The present invention relates to the field of aqueous polyester coating compositions having a low gloss. The present invention also relates to a process for producing a low gloss coating from an aqueous radiation-curable coating composition.

Aqueous polyester coating compositions are widely used in the coating industry. However, usually upon drying of the aqueous coating composition glossy surfaces are obtained. "Low gloss" surfaces give products a much sought-after aesthetic effect, especially in the wood-furniture, flooring and wall covering industry, because they can create a very natural appearance that contribute to giving greater emphasis to the materiality of the article. At present, the creation of matte surfaces frequently involves the use of coating products the formulation of which contains matting agents made from organic and/or inorganic substances which, by positioning themselves on the coated surface and/or emerging on it, are able to act on the degree of reflection of light, giving the observer the visual sensation of a low gloss surface. However, the use of matting agents produces a worsening of the surface performance of the coating since they are not involved in the polymerization process. Further there is a tendency for the matting agent to migrate to the coating surface after application and consequently the matting agent might get lost upon mechanical deformation, caused by for example scratch, resulting in an increase of gloss. The resistance to typical household chemicals, such as coffee, red wine and mustard, is also strongly reduced by the use of matting agents. Long-term action of these household chemicals leads at least to a reduction in quality of the coating and possibly even to its complete destruction. Silica-based compounds are the majorly used matting agents. In general, silica based matting agents are porous illustrated by its oil absorption values ranging from 100-500 mL/100 g. The disadvantage of using this type of matting agent in coating formulations is that it not only deteriorates the quality of the final coating, but can also result in an undesired coloration of the exposed coating area, because especially colored household stains like coffee, red wine and mustard (part of DIN 1B) are easily absorbed by the porous silica and because these stains contain organic dyes, this can result in a undesired coloring of the exposed coating area.

The object of the present invention is to provide a method for obtaining a low gloss coating from an aqueous polyester coating composition without having to use matting agent. According to the invention there is provided a process for producing a coating from an aqueous, radiation-curable coating composition, wherein the process comprises the steps in the sequence (1) to (4):

(1) applying an aqueous, radiation-curable coating composition on a surface of a substrate,

(2) drying the aqueous, radiation-curable coating composition, affording an at least partially dried coating composition,

(3) irradiating the at least partially dried coating composition with UV light having a wavelength < 220 nm under inert atmosphere, followed by

(4) irradiating with UV light having a wavelength > 300 nm or with E-beam, wherein the aqueous, radiation-curable coating composition is a dispersion comprising:

(A) at least one water-dispersed polyester (A), wherein the at least one water-dispersed polyester (A) has a glass transition temperature T _g , determined using Differential Scanning Calorimetry as described in the description, of less than or equal to 70°C, the at least one water-dispersed polyester (A) has an acid value AV, determined titrimetrically by the ISO 2114-2000, of less than or equal to 100 mg KOH/g of the polyester (A),

(B) at least one radiation-curable diluent (B) with a molar mass less than 750 g/mol and with an acrylate functionality of from 2 to 5, and

(C) water and optionally organic solvent, whereby the optional organic solvent is present in an amount of at most 30 wt.%, based on the total amount of water and organic solvent, wherein the amount of (A) is from 15 to 85 wt.% and the amount of (B) is from 15 to 85 wt.%, based on the total amount of (A) and (B).

It has surprisingly been found that, without the use of matting agent, the method of the present invention, which method includes the pre-treatment of the coating composition with UV light with a wavelength < 220 nm (further also referred to as the excimer radiation step), makes it possible to obtain low gloss coatings from aqueous, radiation-curable polyester dispersions as defined herein and this while the water-dispersed polyester may be essentially free of radiation-curable, ethylenically unsaturated bonds. More in particular with the process of the invention a coating can be obtained with a gloss measured at 20° geometry of angle lower than 10 gloss units and preferably with a gloss measured at 60° geometry of angle lower than 40 gloss units (further referred to as low gloss) and more preferably with a gloss measured at 60° geometry of angle lower than 30 gloss units. The aqueous, radiation-curable coating composition according to the invention allows to obtain a difference in gloss measured at 60° geometry of angle with and without the excimer radiation step of at least 30 gloss units, preferably of at least 40 gloss units, more preferably of at least 50 gloss units, more preferably of at least 60 gloss units. It has furthermore surprisingly been found that the method of the present invention makes it possible to obtain low gloss coatings from aqueous, radiation-curable polyester dispersions as defined herein, without the use of matting agents, while improving the coffee, red wine and/or mustard resistance of the coating compared to when the dispersions contain matting agent. It has furthermore surprisingly been found that, without the use of matting agent, the method of the present invention makes it possible to obtain low gloss coatings from aqueous, radiation-curable polyester dispersions as defined herein, with improved coffee, red wine and/or mustard resistance compared to when the coating is obtained without the excimer radiation step and this while the water-dispersed polyester may be essentially free of radiation-curable, ethylenically unsaturated bonds.

An additional advantage of the present invention is that handling of matting agents is not required, which is advantageous since matting agents have a large surface area and contain a large proportion of dust-forming small particles that may create exposure and explosion hazards. An additional advantage of not having to use matting agents for obtaining low gloss coatings is that coating compositions with less or no settling and thus improved storage stability can be achieved. An additional advantage of the method of the present invention is that coatings with a significantly higher smoothness can be obtained compared to when the coatings contained matting particles.

