferably the two-pack solvent-borne clearcoat material consist of an A-pack and a B-pack.The UV radiation curable, two-pack solvent-borne material (i.e., A-pack plus B-pack, plus further packs, if present) in general preferably has a solids content in the range from 30 wt.-% to 90 wt.-%, more preferably in the range from 35 wt.-% to 85 wt.-%, even more preferred 40 wt.-% to 80 wt.-%, and most preferred 45 wt.-% to 75 wt.-%. The solids content is determined as described in the experimental part of the specification.A-Pack of Solventborne Clearcoat Material (CA)The A-pack of the two-pack solventborne clearcoat material at least comprises• one or more urethane (meth)acrylate CA1 each having on average > 1.5 to 6.0 (meth)acrylic functionalities;• one or more (meth)acrylated resins CA2a each having on average 6.1 to 10 (meth)acrylic functionalities and / or• one or more (meth)acrylated resins CA2b having a hydroxy value from 26 to 180 mg KOH / g; and• one or more diluents selected from UV reactive monomers CA3, protic organic solvents CA7 and aprotic organic solvents CA8.The one or more urethane (meth)acrylates (CA1)The one or more urethan (meth)acrylates (CA1) have a rather low functionality with respect to hydroxyl groups and (meth)acrylic groups, compared to the (meth)acrylated resins CA2, which are described herein below.The A-pack of the two-pack solvent-borne clearcoat material comprises one or more urethane (meth)acrylates CA1 having a hydroxyl number in the range of 0 to 25, preferably from 0 to 20 mg KOH / g, more preferred from 0 to 15 mg KOH / g such as 1, 2, 3 or 4 to 15 mg KOH / g.Each of the one or more urethane (meth)acrylates CA1 has a (meth)acrylic group functionality of at least 1.5, preferably at least 1 .8 and most preferably at least 2.0; as preferably from 2.0 to 5.5, more preferred 2.0 to 5.0, even more preferred 2.0 to 4.5, most preferred 2.2 to 4.3.The above-mentioned one or more urethane (meth)acrylates may be aliphatic or aromatic and are preferably aliphatic.BASF Coating GmbHDec. 15, 2025Particularly in view of weathering resistance, it was found that aliphatic urethane (meth)acrylates are preferred.Preferably the one or more urethane (meth)acrylates CA1 have a number-average molecular weight in the range from 400 g / mol to 3500 g / mol, more preferred in the range from 500 g / mol to 3000 g / mol, even more preferred in the range from 600 g / mol to 2500 g / mol and most preferred in the range from 700 g / mol to 2000 mg / mol. The number-average molecular weights can be determined by gel permeation chromatography as described in detail in the experimental section of the present invention.Generally, the higher the number-average molecular weight, the higher the viscosity of the resins and thus, preferably, the higher the amount of the one or more reactive diluents CA3, i.e., UV reactive monomers CA3 comprising one or two (meth)acrylic groups and / or one or more organic solvents selected from protic organic solvents CA7 and aprotic organic solvents CA8, are required to obtain a suitable viscosity for spray application, which is the application method of choice.Amongst all of the afore-mentioned urethane (meth)acrylates CA1 , those having an acrylic group are preferred over the ones having a methacrylic groups, because of the higher reactivity or acrylic groups.Urethane (meth)acrylates CA1 , are preferably contained in the solvent-borne two-pack clearcoat material of the present invention, i.e., preferably the clearcoat material obtained by combining the A-pack and B-pack, in an amount from 15 to 35 wt.-%, more preferred 18 to 32 wt.-%, and even more preferred 20 to 30 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material. If the amount of urethane (meth)acrylates CAI drops below 15 wt.-% durability and chemical resistance tend to decrease. If the amount of urethane (meth)acrylates CA1 exceeds 35 wt.-% flexibility of the coating tends to be reduced and the material may tend to become brittle.Such resins are, e.g., available as aliphatic urethane (meth)acrylate resins from BASF SE under the tradenames Laromer® UA 19T, Laromer® UA 8987 N, Laromer® UA 9029, Laromer® UA 9030, Laromer® UA 9033 N, Laromer® UA 9072, and Laromer® UA 9089, all of which have on average 2 to 2.9 (meth)acrylic groups and hydroxyl numbers in the range from 3 to 12 mg KOH / g. An example of an aromatic urethane (meth)acrylate resin, and thus a less preferred resin, is, e.g., Laromer® UA 9073 which is also commercially available from BASF SE, and has a (meth)acrylic group functionality of 2 and a hydroxyl number of 9 mg KOH / g. Similar products are commercially available under the tradename Ebecryl® from Allnex and Sartomer® from Sartomer / Arkema.BASF Coating GmbHDec. 15, 2025The one or more (meth)acrylated resins (CA2), i.e. (CA2a) and (CA2b)The one or more (meth)acrylated resins CA2, i.e., CA2a and CA2b have a rather high functionality with respect to hydroxyl groups and / or (meth)acrylic groups, preferably hydroxyl groups or (meth)acrylic groups, compared to the urethane (meth)acrylates CA1 , which are described herein below.Further, they are preferably selected from urethane (meth)acrylates and (meth)acrylated poly(meth)acrylates.The A-pack of the two-pack solvent-borne clearcoat material comprises one or more (meth)acrylated resins (CA2), having a (meth)acrylic group functionality of at least 5.6, preferably at least 6.0 and most preferably at least 6.5; as preferably from 5.6 to 10.0, more preferred 6.0 to 9.5, even more preferred 6.5 to 9.0, most preferred 7.0 to 8.5 (i.e., (meth)acrylated resins CA2a); and / or a hydroxyl number in the range of 26 to 180 mg KOH / g, preferably from 30 to 150 mg KOH / g, more preferred from 40 to 100 mg KOH / g, most preferred 50 to 90 mg KOH / g (i.e., (meth)acrylated resins CA2b).The higher the functionality, (meth)acrylic group functionality and hydroxy group functionality expressed by the hydroxyl number, or both, the higher the crosslinking density when reacted with the isocyanato (meth)acrylates CB1 and the harder the resulting coating, going along with good scratch resistance and chemical resistance.(Meth)acrylated resins CA2, are preferably contained in the solvent-borne two-pack clearcoat material of the present invention (A-pack plus B-pack) in an amount from 1 .0 to 25 wt.-%, more preferred 1 .5 to 20 wt.-%, and even more preferred 2 to 15 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material. If the amount of (meth)acrylated resins CA2 drops below 1 wt.-% their impact on the improvement of chemical resistance tends to be too low. If the amount of (meth)acrylated resins CA2 exceeds 25 wt.-% embrittlement tends to occur.It is preferred that either (meth)acrylated resins CA2a or (meth)acrylated resins CA2b are contained, however, also mixtures of both are possible. It is particularly preferred to use the multifunctional (meth)acrylated resins CA2a having a (meth)acrylic group functionality of at least 5.6, if the solvent-borne two-pack clearcoat material is used on top of a solvent-borne basecoat material. On the contrary, it is preferred to use the multifunctional (meth)acrylated resins CA2b having a hydroxyl number in the range of 26 to 180 mg KOH / g, if the solvent-borne two-pack clearcoat material is used on top of a basecoat film formed from a water-borne basecoat material, since the hydroxy groups enhance compatibility with such basecoat film.(Meth)acrylated Resin CA2aBASF Coating GmbHDec. 15, 2025It is preferred that the (meth)acrylated resin CA2a is a urethane (meth)acrylate, preferably an aliphatic urethane (meth)acrylate. The manufacture is analogous to the manufacture of urethane (meth)acrylates CA1 , however, the degree of (meth)acrylation, i.e., the number of (meth)acrylic groups on the (meth)acrylated resin is higher.(Meth)acrylated resins CA2a, are preferably contained in the solvent-borne two-pack clearcoat material of the present invention in an amount from 1 .0 to 10 wt.-%, more preferred 1 .5 to 8 wt.-%, even more preferred 2.0 to 6 wt.-%, and most preferred 2.5 to 4 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material.(Meth)acrylated Resins CA2bIt is preferred that the (meth)acrylated resin CA2b is a (meth)acrylic poly(meth)acrylate, i.e. a poly(meth)acrylate having (meth)acrylic groups attached thereon.Such resins can, e.g., be obtained by polymerizing preferably mono ethylenically unsatured monomers, comprising (meth)acrylic acid and / or their esters and amides. However, monomers with vinyl groups, such as styrene, can additionally be used. The resins comprise in polymerized form hydroxy functional monomers, such as hydroxyalkyl (meth)acrylates, which contribute to the targeted hydroxyl numbers. To introduce the unsaturated (meth)acrylic groups the hydroxy functional poly(meth)acrylate, particularly some of its hydroxyl groups may be reacted with, e.g., glycidyl (meth)acrylate by ring-opening reaction.(Meth)acrylated resins CA2b, are preferably contained in the solvent-borne two-pack clearcoat material of the present invention (A-pack plus B-pack) in an amount from 4 to 25 wt.-%, more preferred 6 to 20 wt.-%, even more preferred 8 to 18 wt.-%, and most preferred 10 to 15 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material.The one or more UV reactive monomers (CA3) comprising one or two (meth)acrylic groupsThe A-pack of the two-pack solvent-borne clearcoat material preferably comprises one or more UV reactive monomers CA3, preferably comprising at least one (meth)acrylic group, even more preferred 1 to 4 (meth)acrylic groups, and most preferred 1 or 2 (meth)acrylic groups. They are typically used as reactive diluents for the urethane (meth)acrylates CA1 , and / or (meth)acrylated resins CA2, preferably CA1 and CA2a.The UV reactive monomers CA3 may by aliphatic or aromatic monomers, aliphatic monomers being preferred, and the aliphatic monomers may contain - besides the (meth)acrylic groups - one or more further unsaturated groupsBASF Coating GmbHDec. 15, 2025 and / or hetero atoms. However, they do preferably not contain functional groups which are reactive with isocyanate groups. Thus, they preferably do not contain hydroxyl groups.The one or more UV reactive monomers CA3 comprising one (meth)acrylic group may contain aromatic groups, as e.g., phenoxyethyl (meth)acrylate; they may also contain heteroatoms such as, e.g., in trimethylolpropane formal mono(meth)acrylate, or may contain further unsaturated groups such as, e.g., in dicyclopentenyl (meth)acrylate.Further preferred UV reactive monomers CA3 comprising one (meth)acrylic group are the mono (meth)acrylic esters of alkane mono alcohols, dialkylene glycol monoalcohols and trialkylene glycol monoalcohols, wherein the alkane mono alcohols preferably contain from 2 to 20, more preferred 4 to 16 carbon atoms; and glycols in the dialkylene glycol monoalcohols and triethylene glycol monoalcohols are either ethylene glycol or propylene glycol or both. Examples of preferred mono (meth)acrylic esters of alkane mono alcohols are 2-ethy lhexy I (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate and isobornyl (meth)acrylate. Most preferred amongst the UV reactive monomers comprising one (meth)acrylic group are trimethylolpropane formal mono(meth)acrylate and the mono (meth)acrylic esters of alkane mono alcohols with 6 to 12 carbon atoms.The one or more UV reactive monomers CA3 comprising two (meth)acrylic groups are preferably the di (meth)acry lie esters of alkane diols, dialkylene glycols and trialkylene glycols, wherein the alkane diols preferably contain from 2 to 12 carbon atoms and the alkylene glycols in the dialkylene glycols and trialkylene glycols are ethylene glycol and / or propylene glycol. Examples of preferred mono (meth)acrylic esters of alkane mono alcohols are hexanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate and tripropylene glycol di(meth)acrylate.Amongst all the afore-mentioned UV reactive monomers CA3 the acrylates are preferred over the methacrylates, because of their higher reactivity; and further the aliphatic UV reactive monomers are preferred over the aromatic UV reactive monomers.The UV reactive monomers CA3 are diluents and act as reactive thinners (also called "reactive diluents”), i.e., as solvents which typically reduce the viscosity of the composition, and become part of the cured network by being incorporated by reaction into the network. Herein, the UV reactive monomers CA3 do preferably not contain any groups which are reactive towards isocyanate groups.The UV reactive monomers CA3 have distinct molecular weight and are thus not considered as oligomers or polymers, since oligomers and polymers typically possess a polydispersity, i.e., they have different number-average and weight-average molecular weights.The coating compositions of the present invention preferably contain at least one UV reactive monomer CA3 having one (meth)acrylic groups and at least one UV reactive monomer CA3 having two (meth)acrylic groups.BASF Coating GmbHDec. 15, 2025Non-reactive aprotic organic solvents will be described herein below as CA8.The combined amount of UV reactive monomers CA3, protic and aprotic organic solvents CA7 and CA8, and solvents CB2 contained in the solvent-borne two-pack clearcoat material of the present invention (A-pack plus B- pack) is preferably in the range from 20 to 55 wt.-%, more preferred 25 to 50 wt.-%, even more preferred 28 to 48 wt.-%, and most preferred 30 to 46 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material.One or more Photoinitiators (CA4)As photoinitiators CA4 it is possible to use photoinitiators known to the skilled person, examples being those stated in "Advances in Polymer Science”, Volume 14, Springer Berlin 1974 or in K. K. Dietliker, Chemistry and Technology of UV- and EB-Formulation for Coatings, Inks and Paints, Volume 3; Photoinitiators for Free Radical and Cationic Polymerization, P. K. T. Oldring (ed.), SITA Technology Ltd, London.Examples of those contemplated include phosphine oxides, benzophenones, a-hydroxyalkyl aryl ketones, thioxanthones, anthraquinones, acetophenones, benzoins and benzoin ethers, ketals, imidazoles, phenylglyoxylic acids and phenylglyoxylates, the latter ones being most preferred.Photoinitiators contemplated are those as described in WO 2006 / 005491 A1 , page 21 , line 18 to page 22, line 2 (corresponding to US 2006 / 0009589 A1 , paragraph

