The present invention relates to the field of coating methods and coating compositions, in particular coatings for construction materials.

Coatings for construction materials are often provided by applying layer after layer onto the material until the final coating is achieved.

Exemplary state of the art coating methods comprise the steps of i. providing a substrate, in particular a construction material, ii. applying a first layer of a first liquid coating composition onto said substrate, iii. applying a second layer of a second liquid, radiation curable coating composition.

The first liquid coating composition is typically used as a primer layer. Said primer (= first coating layer) provides on the one hand good compatibility between said primer composed of the first coating composition and the second coating layer composed of the second coating composition, and on the other hand provides good adherence to the surface of the substrate and to the further coating layer. Additionally, said primer needs to provide good water resistance, high weatherability and sufficient flexibility. UV-curable (UV) or light emitting diode (LED) curable or electron beam (EB) curable compositions are preferably used as primers.

The second coating layer may be similar to the first coating layer. Most often, UV-curable or LED curable or electron beam (EB) curable compositions are preferably used.

One disadvantage of UV-curable coating compositions is the shrinkage behaviour upon curing. High shrinkage leads to increase of the internal stress in the coating and therefore, the impact resistance of the coatings may be decreased.

EP 1 110926 relates to a process for the surface treatment of cement-bound building materials, in particular concrete wherein a radiation curable, water- and solvent free lacquer comprising at least 63 % by weight of pentaerythritol triacrylate, 22.5 - 27.5 % by weight of N-vinyl-2-pyrrolidone, 4.3 - 5.3 % by weight of photoinitiator and 0.18 - 0.22 % by weight of wetting agents is applied to the surface of the building material and subsequently treated with radiation.

EP 2 147 157 relates to an anti-abrasion layer comprising a mixture of irregular hard material particles and round solid material particles embedded in a matrix material, wherein the hard material particles have a Mohs hardness rating of at least 6 and the solid material particles have a Mohs hardness rating of at least 3 wherein the mean particle diameter of the solid material particles is equal to or less than the mean particle diameter of the hard material particles, wherein the irregular hard material particles are selected from the group consisting of aluminium oxide, corundum, molten corundum, sintered corundum, zirconium corundum, sol-gel corundum, silicon carbide and boron carbide, wherein the round solid material particles that are substantially free of cutting edges are full spheres made of glass and/or sintered ceramic, wherein the ratio of round solid material particles that are substantially free of cutting edges in the embedded mixture is 10 - 50 wt.-%, based on the total amount of embedded particles. Additionally, EP 2 147 157 also relates to the use of an anti-abrasion layer as described above for antiabrasion surfaces.

US 8 313 809 relates to multi-layered coatings, suitable to be disposed on various substrates, as well as processes for producing the coatings. Coatings according to some embodiments of the disclosure are provided on a substrate by coating the substrate with a first layer, optionally coating the first layer with a second layer, and coating the second layer, when selected to be present with a top layer. Such coating structures can be applied to a substrate such as a garage floor, a truck bed, railcar, seatainer, tractor-trailers and the like within a single day, and can often be ready for human foot traffic within 2-4 hours after application of the top layer and can be ready for heavy traffic such as automobiles within 12- 24 hours after application of the top layer.

US 2012164402 relates to a decorative concrete block comprising a block body made of concrete; and a plurality of ink dots being obtained by curing ink droplets of an active energy curable ink, and forming an image on an outer surface of the block body.

US 20130085218 discloses modifying particles, these particles have, if spherical, an average particle size of approximately 10 microns to approximately 80 microns and a hardness of at least 5 Mohs for inorganic textured particles. If second modifying (textured) particles are used, both first and second particles are organic (made from PMMA), wherein the second modifying particles are slightly smaller, having approximately 10 microns to approximately 40 microns for the first particle diameter and approximately 15 microns to approximately 60 microns for the second particle diameter. Furthermore, such particles have a Shore D hardness of approximately 70 to 90 points.

US 20130122282 relates to an article having an anti-abrasion layer, comprising a mixture of irregular particles of hard material and round particles essentially free of cutting edges embedded in a matrix material and the use thereof for the production of anti-abrasion surfaces. Table 2 discloses the particle size distribution d(50) as used, which seems to have a d(50) of 55.5 μm for the smaller particles and 74.08 μm for the bigger particles. Additionally, in table 5 of this document glass beads with grit 180 reach a d(50) of 90.07 μm, table 6 discloses with example 8 a mixture of 50 wt.-% Alodur ZWSK F 220 with a d(50) of 74.08 μm and 50 wt.-% glass beads grit 180 with a d(50) of 90.07 μm.

US 6852768 B2 discloses texture producing particles, these particles having an average particle size d(50) of from about 10 to about 150 μm and inorganic fillers with from about 3 to about 9 μm.

WO 2016202680 is regarded as the closest prior art and relates to process for manufacturing coated fiber cement products, wherein said process comprises the steps of: (i) providing a cured fiber cement product having at least one surface; (ii) optionally applying a primer to the at least one surface of the cured fiber cement product; (iii) providing a first layer of a first radiation curable composition to the at least one surface; (iv) partially curing the first layer of radiation curable composition by radiation; (v) providing a second layer of a second radiation curable composition to the partially cured first layer, the second radiation curable composition comprising pigments; and (vi) curing the first and the second layer of radiation curable composition by radiation. Additionally, WO 2016202680 also relates to a fiber cement product obtainable by the process as described above. WO 2016202680 describes a two- (or three) layer coating system based on UV-curable coating compositions, whereas the second layer comprises pigments and isocyanate functional polyurethanes with unsaturated double bonds. Although such UV- curable coatings may provide good adhesion between the polymer matrix to the pigments and especially to the substrate, the scratch, abrasion and mar resistance are often insufficient for exterior applications. Further, due to the smooth surface of such coatings, the slip resistance is poor, which is an issue in case the coating is used for horizontal applications (e.g.: for flooring or parking lots). Finally, a glossy surface appearance is often obtained, although a matte or even dull-matte surface appearance would be desirable. The isocyanate (NCO) groups may not react completely during the curing of the coating and residual reactive NCO groups will likely be present in the cured coating. These kinds of reactive groups are able to react with water or humidity and therefore, the long-term exterior durability is significantly reduced.

Summary of the invention:

The present invention was made in order to overcome the disadvantages of the state of the art and in order to provide a topcoat and a coating method that may generate coatings with increased hardness, thereby resulting in enhanced mar and scratch resistance as well as slip resistance. In certain embodiments, topcoats and coatings featuring additionally a matte surface appearance may be obtained. In other embodiments, topcoats and coatings featuring additionally high flexibility and impact resistance may be obtained. A further object of the present invention is to provide an improved coating method, particularly suitable for coating of construction materials, said method providing a protective and/or decorative coating by employing an improved topcoat, particularly suitable for construction materials, with said improved mechanical properties.

Detailed description of the invention:

The objects are achieved by a radiation curable coating composition according to the independent claim 1 and a coating method according to the independent claim 14. Preferred embodiments are specified in the dependent claims. All of the preferred embodiments of this invention are interrelated, and each preferred embodiment and/or disclosed characteristic feature may be combined with each other and also as any combination of two or more preferred embodiments/characteristic features.

The radiation curable coating composition comprises unsaturated prepolymers in an amount of between 10 and 85 wt%, preferably between 15 and 60 wt% and even more preferably between 20 and The composition is characterised in that the composition comprises furthermore hard modifying particles wherein the hard modifying particles have a Mohs hardness of at least 5, preferably at least 6, and a mean particle size d(50) between 30 and 200 μm, preferably between 40 and 150 μm, more preferably between 60 and 130 μm and most preferably between 75 and 120 μm.

According to an alternative embodiment of the invention, he radiation curable coating composition comprises unsaturated prepolymers in an amount of between 10 and 85 wt%, preferably between 15 and 60 wt% and even more preferably between 20 and 45 wt% of the total composition for building up a coating matrix.

The composition is especially characterised in that the composition comprises furthermore at least first and second modifying particles, wherein the at least first and second modifying particles are i ) a combination of first hard and second soft modifying particles; or ii ) a combination of different first and second hard modifying particles; wherein the hard modifying particles have a Mohs hardness of at least 5, preferably at least 6, and a mean particle size d(50) between 30 and 200 μm, preferably between 40 and 150 μm, more preferably between 60 and 130 μm and most preferably between 75 and 120 μm.

Yet in further embodiments said hard modifying particles have a d(50) of 30-200, 40-200, 50- 200, 60-200, 70-200, 80-200, 90-200, or 100-200 μm or yet in other embodiments the d(50) of the hard modifying particles is 30-190, 30-180, 30-170, 30-160, 30-150, 30-140, 30-140, 30-130 or 30-120 μm. In particularly preferred embodiments, the hard modifying particles have a d(50) between 40-130, more preferably between 80-120, even more preferably between 90-120, yet more preferably between 100- 120 μm and most preferably between 100-115 μm.

Within the present application, the term 'modifying particles' is to be understood to comprise all kinds of hard and/or soft modifying particles present in the inventive coating composition, such as f.i. at least first and second (and any further) hard and/or soft modifying particles. Likewise, the term ‘hard modifying particles' is to be understood to comprise all kinds of hard modifying particles present in the inventive coating composition and the term ‘soft modifying particles' is to be understood to comprise all kinds of soft modifying particles present in the inventive coating composition.