WO-A-2013/092521 describes a process for the production of homogeneous matted coatings on flat surfaces based on a so-called 100% radiation-curable coating compositions. In this method, first, the 100% radiation-curable coating composition, that contains a low molecular weight, radiation-curable oligomer as binder and optionally one or more reactive thinners to reduce the viscosity, is coated on the surface of a flat substrate with a spiral blade. This wet paint layer is subsequently irradiated with UV light with a wavelength of from 200 to 420 nm and a radiation dose of 25 to 120 mJ/cm ² resulting in partial gelation of the coating composition. Then the so-obtained coating is irradiated with UV light from an Excimer lamp having a wavelength from 120 nm to 230 nm under inert gas, followed by finish curing using conventional UV emitters. A 100% radiation-curable coating composition refers to a coating composition having a solids content of 100 wt.%. 100% radiation-curable coating compositions are homogeneous systems having only one phase, while the aqueous, radiation-curable polyester coating compositions as defined herein are dispersions having at least two phases where one phase contains discrete particles (colloidally dispersed particles) distributed throughout an aqueous medium, the particles being the dispersed phase and the aqueous medium the continuous phase.

WO-A-2013/092521 does not teach that low gloss coatings could be obtained from aqueous coating compositions, let alone from aqueous, radiation-curable polyester dispersions as defined herein and is furthermore silent on stain resistances of the cured coating.

A further disadvantage of the method described in WO-A-2013/092521 is that the viscosity of 100% radiation-curable coating composition is usually high making some application techniques, such as spraying, for example, difficult or impossible to use to apply the coating composition to the substrate. Spraying applications can advantageously be used to apply coating composition on substrates with more complex shapes, such as for example furniture or decorative frames. The viscosity of 100% radiation-curable coating composition can be reduced by adding monofunctional diluents with low molecular weight, resulting in that a viscosity can be obtained that allows depositing the radiation-curable coating composition on a substrate by spraying. However, applying of 100% radiation-curable coating composition by spraying inherently results in a coating with high coating thickness.

An additional advantage of the use of aqueous, radiation-curable polyester dispersions as defined herein is that the viscosity can be steered by adjusting the solids with water, resulting in that with the process of the invention coatings can also easily be applied by spraying even in a low coating thickness such as for example 25 micron wet coating thickness.

An additional advantage of the fact that the aqueous, radiation-curable polyester polymer dispersions as defined herein are more easily spray-applied is that the method of the invention also makes it possible to obtain low gloss coatings on more complex shaped articles such as, for example, a decorative frame with a more uniform degree of gloss of the coated article. An additional advantage of the use of aqueous, radiation-curable coating composition as defined herein is that coatings with a lower thickness, such as for example a coating thickness of 50 micron or even less, can be rendered low gloss using the method of the invention. A further advantage of the invention is that the gloss level of the coating can be tuned with the residual water and/or organic solvent content that is present in the at least partially dried coating composition.

It has furthermore surprisingly been found that that with the coating composition as claimed a low gloss coating can be obtained in only 2 irradiation steps (i.e. step (3) and (4), in particular for coatings with a wet thickness (before drying) of at most 300 micron, or at most 250 micron, or at most 200 micron or at most 175 micron, in particular of at most 150 micron, more in particular of at most 125 micron, more in particular of at most 100 micron and more in particular of at most 75 micron. WO-A-2013/092521 teaches that an additional partial gelation irradiation step is needed prior to the excimer radiation step (step (3) of the process of the present invention) and the finish curing step (step (4) of the process of the present invention) and thus WO-A-2013/092521 teaches that three irradiation steps are needed to obtain a low gloss/matte coating with a homogeneous surface structure, see in particular Table 2.

The aqueous, radiation-curable coating composition used in the process of the invention comprises polyester in dispersed form, i.e. the composition comprises dispersed particles of the polyester.

A dispersion refers to a system with at least two phases where one phase contains discrete particles (colloidally dispersed particles) distributed throughout a bulk substance, the particles being the dispersed phase and the bulk substance the continuous phase. The continuous phase of an aqueous dispersion is provided at least in part by water. Preferably the continuous phase of the dispersion of the invention comprises at least 75 wt.%, more preferably at least 80 wt.%, even more preferably at least 90 wt.% of water (relative to the continuous phase).

The aqueous coating composition used in the process of the invention is radiation-curable.

By radiation-curable is meant that radiation is required to initiate crosslinking of the dispersion. The aqueous coating composition used in the process of the invention contains ethylenically unsaturated (C=C) bond functionality which under the influence of irradiation, preferably in combination with the presence of a (photo)initiator, can undergo crosslinking by free radical polymerisation.

As used herein, the acrylate functionality of a compound is the number of acrylate functional groups per molecule of the compound.

An acrylate functional group has the following formula: CH ₂ =CH-C(O)O-

For all upper and/or lower boundaries of any range given herein, the boundary value is included in the range given, unless specifically indicated otherwise. Thus, when saying from x to y, means including x and y and also all intermediate values.

Water-dispersed polyester (A)

The at least one water-dispersed polyester (A) has a glass transition temperature T _g , determined using Differential Scanning Calorimetry as described in the description, of less than or equal to 70°C. The at least one water-dispersed polyester (A) has a glass transition temperature T _g of preferably at least -50°C, more preferably of at least -30°C, even more preferably of at least -20°C, even more preferably of at least -10°C. The at least one water- dispersed polyester (A) has a glass transition temperature T _g of preferably at most 65°C.

The at least one water-dispersed polyester (A) has an acid value AV, determined titrimetrically by the ISO 2114-2000, of less than or equal to 100 mg KOH/g of the polyester (A). The at least one water-dispersed polyester (A) preferably has an acid value of at most 90 mg KOH/g of the polyester (A), more preferably at most 80 mg KOH/g of the polyester (A), more preferably at most 70 mg KOH/g of the polyester (A). The at least one water- dispersed polyester (A) preferably has an acid value of at least 0.2 mg KOH/g of the polyester (A), more preferably of at least 0.5 mg KOH/g of the polyester (A).