[0150] ), hereby made part of the present disclosure by reference.The following compounds may be cited as examples of the individual classes.Mono- or bisacylphosphine oxides, such as Irgacure® 819 (bis(2,4,6-trimethylbenzoyl)phenyl-phosphine oxide), of the kind described for example in EP-A 7 508, EP-A 57 474, DE-A 196 18 720, EP-A 495 751 , or EP-A 615 980, examples being 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (Lucirin® TPO), ethyl 2,4,6- trimethylbenzoylphenylphosphinate, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; benzophenone and its derivatives, such as 4-aminobenzophenone, 4,4'-bis(dimethylamino)benzophenone, 4- phenylbenzo-phenone, 4-chlorobenzophenone, Michler's ketone, o-methoxybenzophenone, 2,4,6- trimethylbenzophenone, 4-methylbenzophenone, 2,4-dimethylbenzophenone, 4-isopropylbenzophenone, 2- chlorobenzophenone, 2,2'-dichlorobenzophenone, 4-methoxybenzophenone, 4-propoxybenzophenone, or 4- butoxybenzophenone;1-Benzoylcyclohexan-1-ol (1 -hydroxycyclohexyl phenyl ketone), 2-hydroxy-2,2-dimethylaceto-phenone (2- hydroxy-2-methyl-1-phenylpropan-1-one), 1-hydroxyacetophenone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-BASF Coating GmbHDec. 15, 2025 methyl-1-prop an-1- one, polymer comprising in copolymerized form 2-hydroxy-2-methyl-1-(4-isopropen-2- ylphenyl)propan-1-one (Esacure® KIP 150);10-thioxanthenone, thioxanthen-9-one, xanthen-9-one, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4- diisopropylthioxanthone, 2,4-dichlorothioxanthone, and chloroxanthenone; p-methylanthraquinone, tert-butylanthraquinone, anthraquinonecarbonyl acid esters, benz[de]anthracen-7-one, benz[a]anthracene-7, 12-dione, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1- chloroanthraquinone, 2-amylanthraquinone; acetophenone, acetonaphthoquinone, valerophenone, hexanophenone, a-phenylbutyrophenone, p- morpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone, p-diacetylbenzene, 4'- methoxyacetophenone, a-tetralone, 9-acetylphenanthrene, 2-acetylphenanthrene, 3-acetylphenanthrene, 3- acetylindole, 9-fluorenone, 1 -indanone, 1 ,3,4-triacetylbenzene, 1 -acetonaphthone, 2-acetonaphthone, 2,2- dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1 , 1 -dichloroacetophenone, 1 - hydroxyacetophenone, 2,2-diethoxyacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2,2-dimethoxy-1 ,2-diphenylethan-2-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one;4-morpholinodeoxybenzoin, benzoin, benzoin isobutyl ether, benzoin tetrahydropyranyl ether, benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether, benzoin isopropyl ether, and 7-H-benzoin methyl ether; acetophenone dimethyl ketal, 2,2-diethoxyacetophenone, and benzil ketals, such as benzil dimethyl ketal; phenylglyoxalic acids and phenylglyoxalates as described in DE-A 19826 712, DE-A 199 13 353, or WO 98 / 33761 , examples being phenylglyoxalic acid monoesters and diesters with polyethylene glycols having a molar mass of 62 to 500 g / mol and those which are present in Omnirad® 754; benzaldehyde, methyl ethyl ketone, 1 -naphthaldehyde, triphenylphosphine, tri-o-tolylphosphine, and 2,3- butanedione.Particularly noteworthy mixtures are 2-hydroxy-2-methyl-1-phenylpropan-2-one and 1-hydroxy-cyclohexyl phenyl ketone; bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 2-hydroxy-2-methyl-1-phenylpropan- 1-one; benzophenone and 1 -hydroxycyclohexyl phenyl ketone; bis(2,6-dimethoxybenzoyl)-2,4,4- trimethylpentylphosphine oxide and 1 -hydroxycyclohexyl phenyl ketone; 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2-hydroxy-2-methyl-1-phenylpropan-1-one; 2,4,6-trimethylbenzophenone and 4-methylbenzophenone; 2,4,6-trimethylbenzophenone and 4-methylbenzophenone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide; and particularly preferred oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl- acetic acid 2-[2-hydroxy-ethoxy]-ethyl ester (Omnirad® 754).Likewise conceivable as photoinitiators are polymeric photoinitiators such as, for example, the diester of carboxymethoxybenzophenone with polytetramethylene glycols of various molar weights, specifically 200 to 250 g / mol (CAS 515136-48-8), and also CAS 1246194-73-9, CAS 813452-37-8, CAS 71512-90-8, CAS 886463-10-1 , or other polymeric benzophenone derivatives, of the kind available commercially, for example, under the trade name Omnipol® BP from IGM Resins B.V., Waalwijk, The Netherlands or Genopol® BP1 from Rahn AG,BASF Coating GmbHDec. 15, 2025Switzerland. Also conceivable, furthermore, are polymeric thioxanthones, an example being the diester of carboxymethoxythioxanthones with polytetramethylene glycols of various molar weights, of the kind available commercially, for example, under the trade name Omnipol® TX from IGM Resins B.V., Waalwijk, The Netherlands. Also conceivable, moreover, are polymeric a-amino ketones, as for example the diester of carboxyethoxythioxanthones with polyethylene glycols of various molar weights, of the kind available commercially, for example, under the trade name Omnipol® 910 or Omnipol® 9210 from IGM Resins B.V., Waalwijk, The Netherlands.Further suitable photoinitiators are, e.g., silsesquioxane compounds having at least one initiating group, of the kind described in WO 2010 / 063612 A1 , particularly from page 2, line 21 to page 43, line 9 therein, as is hereby made part of the present disclosure by reference, specifically from page 2, line 21 to page 30, line 5, and also the compounds described in the examples of WO 2010 / 063612 A1.Amongst all of the above-mentioned photoinitiators those are particularly preferred, which are apt to initiate UV- curing of the two-pack solvent-borne clearcoat material of the present invention in at least one of the UV-A, UV-B and UV-C range of the light spectrum, more preferably in at least two of the afore-mentioned ranges, and even further preferred in the complete UV range, i.e., in all three ranges (UV-A, UV-B and UV-C).Particularly preferred as photoinitiators are oxy-phenyl-acetic acids, such oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl- acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic acid 2-[2-hydroxy-ethoxy]-ethy I ester, and mixture thereof.The one or more photoinitiators CA4 are preferably contained in the solvent-borne two-pack clearcoat material of the present invention (A-pack plus B-pack) in an amount from 0.4 to 8 wt.-%, more preferred 0.8 to 6 wt.-%, and most preferred 1 .0 to 5.0 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material. Below 0.4 wt.-%, curing response tends to be too low, while exceeding 8 wt.-% the cured coating might tend to yellowing.One or more Light Stabilizers (CA5)Light stabilizers CA5 can be used alone or together with suitable radical scavengers. Preferred light stabilizers in the present invention are sterically hindered amin light stabilizers (HALS). The transformation of HALS to nitroxy radicals is slower than the photoinitiating step, thus they to not interfere with free radical polymerization. Examples for HALS being amines such as 2,2,6,6-tetramethylpiperidine, 1 ,2,2,6,6-pentamethylpiperidine 2,6-di-tert- butylpiperidine, or derivatives thereof, such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6- pentamethyl-4-piperidyl) sebacate, and methyl-(1 ,2,2,6,6-pentamethyl-4-piperidyl) sebacate, for example, the latter two are, e.g., available in mixture as in Tinuvin® 292. Further commercially available products are, e.g., Tinuvin® 249 and Tinuvin® 123.BASF Coating GmbHDec. 15, 2025Amongst all of the above-mentioned light stabilizers CA5 those are particularly preferred, which do not negatively interfere with UV-curing of the two-pack solvent-borne clearcoat material of the present invention in the UV-A, UV- B and UV-C range of the light spectrum.The one or more light stabilizers CA5 are preferably contained in the solvent-borne two-pack clearcoat material of the present invention in an amount from 0.1 to 3.0 wt.-%, more preferred 0.2 to 2.5 wt.-%, even more preferred from 0.3 to 2.0 wt.-% and most preferred 0.3 to 1 .0 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material.One or more UV absorbers (CA6)Suitable UV absorbers CA6 comprise such as oxanilides, triazines and benzophenones. Most preferred amongst the triazines being hydroxyphenyl triazines (HTP), having a high absorbance in the UV-B region, such as the commercially available Tinuvin® 400. If UV absorbers are used herein, they are preferably used in combination with one or more light stabilizers CA5.Amongst all of the above-mentioned UV absorbers CA6 those are particularly preferred, which do not negatively interfere with UV-curing of the two-pack solvent-borne clearcoat material of the present invention in the UV-A, UV- B and UV-C range of the light spectrum.Preferably the two-pack solvent-borne clearcoat material of the present invention comprises at least one photoinitiator CA4, and at least one of a light stabilizer CA5 and a UV absorber CA6, even more preferred the two- pack solvent-borne clearcoat material of the present invention comprises one or more, preferably one photoinitiator CA4, one or more, preferably one light stabilizer CA5 and one or more, preferably one UV absorber CA6.The one or more UV absorbers CA6 are preferably contained in the solvent-borne two-pack clearcoat material of the present invention (A-pack plus B-pack) in an amount from 0.1 to 3.0 wt.-%, more preferred 0.15 to 2.0 wt.-%, even more preferred from 0.20 to 1 .5 wt.-% and most preferred 0.25 to 1 .0 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material.B-PackThe one or more Isocyanate (Meth)acrylates CB1The B-pack of the two-pack solvent-borne clearcoat material comprises at least one, for example one to two, or two or more, preferably one isocyanato (meth)acrylate, having at least one free isocyanate group and at least one (meth)acrylate group, and which preferably comprises one or more moieties selected from the group consisting ofBASF Coating GmbHDec. 