It was found that the addition of hard modifying particles having a Mohs hardness of at least 5, preferably at least 6 turned out to particularly advantageous as both the mar and scratch resistance as well as the slip resistance were significantly improved.

Additionally, the at least first and second modifying particles may cause microstructures on the surface after curing of the coating and thus reduce the surface area that could be affected by mechanical stress. Furthermore, the micro structuring of the coating surface may increase the slip resistance and the light scattering on the surface, the latter enables the change of visual aspects of the surface, like a glossy or matte optical appearance.

It was also found that by addition of at least first and second modifying particles the shrinkage of the coating composition upon curing may be reduced leading to improved mechanical properties.

Additionally, the at least first and second modifying particles may absorb UV light and therefore, the coating composition may serve as a UV barrier for the beneath coating layers, resulting in improved UV stability of the layer package.

The unsaturated prepolymers are capable to react and crosslink with each other and optionally also with other components within the composition in a radical mechanism, which may be triggered by photo initiators, which may also be present in the composition, thereby forming a cross-linked network. However, the crosslinking reaction may also be induced by high energy radiation or electron beams without any photo initiators. In addition to said unsaturated prepolymers, the compositions may comprise diluents, in particular reactive diluents, pigments, fillers and additives such as, light and/or heat stabilizers, defoaming agents, surfactants, catalysts, synergists and further additives as known in the art.

Reactive diluents may be added to the composition in order to adjust the rheological properties, such as the viscosity, of the composition. Additionally, the network density may be influenced by addition of these compounds. Often, a mixture of various reactive diluents may be useful to adjust the properties as desired. Reactive diluents are typically regarded as low molecular weight compounds, solvents, monomers or short oligomers with at least one functional group that is capable of reacting with at least one other component of the composition, in particular with the unsaturated prepolymers. Preferably, acrylate functional reactive diluents with a functionality of 1-3 are used. Commercially available, non-limiting, examples of suitable reactive diluents are monofunctional acrylates like isobornylacrylate (IBOA) (Allnex), cyclic trimethylolpropane formal acrylate SR531 (Sartomer) lauryl acrylate SR335 (Sartomer), tridecyl acrylate Miramer M124 (Miwon); difunctional acrylates like hexanediol diacrylate (HDDA), dipropylene glycol acrylate, esterdiol diacrylate (EDDA) SR606A (Sartomer), tricyclo aluminum decanedimethanol diacrylate (TCDDMDA) SR833S (Sartomer), tricyclodecanediol diacrylate Ebecryl 130 (Allnex), dipropylene glycol diacrylate (DPGDA) Miramer M222 (Miwon), triethylene glycol diacrylate (TEGDA) Miramer M220 (Miwon); trifunctional acrylates like trimethylolpropane triacrylate (TMPTA) Miramer M300 (Miwon), trimethylolpropane triacrylate TMP(EO)6TA M3160 (Miwon), Laromer ^® LR 8863 (BASF), tris (2-hydroxy ethyl) isocyanurate triacrylate (THEICTA) SR368 (Sartomer).

According to a preferred embodiment, the reactive diluent comprises IBOA, HDDA, TCDDMDA, DPGDA and/or TEGDA. The use of IBOA and HDDA may improve the adhesion of the coating layer to the previous layer(s). TCDDMDA and DPGDA may improve the thermal stability and TEGDA may improve the flexibility and hydrophobic behavior of the coating.

In general, various materials for the hard modifying particles may be employed for the present invention. However, glass particles, in particular filled glass particles and/or aluminum oxide particles, preferably corundum particles, as well as carbide particles, in particular boron and/or silicon carbide particles, are preferably used. However, also other materials with a Mohs hardness of at least 5, such as certain organic, in particular polymeric, materials may be employed as hard modifying particles.

According to a particularly preferred embodiment of the invention, the hard-modifying particles are selected from the group consisting of glass particles, preferably filled glass particles, and/or aluminium oxide particles, preferably corundum particles.

According to a preferred embodiment, matte hard modifying particles, preferably matte glass particles, more preferably matte filled glass particles are employed as said hard modifying particles. The addition of matte hard modifying particles may lead to a more matte optical appearance of the coating as compared to the very same coating with the very same hard modifying particles which are not matted. Matte hard modifying particles may be obtained by surface treatment of hard modifying particles; e.g. by increasing the surface roughness of the hard-modifying particles by chemical and/or mechanical treatment.

According to a further particularly preferred embodiment of the invention, the coating composition comprises at least first and second hard modifying particles, wherein the difference of the maximum particle size and/or d(90) of the first and second hard modifying particles is at least 15 μm, preferably 20 μm, preferably at least 25 μm and more preferably at least 30 μm and/or the difference of the minimum particle size and/or d(10) of the first and second hard modifying particles is at least 10 μm, preferably at least 15 μm and more preferably at least 20 μm and/or the difference in the mean particle size d(50) of the first and second hard modifying particles is at least 10 μm, preferably at least 20 μm and more preferably at least 25 μm, wherein preferably the difference of the maximum particle size and/or d(90), and/or the minimum particle size and/or d(10), and/or the mean particle size d(50) does not exceed 80 μm, and wherein preferably the first and second hard modifying particles have a mean particle size d(50) between 30 and 200 μm, preferably between 40 and 150 μm, more preferably between 60 and 130 μm and most preferably between 75 and 120 μm.

According to a preferred embodiment the first hard modifying particles have a mean particle size d(50) between 30 μm and 110 μm, preferably between 70 μm and 110 μm, more preferably between 75 and 110 μm, yet more preferably between 80 μm and 100 μm, even more preferably between 90 μm to 100 μm and most preferably between 85 μm and 90 μm and the second hard modifying particles preferably have a mean particle size d(50) between 90 and 200 μm, preferably between 90 and 200 μm, more preferably between 90 μm and 150 μm, yet more preferably between 95 μm and 130 μm, yet even more preferably between 100 μm to 130 μm, even more preferably between 100 μm and 120 μm and most preferably between 105 μm and 115 μm, preferably with disclosed differences in particle size. For example, the first hard modifying particles may have a mean particle size d(50) between 80 and 90 μm, e.g.: 85 μm and the second hard modifying particles may have a mean particle size d(50) between 105 and 120 μm, e.g.: 112 μm, with the disclosed differences in particle size.

A certain difference in the minimum, maximum, mean particle sizes d(50), the d(10) value and/or d(90) value significantly improves the slip resistance and the surface hardness of the coating layer, whereby the difference in the d(50) values of the first and second modifying particles is the most important factor to achieve the desired technical benefits. Said differences in the particle sizes of the at least first and second modifying particles further improve the formation of a micro structure on the surface during the curing of the coating composition. If the difference in the minimum, maximum, mean particle sizes d(50), d(10) and/or d(90) of the at least first and second modifying particles exceeds a certain value, the surface may become non-uniform and the hardness of the coating layer may deteriorate. Preferably, the difference of the maximum particle size and/or d(90), and/or the minimum particle size and/or d(10), and/or the mean particle size d(50) of the first and second modifying particles does not exceed 80 μm.

Different kinds of the hard-modifying particles may be chosen from the same or different materials. For example, both the first and second hard modifying particles may be corundum particles, or the first hard modifying particles may be glass particles and the second hard modifying particles may be corundum particles. As a further preferred embodiment, both the first and second hard modifying particles are glass particles, preferably filled glass particles. Also, the first hard modifying particles may be glass particles, the second hard modifying particles may be corundum particles and as additional hard modifying particles, a different type of glass particles, e.g.: with a different particle size distribution, may be employed. Modifying particles may be chosen from the same or different material and may have different particles size distributions, in particular d(10) and/or d(50) and/or d(90) and/or minimum particle size and/or maximum particle size.

Commercially available, non-limiting examples of suitable, hard modifying particles are SiLibeads 5210 (Sigmund Lindner), SiLibeads 5212 (Sigmund Lindner), SiLibeads 5213 (Sigmund Lindner), Alodur ZWSK (Treibacher Schleifmittel), for example Alodur ZWSK F280, Cerablast (Cerblast), for example Cera- blast F220.

In addition to the hard-modifying particles, soft modifying particles may also be added to the composition. These soft modifying particles have a Mohs hardness of below 5, preferably below 4.

In a preferred embodiment, these soft modifying particles are polyurethane based modifying particles.

In a particularly preferred embodiment, the first and optionally the second hard modifying particles are glass particles, further characterised in that polyurethane based modifying particles are present as soft modifying particles.

According to a further particularly preferred embodiment of the invention, the coating composition is characterised in that the composition further comprises silica, wherein preferably silica accounts for 1-15 wt%, more preferably for 5-10 wt% of the composition. The addition of silica may significantly decrease the gloss of the coating and thus coatings with matte or dull-matte appearance may be obtained. Thus, silica may on the one hand be regarded as matting agent. Further, the addition of silica may be used to adjust the viscosity of the coating composition, as in general, higher contents of silica result in an increase of the viscosity of the composition. The adjustment of the viscosity of the composition is very important, as on the one hand, a suitable viscosity is required to obtain the desired layer thickness of the coating upon application of the layer and on the other hand, the viscosity may be adjusted such that a sedimentation of the modifying particles is avoided. Different kind of silica particles, e.g.: having different particle size distributions may be added to the composition. Preferably, a mixture of a first type of silica particles with a mean particle size d(50) of between 3 and 7 μm and a second type of silica particles with a mean particle size d(50) between 8 and 15 μm is employed; for example, the first type of silica particles may have a d(50) of 5 μm and the second type of silica particles may have a d(50) of 10 μm. The ratio of the first and second type of silica particles may be between 1:1 and 5:1, preferably between 1.5:1 and 4:1 and more preferably between 1.8:1 and 2.5:1, e.g.: 2:1. Further, the silica may be modified on the surface with functional groups that are capable of reacting with at least one other component of the composition, in particular with the unsaturated prepolymers. Preferably, these functional groups are chosen from the group consisting of vinyl, acrylate, methacrylate, allyl and mixtures thereof. Apart from silica, other mineral or inorganic particles with the properties as defined above may be used instead or in a combination with silica.