The hydroxyl value of the at least one water-dispersed polyester (A), determined titrimetrically by the ISO 4629-2-2016, may range from 0 to 250 mg KOH/g of the polyester (A). Preferably the hydroxyl value of the at least one water-dispersed polyester (A) is preferably at most 150 mg KOH/g of the polyester (A), more preferably at most 100 mg KOH/g of the polyester (A), and preferably at least 1 mg KOH/g of the polyester (A), more preferably at least 1.5 mg KOH/g of the polyester (A). The at least one water-dispersed polyester (A) preferably has a number average molecular weight M _n , determined using Size Exclusion Chromatography (SEC) according to ISO 13885-1 :2020, of at at least 1000 g/mol, preferably of at least 2000 g/mol, more preferably at least 2500 g/mol, and preferably of at most 15000 g/mol, more preferably of at most 12000 g/mol, more preferably of at most 11000 g/mol.

The at least one water-dispersed polyester (A) preferably has a weight-average molecular weight M _w , determined using Size Exclusion Chromatography (SEC) according to ISO 13885-1 :2020, of at at least 1000 g/mol, more preferably of at least 2000 g/mol, more preferably at least 30000 g/mol, and preferably of at most 100000 g/mol, more preferably of at most 80000 g/mol, more preferably of at most 70000 g/mol.

Preferably, the at least one water-dispersed polyester (A) is amorphous. With amorphous is meant herein that the polyester has a melting enthalpy (AHm), determined using Differential Scanning Calorimetry as described further herein, lower than 40 J/g. More preferably, the at least one water-dispersed polyester (A) is fully amorphous, i.e. does not have a melting temperature (Tm), determined using Differential Scanning Calorimetry as described further herein.

By ‘polyester’ is meant in the specification any resin consisting of reacted residues wherein the constituents are linked via ester bonds.

By the term ‘polycondensation’ is meant in the specification condensation polymerization as this type of polymerization is known to one of ordinary skill in the art, and is meant to refer to one or both of: a) polyesterification, and b) polytransesterification, as each of a) and b) are known to one of ordinary skill in the art.

The water-dispersed polyester (A) is obtained by

(1) preparing a polyester, and

(2) dispersing the polyester in water.

The polyester can be produced by polycondensation comprising a single or multiple reaction steps in presence of a solvent (e.g. xylene as azeotrope) and/or in the bulk synthesis. Preferably polyester according to the invention is prepared by bulk synthesis polycondensation reaction.

The polycondensation usually takes place under a nitrogen atmosphere at temperatures in a range typically of from 160 to 260 °C. Catalysts such as dibutyl tin oxide, butyl chlorotin dihydroxide, butyl stannoic acid or tetrabutoxytitanate and antioxidants such as phosphorous acid, trisnonylphenylphosphite or triphenylphosphite can be added as additives. During the reaction, water is released and is preferably removed through distillation. The desired degree of esterification can be achieved by applying azeotropic distillation and/or vacuum distillation.

The obtained polyester is subsequently dispersed to obtain a water-dispersed polyester (A). Usually it is necessary for the polyester to contain ionic groups in order to become dispersed in aqueous medium.

One way to obtain the ionic groups is to neutralize the carboxylic groups of the polyester with a neutralising agent. Suitable neutralizing agents include but are not limited to ammonia, dimethyl ethanol amine, triethyl amine, aminomethyl propanol, tributyl amine, sodium hydroxide and potassium hydroxide. The neutralizing agent can be directly added to the polyester followed by the addition of water or first dissolved in the aqueous medium and then added to the polyester. It is also possible to add the polyester to the neutralizing agent aqueous medium.

Another way is to build carboxylic acids containing ionic functional groups like 5- (sulfo)isophthalic acid sodium salt and 5-(sulfo)isophthalic acid lithium salt into the backbone of the polyester. In this case the addition of the neutralizing agent is not necessary and the polyester dispersion can be obtained by simply adding the water.

Sometimes isopropanol, 2-butanol, 2-butoxyethanol, acetone or methyl ethyl ketone or 2-(2- butoxyethoxy)ethanol can be used as co-solvents to ease the dispersion process.

It is also possible to obtain waterborne dispersion or emulsion of the polyester by using at least one external surfactant in the aqueous medium. The process and surfactants that may be used are well known to those skilled in the art. Preferably a mixture of surfactants is used, more preferably a combination of anionic and non- ionic surfactant systems.

Examples of surfactant systems that may be used to emulsify the polyester are described in US2003-144397 (I Cl) and in 'Emulsification and Polymerization of Alkyd Resins' by Jan W. Gooch, Springer, first edition 1 st December 2001 (ISBN 0306467178) and the contents of both of these are incorporated herein by reference.

Yet another way to obtain a waterborne dispersion of the polyester is by using the solvent assistance process, where the polyester is first dissolved in low boiling point solvent (for example acetone or methylethylketone). Ones the polyester is dissolved, the desired amount of water can be added to the solution, followed by distilling of the organic solvent by means of vacuum. The temperature during the dispersion process can be in the range of from 20 to 90°C, preferably in the range from 30 to 80°C more preferably in the range from 40 to 60°C. The solid content of the dispersion can be in the range typically of from 10 to 60%, preferably in the range from 20 to 50% more preferably in the range from 25 to 50%.