15, 2025 urethane moieties, allophanate moieties, biuret moieties, uretdione moieties, iminooxadiazindione moieties and isocyanurate moieties.Each isocyanato (meth)acrylate CB1 contained in the B-pack of the two-pack solvent-borne clearcoat material has at least one, preferably at least two free isocyanate groups. The free NCO content (calculated as 42 g / mol) of the one or more isocyanato (meth)acrylates CB1 of the B-pack of the clearcoat material should preferably be at least 5 % by weight, preferably from 6 to 25, more preferably from 6 to 20 and most preferably from 7 to 16% by weight.The number average molecular weight of each of the one or more isocyanato (meth)acrylates CB1 contained in the B-pack of the two-pack solvent-borne clearcoat material is preferably from 300 to 2500 g / mol, more preferably 400 to 2000 and most preferably from 450 to 1500 g / mol.The one or more isocyanato (meth)acrylate CB1 of the B-pack of the two-pack solvent-borne clearcoat material have on average at least one, preferably one to three, more preferably at least two (meth)acrylate groups.Most preferably the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material, each on average have 2 to 3, preferably 2 free NCO groups and 1 to 3, preferably 1 to 2 (meth)acrylate groups.It is assumed that the presence of the one or more isocyanato (meth)acrylates CB1 , preferably comprising one or more moieties selected from the group consisting of urethane moieties, allophanate moieties, biuret moieties, uretdione moieties, iminooxadiazindione moieties and isocyanurate moieties, each isocyanato (meth)acrylate CB1 having at least one free isocyanate group and at least one (meth)acrylate group strongly contribute to the improved adhesion of the coating layer formed from the coating composition according to the present invention to the subjacent coating layer, such as a basecoat layer, in that the free isocyanate groups bind to hydroxyl groups present on the surface of such subjacent coating layer, while the at least one (meth)acrylate groups is incorporated into the UV radiation cured network formed in the coating layer obtained by the coating composition of the present invention. In case components CA1 , CA2a and / or CA2b, as described herein above, are hydroxy-functional, the isocyanate group(s) of isocyanato (meth)acrylate CB1 may additionally react with hydroxy-functions on CA1 , CA2a and / or CA2b, thus, also contributing to the network formation in the clearcoat film.Preferably the one or more isocyanato (meth)acrylates CB1 , as defined above, are reaction products of• at least one polyisocyanate I, preferably an aliphatic polyisocyanate,• with at least one compound R having at least one isocyanate-reactive group and at least one (meth)acrylate group; and• optionally, but not preferred, with at least one compound E having at least two isocyanate-reactive groups.BASF Coating GmbHDec. 15, 2025The term "aliphatic” as used herein and defined by IUPAC includes acyclic or cyclic, saturated or unsaturated carbon containing compounds or residues, excluding aromatic compounds or residues.Herein, aliphatic compounds are preferably saturated aliphatic compounds.Polyisocyanates IHerein below, the polyisocyanates I, which are preferably used in the manufacture of the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material are described.The term "polyisocyanate” as used herein encompasses all isocyanates having 1 .5 or more free isocyanate groups, such as up to 5, preferably up to 4, more preferred up to 3 free isocyanate groups, while a "diisocyanate” is encompassed by the term "polyisocyanate”, but has on average just at least 1 .5 up to less than 2.5 free isocyanate groups.Aromatic polyisocyanates are preferably aromatic diisocyanates having a divalent hydrocarbon residue between the two isocyanate groups, the divalent hydrocarbon residue being aromatic and containing 6 to 20, more preferred 7 to 16, even more preferred 7 to 14 carbon atoms.The aliphatic polyisocyanates, which are preferred herein, are preferably saturated aliphatic diisocyanates having a divalent hydrocarbon residue between the two isocyanate groups, the divalent hydrocarbon residue containing 4 to 20, more preferred 4 to 16, even more preferred 4 to 12 and most preferred 6 to 10 carbon atoms.Examples of customary aliphatic diisocyanates are acyclic diisocyanates, such as tetramethylene diisocyanate, 1 ,6-hexamethylene diisocyanate (1,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, derivatives of lysindiisocyanate, tetramethylxylylene diisocyanate, trimethylhexane diisocyanate or tetramethylhexane diisocyanate; cycloaliphatic diisocyanates such as 1 ,4-, 1 ,3- or 1 ,2-diisocyanatocyclohexane, 4,4'- or 2,4'-di (isocyanatocyclohexyl) methane, 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl) cyclohexane (isophorone diisocyanate), 1 , 3- or 1 ,4- bis(isocyanatomethyl) cyclohexane or 2,4- or 2, 6-diisocyanato-1 -methylcyclohexane. Most preferred are 1 ,3- bis(isocyanatomethyl) cyclohexane, di(isocyanatocyclohexyl)methane, 1 ,6-hexamethylene diisocyanate and isophorone diisocyanate, amongst which isophorone diisocyanate and 1 ,6-hexamethylene diisocyanate, particularly the latter one is even more preferred.Of course, mixtures of diisocyanates, such as the afore-mentioned diisocyanates may also be used.BASF Coating GmbHDec. 15, 2025As polyisocyanates I any dimerization or trimerization products of the afore-mentioned diisocyanates may be employed in the manufacture of the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material. Such dimerization and / or trimerization products of the afore-mentioned diisocyanates may already contain one or more moieties selected from urethane moieties, allophanate moieties, biuret moieties, uretdione moieties, urethane moieties, iminooxadiazindione moieties and isocyanurate moieties. Some of the moieties, such as allophanate groups and urethane groups may be formed by oligomerization of the diisocyanates in the presence of hydroxyl functional compounds or water in case of biuret groups.Any of the polyisocyanates I can be used in mixture with other polyisocyanates and / or diisocyanates.Compound R with an Isocyanate-reactive group and a (Meth)acrylate groupHerein below, compounds R, which are preferably used in the manufacture of the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material, are described.Compounds R are those which carry at least one isocyanate-reactive group and at least one (meth)acrylate group. With these compounds the one or more (meth)acrylate groups are introduced into the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material by reaction between at least one of the isocyanate groups of the polyisocyanates P and the isocyanate-reactive group(s) of compounds R.Preferably, the compound R is a compound having exactly one isocyanate-reactive group and one (meth)acrylate group. Compounds R are preferably monomers preferably having a molecular weight below 500 g / mol, even more preferred below 300 g / mol.Isocyanate-reactive groups are preferably selected from the group consisting of hydroxyl groups, thiol groups, primary and secondary amino group.Preferred examples of compounds R are the monoesters of (meth)acrylic acid with diols, which preferably comprise 2 to 20 carbon atoms, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,1-dimethyl-1 ,2-ethanediol, dipropylene glycol, tripropylene glycol, 1 ,2-,1 ,3- or 1 ,4-butanediol, 1 ,5-pentanediol, neopentyl glycol, 1 ,6-hexanediol, 2-methyl-1 , 5-pentanediol, 2-ethyl-1 ,4- butanediol, 1 ,4-dimethylolcyclohexane, 2,2-bis(4-hydroxycyclohexyl) propane. Amides of (meth)acrylic acid with amino alcohols may also be used, e.g., 2-aminoethanol, 2-(methylamino) ethanol, 3-amino-1 -propanol, 1-amino-2- propanol or 2-(2-ami noethoxy) ethanol, such as ethylenediamine or diethylenetriamine.BASF Coating GmbHDec. 15, 2025Preference is given to using hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2- or 3- hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, neopentyl glycol mono (meth)acrylate, 5- hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate,Compound E having at least two isocyanate-reactive groupsHerein below, exemplary compounds E, which might be used in the manufacture of the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material are described. However, the use of such compounds in the manufacture of the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material is not preferred.If used, compounds E are preferably linear, branched, or cyclic alkane diols, the alkane in the alkane diol having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms.Most preferably, the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material are manufactured by reacting one or more aliphatic polyisocyanates P, even more preferred aliphatic diisocyanates, most preferred hexamethylene-1,6-diisocyanate and / or isophorone diisocyanate with one or more hydroxyalkyl (meth)acrylates, even more preferred hydroxyalkyl (meth)acrylates, most preferred hydroxyethyl (meth)acrylate and / or hydroxypropyl (meth)acrylate. Amongst the afore-mentioned reaction products those are preferred, which have on average have 1 to 3, 1 or 2 (meth)acrylate groups. Amongst the (meth)acrylates, the acrylates being preferred, again.Most preferred, the one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material contain allophanate groups and having the following formula (I)whereinRais a divalent linear or branched or cyclic alkylene radical which preferably has 2 to 20 carbon atoms, more preferred 2 to 12, even more preferred 4 to 10 and most preferred 4 or 8 carbon atoms, and particularly preferred 6 carbon atoms;BASF Coating GmbHDec. 