Commercially available, non-limiting examples of suitable silica and other mineral/inorganic particles are (ACEMATT ^® OK 412; Evonik) kaolin (e.g. DORKAFILL ^® PRO_VOID; Dorfner) or sodium aluminium silicate (e.g. SIPERNAT ^® 820; Evonik).

Apart from silica and other mineral/inorganic particles, also other matting agents, such as polymethyl urea resin (e.g. PERGOPAK ^® M3; Martinswerk (Huber)) or polymeric matting agents (e.g.: DEUTERON MK, MK- F, MK-F6, ST-L, ST, ST-G, ST_M; Deuteron) may be employed. A matting agent is to be understood as a compound which reduces the gloss of a coating compared to a coating that is formulated without said matting agent. Preferably, the matting agent, if present, accounts for 1 - 15 wt%, more preferably 5- 10 wt% of the composition.

According to a further particularly preferred embodiment of the invention, the coating composition has a viscosity of between 300 and 600 mPas, preferably between 350 and 500 mPas, more preferably between 300 and 400 mPas, even more preferably between 300 and 350 mPas and most preferably between 400 and 450 mPas at 50°C as measured according to Method B as defined herein. Adjusting the viscosity as described above turned out advantageous in order to obtain the desired layer thickness of the coating upon application of the coating composition, and on the other hand to avoid the sedimentation of all the modifying particles, i.e. all hard and soft modifying particles, in particular upon storage of the composition.

Additionally, it was also found that the shape of all the modifying particles plays a role for the functionality of the modifying particles, however, in general, any shape of the modifying particles may be used for the invention as described within this application.

According to a further particularly preferred embodiment of the invention, the coating composition is characterised in that the modifying particles have a spherical-like shape with a sphericity of at least 0.7, preferably at least 0.8, and even more preferably at least 0.85. The use of essentially spherical particles with a sphericity of at least 0.7, preferably at least 0.8 and even more preferably at least 0.85 was found to be advantageous because the spherical-like shape of such particles may induce a slide bearing-like effect to the surface of the coating, especially when the surface is attacked by sharp or acute articles. Hence, the surface is generally higher resistant against scratches and abrasion and additionally, the resistance against chemical attacks, e.g. from solvents, alkaline and acidic solutions may be improved.

According to a preferred embodiment, at least some of the modifying particles comprise functional groups on their surface, preferably groups comprising unsaturated bonds, more preferably unsaturated carbon-carbon bonds and most preferably carbon-carbon double bonds. Such modifying particles are referred to “functional modifying particles” herein. Surprisingly, it was found that functional modifying particles have a beneficial effect on the properties of the coating layer. Functional modifying particles are to be understood within the present application as modifying particles that possess functional groups, such as groups comprising unsaturated bonds, on the surface that are preferably capable of reacting with at least one other component, in particular the unsaturated prepolymers, of the coating composition during the curing reaction of the coating. However, in general, both functional and non-functional modifying particles as well as mixtures may be employed, but functional modifying particles are preferably used. Functional modifying particles are preferably employed as hard modifying particles. According to a preferred embodiment, the functional groups of the functional modifying particles are selected from the group consisting of amine, epoxy, hydroxyl, carboxylic acid, isocyanate, blocked isocyanate, peroxide, azo, allyl, vinyl, acrylate, and methacrylate groups, groups comprising carbon-carbon unsaturated bonds and/or mixtures thereof. Simple derivatives of such functional groups which are readily known to a person skilled in the art are also encompassed by the scope of the present invention.

These functional modifying particles may improve the mechanical, chemical, thermal and weather resistance of the cured coating. Functional glass beads are preferably used as functional, hard modifying particles). In case reactive groups are present on the surface of the modifying particles, these are able to react with the matrix of the coating composition during curing and due to the covalent bonding with the matrix, the previously mentioned properties may be improved.

According to a further particularly preferred embodiment of the invention, the coating composition is characterised in that at least some of the hard-modifying particles comprise functional groups on their surface, such as groups comprising unsaturated bonds, preferably unsaturated carbon-carbon bonds and more preferably carbon-carbon double bonds; however, other functional groups may also be employed. Hence, the hard-modifying particles may be incorporated into the coating matrix by chemical reactions resulting in the formation of covalent bonds between the functional hard modifying particles and the coating matrix. This leads to a tougher structure of the layer resulting in a significant improvement of the mar and scratch resistance of the layer. Additionally, the weatherability as well as the long-term stability of the layer and thereby of the entire coating may be improved by the tougher network structure of the layer.

According to a further particularly preferred embodiment of the invention, the coating composition is characterised in that the functional groups of at least some of the hard-modifying particles are selected from the group consisting of vinyl, amine, allyl, acrylate, methacrylate groups and mixtures thereof, whereas amine and/or vinyl groups are particularly preferred. Again, simple derivatives of such functional groups which are readily known to a person skilled in the art are also encompassed by the scope of the present invention.

These functional groups turned out to be particularly suitable to react with at least one component of the coating composition, in particular with the unsaturated prepolymers, during the curing reaction, resulting in the highest improvement of the scratch and mar resistance of the coating.

In general, various unsaturated prepolymers may be used for the liquid radiation-curable composition. Preferably, polyurethane, polyacrylate, polyether, polyester and/or silicone based unsaturated prepolymers are used. The unsaturations may f.i. be incorporated into the prepolymer either by an endcapping approach or by the selection of monomers in the backbone of the prepolymer. Preferably, the unsaturations are groups comprising carbon-carbon double and/or triple bonds, in particular (meth)acrylate, vinyl, and/or allyl groups and derivatives and mixtures thereof. Acrylate functional groups are particularly preferred. The content of the unsaturated prepolymers within the composition is between 10 and 85 wt%, preferably between 15 and 60 w% and even more preferably between 20 and 45 wt%. Preferably, the number average molecular mass (Mn) of said prepolymers is between 1000 and 60000 g/mol, more preferably between and 1000 and 8000 g/mol, and most preferably between 1000 and 8000 g/mol. Due to the number average molecular mass (Mn) as stated above, the shrinkage of the coating composition is reduced during curing. Furthermore, the viscosity of the coating composition depends on the Mn of the said prepolymers and with the increase of Mn, the viscosity of the composition also increases. Therefore, the flow properties of the coating composition may be deteriorated in case Mn of said prepolymers exceeds 60000 g/mol. It turned out to be particularly advantageous to use prepolymers with a functionality of 4-15, preferably 5-10, even more preferably 6-10 and most preferably 8-10. Preferably, prepolymers with a functionality of 4-15, preferably 5-10, even more preferably 6-10 and most preferably 8-10 may provide a high crosslinking density to the coating and therefore, a coating with high hardness and good mar- and abrasion resistance properties may be achieved. The use of prepolymers with a functionality of 4-15, preferably 5-10, even more preferably 6-10 and most preferably 8-10 increases the crosslinking density in the cured coating layer and therefore, the mechanical and chemical properties of the coating may be highly improved. However, a certain degree of flexibility is still preserved, which is of high importance to avoid brittleness of the coating and to ensure sufficient impact resistance. The functionality of an unsaturated compound such as an unsaturated prepolymer is to be understood as the number of unsaturations that may be used for chemical cross-linking of the composition. Aliphatic prepolymers are preferably used.

According to a further particularly preferred embodiment of the invention, the coating composition is characterised in that the unsaturated prepolymers are selected from the group consisting of acrylate and/or methacrylate and/or vinyl and/or allyl functionalized polyurethanes, preferably with a number average molecular mass (Mn) between 2000 and 60000 g/mol, more preferably between 3000 and 20000 and most preferably between 3000 and 10000 g/mol.

According to another preferred embodiment, acrylic acrylate and/or urethane acrylate and/or silicone acrylate prepolymers are used, wherein preferably said prepolymers are aliphatic prepolymers and wherein preferably said prepolymers have a functionality of 4-15, preferably 5-10 and more preferably 6- 10 and even more preferably 8-10, and preferably a Mn between 1000 and 30000 g/mol, preferably 1000- 10000 g/mol and more preferably 1000-8000 g/mol. Silicone acrylate prepolymers feature low surface energies and coating compositions comprising silicon acrylates typically exhibit lower surface energies compared to the identical composition without presence of silicon acrylate prepolymers. Low surface energies may lead to reduced wettability of the cured coating and thus a dirt repellent and/or anti-graffiti effect may be generated on the surface.

The backbone of the preferably used aliphatic prepolymers comprises CH2 groups and therefore, the so-obtained cured coating layer has an inherent chemical stability against bases and acids. Additionally, these kinds of prepolymers exhibit high exterior durability. Additionally, the use of aliphatic prepolymers may improve the flexibility and the impact resistance of the cured coating and it may also reduce the shrinkage behaviour during the curing of the composition.