Suitable polyesters for inclusion in the radiation-curable coating compositions used in the process of the invention include polyesters with no radiation-curable, ethylenically unsaturation and polyesters with radiation-curable, ethylenically unsaturation. In case the polyester comprises radiation-curable, ethylenically unsaturation, the polyester preferably has an average weight per radiation-curable, ethylenically unsaturation (WPU), as determined using ¹ H NMR as described herein, of from 500 to 5000 g/mol.

The WPU of a polyester is determined via ¹ H-NMR spectroscopy according to the method described below. More specifically, the WPU of a polyester is calculated according to the following equation: wherein,

Wpyr is the weight of pyrazine (internal standard),

Wresin is the weight of polyester,

Wpyr and Wresin are expressed in the same units.

MWpyr is the molecular weight of the pyrazine (= 80 Da) (internal standard).

Apyr is the peak area for methine protons attached to the aromatic ring of pyrazine, and

Npyr is the number of the methine protons of pyrazine that is equal to 4.

Ac=c is the peak area for methine protons (,..-CH=...) of the carbon-carbon double bond moiety (... >C=C< ...) present

Nc=c is the number of methine protons (,..-CH=...) attached to the carbon-carbon double bond moiety (... >C=C< ...) present

The peak areas of the methine protons of pyrazine and methine protons are determined as follows: a sample of 75 mg of polyester is diluted at 25 °C in 1 ml deuterated chloroform containing a known amount (mg) of pyrazine as internal standard for performing ¹ H-NMR spectroscopy. Subsequently, the ¹ H-NMR spectrum of the polyester sample is recorded at 25 °C on a 400 MHz BRLIKER NMR-spectrometer. Afterwards, the chemical shifts (ppm) of the methine protons of pyrazine and the methine protons of A _c = _c are identified.

Subsequently, with the help of suitable commercially available software for analyzing ¹ H- NMR spectra such as the ACD/Spectrus Processor software provided by ACD/Labs, the peak areas of the methine protons of pyrazine and of A _c =c are determined and these values are used in above mentioned equation to calculate the WPU.

Preferably, the polyester is prepared by polycondensation of at least the following components:

(A1) At least one difunctional acid, and

(A2) At least one difunctional alcohol, and

(A3) Optionally at least one difunctional acid other than (A2) that contains at least one salt group which is capable to render the polyester dispersible in water,

(A4) Optionally at least one monofunctional acid,

(A5) Optionally at least one tri- or higher functional acid, and

(A6) Optionally at least one tri- or higher functional alcohol, wherein the total amounts of components (A1) and (A2) used to prepare the polyester (A) is from 20 to 100 wt.%, more preferably from 30 to 100 wt.%, and the total amounts of components (A3), (A4), (A5) and (A6) used to prepare the polyester (A) is from 0 to 80 wt.%, more preferably from 0 to 70 wt.%.

Examples of difunctional carboxylic acids (A1) for preparing the polyester include but are not limited to terephthalic acid, isophthalic acid, phthalic acid (anhydride), ,2,6- naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic acid (anhydride), tetrahydrophthalic acid (anhydride), azelaic acid, sebacic acid, dodecanedioic acid acid, dimer fatty acid, adipic acid, succinic acid (anhydride), fumaric acid, glutaric acid, itaconic acid, pimelic acid, suberic acid, maleic acid (anhydride), malonic acid and any mixture thereof.

Examples of difunctional alcohols (A2) for preparing the polyester include but are not limited to ethanediol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol (Mn=600-4000 g/mol), polyalkylene glycol, 1,2-propanediol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3- butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, 1 ,4-dihydroxycyclohexane, 1,8-octanediol, 1 ,10-decanediol, 1 ,12-dodecanediol, 2-methyl- 1 ,3-propanediol, 3-methyl-1 ,5 pentanediol, hydroxypivalic neopentyl glycol ester, tricyclodecane dimethanol or any mixture thereof.

Examples of difunctional carboxylic acids (A3) that contains at least one salt group which is capable to render the polyester dispersible in water include 5-(sulfo)isophthalic acid salts, such as metal (Na ⁺ , Li ⁺ , K ⁺ , Mg ⁺⁺ , Ca ⁺⁺ , Cu ⁺⁺ , Fe ⁺⁺ or Fe ⁺⁺⁺ ) salts and/or ammonium salts. The preferred 5-(sulfo)isophthalic acid salts are 5-(sulfo)isophthalic acid sodium salt and/or 5-(sulfo)isophthalic acid lithium salt.

Examples of tri- or more functional carboxylic acids (A5) for preparing the polyester include but are not limited to trimellitic acid (anhydride), citric acid (anhydride), pyromellitic acid (anhydride) and mixtures thereof.

Examples for tri- or more functional alcohols (A6) for preparing the polyester include but are not limited to trimethylolpropane, trimethylolethane, glycerol, pentaerythritol, bis(trimethylolpropane) ether, xylitol, dipentaerythritol, sorbitol, and mixtures thereof

More preferably, the polyester is prepared by polycondensation of at least the following components:

(A1) At least one difunctional acid comprising terephthalic acid, isophthalic acid, phthalic acid, adipic acid or any mixture thereof, and

(A2) At least one difunctional alcohol comprising diethylene glycol, ethylene glycol, 1 ,4- butanediol, 1 ,3-propanediol, 1 ,4-cyclohexanedimethanol, neopentyl glycol, 1 ,5-pentanediol, 1 ,6-hexanediol or any mixture thereof, and

(A3) Optionally at least one difunctional acid other than (A2) that contains at least one salt group which is capable to render the polyester dispersible in water, preferably one or more 5-(sulfo)isophthalic acid salts,