15, 2025Rbis a divalent branched or linear alkylene radical which preferably has 2 to 10 carbon atoms, more preferred 2 to 8, even more preferred 2 to 4 and most preferred 2 or 3 carbon atoms; and particularly preferred an ethylene radical;Rcis H or methyl, most preferred H; and x is a positive number being on average more than 1 up to 4, more preferred 1 to 3, most preferred 1 or 2.Such products are commercially available, for example, under the trade name Laromer® PR 9000 from BASF SE, Ludwigshafen, having on average 2 (meth)acrylic functional groups and 2 NCO groups (14 to 15 wt.-% NCO groups). Other suitable isocyanato (meth)acrylates CB1 are, e.g., aliphatic isocyanate functional urethane acrylates available under the tradenames Ebecryl® 4150 having on average 1 (meth)acrylic functional group and 2 NCO groups (approx. 13 wt.-% NCO groups), Ebecryl® 4396 having on average 1 (meth)acrylic functional group and 2.2 NCO groups; Ebecryl® 4397 having on average 1 (meth)acrylic functional groups and 3 NCO groups (approx. 6.7 wt.-% NCO groups) Ebecryl® 4510 having on average 1.5 (meth)acrylic functional group and 1.5 NCO groups (approx. 7 wt.-% NCO groups), Ebecryl® 4141 having on average 2 (meth)acrylic functional groups and 2 NCO groups (approx. 12 wt.-% NCO groups), Ebecryl® 4765 having on average 2 (meth)acrylic functional groups and 2.5 NCO groups (approx. 4.5 wt.-% NCO groups), Ebecryl® 4250 having on average 3.4 (meth)acrylic functional groups and 1 .4 NCO groups (approx. 5 wt.-% NCO groups), all of the afore-mentioned products being available from Allnex.The one or more isocyanato (meth)acrylates CB1 of the B-pack of the two-pack solvent-borne clearcoat material are preferably contained in the solvent-borne two-pack clearcoat material of the present invention (A-pack plus B- pack) in an amount from 15 to 40 wt.-%, more preferred 18 to 36 wt.-%, even more preferred from 20 to 34 wt.-% and most preferred 22 to 30 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat material.Further Ingredients of the A-pack or B-packIn the following, further ingredients are described which may be comprised in the A-pack or B-pack.Protic Organic Solvents CATThe A-pack of the two-pack solvent-borne clearcoat material may also encompass protic organic solvents CA7 such as alcohols. The amount of protic solvents should preferably in the range from 0 wt.-% to 20 wt.-%, more preferably 0 wt.-% to 18 wt.-%, and most preferably in the range from 0 to 15 wt.-%, based on the total weight of the two-pack solvent-borne clearcoat material (A-pack plus B-pack). Preferably, they are in the A-pack of the two- pack solvent-borne clearcoat material of the invention, if CA2 is CA2b.BASF Coating GmbHDec. 15, 2025Aprotic Organic Solvents CB2 and CA8One or more aprotic organic solvents may be comprised in the A-pack and / or B-Pack, which do not react with any of the other ingredients comprised in the respective A-pack or B-pack, particularly which do not react with any of the other components They may be polar or non-polar aprotic organic solvents. The requirement "do not react with any of the other ingredients comprised in the respective A-pack or B-pack” clearly distinguishes the aprotic organic solvents CB2 and CA8 from the one or more UV reactive monomers CA3 comprising one or two (meth)acrylic groups (also called "reactive diluents”) as present in the A-pack. This also means that the aprotic organic solvents CB2 and CA8 have no UV curable groups, no groups which are reactive towards hydroxyl groups and no groups which are reactive towards isocyanate groups.One main aspect is to preferably select the aprotic organic solvent CB2 and CA8 amongst those having a high evaporation rate at room temperature, thus, allowing the organic solvent to evaporate from the coating film in a very short time ("flash-off”) after application of the coating composition to the substrate, which comprises the dried basecoat film(s).The aprotic organic solvents CB2 and CA8 may be non-polar, such as Solvent Naphtha, however, they are preferably polar aprotic solvent, preferably selected from the group consisting of esters and ketones. Suitable ketones are, e.g., methyl isobutyl ketone, methyl ethyl ketone, diethyl ketone, tert.-butyl methyl ketone, methyl isoamyl ketone and acetone, while suitable esters are, e.g., ethyl acetate, 1 -methoxy propy I acetate-2, 2- methoxyethyl acetate and butyl acetate. It is also possible and preferred to use mixtures of such solvents, e.g., mixtures of esters with ketones.Most preferably, the aprotic organic solvents CB2 and CA8 are inert, i.e., they do not react with any of the other components or ingredients of the A-pack or B-pack or any other pack, if applies, under curing conditions.Preferably, the amount of aprotic organic solvents the two-pack solvent-borne clearcoat material, is the range from 0 wt.-% to 45 wt.-%, more preferably 5 wt.-% to 40 wt.-%, and even more preferred in the range from 10 to 38 wt.- %, and most preferred in the range from 15 to 35 wt.-% based on the total weight of the two-pack solvent-borne clearcoat material (A-pack plus B-pack).Polyisocyanates with no (Meth)acrylic group CB3Due to the manufacturing process of the one or more isocyanato (meth)acrylates CB1 described above, sometimes by-products containing no (meth)acrylic groups in the species are present in the reaction mixture, such as oligomers or polymers of the polyisocyanates or diisocyanates used in the manufacture of CB1 . Thus, such products, even the commercially available ones may contain varying contents of, e.g., homopolymers of diisocyanates such asBASF Coating GmbHDec. 15, 2025 hexamethylene diisocyanate homopolymers. Furthermore, it cannot be excluded that low amounts of starting products, such as diisocyanate monomers are contained in such reaction products.Therefore, if present at all, the polyisocyanates with no (meth)acrylic groups CB3 are necessarily part of the B-pack of the two-pack solvent-borne clearcoat material.If the polyisocyanates with no (meth)acrylic groups CB3 are polymers, their content based on the combined weight of the one or more isocyanato (meth)acrylates CB1 as defined above and the polyisocyanates with no or less than one (meth)acrylic groups CB3, should preferably be less than 15 wt.-%, more preferred less than 10 wt.-% and even more preferred 0 to 5 wt.-%.If the polyisocyanates with no (meth)acrylic groups CB3 are monomers, their content based on the combined weight of the one or more isocyanato (meth)acrylates CB1 as defined above and the polyisocyanates with no or less than one (meth)acrylic groups CB3, should preferably be less than 5 wt.-%, more preferred less than 2 wt.-% and even more preferred less than 1 wt.-%, such as 0 to 0.5 wt.-%.One or more UV reactive monomers (CB4) comprising one or two (meth)acrylic groupsThe B-pack of two-pack solvent-borne clearcoat material may also contain, independently selected, one or more UV reactive monomers (CB4), which are defined as the one or more UV reactive monomers (CA3) of the A-pack of two-pack solvent-borne clearcoat material of the invention. Preferably, the B-pack does not contain UV reactive monomers CB4.One or more Catalysts CA9The A-pack of two-pack solvent-borne clearcoat material may also contain one or more catalysts CA9, particularly those catalyzing a reaction between free isocyanate groups and hydroxy groups. Preferably, the catalyst is an organotin compound such as dibutyltin.From the environmental view, it is preferred that one or more catalysts are used which are tin-free, preferably, if catalysts are used, it is preferred that all catalysts are tin-free. Suitable metal comprising, but tin-free catalysts are selected from zinc, zirconium, bismuth and potassium compounds, particularly the carboxylates of the aforementioned metals.One or more Further Coatings Additives CB5 and CA10The additives in this section differ from any other afore-mentioned ingredients, particularly CA5, CA6 and CA8.BASF Coating GmbHDec. 15, 2025Amongst the coating additives CB5 and CA10, it may be distinguished between additives which affect the properties before cure and those after cure.Additives CB5 and CA10 affecting the properties of the two-pack solvent-borne clearcoat material before cure may be, e.g., substrate wetting additives, defoamers and deaerators, antioxidants and formulation stabilizers, rheological additives, and if pigments are present, also wetting and dispersing additives for pigments. Preferably, the UV curable coating compositions of the present invention do not contain pigments and do also not contain fillers, such as silicas.Additives CB5 and CA10 affecting the properties of the two-pack solvent-borne clearcoat material after cure may be, e.g., surface control additives, improving levelling / flow, slip and scratch resistance properties, such as, e.g., waxes and polysiloxanes; matting agents; and agents to improve adhesion such as reactive adhesion promoters and thermoplastic co-binders.Preferably surface control agents are contained, most preferably in the A-pack of the solvent-borne two-pack clearcoat composition of the present invention, preferably in an amount in the range from 0.01 to 1.0 wt.-%, more preferred in an amount in the range of 0.04 to 0.8 wt.-% and most preferred in an amount in the range from 0.08 to 0.5 wt.-%, based on the total weight of the solvent-borne two-pack clearcoat composition of the present invention (A-pack plus B-pack).Further coatings additives of the two-pack solvent-borne clearcoat material, which might optionally be contained, are also colorants CB5 and CA10. The colorants are typically selected from dyes (i.e., colorants which are soluble in the coating compositions) and much less preferred pigments (i.e., colorants which are insoluble in the coating compositions). Since the coating compositions of the present invention are preferably clearcoat compositions, pigments should preferably not be contained, but, if at all, in very low amounts (tinting amounts) or as transparent pigments, thus allowing light to transmit through the cured coating layer obtained from the coating compositions according to the present invention.Finally protic solvents may also be contained, however, they are not preferred, and if contained they are contained in additive amounts as CA10 in the A-pack only, because there would be a risk of a premature reaction with the isocyanate groups of CB1 .BASF Coating GmbHDec. 