The content of acrylic acrylate prepolymers preferably is between 0 and 50 wt%, more preferably between 0 and 30 wt%, even more preferably between 0 and 20 wt%, even more preferably between 5 and 20 wt% and most preferably between 10 and 20 wt%. The content of urethane acrylate prepolymers is preferably between 5 and 50 wt%, more preferably between 10 and 40 wt%, even more preferably between 20 and 40 wt% and most preferably between 25 and 38 wt%. The content of silicone acrylate prepolymers is preferably between 0 and 5 wt%, more preferably between 0 and 4 wt% and most preferably between 1 and 3 wt%.

Commercially available, non-limiting examples of suitable, unsaturated prepolymers are Miramer PU2104 (Miwon), PU340 (Miwon), Ebecryl 244 (Allnex), Ebecryl 4101 (Allnex), Ebecryl 4858 (Allnex), PU340 (Miwon), Ebecryl 244 (Allnex), Ebecryl 4101 (Allnex), Miramer PU620 NT, Miramer MU9800NT (Miwon), Ebecryl 5129 (Allnex), Ebecryl 1291 (Allnex) Miramer S5242 (Miwon), Miramer PS460 (Miwon), CN203 (Sartomer), CN2208 (Sartomer), Ebecryl 884 (Allnex), Ebecryl 154 (Allnex).

According to a further particularly preferred embodiment of the invention, the coating composition cures to a transparent coating layer. That is, the substrate or the coating layer beneath the cured transparent coating layer is still recognizable, or, in other words, visible with the naked eye, if the thickness of the cured transparent coating layer is at least 60 μm. This is particularly desirable in case a decorative coating layer has been applied below in order to ensure the visibility of said decorative coating layer below. A transparent coating layer may be achieved by avoiding the addition of opaque pigments, such as titanium dioxide based pigments. However, dyes or non-opaque fillers may still be present in an essentially transparently curing coating composition.

Preferably, the hard modifying particles have a mean particle size d(50) between 30 and 300 μm, more preferably between 30 and 200 μm, even more preferably between 40 and 150 μm, yet more preferably between 60 and 130 μm, even more preferably between 75 and 120 μm, yet even more preferably between 90 μm and 120 μm, even more preferably between 100 μm and 120 μm and most preferably between 100 μm to 115 μm.

According to a further particularly preferred embodiment of the invention, the coating composition is characterised in that the modifying particles, preferably the at least first and second hard modifying particles, are embedded into the matrix and less than 1/3 of the modifying particles, preferably the at least first and second hard modifying particles, protrude from the final surface.

The amount of modifying particles that protrude from the final surface can be calculated from microscopic images of the cross-section of the coating composition.

Alternatively, the amount of modifying particles that protrude from the final surface can be determined by combined use of atomic force microscopy (AFM) and an etching process. This method is only applicable to determine the amount of modifying particles that protrude from the final surface which are not etched away during the etching process. With AFM, the surface roughness is determined in order to assess the surface area of modifying particles that protrude from the surface with respect to the total surface area of a definite sample of the coating composition. To determine the volume ratio of the modifying particles, (a) the volume of a definite sample of the coating composition is calculated, (b) the coating matrix is removed by means of an etching treatment, and (c) the volume content of the remaining modifying particles as well as their particle size is determined. The knowledge of the volume ratio and size of the modifying particles along with the surface ratio of the protruding particles allows for an assessment of the amount of modifying particles that protrude from the surface.

The above-mentioned mean particle sizes are preferably chosen because of the anchoring of such modifying particles within the matrix. Depending on the final thickness of the applied coating, normally in the range of 30-200 μm, preferably 30-100 μm and more preferably 50-90 μm, most of all modifying particles are largely embedded into the matrix and only less than approximately 1/3 of the modifying particles protrude significantly from the final surface. On the other hand, modifying particles with a d(50) smaller than 30 μm lead to undesired agglomerates and stacking. These undesired effects caused by small modifying particles may cause poor embedding of said particles into the matrix, resulting in poor mechanical properties. Exemplary, an agglomerate of such small modifying particles that is located at the surface of the coating may easily break off under mechanical stress. Additionally, modifying particles with a d(50) smaller than 30 μm have a higher specific surface area, which, in case functional modifying particles are used, exhibit more functional groups on the surface that could react with the matrix. Although the higher content of the functional groups on the surface will provide for a higher crosslinking density and improve the mechanical properties, it may also lead to higher internal stress of the coating layer and the impact resistance of the coating may be reduced. Furthermore, modifying particles with a mean particles size d(50) below 30 μm have a higher volume fraction and surface area in the coating layer compared to modifying particles with a mean particle size d(50) above 30 μm. Due to the higher volume fraction and surface area, the modifying particles may absorb higher amounts of radiation, in particular UV-radiation, during curing, which may have a negative effect on the curing of the coating composition. The polymer matrix may not be fully cured and the chemical, mechanical and physical properties of the cured coating layer may be significantly decreased. Another disadvantage of modifying particles with a d(50) smaller than 30 μm may be their higher tendency of agglomeration than modifying particles with a d(50) larger than 30 μm. The modifying particles in the agglomerate typically do not significantly crosslink with each other and also the crosslinking between the modifying particle agglomerates and the polymer matrix may be highly reduced. Therefore, the mechanical resistance and the hardness of the coating may be reduced.

In addition to the hard modifying particles, soft modifying particles may also be added to the composition. Such soft modifying particles have a Mohs hardness of below 5, preferably below 4 and are typically polymeric particles. According to a preferred embodiment, the soft modifying particles are selected from the group consisting of polyester, polyamide, polyurethane, poly(meth)acrylate such as polymethylmethacrylate (PMMA), polyolefine, such as polyethylene or polypropylene, particles and mixtures thereof. Also, core-shell-type polymeric soft-modifying particles may be employed. Also, inorganic soft modifying particles such as talc, anhydrite and mica may be employed. These soft modifying particles may have a spherical-like shape, but also irregular, even acicular or plate-like or rod-like shapes are possible. However, spherical-like soft modifying particles with a sphericity of at least 0.7, preferably at least 0.8 and even more preferably at least 0.85 are preferably employed. The addition of such soft modifying particles may increase the flexibility and impact resistance of the coating and also an improved matting effect may be achieved.

Preferably, the soft modifying particles have a mean particle size d(50) between 30 and 300 μm, more preferably between 30 and 200 μm, even more preferably between 40 and 150 μm, yet more preferably between 50 and 130 μm, even more preferably between 50 μm and 120 μm, even more preferably between 50 μm and 110 μm and most preferably between 50 and 100 μm, e.g. between 60 μm and 90 μm or between 70μm and 80 μm or between 75 μm and 80 μm, for the same reasons as mentioned previously for the hard modifying particles. Preferably, the soft modifying particles are smaller than the hard modifying particles.

Both functional and non-functional soft modifying particles may be used. Non-functional soft modifying particles are preferably used.

According to a particularly preferred embodiment, the soft modifying particles are polyurethane particles with a mean particle size d(50) between 30 and 200 μm, preferably between 50 and 150 μm, and more preferably between 60 and 90 μm.

The composition may comprise different kinds of soft modifying particles, e.g.: at least first and second soft modifying particles, preferably within the range of particle sizes given above and also with the difference in particle sizes disclosed herein for the hard modifying particles. The different kinds of soft modifying particles may for instance be made of different materials, e.g. the first soft modifying particles may be PMMA particles and the second soft modifying particles may be polyurethane particles; or the at least first and second soft modifying particles may both be polyurethane particles, which differ in the particle size distribution or in another property.

According to a preferred embodiment of the invention, the composition comprises at least first and second hard modifying particles and additionally soft modifying particles, for instance one kind of soft modifying particles or first and second soft modifying particles. Preferably, the at least first and second hard modifying particles are glass particles and the soft modifying particles are polyurethane particles.

According to a further particularly preferred embodiment of the invention, the coating composition comprises at least first and second hard modifying particles and additionally soft modifying particles, wherein the difference of the maximum particle size and/or d(90) of the first and second hard modifying particles is at least 15 μm, preferably at least 20 μm, preferably at least 25 μm and more preferably at least 30 μm and/or the difference of the minimum particle size and / or d(10) of the first and second hard modifying particles is at least 10 μm, preferably at least 15 μm and more preferably at least 20 μm and/or the difference in the mean particle size d(50) of the first and second hard modifying particles is at least 10 μm, preferably at least 20 μm and more preferably at least 25 μm, wherein preferably the difference of the maximum particle size and/or d(90), and/or the minimum particle size and/or d(10), and/or the mean particle size d(50) does not exceed 80 μm, and wherein preferably the first and second hard modifying particles have a mean particle size d(50) between 30 μm and 200 μm, preferably between 40 μm and 150 μm, more preferably between 60 and 130 μm, and most preferably between 75 μm and 120 μm, and the soft modifying particles preferably have a mean particle size d(50) between 30 μm and 200 μm, preferably between 50 and 150 μm and more preferably between 60 and 90 μm.

According to a further preferred embodiment the first hard modifying particles have a mean particle size d(50) between 30 μm and 110 μm, preferably between 70 μm and 110 μm, more preferably between 75 and 110 μm, more preferably between 80 μm and 100 μm, even more preferably between 90 μm to 100 μm and most preferably between 85 μm and 90 μm and the second hard modifying particles have a mean particle size d(50) between 90 μm and 150 μm, more preferably between 95 μm and 130 μm, more preferably between 100 μm to 130 μm, even more preferably between 100 μm and 120 μm and most preferably between 105 μm and 115 μm and the soft modifying particles preferably have a mean particle size d(50) between 30 μm and 150 μm, preferably between 50 and 120 μm and more preferably between 50 and 100 μm.