(A4) Optionally at least one monofunctional acid comprising benzoic acid, soybean oil fatty acids, tall oil fatty acids, soybean oil, tall oil or any mixture thereof,

(A5) Optionally at least one tri- or higher functional acid comprising trimellitic anhydride, citric acid or any mixture thereof, and

(A6) Optionally at least one tri- or higher functional alcohol comprising glycerol, trimethylol propane, pentaerythritol or any mixture thereof, wherein the total amounts of components (A1) and (A2) used to prepare the polyester (A) is from 20 to 100 wt.%, more preferably from 30 to 100 wt.%, and the total amounts of components (A3), (A4), (A5) and (A6) used to prepare the polyester (A) is from 0 to 80 wt.%, more preferably from 0 to 70 wt.%. Even more preferably, the polyester is prepared by polycondensation of at least the following components:

(A1) At least one difunctional acid comprising terephthalic acid, isophthalic acid, phthalic acid, adipic acid or any mixture thereof, and

(A2) At least one difunctional alcohol comprising diethylene glycol, ethylene glycol, 1,4- butanediol, 1,3-propanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, 1,5-pentanediol, 1 ,6-hexanediol or any mixture thereof,

(A3) At least one difunctional acid other than (A2) that contains at least one salt group which is capable to render the polyester dispersible in water, preferably one or more 5- (sulfo)isophthalic acid salt, and

(A4) Optionally at least one monofunctional acid comprising benzoic acid, soybean oil fatty acids, tall oil fatty acids, soybean oil, tall oil or any mixture thereof,

(A5) Optionally at least one tri- or higher functional acid comprising trimellitic anhydride, citric acid or any mixture thereof, and

(A6) Optionally at least one tri- or higher functional alcohol comprising glycerol, trimethylol propane, pentaerythritol or any mixture thereof, wherein the total amounts of components (A1) and (A2) used to prepare the polyester (A) is from 30 to 99 wt.%, the amount of component (A3) is from 1 to 10 wt.% and the total amounts of components (A4), (A5) and (A6) used to prepare the polyester (A) is from 0 to 69 wt.%.

Radiation-curable diluent (B)

The aqueous, radiation-curable coating composition comprises at least one radiation-curable diluent (B) with a molar mass less than 750 g/mol and with an acrylate functionality of from 2 to 5, preferably from 2 to 4. The molar mass of the radiation-curable diluents (B) is calculated from their corresponding molecular formulas indicating the numbers of each type of atom in the radiation-curable diluent. Thus, the molar mass of (B) is the calculated molar mass obtained by adding the atomic masses of all atoms present in the structural formula of the compound.

In a preferred embodiment of the invention, at least 10 wt.%, preferably at least 20 wt.%, more preferably at least 30 wt.%, more preferably at least 40 wt.%, more preferably at least 50 wt.%, more preferably at least 60 wt.%, more preferably at least 70 wt.%, more preferably at least 80 wt.%, more preferably at least 90 wt.% and most preferably 100 wt.% of the radiation-curable diluents (B) is selected from the group consisting of: di(trimethylolpropane) tetra-acrylate (di-TMPTA) with the corresponding molecular formula C24H34O9 and its corresponding molar mass of 467 g/mol, di(trimethylolpropane) tetra-acrylate comprising alkoxy groups, di(trimethylolpropane) tri-acrylate (di-TMP3A) with the corresponding molecular formula C21 H32O8 and its corresponding molar mass of 412 g/mol, di(trimethylolpropane) tri-acrylate comprising alkoxy groups, glyceryl propoxy triacrylate (GPTA) with the corresponding molecular formula C21H32O9 and its corresponding molar mass of 428 g/mol, glyceryl propoxy triacrylate comprising additional alkoxy groups, pentaerythritol tetra-acrylate (PET4A) with the corresponding molecular formula C17H20O8 and its corresponding molar mass of 352 g/mol, pentaerythritol tetra-acrylate comprising alkoxy groups, pentaerythritol tri-acrylate (PET3A) with the corresponding molecular formula C14H18O7 and its corresponding molar mass of 298 g/mol, pentaerythritol tri-acrylate comprising alkoxy groups, trimethylolpropane triacrylate (TMPTA) with the corresponding molecular formula C15H20O6 and its corresponding molar mass of 296 g/mol, trimethylolpropane triacrylate comprising alkoxy groups, dipropyleneglycol diacrylate (DPGDA) with the corresponding molecular formula C12H18O5 and its corresponding molar mass of 242 g/mol, dipropyleneglycol diacrylate comprising additional alkoxy groups, and any mixture thereof.

In case radiation-curable diluent (B) comprises (additional) alkoxy groups, the maximum number of alkoxy groups is such that the molar mass remains lower than 750 g/mol.

In a more preferred embodiment of the invention, at least 10 wt.%, preferably at least 20 wt.%, more preferably at least 30 wt.% more preferably at least 40 wt.%, most preferably at least 50 wt.%, more preferably at least 60 wt.%, more preferably at least 70 wt.%, more preferably at least 80 wt.%, more preferably at least 90 wt.% and most preferably 100 wt.% of the radiation-curable diluents (B) is selected from the group consisting of: di(trimethylolpropane) tetra-acrylate (di-TMPTA) with the corresponding molecular formula C24H34O9 and its corresponding molar mass of 467 g/mol, di(trimethylolpropane) tetra-acrylate comprising alkoxy groups, di(trimethylolpropane) tri-acrylate (di-TMP3A) with the corresponding molecular formula C21H32O8 and its corresponding molar mass of 412 g/mol, di(trimethylolpropane) tri-acrylate comprising alkoxy groups, glyceryl propoxy triacrylate (GPTA) with the corresponding molecular formula C21H32O9 and its corresponding molar mass of 428 g/mol, glyceryl propoxy triacrylate comprising additional alkoxy groups, trimethylolpropane triacrylate (TMPTA) with the corresponding molecular formula C15H20O6 and its corresponding molar mass of 296 g/mol, trimethylolpropane triacrylate comprising alkoxy groups, dipropyleneglycol diacrylate (DPGDA) with the corresponding molecular formula C12H18O5 and its corresponding molar mass of 242 g/mol, dipropyleneglycol diacrylate comprising additional alkoxy groups, and any mixture thereof.