15, 2025Further Preferred Embodiments of the Method according to the InventionFrom an environmental view it is preferred to avoid the extensive use of solvents, i.e., solvent-based coating materials. On the other hand, with respect to the energy input necessary to evaporate water and / or organic solvents, it is also reasonable to use organic solvents due to their often higher evaporation rates.Thus, more specific embodiments for both approaches are described herein below.Method according to the invention making use of water-borne primer material and water-borne basecoat materialThis method is characterized in that the steps are as follows a. providing a substrate; b. applying a water-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min, preferably 7 min to 18 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a primer film; c. applying one or more water-borne basecoat materials onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 1 min to 10 min, preferably 3 min to 10 min, more preferred 4 min to 9 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min, preferably 6 min to 15 min at a temperature of 60 °C to 95 °C, preferably 70 °C to 95 °C, more preferred 75 °C to 90 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min, preferably 3 min to 12 min at a temperature in the range of 15 °C to 40 °C, preferably 18 to 30 °C to form a clearcoat film; and f. curing the clearcoat film obtained in step e. by UV radiation curing; wherein the two-pack primer material comprises in the A-pack PABASF Coating GmbHDec. 15, 2025 one or more hydroxy-functional polymers PA1 being selected from polyester-polyurethanes and poly(meth)acrylates; and / or, preferably and the hydroxy-functional polymers PA1 having a hydroxyl number in the range from 5 to 180 mg KOH / g, preferably 10 to 150 mg KOH / g; and in the B-pack PB one or more polyisocyanates PB1 having on average at least 2.0 isocyanate groups; the basecoat material(s) and being selected from the group of physically drying basecoat materials and one-pack basecoat materials; and the two-pack clearcoat material comprises in the A-pack CA one or more urethane (meth)acrylate CA1 each having on average > 2.0 to 5.5 (meth)acrylic functionalities, preferably 2.5 to 5 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g; one or more (meth)acrylated resins CA2b having a hydroxy value from 26 to 180 mg KOH / g, preferably in the range from 30 to 130 mg KOH / g, even more preferred 40 to 110 mg KOH / g, most preferred 50 to 100 mg KOH / g; and one or more diluents selected from protic organic solvents CA7 and aprotic organic solvents CA8; and in the B-pack OB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality and at least one isocyanate functionality, preferably at least two isocyanate functionalities.All preferred features and embodiments, particularly with respect procedural steps a. to f., such as temperature ranges, duration ranges, energy doses, application methods and the like as explicitly mentioned herein above in general, but also in particular in view of the method making use of the water-borne two-pack primer material and water-borne basecoat material also apply to the further preferred method according to the invention making use of water-borne primer material and water-borne basecoat material. This, particularly also applies to the ingredients of the coating material, namely the water-borne two-pack primer material, the water-borne basecoat material, and the solvent-borne two-pack clearcoat material. Just those features and embodiments which are explicitly restricted to the solvent-borne two-pack primer material and the solvent-borne basecoat material, or the method steps making use of them do not apply to the method according to the invention making use of water-borne primer material and water-borne basecoat material.Consequently, it is explicitly referred to the general description to avoid an unnecessary repetition of the respective parts of the description.BASF Coating GmbHDec. 15, 2025Method according to the invention making use of solvent-borne primer material and solvent-borne basecoat materialThis method is characterized in that the steps are as follows a. providing a substrate; b. applying a solvent-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min, preferably 7 min to 18 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a primer film; c. applying one or more solvent-borne basecoat materials onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 1 min to 10 min, preferably 1 min to 8 min, more preferred 2 min to 7 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min, preferably 3 min to 10 min at a temperature of 60 °C to 95 °C, preferably 65 °C to 90 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min, preferably 3 min to 12 min at a temperature in the range of 15 °C to 40 °C, preferably 18 to 30 °C to form a clearcoat film; f. curing the clearcoat film obtained in step e. by UV radiation curing; wherein the two-pack primer material comprises in the A-pack PA one or more hydroxy-functional polymers PA1 being selected from branched polyester resins and poly(meth)acrylates, the poly(meth)acrylates preferably being modified with a chlorinated polyolefin; and the hydroxy-functional polymers PA1 having a hydroxyl number in the range from 20 to 250 mg KOH / g; and in the B-pack PB one or more polyisocyanates PB1 having on average at least 2.0 isocyanate groups, and which in addition are preferably partially silylated with monosilanes and / or bissilanes, the monosilanes and bissilanes comprising at least one hydrolysable, preferably at least two hydrolysable silane groups;BASF Coating GmbHDec. 15, 2025 the basecoat material(s) being selected from the group of physically drying basecoat materials and one-pack basecoat materials; and the two-pack clearcoat material comprises in the A-pack CA one or more urethane (meth)acrylate CA1 each having on average > 1.5 to 4.0, preferably 1.8 to 3.5, even more preferred 2.0 to 3.0 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g, more preferably 5 to 20 mg KOH / g, most preferred 8 to 15 mg KOH / g; one or more (meth)acrylated resins CA2a each having on average 5.6 to 10, preferable 6.0 to 9.0 and, even more preferred 6.5 to 7.5 (meth)acrylic functionalities; and one or more diluents selected from UV reactive monomers CA3 and aprotic organic solvents CA8; and in the B-pack CB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality, preferably at least two (meth)acrylic functionalities and at least one isocyanate functionality, preferably at least two isocyanate functionalities.All preferred features and embodiments, particularly with respect procedural steps a. to f., such as temperature ranges, duration ranges, energy doses, application methods and the like as explicitly mentioned herein above in general, but also in particular in view of the method making use of the solvent-borne two-pack primer material and solvent-borne basecoat material also apply to the further preferred method according to the invention making use of solvent-borne primer material and solvent-borne basecoat material. This, particularly also applies to the ingredients of the coating material, namely the solvent-borne two-pack primer material, the solvent-borne basecoat material, and the solvent-borne two-pack clearcoat material. Just those features and embodiments which are explicitly restricted to the water-borne two-pack primer material and the water-borne basecoat material, or the method steps making use of them do not apply to the method according to the invention making use of solvent- borne primer material and solvent-borne basecoat material.Consequently, it is explicitly referred to the general description to avoid an unnecessary repetition of the respective parts of the description.Multilayer Coated Substrate and its UseThe invention also provides a multilayer coated substrate. Such multilayer coated substrate is obtainable by the method according to the invention. Since flash-off conditions and time, drying times and temperatures and UVBASF Coating GmbHDec. 15, 2025 curing conditions influence the predominant reactions in the coating materials, particularly crosslinking reactions, but also the migration of ingredients, such as polymers and catalysts from one coating film into the adjacent coating film and even from an adjacent coating film to another, the multilayer coated substrates differ from those cured under different conditions.Furthermore, all information provided for the method according to the invention and the therein used substrate and coating materials apply in the same way for the multilayer coated substrate according to the invention, without further need to repeat the same.Further object of the invention is the use of a multilayer coated substrate as a part of a vehicle, such as a vehicle body or part thereof.Further object of the invention is the use of the method for producing a multilayer coating system according to the invention in original equipment manufacturer (OEM) coating, preferably automotive OEM coating.In the following the invention will be described by use of working examples.BASF Coating GmbHDec. 15, 2025EXPERIMENTAL PARTIn the following the invention will be described in more detail by use of examples.Testing MethodsAll testing methods described herein below are valid for the whole application and its definitions and not just applicable to the Examples. For any undated standards, the respective standard at the date of filing this application shall be effective.Solids ContentThe solids content is determined by weighing approx. 