For example, the first hard modifying particles may have a mean particle size d(50) between 80 and 90 μm, e.g.: 85 μm and the second hard modifying particles may have a mean particle size between 105 and 120 μm, e.g.: 112 μm and the soft modifying particles may have a mean particle size d(50) between 60 and 100 μm, e.g.: 75 μm. In such embodiments, the first and second hard modifying particles are preferably glass particles and the soft modifying particles are preferably polyurethane particles.

Commercially available, non-limiting examples of suitable, soft modifying particles are HOSBead U 90 TR (HOS Technik GmbH) Degacryl (Evonik), MICA Muskovit (HPF The Mineral Engineers), TREMICA® Muskovit (HPF The Mineral Engineers), TREFIL® Phlogopit (HPF The Mineral Engineers), TREFIL® 1313 (HPF The Mineral Engineers) and Aspolit F100 (Aspanger).

According to a preferred embodiment, a coating, obtainable from the coating composition as described above, is employed as topcoat in a multi-layer coating.

Another objective of the invention is to provide an improved coating method using the coating composition described above.

The coating method comprising the steps of: i. providing a substrate, in particular a construction material; ii. applying a first layer of a first liquid coating composition onto said substrate; iii. optionally applying a second layer of a second coating composition onto the first layer, preferably a decorative coating layer, more preferably a print, even more preferably a digital print and most preferably an inkjet or electro photographic-print; iv. optionally applying a third layer of a third liquid, radiation curable coating composition onto the first or second layer; v. applying a fourth layer, the fourth layer being a coating composition as described above.

A preferred embodiment of the present invention is as follows: i. providing a substrate, ii. applying a first layer of a first liquid coating composition onto said substrate, iii. treating the coating with energy, iv. optionally applying a second layer of a second coating composition, preferably a decorative coating layer, more preferably a print, even more preferably a digital print and most preferably an inkjet or electro photographic-print, v. treating the coating with energy in case the second optional layer has been applied, vi. optionally applying a third layer of a third liquid, radiation curable coating composition, vii. treating the coating with energy in case the third optional layer has been applied, viii. applying a fourth layer of a fourth liquid, radiation curable coating composition, the fourth layer being a coating composition as described above. ix. treating the coating with energy.

A particularly preferred embodiment of the present invention is as follows: i. providing a substrate, ii. applying a first layer of a first liquid, radiation curable coating composition onto said substrate, iii. treating the coating with energy to partially cure the coating, iv. optionally applying a second layer of a second, radiation curable coating composition, preferably a decorative coating layer, more preferably a print, even more preferably a digital print and most preferably an inkjet or electro photographic-print, v. treating the coating with energy in case the second optional layer has been applied to partially cure the coating, vi. optionally applying a third layer of a third liquid, radiation curable coating composition, vii. treating the coating with energy in case the third optional layer has been applied to partially cure the coating, viii. applying a fourth layer of a fourth liquid, radiation curable coating composition, ix. treating the coating with energy to fully cure the coating.

It is particularly advantageous if a previous coating layer is only partially cured before the next coating layer is applied because in this case, the previous coating layer still has sufficient functional groups left that can react with the next coating layer and therefore, the interlayer adhesion may be significantly improved. Additionally, the partial curing of the previous coating layer may transfer the very same coating layer into a gel-like state and therefore, the handling of the substrate and the following application of the next coating layer may be significantly facilitated.

Coating Layer application

The first, third and fourth coating layers may be applied by conventional techniques that are suitable to apply liquid coating compositions, such as roll-coating or spray coating techniques, onto substrates. In addition, in certain cases, said coating layers may be also be applied by printing techniques, in particular inkjet printing. Inkjet printing is particularly suitable for embodiments wherein the first coating layer is composed of two sub-layers, i.e. a transparent coating layer and an opaque coating layer. In such embodiments, the inkjet printing is preferably used to apply the first coating layer on top of a conventionally applied transparent coating layer. Thus, a thin opaque layer may be achieved by the combined use of the transparent coating layer and the opaque coating layer as the first coating layer. This may improve the overall adhesion of the coating, as the risk of cohesion breakage is decreased by decreasing the layer thickness of the opaque coating layer. The third and fourth coating layers are preferably applied via conventional techniques, in particular roll-coating techniques. The second, decorative layer may be applied by any technique that is suitable to provide a decorative layer as described herein. Preferably, printing techniques, in particular inkjet and electrophotographic techniques, are employed.

Curing

The term curing or cure as used within this application is to be understood as the treatment of a coating composition with energy, such as radiation or heat energy, and thereby induce chemical reactions to form covalent bonds, resulting in the chemical crosslinking of the curable components to a chemical network. Non curable components that are present in such curable compositions are intercalated in said chemical network. The term partial curing as used within this application is to be understood as an incomplete curing reaction, leaving a certain amount (e.g.: at least 10%) of functional groups unreacted, which may be fully cured by subsequent energy treatment.

The term full curing or fully cured as used within this application is to be understood as a complete curing reaction, leaving a low amount of functional groups unreacted (e.g.: at least 90%, preferably at least 95% and more preferably at least 98% of the functional groups have reacted). Non-curable compositions may also be employed as the first and/or second coating layer. Of course, non-curable compositions may also be treated with energy, in particular radiation or heat energy, in order to remove solvent and/or to sinter/fuse the compositions. However, chemical reactions to form covalent bonds are not induced by this treatment to a significant extent.

In case curable coating compositions are used, which may be the case for the first and/or second coating layer and which is always the case for the third and fourth coating layer, the curing can be generally performed layer by layer or at once after all layers have been applied or even both of these methods may be combined. Partial curing of a layer may be performed before the next coating layer is applied, followed by full curing of both layers or followed again by partial curing of the second layer before the very next layer is applied. When all coating layers have been applied, the coating is fully cured. Whether a coating is fully or only partially cured can be determined by adjusting the energy input and the time of the energy treatment. It is a standard experimental procedure for a person skilled in the art to properly adjust the curing conditions in order to obtain a desired curing state of a coating.

Preferred embodiments of the first composition for the first layer of the coating method as described above:

Surprisingly, it was found, that radiation curable compositions show significant advantages when compared to non-curable compositions. Typically, said radiation curable compositions comprise unsaturated prepolymers and/or oligomers (within the present application, the terms “oligomer”, “polymer”, “resin” and “prepolymer” are used synonymously) that are capable to react and crosslink with each other in a radical mechanism which may be triggered by photo initiators, which may also be present in the composition, thereby forming a cross-linked network. However, the crosslinking reaction may also be induced by high energy radiation or electron beams without any photo initiators.

According to a further particularly preferred embodiment of the invention, the first coating composition is characterised in that the first coating composition comprises pigments, preferably color pigments and even more preferably white pigments. Within this application, black and white are considered as colors. Thus, black and white pigments are to be understood as color pigments.

According to a preferred embodiment, the first coating composition comprises pigments and/or dyes. Both organic and inorganic pigments may be used, but inorganic pigments are preferred. Preferably, the first coating composition provides for an opaque appearance of the first coating layer after curing. It is particularly preferred to use white pigments, in particular inorganic white pigments, and further in particular titanium dioxide based pigments, to obtain an opaque first coating layer after curing. Obtaining a first coating layer with an opaque appearance after curing is particularly desirable, in case a second, decorative coating layer is applied. The opaque first coating layer may ensure good visibility and high contrast of the second, decorative layer. According to a further preferred embodiment, the composition is formulated in such a way that an essentially transparent first coating layer is obtained after curing. A transparent coating layer may be achieved by avoiding the addition of opaque pigments, such as titanium dioxide based pigments. However, dyes or non-opaque fillers may still be present in an essentially transparently curing coating formulation. Preferably, such a transparent first coating layer is obtained from a composition that is free of both pigments and fillers as thus the adhesion of the coating to the substrate may be improved.

According to a further preferred embodiment, two layers of the first coating composition are applied to the substrate, wherein the first sub-layer of the first layer is a transparent layer and the second sub-layer of the first layer is an opaque layer, both of which are obtainable from first coating compositions as described herein. As a result, the adhesion of the coating to the substrate may be improved and at the same time, good visibility and high contrast of the second layer, i.e. the decorative layer, may be achieved.

The viscosity of the first coating composition is preferably between 10-500 mPas, more preferably between 10-300 mPas, even more preferably between 10-200 mPas, even more preferably between 10-170 and most preferably between 50-170 mPa s at 35 °C as measured according to Method A as defined herein. The viscosity depends on the molecular weight of the used prepolymers in the coating composition. Compositions with a viscosity below 10 mPas at 35 °C show a higher crosslinking density after the curing than compositions with a viscosity of 10 mPas or above at 35 °C. This leads to a higher internal stress in the coating and higher shrinkage upon curing and thus, the impact resistance of the cured coating may be decreased. Furthermore, the mechanical anchoring of the coating system to the substrate will be reduced due to the higher shrinkage of a coating composition with a viscosity below 60 mPas, preferably below 10 mPas at 35 °C. The application of a coating composition with a viscosity above 500 mPas at 35 °C onto the substrate surface requires additional heating to decrease the viscosity during application. This additional heat could cause pre-reactions and accelerated curing, which leads to nonintended increase of viscosity and decrease of the recyclability of the residual coating composition.