Preferably, at least one of the radiation-curable diluents (B) has an acrylate functionality of 2 or 3, as this advantageously may result in a more pronounced matting effect. The radiation- curable diluents (B) with an acrylate functionality of 2 are preferably selected from the group consisting of dipropyleneglycol diacrylate (DPGDA) (with the corresponding molecular formula C12H18O5 and its corresponding molar mass of 242 g/mol); dipropyleneglycol diacrylate comprising additional alkoxy groups, preferably propoxy groups; and any mixture thereof.

The radiation-curable diluents (B) with an acrylate functionality of 3 are preferably selected from the group consisting of glyceryl propoxy triacrylate (GPTA) (with the corresponding molecular formula C21H32O9 and its corresponding molar mass of 428 g/mol); glyceryl propoxy triacrylate comprising additional alkoxy groups, preferably propoxy groups; trimethylolpropane triacrylate (TMPTA) (with the corresponding molecular formula C15H20O6 and its corresponding molar mass of 296 g/mol); trimethylolpropane triacrylate comprising alkoxy groups, preferably propoxy groups; di(trimethylolpropane) tri-acrylate (di-TMP3A) with the corresponding molecular formula C21H32O8 and its corresponding molar mass of 412 g/mol; di(trimethylolpropane) tri-acrylate comprising alkoxy groups, preferably propoxy groups; pentaerythritol tri-acrylate (PET3A) (with the corresponding molecular formula C14H18O7 and its corresponding molar mass of 298 g/mol); pentaerythritol tri-acrylate comprising alkoxy groups, preferably propoxy groups; and any mixture thereof. The radiation-curable diluents (B) with an acrylate functionality of 2 or 3 preferably comprises alkoxy groups, preferably propoxy groups (-C3H6O-).

Preferably, the composition further comprises at least one of the radiation-curable diluents (B) with an acrylate functionality of 4 or 5, as this advantageously may result in further improved chemical resistances. The radiation-curable diluents (B) with an acrylate functionality of 4 are preferably selected from the group consisting of di(trimethylolpropane) tetra-acrylate (di-TMPTA) (with the corresponding molecular formula C24H34O9 and its corresponding molar mass of 467 g/mol); di(trimethylolpropane) tetra-acrylate comprising alkoxy groups, preferably propoxy groups; pentaerythritol tetra-acrylate (PET4A) (with the corresponding molecular formula C17H20O8 and its corresponding molar mass of 352 g/mol); pentaerythritol tetra-acrylate comprising alkoxy groups, preferably propoxy groups; and any mixture thereof.

The radiation-curable diluents (B) with an acrylate functionality of 5 is preferably dipentaerythritol penta-acrylate (DPPA) with the corresponding molecular formula C25H32O12 and its corresponding molar mass of 525 g/mol.

In a preferred embodiment, the aqueous, radiation-curable coating composition used in the process of the present invention comprises at least two radiation-curable diluents (B) and the radiation-curable diluents (B) present in the aqueous, radiation-curable coating composition

— V ^k f have an average acrylate functionality according to formula f = of from 2 to 4, preferably from 2 to 3, in which Wk is the amount of acrylate diluents (B) in g present in the aqueous, radiation-curable coating composition with a molar mass Mk and with an acrylate functionality fk. We illustrate the average acrylate functionality calculation with a theoretical example:

For a formulation consisting of 60 grams of polyester, 30 grams of DPGDA (having molar mass 242 g/mol and acrylate functionality of 2), 10 grams of Di-TMPTA (having molar mass

466 g/mol and acrylate functionality of 4), and 2.5 grams of photoinitiator: the summation over components k includes only DPGDA and Di-TMPTA and the calculated average

_{X 2 +} ^ ><4 functionality of acrylate diluents of this theoretical formulation is f = ²⁴² nfel ⁴⁶⁶ nfel 30g 10g = 2.3. 242 — £ ^s — '*’ 466 — £ ^s — mol mol The aqueous, radiation-curable coating composition used in the process may also comprise acrylate diluents with a molar mass as defined for the (B) compounds present in the radiation-curable coating composition (i.e. lower than 750 g/mol) but with a different acrylate functionality than defined for (B), for example with an acrylate functionality of 6. However, such acrylate diluents may only be present in the aqueous radiation-curable coating composition in such an amount that the average acrylate functionality of the acrylate diluents with a molar mass as defined for (B) (i.e. lower than 750 g/mol) is in the range of preferably from 2 to 5, more preferably from 2 to 4, even more preferably from 2 to 3.

Preferably, the aqueous, radiation-curable coating composition used in the process of the present comprises monofunctional diluent in an amount less than 7 wt.%, more preferably at less than 5 wt.%, more preferably less than 3 wt.%, more preferably less than 1 wt.%, most preferably less than 0.5 wt.%, relative to the weight of the entire aqueous, radiation-curable coating composition.