2 g of a sample of the respective composition (coating material or ingredient of a coating material) and dry the respective sample at a temperature of 110 °C for 60 min. The mass of the remainder is divided by the mass of the sample and multiplied by 100 to receive the solids content of the sample in weight percent. The difference to 100 wt.-% is the volatile content of the sample.Weight-Average Molecular WeightsThe weight-average molecular weights Mwwere determined by gel permeation chromatography (GPC). To determine polymer molecular weights by GPC, fully dissolved molecules of the polymer sample were fractionated on a porous column stationary phase. A 0.1 mol / l acetic acid solution in tetrahydrofuran (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 were 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 was injected into the column at a flow rate of 1.0 ml / min. Separation took place according to the size of the polymer coils which form in the eluent solvent. Small molecules diffused into the pores of the column material more frequently and are therefore retarded more than large molecules. Thus, large molecules were eluted earlier than small molecules. The molecular weight distribution, the averages and the polydispersity Mw / Mnof the polymer samples were 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.Dry Film ThicknessDry film thickness is determined using methods suitable to the substrate as detailed in Paints and varnishes - Determination of film thickness ISO 2808.Calculated Average Number of (Meth)acrylic groupsThe (meth)acrylic group functionality is typically introduced into a product via monomers containing (meth)acrylic groups and the (meth)acrylic functionality is not consumed in such a reaction. Thus, the (meth)acrylic groupBASF Coating GmbHDec. 15, 2025 functionality can be calculated knowing the amount of such monomers introduced and knowing the number average molecular weight of said product, which can be obtained as described below.Calculated Average Number of Free Isocyanate GroupsThe content of NCO groups (in wt.-%) was determined by reacting the NCO groups with an excessive amount of dibutyl amine and titration of the non-reacted dibutyl amine with hydrochloric acid in accordance with DIN EN ISO 11909 (May 2007). Knowing the number average molecular weight of the product containing the NCO groups, which can be obtained as described below, the average number of free isocyanate groups can be calculated.Hydroxyl Number / Hydroxyl ValueThe hydroxyl number was determined in accordance with UNE-EN ISO 4629-2:2018-04-04.Adhesion Testing (Initial Adhesion)As the adhesion testing method crosscut adhesion testing was carried out. The initial adhesion denotes the adhesion tested at 72 hours following the curing process using ISO 2409.Adhesion Testing (Post Humidity)For testing the post-humidity adhesion, GMW 14729 was carried out, which describes the method of humidity exposure and cutting should be carried out to evaluate adhesion. The cutting method is described by ISO 2409Dry Scratch Resistance Test (Scratch Resistance Test)The dry scratch resistance test was carried out in accordance with the GMW 14865 standard.Acid Resistance TestAcid resistance test was carried out with sulfuric acid solution pH = 0 as spot test according to the GMW 14701 standard at 70 °C for 30 min.Windshield Bonding TestThe windshield bonding test is GMW 16569 (Glass Bonding). Quick Knife Adhesion (the mode of testing) is described by GMW 3368.Appearance Test (long wave, short wave, R-value)The appearance of dried and cured clearcoat is evaluated by its surface texture, which is measured by BYK wavescan dual (available from Byk-Gardner GmbH, Geretsried, Germany). Surface texture is a mixture of various textures, ranging from very fine to very course. BYK wave-scan dual measures the surface textures at different scale levels, which is differentiated to six categories, identified by wavelength (Du, Wa, Wb, Wc, Wd, We). Based on these measured data, long wave, short wave and R values are calculated by the equipment and denotes theBASF Coating GmbHDec. 15, 2025 appearance level of the paint. A lower long wave and short wave value represents a better performance in appearance. Long wave is majorly defined by the clearcoat layer, while short wave is also highly influences by the primer layer and basecoat layer.Tukon Hardness / MicrohardnessHardness of the coating is evaluated by Tukon hardness, which follows the ASTM D1474 using Wilson Tukon 1102 tester.2K-Primer MaterialsAll primer materials used in the method for producing a multilayer coating material are 2K-primer (I ,e. , 2-pack primer materials). The compositions of the solvent-borne primer materials IPM1 and IPM2 are shown in Table 1a below, and the composition of the water-borne primer materials IPM3 is shown in Table 1b.BASF Coating GmbHDec. 15, 2025Table 1a - solvent-borne primer materialsSP1 : Mw= 2,300 g / mol; hydroxyl number: 126 mg KOH / g; SP2: Mw= 5,500 g / mol; hydroxyl number: 190 mg KOH / g; SP3: hydroxyl number: 29-38 mg KOH / g; Tg= 60 °C; SP4: microgel particle dispersion; particle size 250-300 nm; SP5: dispersion of TO2 pigment; SP6: dispersion of carbon black pigment; SP7: flow additive; SP8: silica dispersion; SP9: UV absorber; SP10: hindered amine light stabilizer; SP11 : sulfonic acid catalyst; SP12: phosphate acid catalyst; SP13: amine-neutralized sulfonic acid catalyst; SP14: amine-neutralized phosphate acid catalyst; SP15: organotin catalyst; SP16: 9.4 wt.-% protic organic solvent, 42.1 wt.-% aprotic non-polar solvent, 48.5 wt.-% aprotic polar solvent; SP17: reaction product of HDI-trimer and a mixture of bissilane & monosilane, wherein approx. 10 % of the original NCO groups were silane modified; SP18: HDI trimer, NCO content 23 wt.-%; SP19: butyl acetateBASF Coating GmbHDec. 15, 2025Table 1b - water-borne primer materialsBASF Coating GmbHDec. 15, 2025WP1 : aliphatic polyester-polyurethane dispersion; OH value: 17 mg KOH / g; WP2: polyacrylic resin; OH value: 17 mg KOH / g; WP3: acrylated polyester-polyurethane; OH value: 115 mg KOH / g; WP4: crosslinked polyacrylate; WP5: acrylated polyester-polyurethane dispersion; WP6: white tinting paste, 49.45 TO2, main binder see WP1; WP7: amine for neutralization; WP8: polyacrylate type; WP9: 10 wt.-% pigment carbon black, 20.9 wt.-% binder, total solids 30.9 wt.-% in solvent / water w / w 11.6 / 56.5; WP10: TMDD; WP11 : silicon based wetting agent; WP12: HDI trimerBasecoat MaterialThe composition of the solvent-borne basecoat material IBM 1 is shown in Table 2a below, and the composition of the water-borne basecoat materials I BM2 is shown in Table 2b.Solvent-Borne Basecoat MaterialTable 2a - solvent-borne basecoat materialBASF Coating GmbHDec. 15, 2025Water-borne Basecoat MaterialTable 2b - water-borne basecoat materialsSee Table 1b: WB1 = WP1; WB2 = WP2; WB3 = WP4; WB4 = WP5; WB5 = WP9; WB6 = WP7; WB7 = WP8; WB8 = WP10; WB9 = WP11BASF Coating GmbHDec. 15, 20252K-Clearcoat MaterialsAll clearcoat materials used in the inventive method for producing a multilayer coating material are solvent-borne 2K-clearcoat materials (i.e., 2-pack clearcoat materials). Comparative Clearcoat Material CCM1 is a 1-pack composition, because it does not contain a crosslinker comprising NCO groups. The composition of the clearcoat materials ICM1, CCM1 and ICM2 are shown in Table 3 below.BASF Coating GmbHDec. 15, 2025Table 301 : CA1 = aliphatic urethane (meth)acrylate; (meth)acrylic functionality: 2.4; OH value: 11 mg KOH / g; CA3 =UV reactive monomer according to CA3 of the description02: CA2a = aliphatic urethane (meth)acrylate with isocyanurate and allophanate structures; (meth)acrylic functionality 7.5; OH value: 10 mg KOH / g; CA3 = UV reactive monomer according to CA3 of the description03: aliphatic allophanate urethane (meth)acrylate; (meth)acrylic functionality = 4; 100 wt.-% solidsBASF Coating GmbHDec. 15, 2025C4: CA2b = (meth)acrylated acrylic resin, OH value: 75 mg KOH / g; CA8 = aprotic organic solvent according to CA8 of the descriptionC5: mix of isopropanol / ethanol (2:1 w / w)06: aliphatic urethane acrylate; NCO functionality = 2; acrylate functionality = 2; 100 wt.-% solids07: aliphatic urethane acrylate; NCO functionality = 2.2; acrylate functionality = 1; 100 wt.-% solidsC8: mix of butyl acetate, acetone and methylethyl ketonePreparation of Multilayer Coating SystemsThe primer materials, basecoat materials and clearcoat materials were applied by electrostatic spray application to an electrocoated galvanized steel substrate to produce the multilayer coating systems. The sequence of layers, and manufacturing conditions are as follows and given in Tables 4a and 4b, below.The solvent-borne two-pack primer film was applied in a dry film thickness of 17.5 ± 2.5 pm. The solvent-borne basecoat film was applied in a dry film thickness of 17.5 ± 2.5 pm. The solvent-borne two-pack clearcoat material was applied in a dry film thickness of 52 ± 4 pm.The water-borne two-pack primer film was applied in a dry film thickness of 20 ± 2 pm. The water-borne basecoat film was applied in a dry film thickness of 10 ± 2 pm. The solvent-borne two-pack clearcoat material was applied in a dry film thickness of 45 ± 5 pm.Table 4a: solvent-borne primer / solvent-borne basecoat / solvent-borne clearcoatBASF Coating GmbHDec. 15, 2025Table 4b: water-borne primer / water-borne basecoat / solvent-borne clearcoatResultsTable 5a: solvent-borne primer / solvent-borne basecoat / solvent-borne clearcoatBASF Coating GmbHDec. 15, 2025Table 5b: water-borne primer / water-borne basecoat / solvent-borne clearcoatAs shown above, the multi-layer coatings according to the invention IMLC1, IMLC2, and IMLC3, show - compared to the comparative example CMLC1 - an excellent adhesion, particularly windshield bonding adhesion, acid resistance, scratch resistance and appearance as required in OEM coating applications.