Preferably, polyurethane, polyacrylate, polyether, polyester and/or silicone based unsaturated prepolymers are used. The unsaturations may f.i. be incorporated into the prepolymer either by an endcapping approach or by the selection of monomers in the backbone of the prepolymer. Preferably, the unsaturations are groups comprising carbon-carbon double and/or triple bonds, in particular acrylate, vinyl, and/or allyl groups and derivatives and mixtures thereof. Acrylate functional groups are particularly preferred.

According to a preferred embodiment, polyurethane acrylates and/or acrylic acrylates are employed. The content of the unsaturated prepolymers within the first coating composition is between 10 and 85 wt%, preferably between 15 and 60 wt% and even more preferably between 20 and 45 wt%. Aliphatic prepolymers are preferably used.

The number average molecular mass (Mn) of said prepolymers is between 1000 and 30000 g/mol, preferably between 1000 and 10000 g/mol, and more preferably between 1000 and 8000 g/mol. It turned out to be particularly advantageous to use prepolymers with a functionality of 1-4, preferably 1-3 and even more preferably 1-2. It was found that prepolymers with a functionality of 1-4, preferably 1-3 and even more preferably 1-2 provide high flexibility of the cured coating layer and also improve the adhesion to the substrate as well as to the next layer(s). The adhesion between the coating layer and the substrate may be generated by van der Waals interactions, hydrogen bonds and mechanical anchoring of the polymer matrix to the substrate surface. The mechanical anchoring is usually regarded as the most important adhesion type between UV curable coatings and substrate surfaces. However, due to the shrinkage behaviour upon curing of UV curable coating compositions, the mechanical anchoring is getting significantly reduced. Shrinkage of the coating composition upon curing is highly decreased by use of unsaturated prepolymers with a functionality of 1-4, and thus the mechanical anchoring of the UV curable coating composition upon curing may be significantly improved.

According to a preferred embodiment, acrylic acrylate and/or urethane acrylate prepolymers are used, wherein preferably said prepolymers are aliphatic prepolymers, and wherein preferably said prepolymers have a functionality of 1-4, preferably 1-3 and more preferably 1-2, and preferably a Mn between 1000 and 30000 g/mol, preferably 1000 - 10000 g/mol and more preferably 1000 - 8000 g/mol. The backbone of the used aliphatic prepolymers comprises CH2 groups and therefore, the cured coating layer has an inherent chemical stability against bases and acids. Additionally, this kind of prepolymers exhibit high exterior durability. The content of acrylic acrylate prepolymers is preferably between 0 and 50 wt%, preferably between 0 and 30 wt%, more preferably between 0 and 20 wt%, even more preferably between 5 and 20 wt% and most preferably between 10 and 20wt%. The content of urethane acrylate prepolymers is preferably between 5 and 35 wt%, more preferably between 5 and 30 wt%, even more preferably between 10 and 25 wt% and most preferably between 15 and 25 wt%.

Commercially available, non-limiting examples of suitable, unsaturated prepolymers are Miramer PU2104 (Miwon), PU340 (Miwon), Ebecryl 244 (Allnex), Ebecryl 4101 (Allnex), Ebecryl 4858 (Allnex).

Preferably, acrylate functional reactive diluents with a functionality of 1-3 are used for the first coating composition. The content of reactive diluents is preferably between 0 and 70 wt%, more preferably between 0 and 60 wt%, even more preferably between 10 and 60 wt% and most preferably between 30 and 55 wt%. Commercially available, non-limiting, examples of suitable reactive diluents are monofunctional acrylates like isobornylacrylate (I BOA) (Allnex), cyclic trimethylolpropane formal acrylate SR531 (Sartomer) lauryl acrylate SR335 (Sartomer), tridecyl acrylate Miramer M 124 (Miwon), difunctional acrylates like hexanediol diacrylate (HDDA), dipropylene glycol acrylate, esterdiol diacrylate (EDDA) SR606A (Sartomer), tricyclodecanedimethanol diacrylate (TCDDMDA) SR833S (Sartomer), tricyclodeca- nediol diacrylate Ebecryl 130 (Allnex), triethylene glycol diacrylate (TEGDA) Miramer M220 (Miwon), trifunctional acrylates like trimethylolpropane triacrylate (TMPTA) Miramer M300 (Miwon), trimethylolpropane triacrylate(TMPTA) TMP(EO)6TA M3160 (Miwon), Laromer ^® LR 8863 (BASF), tris (2-hydroxy ethyl) isocyanurate triacrylate (THEICTA) SR368 (Sartomer).

According to a preferred embodiment, the reactive diluent comprises lauryl acrylate for the first coating composition. The addition of lauryl acrylate may impose a hydrophobic nature to the coating, resulting in improved water resistance of the cured coating due to the aliphatic, non-polar chain of lauryl acrylate.

According to a particularly preferred embodiment, the reactive diluent comprises lauryl acrylate, IBOA, HDDA and/or TMPTA and any possible combination thereof. Surprisingly, it was found that said mixtures result in improved rheological properties of the coating composition as well as high water resistance of the cured coating.

Preferred embodiments of the second composition for the second layer of the coating method as described above:

Within the present application, a decorative coating is to be understood as a non-uniform coating layer or a colored coating layer. A non-uniform coating layer may represent an image, a character or a lettering, a decorative pattern, a QR-code and the like. The requirements for the optional second coating layer are good water resistance and good adhesion to the first coating layer as well as to the third coating layer and/or fourth coating layer. Additionally, good weatherability and light fastness is of high importance in order to provide a long lasting and brilliant decorative coating, in particular for exterior applications. Therefore, the second coating composition needs to be formulated accordingly in order to achieve the above- mentioned properties. Said non-uniform coating layer may be applied as a print. In that sense, said non- uniform coating layer may comprise different second coating compositions, e.g.: ink and/or toner compositions with different color such as cyan (C), magenta (M), yellow (Y) and black (K), so called CMYK colors. However, other colors, such as white, red, orange, may also be used.

Both analogous and digital printing methods may be used to apply the second layer.

According to a preferred embodiment, digital printing methods are particularly preferred due to the higher flexibility in case the desired printing pattern is changed. Among the digital printing methods, electro photographic and inkjet printing is preferably used, wherein both direct and indirect printing (e.g.: use of a transfer foil) is possible.

According to a preferred embodiment, radiation curable, in particular UV/LED/EB curable inkjet inks, preferably as disclosed in WO 2016016112, are used as second coating composition, which reference is hereby incorporated herein in its entirety.

Preferred embodiments of the third composition for the third layer of the coating method as described above:

For horizontal applications (e.g. flooring), the third coating layer is typically used when good flexibility and impact resistance are required; however, for vertical applications (e.g. walls) the third coating layer is optional and may be omitted.

As third coating composition according to the present invention, a liquid, radiation-curable coating composition is employed. The third coating layer, which is formed from said third coating composition acts as the link between the first coating layer and/or the second layer (if present) with the fourth coating layer. Therefore, the adhesion of the third coating layer to the first and/or second coating layer and to the fourth coating layer is of great importance. It is essential that the third coating layer (if present) features sufficient flexibility in order to provide the entire coating with a decent degree of flexibility. Additionally, the third layer needs to be sufficiently tough and hard in order to be used for the coating of a construction material. In order to achieve the above-mentioned properties, a liquid, radiation curable coating composition is used. UV/LED/EB curable compositions are used preferably. Typically, said radiation curable compositions comprise unsaturated prepolymers that are capable to react and crosslink with each other in a radical mechanism which may be triggered by photo initiators, which may also be present in the composition, thereby forming a cross-linked network. However, the crosslinking reaction may also be induced by high energy radiation or electron beams without any photo initiators. In addition to said unsaturated prepolymers, the compositions may comprise diluents, in particular reactive diluents, pigments, fillers, and additives such as light and/or heat stabilizers, antioxidants, surface modifying agents, defoaming agents, surfactants, catalysts, synergists and further additives as known in the art.

According to a preferred embodiment, the third coating composition is formulated in such a way that an essentially transparent third coating layer is obtained after curing. This is particularly desirable, in case a second, decorative coating layer has been applied in order to ensure the visibility of said second, decorative coating layer. A transparent coating layer may be achieved by avoiding the addition of opaque pigments, such as titanium dioxide based pigments. However, dyes or non-opaque fillers may still be present in an essentially transparently curing coating formulation.

In general, various unsaturated prepolymers may be used for the third, liquid radiation-curable composition. Preferably, polyurethane, polyacrylate, polyether, polyester and/or silicone based unsaturated prepolymers are used. The unsaturations may f.i. be incorporated into the prepolymer either by an endcapping approach or by the selection of monomers in the backbone of the prepolymer. Preferably, the unsaturations are incorporated as groups comprising carbon-carbon double and/or triple bonds, in particular acrylate, methacrylate, vinyl, and/or allyl groups and derivatives and mixtures thereof. Acrylate functional groups are particularly preferred.