In an even more preferred embodiment of the invention, at least 60 wt.%, preferably at least 70 wt.%, more preferably at least 80 wt.%, more preferably at least 90 wt.% and most preferably 100 wt.% of the radiation-curable diluents (B) is a mixture of

(1) di(trimethylolpropane) tetra-acrylate (di-TMPTA) with the corresponding molecular formula C24H34O9 and its corresponding molar mass of 467 g/mol and/or di(trimethylolpropane) tetra-acrylate comprising alkoxy groups, preferably propoxy groups and/or pentaerythritol tetra-acrylate (PET4A) with the corresponding molecular formula C17H20O8 and its corresponding molar mass of 352 g/mol and/or pentaerythritol tetra-acrylate comprising alkoxy groups, preferably propoxy groups, and

(2) glyceryl propoxy triacrylate (GPTA) with the corresponding molecular formula C21H32O9 and its corresponding molar mass of 428 g/mol and/or glyceryl propoxy triacrylate comprising additional alkoxy groups, preferably propoxy groups and/or dipropyleneglycol diacrylate (DPGDA) and/or dipropyleneglycol diacrylate comprising additional alkoxy groups, preferably propoxy groups.

The amounts of (A) and (B) in the aqueous, radiation-curable coating composition can vary within wide ranges as water and optional organic solvent can be used to adopt the viscosity and to tune the layer thickness of the applied coating. Preferably, the amount of (A) is from 20 to 80 wt.% and the amount of (B) is from 20 to 80 wt.%, more preferably the amount of (A) is from 25 to 75 wt.% and the amount of (B) is from 25 to 75 wt.%, more preferably the amount of (A) is from 30 to 70 wt.% and the amount of (B) is from 30 to 70 wt.%, more preferably the amount of (A) is from 40 to 60 wt.% and the amount of (B) is from 40 to 60 wt.%, based on the total amount of (A) and (B).

The summed amount of (A) and (B) is preferably from 10 to 60 wt.%, more preferably from 15 to 50 wt.%, more preferably from 15 to 45 wt.%, even more preferably from 20 to 40 wt.%, even more preferably from 25 to 35 wt.%, based on the entire weight of the aqueous, radiation-curable coating composition.

The amount of water in the aqueous, radiation-curable coating composition is preferably at least 30 wt.%, or at least 35 wt.%, or at least 40 wt.%, or at least 45 wt.%, or at least 50 wt.%, or at least 55 wt.%, or at least 60 wt.%, or at least 70 wt.%, based on the entire weight of the aqueous, radiation-curable coating composition.

The optional organic solvent is present in an amount of at most 30 wt.%, preferably at most 25 wt.%, more preferably at most 20 wt.%, more preferably in an amount of at most 15 wt.%, more preferably in an amount of at most 10 wt.%, more preferably in an amount of at most 5 wt.%, more preferably in an amount of at most 4 wt.%, more preferably in an amount of at most 3 wt.%, more preferably in an amount of at most 2 wt.%, more preferably in an amount of at most 1 wt.%, wherein the amount of organic solvent is given based on the total amount of water and organic solvent present in the aqueous, radiation-curable coating composition. Suitable organic solvents are solvents which are inert in respect of the functional groups present in the coating composition. Suitable solvents are for example hydrocarbons, alcohols, ketones and esters, such as co-solvents also having the function of coalescent such as 1-methyl-2-pyrrolidinone, glycols and glycol ethers such as butyldiglycol, dipropylene glycol methyl ether, acetone, methyl ethyl ketone and alkyl ethers of glycol acetates or mixtures thereof.and ester alcohol like 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol). Most preferably the aqueous, radiation-curable coating composition is essentially free of organic solvent, i.e. organic solvent is preferably not deliberately be added (i.e. small amounts of organic solvent may be present in the additives used to prepare the composition) to the aqueous, radiation-curable coating composition. The viscosity of the dispersion consisting of (A), (B) and (C) and containing from 10 to 60 wt.% of (A) and (B), relative to the total amount of (A), (B) and (C), is preferably from 10 to 1000 mPa.s, or from 10 to 800 mPa.s, or from 10 to 500 mPa.s. The viscosity is determined as further described herein.

The z-average particle size of the dispersion consisting of (A), (B) and (C) is preferably from 20 to 1000 nm, more preferably from 25 to 500 nm, whereby the z-average particle size is determined as further described herein.

The coating composition usually further contains an additive compound; that is, a collection of one or more than one individual additives having one or more than one specified structure or type. Suitable additives are for example light stabilizers, such as UV absorbers and reversible free-radical scavengers (HALS), photosensitizers, antioxidants, degassing agents, wetting agents, emulsifiers, slip additives, waxes, polymerization inhibitors, adhesion promoters, flow control agents, film-forming agents, rheological aids such as thickeners, flame retardants, corrosion inhibitors, waxes, driers and biocides. One or more of the aforementioned additives can be employed in the coating composition used in the process of the present invention in any suitable amount and may be chosen singly or in combination of one or more of the types enumerated herein. In a preferred embodiment, the additive compound is present in an amount, relative to the entire weight of the radiation-curable coating composition, of from about 0 wt.% to 40 wt.%, or from 0 wt.% to 30 wt.%, or from 0 wt.% to 20 wt.%, or from 0 wt.% to 10 wt.%, or from 0 wt.% to 5 wt.%; or from 0.01 wt.% to 40 wt.%; or from 0.01 wt.% to 30 wt.%, or from 0.01 wt.% to 20 wt.%, or from 0.01 wt.% to 10 wt.%, or from 0.01 wt.% to 5 wt.%, or from 0.1 wt.% to 2 wt.%. An additional advantage of the present invention is that the coating composition can also be pigmented, while this does not significantly complicate the application of the coating composition on the substrate. The coating composition then contains at least one pigment. In the art titanium dioxide (TiC>2) is considered as a commercially important white pigment. Despite the porous nature of this type of pigment, it has furthermore surprisingly been found that the presence of such type of pigments in the coating composition as defined herein, hardly impair the coffee, red wine and/or mustard resistance of the coating or only deteriorates to such an extent that the resistance to coffee, red wine and/or mustard remains at an acceptable level.