Claims

BASF Coating GmbHDec. 15, 2025CLAIMS1 . A method for producing a multilayer coating system on a substrate, comprising the steps of a. providing a substrate; b. applying a water-borne two-pack primer material or solvent-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min at a temperature in the range of 15 °C to 40 °C to form a primer film; c. applying one or more water-borne basecoat materials, if the two-pack primer is a water-borne two- pack primer material or applying one or more solvent-borne basecoat materials, if the two-pack primer is a solvent-borne primer material, onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 5 min to 20 min at a temperature in the range of 15 °C to 40 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min at a temperature of 60 °C to 95 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min at a temperature in the range of 15 °C to 40 °C to form a clearcoat film; and f. curing the clearcoat film obtained in step e. by UV radiation curing; wherein the two-pack primer material comprises in the A-pack PA one or more hydroxy-functional polymers PA1 ; and in the B-pack PB one or more polyisocyanates PB1 having on average at least 1.5 isocyanate groups; the basecoat material(s) being selected from the group of physically drying basecoat materials, one- pack basecoat materials, and two-pack basecoat materials; and the solvent-borne, UV radiation curable, two-pack clearcoat material comprises in the A-pack CABASF Coating GmbHDec. 15, 2025 one or more urethane (meth)acrylate CA1 each having on average > 1.5 to 5.5 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g; one or more (meth)acrylated resins CA2a each having on average 5.6 to 10 (meth)acrylic functionalities and / or one or more (meth)acrylated resins CA2b having a hydroxy value from 26 to 180 mg KOH / g; and one or more diluents selected from UV reactive monomers CA3, protic organic solvents CA7 and aprotic organic solvents CA8; and in the B-pack CB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality and at least one isocyanate functionality.