According to a preferred embodiment, polyurethane acrylates and/or acrylic acrylates are employed. The content of the unsaturated prepolymers within the third coating composition is between 10 and 85 wt%, preferably between 20 and 65 wt% and even more preferably between 30 and 55 wt%. Aliphatic prepolymers are preferably used. The number average molecular mass (Mn) of said prepolymers is between 1000 and 30000 g/mol, preferably between 1000 and 10000 g/mol, and more preferably between 1000 and 8000 g/mol. It turned out to be particularly advantageous to use prepolymers with a functionality of 1-6, preferably 1-3 and even more preferably 2-3. It was found by the applicant that prepolymers with a functionality of 1-6, preferably 1-3 and even more preferably 2-3 provide high flexibility of the cured coating layer and also improve the adhesion to the previous layer(s) as well as to the next layer. The adhesion between the coating layers may be generated by van der Waals interactions, hydrogen bonds and mechanical anchoring of the polymer matrix to the previous layer. The mechanical anchoring is usually regarded as the most important adhesion type between UV curable coatings layers. However, due to the shrinkage behaviour upon curing of UV curable coating compositions, the mechanical anchoring is getting significantly reduced. Shrinkage of the coating composition upon curing is highly decreased by use of unsaturated prepolymers with a functionality of 1-6, and thus the mechanical anchoring of the UV curable coating composition upon curing may be significantly improved.

According to a preferred embodiment, acrylic acrylates and/or urethane acrylate based prepolymers are used, wherein preferably said prepolymers are aliphatic prepolymers and wherein preferably said prepolymers have a functionality of 1-6, more preferably 1-3, and even more preferably 2-3 and preferably a Mn between 1000 and 30000 g/mol, preferably 1000 - 10000 g/mol and more preferably 1000 - 5000 g/mol. The backbone of the used aliphatic prepolymers comprises CH2 groups and therefore, the cured coating layer has an inherent chemical stability against bases and acids. Additionally, this kind of prepolymers exhibit high exterior durability. The content of acrylic acrylate prepolymers is preferably between 0 and 50 wt%, preferably between 0 and 30 wt% and more preferably between 0 and 20 wt%. The content of urethane acrylate prepolymers is preferably between 10 and 70 wt%, more preferably between 30 and 60 wt%, even more preferably between 40 and 60 wt% and most preferably between 45 and 55 wt%. Commercially available, non-limiting examples of suitable, unsaturated prepolymers are PU340 (Miwon), Ebecryl 244 (Allnex), Ebecryl 4101 (Allnex), Miramer PU620 NT (Miwon), Miramer MU9800NT (Miwon), Ebecryl 5129 (Allnex), Ebecryl 1291 (Allnex), Miramer S5242 (Miwon), Miramer PS460 (Miwon), CN203 (Sartomer), CN2208, Ebecryl 884 (Allnex), Ebecryl 154 (Allnex).

Reactive diluents may be added to the composition in order to adjust the rheological properties, such as the viscosity, of the composition. Additionally, the network density may be influenced by addition of these compounds. Often, a mixture of various reactive diluents may be useful to adjust the properties as desired. Reactive diluents are typically regarded as low molecular weight compounds, solvents, monomers or short oligomers with at least one functional group that is capable of reacting with at least one other component of the composition. Preferably, acrylate functional reactive diluents with a functionality of 1-3 are used for the third coating composition. Commercially available, non-limiting, examples of suitable reactive diluents are monofunctional acrylates like isobornylacrylate (IBOA) (Allnex), cyclic trime- thylolpropane formal acrylate SR531 (Sartomer) lauryl acrylate SR335 (Sartomer), tridecyl acrylate Miramer M124 (Miwon), difunctional acrylates like hexanediol diacrylate (HDDA), dipropylene glycol acrylate, esterdiol diacrylate (EDDA) SR606A (Sartomer), tricyclodecanedimethanol diacrylate (TCDDMDA) SR833S (Sartomer), tricyclodecanediol diacrylate Ebecryl 130 (Allnex), triethylene glycol diacrylate (TEGDA) Miramer M220 (Miwon), trifunctional acrylates like trimethylolpropane triacrylate (TMPTA) Miramer M300 (Miwon), trimethylolpropane triacrylate TMP(EO)6TA M3160 (Miwon), Laromer ^® LR 8863 (BASF), tris (2-hydroxy ethyl) isocyanurate triacrylate (THEICTA) SR368 (Sartomer).

According to a preferred embodiment, the reactive diluent consists essentially of difunctional acrylate functional compounds, in particular HDDA, because the flexibility of the coating layer may be significantly improved.

Test methods

[Mohs hardness] The Mohs hardness of the used materials is defined by the ability of a reference material to scratch an employed material. For example, if the used material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5. The Mohs hardness is determined according to DIN EN 15771:2010-07.

[Particle size distribution (PSD)] The PSD, in particular d(10), d(50) and d(90) values of the particles, are determined by using a Scirocco 2000 machine commercially available from Malvern Instruments GmbH employing a laser diffraction method. Within the present application, the d(50) value is defined as mean particle size. The d(50) value means that 50 % of the particles are smaller than the d(50) value and 50 % of the particles are larger than the d(50) value in a cumulative distribution. The d(10) value means that 10 % of the particles are smaller than the d(10) value in a cumulative distribution. E.g., if the particle size d(10) is 50 μm, 10 % of the particles in the tested sample are smaller than 50 μm or the percentage of particles smaller than 50 μm is 10%. The d(90) value means that 90% of the particles are smaller than the d(90) value in a cumulative distribution. E.g., if the particle size d(90) is 100 μm, 90 % of the particles in the tested sample are smaller than 100 μm or the percentage of particles smaller than 100 μm is 90 %. The minimum particle size defines the lower cut of the particles; for example, if the minimum particle size is 50 μm, there are essentially no particles smaller than 50 μm in the sample. The maximum particles size defines the upper cut of the particles; for example, if the maximum particle size is 100 μm, there are essentially no particles larger than 100 μm in the sample. Particles with suitable minimum and/or maximum particles size may be obtained by sieving or other suitable classification methods. Sieving methods are also employed to determine the minimum and/or maximum particles size.

[Viscosity] Method A: The viscosity of low viscosity compositions (10-500 mPas at 35°C) is determined using a rotational viscometer (Brookfield DV-ll+Pro with spindle SSA18 with 25 - 200 rμm at 35 °C). Method B: The viscosity of high viscosity compositions (> 500 mPas at 35 °C; Method A is not suitable) is determined using the plate-plate method with a Brookfield CAP2000+ viscometer at a rotation speed of 300 rμm at 50°C according to DIN EN ISO 2884-2:2006 09.

[Number average molecular mass (Mn)]: The number average molar mass is determined by gel permeation chromatography. As an eluent, chloroform was used at a flow rate of 1 ml/min. Calibration of the separation columns (three columns of 8 mm x 300 mm each, PSS SDV, 5 μm, 100, 1000 and 100000 A) was done by narrowly distributed polystyrene standards, and detection via refractive index detector.

[sphericity] The sphericity is a measure of how closely the shape of a particle resembles the shape of a sphere. Generally, the sphericity (S) of a particle is defined as the ratio of a surface area (As) of a sphere of the same volume as the particle over the surface area of the particle (Ap). Hence, S = As/Ap. However, as the surface area of the particle may be difficult to measure, in particular for a plurality of particles, sophisticated methods have been developed which are implemented in commercially available apparatuses, as for example Sysmex FPIA-3000, available from Malvern Instruments GmbH, Germany, www.mal- vern.com, which is employed herein.

[Abrasion Resistance Test]: The abrasion resistance is tested according to ASTM D4060 (Taber Abraser, Model 1700/1750, Taber Industries, S42 sand paper stripe on CS-0 rubber wheel with 1000 g weight).

[Scratch Resistance]: The scratch resistance is measured according to EN ISO 1518-1:2011 and ISO 1518- 2:2011 (Hardness Test Pencil Model 318 S, Erichsen, Metal Tip No. 2 with 0 1.0 mm made of tungsten carbide, spring load 0-20 N).

[Flexibility Test (T-Bend test)]: The flexibility test is performed according to EN ISO 17132:2007.

[Gloss Test]: The gloss value is determined according to EN ISO 2813:2014 (Micro-Tri-Gloss, Byk Instruments). EN ISO 2813 specifies a method for determining the gloss value of coatings under the measuring geometries using 20°, 60° or 85° angles.

Examples

The following examples are supposed to further illustrate the invention as described within this application without any intention to limit the scope of the invention.

The specified amounts of compounds (given in %) used for a specific coating composition are given in wt% with respect to the total weight of the coating composition, unless otherwise noted. % and wt% are used synonymously within the present application.

A small particle size as used in the specific coating compositions in the following examples defines particles with a d(50) value of 32 μm, a medium particle size defines particles with a d(50) value of 85 μm and a large particle size defines particles with a d(50) value of 112 μm.

[Surface functionalization of particles] Surface functionalized particles were prepared by a silani- zation process. This means the chemical bonding of organofunctional alkoxysilane molecules to the surface of the modifying particles. The binding is achieved by a condensation reaction between hydrolysable groups of the alkoxysilane molecules and between suitable functional groups of the surface of the modifying particles.

[Preparation of matte particles] Matte glass particles were prepared by increasing the roughness of the particles by chemical and/or mechanical treatment.

Table 1: First Coating Composition 1 Second Coating Composition 2:

Any of examples 1 - 12 of WO 2016016112 may be employed, however, herein an ink according to Example 8 was used. Also inks according to examples 6 and 7 turned out to be particularly suitable.

Table 1a: Second Coating Composition 2

Table 2: Third Coating Composition 3

Table 3: Fourth Coating Composition without modifying particles (comparative) A Table 4: Fourth Coating Composition with only one kind of soft modifying particles (polyurethane) (comparative) B

Table 5: Fourth Coating Composition with one kind of hard modifying particles B2

Table 6: Fourth Coating Composition with two kinds of hard modifying particles (combination of glass beads with large and medium particle size) C

Table 7: Fourth Coating Composition with two kinds of hard modifying particles (combination of glass beads with large and small particle size) D

Table 8: Fourth Coating Composition with two kinds of functional hard modifying particles (combination of glass beads with small and large particle size, both modified with cross-linkable functional groups on the surface) E

Table 9: Fourth Coating Composition with two kinds of hard modifying particles (combination of glass beads with small and large particle size) and soft modifying particles (polyurethane beads) F

Table 10: Fourth Coating Composition with two kinds of matte, hard modifying particles (combination of matte glass beads with medium and large particle size) G

Table 11: Fourth Coating Composition with two kinds of matte, hard modifying particles and silica (combination of glass beads with large and medium particle size) H

Manufacture of the coating compositions:

The first coating composition 1 is prepared by weighing components # 1 to 6 (unsaturated prepolymers and reactive diluents) in a container followed by stirring at 800 rμm for 30 minutes. In a second step components # 9, 10, 11 and 12 (additives) are added one after the other while stirring at 800 rμm. Finally, components # 7 and 8 (photo initiators) are added. The composition is further stirred at 800 rμm for 20 min. The preparation takes place under ambient conditions (1 atm, 25°C).

The preparation of the second coating composition (ink) composition 2 is done in accordance with WO 2016016112.

The third coating composition 3 is prepared by weighing components # 1 to 3 (unsaturated prepolymers and reactive diluent) in a container followed by stirring at 800 rμm for 30 minutes. In a second step, components # 7, 8, 9 and 10 (additives) are added one after the other while stirring at 800 rμm. In a third step, component # 4 (filler, silica-based) is added and followed by stirring for 15 min at 800 rμm. Finally, components # 5 and 6 (photoinitiators) are added. The composition is further stirred at 800 rμm for 20 min. The preparation takes place under ambient conditions (1 atm, 25°C).

The fourth coating composition B2 is prepared by weighting component # 1 to 7 (unsaturated prepolymers and reactive diluent) in a container followed by stirring at 800 rμm for 30 minutes. In a second step components # 11, 12, 13 and 15 (additives) are added one after the other while stirring at 800 rμm. In a third step components # 9 and 10 (photoinitiators) are added followed by stirring at 800 rμm for 10 minutes. Finally, component #8 (hard modifying particles) is added. The composition is further stirred at 600 rμm for 10 min. The preparation takes place under ambient conditions (1 atm, 25°C).

The other examples of the fourth coating composition (inventive & comparative) are manufactured analogously to coating composition B2.

Comparison of Scratch Resistance according to ISO 1518-1:2011 and ISO 1518-2:2011 with tungsten carbide tip (ISO 0 1.0 mm) (Table 12)

Substrate: Concrete slabs (100 mm x 150 mm x 40 mm)

All layers (layer 1 to 4), except layer 2, were applied by a lab coating line (Roller applicator, DDWO, Wirth Maschinen GmbH. Transfer roller (foam roller) with Shore D hardness of 8 points and 7.5 m/min speed. Dosage roller (steel roller) with 3.5 m/min speed. Conveyer belt with 7.5 m/min speed) onto the concrete slabs.

Layer 1 is cured with 511 mj/cm ² (Hg-lamp with 240 Watt).

Layer 2 (print) is cured with 17,674 mj/cm ² using a LED lamp with a light intensity of 6,262 mW/cm ² . Layer 3 is cured with 646 mj/cm ² (Hg-lamp with 240 Watt).

Layer 4 is cured with 1,106 mj/cm ² (Hg/Ga-lamp with 240 Watt).

Finally, the multilayer system is cured with 1172 mj/cm ² (Hg-lamp with 240 Watt).

Table 12: Scratch Resistance

By employing only soft modifying particles in the fourth coating composition (layer B, Table 12, entry #4), the scratch resistance is only slightly improved compared to layer A (Table 12, entry #5) comprising no modifying particles. By employing a combination of two kinds of hard modifying particles with medium and large particles size (layer C, Table 12, entry #3) the scratch resistance can be improved. By employing a combination of two kinds of hard modifying particles with small and large particle size (layer D, Table 12, entry #2) the scratch resistance is significantly improved. By employing a combination of two kinds of functional hard modifying particles with small and large particle size (layer E, Table 12, entry #1), the scratch resistance can be even further improved. Also, it can be seen that the presence of the third coating layer also improves the scratch resistance (compare Table 12, entries #1 & 6). Abrasion Resistance Tests according to ASTM D4060 (Table 13)

Substrate: Concrete slabs (100 mm x 100 x mm 10 mm). Concrete slabs with a hole in the middle for fixing it in the testing device.

Device: Taber Abraser, Taber Industies, Model 1700/1750 Wheels: CS-0 rubber with S-42 sand paper stripe Weight: 1000 g

The application of the layers onto the substrate for abrasion resistance tests was performed with the same parameters as used for the scratch resistance test described above.

Table 13: Abrasion Resistance

By employing a combination of two kinds of hard modifying particles with small and large particle size as in layer D (Table 13, entry #2) the weight loss after 50 cycles can be reduced by 16% compared to layer B (Table 13, entry #3). By employing a combination of two kinds of functional hard modifying particles with small and large particle size as in layer E (Table 13, entry #1), the weight loss after 50 cycles can be even further reduced by 31% compared to layer B (Table 13, entry #3). The smaller the weight loss, the better the abrasion resistance.

Flexibility Test (T-Bend test, T1) according to EN ISO 17132:2007 (Table 14)

Substrate: Steel panels (76 mm x 132 mm x 1 mm) Coating layer application device: K HAND COATER 620, Model 620-long, Erichsen, Spiral film applicator. For the substrate preparation a 60 μm thick layer of the coating composition is applied by hand onto the steel panels. The coating composition is cured with 600 mj/cm ² (Hg-lamp with 240 Watt).

Table 14: Flexibility

Gloss Tests according to EN ISO 2813:2014 (Micro-Tri-Gloss, Byk Instruments) (Table 15)

Substrate: Concrete slabs (100 mm x 150 mm x 40 mm)

The application of the layers onto the substrate for the gloss test was performed with the same parameters as used for the scratch resistance test described above.

Table 15: Gloss value of coatings at different angles in gloss units (G.U.)

By employing matte, hard surface modifying particles as in layer G (Table 15, entry #2), the gloss at 60' was reduced by 29% and the gloss at 85° was reduced by 41% as compared to layer C (Table 15, entry #1). By additionally employing silica as matting agent as in layer H (Table 15, entry #3), the gloss at 60° was further reduced by 56% compared to layer G (Table 15, entry #2) and by 69% compared to layer C (Table 15, entry #1) and the gloss at 85° was reduced by 59% compared to layer G (Table 15, entry #2) and by 76% compared to layer C (Table 15, entry #1).

Brief Description of the Drawings

Fig. 1 is a schematic view of a coating system including 3 layers.

Fig. 2 is a schematic view of a coating system including 4 layers.

Fig. 3 is a schematic view of a coating system including 3 layers as well as a fourth layer modified with glass beads of different size.

Fig. 4 is a schematic view of a coating system including 3 layers as well as a fourth layer modified with glass beads (hard modifying particles and polyurethane (PU) beads (soft modifying particles) of different size.

Fig. 5 shows the modification of glass beads with trimethoxyvinylsilane.

Fig. 1 shows a substrate 10, in particular a construction material on which a first layer 1 of a first liquid coating composition, a second layer 2 of a second coating composition and a third layer 3 of a third coating composition are applied.

Fig. 2 shows a substrate 10, in particular a construction material on which, as shown in Fig. 1, a first layer 1 of a first liquid coating composition, a second layer 2 of a second coating composition and a third layer 3 of a third coating composition are applied. The second layer 2 comprises a decorative print. Additionally, there is a fourth layer 4 being a coating composition according as described above applied onto the third layer 3.

Fig. 3 shows a substrate 10, in particular a construction material on which as shown in Fig. 2, a first layer 1 of a first liquid coating composition, a second layer 2 of a second coating composition, comprising a print on at least a part of the layer, a third layer 3 of a third coating composition and a fourth layer 4 being a coating composition as described above are applied. The fourth layer 4 having embedded glass beads 41, 42 of different size, the bigger glass beads 41 having a size of about 90-150 μm and the smaller glass beads 42 having a size of about 70-110 μm.

Fig. 4 shows a substrate 10, in particular a construction material on which, as shown in Fig. 3, a first layer 1 of a first liquid coating composition, a second layer 2 of a second coating composition, comprising a print on at least a part of the layer, a third layer 3 of a third coating composition and a fourth layer 4 being a coating composition as described above, comprising embedded glass beads 41, 42 of different size and additional polyurethane (PU) beads 43 of a size about 90 μm, are applied.

Fig. 5 shows a schematic glass bead with silane functionalization to introduce functional groups, i.e. vinyl groups, onto the surface of the glass beads. The silane molecules covalently attach to the surface of the glass beads and react with themselves via esterification. The functional groups are suitable to react with at least one component of the coating composition, in particular with the unsaturated prepolymers, during the curing reaction.