2. The method according to claim 1 , characterized in that all steps of the method are carried out at a temperature not exceeding 120 °C, preferably not exceeding 110 °C, more preferred not exceeding 100 °C, and most preferred not exceeding 95 °C.

3. The method according to claim 1 or 2, characterized in that UV radiation curing in step f. is accomplish by using UV-A, UV-B and UV-C radiation.

4. The method according to any one or more of claims 1 to 3, characterized in that total energy density of UV-A, UV-B and UV-C light applied in step f. is in the range from 0.5 J / cm2to 12 J / cm2, preferably 1.0 J / cm2to 10 J / cm2, further preferred from 1.5 J / cm2to 8 J / cm2, most preferred 1.5 to 6 J / cm2.

5. The method according to any one or more of the preceding claims, characterized in that the one or more hydroxy functional polymers PA1 and the one or more polyisocyanates PB1 are aliphatic hydroxy functional polymers PA1 and aliphatic polyisocyanates PB1 .

6. The method according to any one or more of the preceding claims, characterized in that the polyisocyanates PB1 have one average at least 2.0 isocyanate groups.

7. The method according to any one or more of the preceding claims, characterized in that the polyisocyanates PB1 have one average at least 1.5 isocyanate groups, preferably at least 2.0 isocyanate groups and in addition are partially silylated with monosilanes and / or bissilanes, the monosilanes and bissilanes comprising at least one hydrolysable, preferably at least two hydrolysable silane groups.

8. The method according to any one or more of the preceding claims, characterized in that the one or more urethane (meth)acrylates CA1 and the one or more (meth)acrylates resins CA2a and CA2b, and the one or more isocyanato (meth)acrylates CB1 are aliphatic urethane (meth)acrylates CA1 , aliphatic (meth)acrylates resins CA2a and CA2b, and aliphatic isocyanato (meth)acrylates CB1.BASF Coating GmbHDec. 15, 20259. The method according to any of the preceding claims, characterized in that the isocyanato (meth)acrylate comprise on average two or more isocyanato groups.

10. The method according to any of the preceding claims, characterized in that the substrate is a polymeric substrate or a metal substrate, preferably a metal substrate.11 . The method according any of the preceding claims, characterized in that the steps are as follows a. providing a substrate; b. applying a water-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min, preferably 7 min to 18 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a primer film; c. applying one or more water-borne basecoat materials onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 1 min to 10 min, preferably 3 min to 10 min, more preferred 4 min to 9 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min, preferably 6 min to 15 min at a temperature of 60 °C to 95 °C, preferably 70 °C to 95 °C, more preferred 75 °C to 90 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min, preferably 3 min to 12 min at a temperature in the range of 15 °C to 40 °C, preferably 18 to 30 °C to form a clearcoat film; and f. curing the clearcoat film obtained in step e. by UV radiation curing; wherein the two-pack primer material comprises in the A-pack PA one or more hydroxy-functional polymers PA1 being selected from polyester-polyurethanes and poly(meth)acrylates; and / or, preferably and the hydroxy-functional polymers PA1 having a hydroxyl number in the range from 5 to 180 mg KOH / g, preferably 10 to 150 mg KOH / g; and in the B-pack PB one or more polyisocyanates PB1 having on average at least 2.0 isocyanate groups;BASF Coating GmbHDec. 15, 2025 the basecoat material(s) and being selected from the group of physically drying basecoat materials, and one-pack basecoat materials; and the solvent-borne, UV radiation curable, two-pack clearcoat material comprises in the A-pack CA one or more urethane (meth)acrylate CA1 each having on average > 2.0 to 5.5 (meth)acrylic functionalities, preferably 2.5 to 5 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g; one or more (meth)acrylated resins CA2b having a hydroxy value from 26 to 180 mg KOH / g, preferably in the range from 30 to 130 mg KOH / g, even more preferred 40 to 110 mg KOH / g, most preferred 50 to 100 mg KOH / g; and one or more diluents selected from protic organic solvents CA7 and aprotic organic solvents CA8; and in the B-pack OB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality and at least one isocyanate functionality, preferably at least two isocyanate functionalities.

12. The method according any of the preceding claims, characterized in that the steps are as follows a. providing a substrate; b. applying a solvent-borne two-pack primer material onto at least part of the substrate, subsequently evaporating at least part of the volatile content of the primer material in a time from 5 min to 20 min, preferably 7 min to 18 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a primer film; c. applying one or more solvent-borne basecoat materials onto at least part of the primer film formed in step b, whereas the basecoat material differs from the primer material, and subsequently evaporating at least part of the volatile content of the basecoat material or basecoat materials in a time from 1 min to 10 min, preferably 1 min to 8 min, more preferred 2 min to 7 min at a temperature in the range of 15 °C to 40 °C, preferably 18 °C to 30 °C to form a basecoat film; d. subsequently drying the primer film and basecoat film in a time range from 3 min to 15 min, preferably 3 min to 10 min at a temperature of 60 °C to 95 °C, preferably 65 °C to 90 °C; and e. subsequently applying a solvent-borne, UV radiation curable, two-pack clearcoat material onto at least part of the basecoat film obtained in the previous steps, and subsequently evaporating at least part of the organic solvents comprised in the volatile content of the two-pack clearcoat material in a time from 1 min to 15 min, preferably 3 min to 12 min at a temperature in the range of 15 °C to 40 °C, preferably 18 to 30 °C to form a clearcoat film; f. curing the clearcoat film obtained in step e. by UV radiation curing;BASF Coating GmbHDec. 15, 2025 wherein the two-pack primer material comprises in the A-pack PA one or more hydroxy-functional polymers PA1 being selected from branched polyester resins and poly(meth)acrylates, the poly(meth)acrylates preferably being modified with a chlorinated polyolefin; and the hydroxy-functional polymers PA1 having a hydroxyl number in the range from 20 to 250 mg KOH / g; and in the B-pack PB one or more polyisocyanates PB1 having on average at least 2.0 isocyanate groups, and which in addition are preferably partially silylated with monosilanes and / or bissilanes, the monosilanes and bissilanes comprising at least one hydrolysable, preferably at least two hydrolysable silane groups; the basecoat material(s) being selected from the group of physically drying basecoat materials, and one-pack basecoat materials; and the solvent-borne, UV radiation curable, two-pack clearcoat material comprises in the A-pack CA one or more urethane (meth)acrylate CA1 each having on average > 1.5 to 4.0, preferably 1.8 to 3.5, even more preferred 2.0 to 3.0 (meth)acrylic functionalities and a hydroxy value from 0 to 25 mg KOH / g, more preferably 5 to 20 mg KOH / g, most preferred 8 to 15 mg KOH / g; one or more (meth)acrylated resins CA2a each having on average 5.6 to 10, preferable 6.0 to 9.0 and, even more preferred 6.5 to 7.5 (meth)acrylic functionalities; and one or more diluents selected from UV reactive monomers CA3 and aprotic organic solvents CA8; and in the B-pack OB one or more one isocyanato (meth)acrylates CB1 having on average at least one (meth)acrylic functionality, preferably at least two (meth)acrylic functionalities and at least one isocyanate functionality, preferably at least two isocyanate functionalities.

13. A multilayer coated substrate, obtainable by a method as defined in any one or more of claims 1 to 11 .

14. Use of the multilayer coated substrate as a part of a vehicle, such as a vehicle body or part thereof.BASF Coating GmbHDec. 15, 202515. Use of the method according to any one or more of claims 1 to 12 in original equipment manufacturer (OEM) coating, preferably automotive OEM coating.

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