The coating composition can also contain one or more inorganic fillers. The coating composition can also contain external matting agents which have an additional matting effect, although this is not preferred. Suitable external matting agents are for example inorganic silica or organic waxes. The maximum amount of external matting agents is preferably at most 1.5 wt.%, more preferably at most 1 wt.% and most preferably at most 0.5 wt.%, relative to the entire weight of the coating composition.

The process of the invention optionally comprises a pre-curing step (2a). Performing the precuring step (2a) may be advantageous for improving adhesion, in particular for improving intercoat adhesion. In this optional step (2a) pre-curing of the at least partially dried coating composition is effected, affording an at least partially cured coating composition. In optional step (2a) some of the reactive ethylenically unsaturated double bonds of the curable compounds polymerize in the uncured coating layer, so that the coating layer partially cures but is not yet fully cured. This process is also known as pre-curing.

Accordingly, the process of the invention comprises the steps in the sequence (1), (2), (2a), (3) and (4):

(1) Applying an aqueous, radiation-curable coating composition on a surface of a substrate,

(2) Drying the aqueous, radiation-curable coating composition, affording an at least partially dried coating composition,

(2a) Optionally pre-curing the at least partially dried coating composition by irradiating the at least partially dried coating composition with UV light having a wavelength of from 300 to 450 nm, preferably from 300 to 420 nm with a radiation dose which results in partial curing of the layer, preferably with a radiation dose from 20 to 200 mJ/cm ² , more preferably with a radiation dose from 30 to 100 mJ/cm ² , affording an at least partially cured coating composition,

(3) Irradiating the at least partially dried coating composition or the at least partially cured coating composition with UV light having a wavelength < 220 nm preferably with a wavelength > 120 nm, more preferably > 150 nm, particularly preferably 172 nm or 195 nm, under inert atmosphere, followed by

(4) Irradiating with UV light having a wavelength > 300 nm or with E-beam.

In step (1) of the process of the invention, the aqueous, radiation-curable coating composition is applied to a substrate by methods known to the person skilled in the art, such as for example knife coating, brushing, roller coating, spraying. The coating composition is applied to the substrate in a coating thickness (before drying) of preferably from 5 to 300 micron, more preferably from 15 to 175 micron, more preferably from 20 to 150 micron, more preferably from 25 to 125 micron.

In step (2) of the process of the invention, drying of the aqueous, radiation-curable coating composition that is applied to the substrate is preferably effected at a temperature higher than 30 °C to evaporate water and optionally organic solvent and other volatile compounds, affording an at least partially dried coating composition. The term “drying” refers to the loss of water and, if present, organic solvent and other volatile compounds such as for example neutralizing amines, from the aqueous coating composition by evaporation to such extend that preferably at least 80 wt.% of the water is removed.

The irradiating in the optional pre-curing step (2a) preferably takes place under atmospheric conditions, in other words not under inert gas conditions and/or not in an oxygen-reduced atmosphere. UV-A-emitting radiation sources (e.g. fluorescent tubes, LED lamps), high- or medium-pressure mercury vapour lamps, wherein the mercury vapour can be modified by doping with other elements such as gallium or iron, pulsed lamps (known as UV flash lamps) or halogen lamps are suitable as radiation sources for UV light in the specified wavelength range in step (2a). In a preferred embodiment of the invention, the process is performed without step (2a), i.e., the curing of the radiation-curable coating composition is effected in only 2 irradiation steps (i.e. step (3) and (4)).

Suitable radiation sources for step (3) are excimer UV lamps, which emit UV light with a wavelength < 220 nm and preferably with a wavelength > 120 nm, more preferably > 150 nm, particularly preferably 172 nm or 195 nm. The radiation dose used in step (3) is usually in the range from 0.1 to 150 mJ/cm ² , preferably in the range of from 1 to 100 mJ/cm ² , more preferably from 1 to 20 mJ/cm ² , more preferably from 2 to 15 mJ/cm ² . Step (3) must be performed in an inert gas atmosphere. An inert gas atmosphere is understood to mean an essentially oxygen-free atmosphere, i.e. an atmosphere which contains less than 0.5 percent by volume of oxygen, preferably less than 0.1 percent by volume of oxygen and especially preferably less than 0.05 percent by volume of oxygen. As a rule, an inert gas atmosphere is achieved by flushing the area which is exposed to the UV radiation with a stream of inert gas. The inert gas atmosphere prevents undesired ozone formation on the one hand and prevents the polymerization of the lacquer layer from being inhibited on the other hand. Examples of inert gases are nitrogen, helium, neon or argon. Nitrogen is particularly preferably used. This nitrogen should only contain very small amounts of foreign gases such as oxygen, preferably with a purity grade of < 300 ppm oxygen.

In step (4) of the process of the present invention, the coating layer obtained in step (3) is irradiated with UV light having a wavelength > (higher than or equal to) 300 nm or with E- beam to achieve that the radiation-curable compounds of the coating composition largely or preferably completely polymerizes, so that the coating layer is preferably fully cured. In case E-beam irradiation (150 to 300 kV) is applied in step (4), usually a dose of 10 to 100 kGy, preferably 20 to 50 kGy, is applied. In step (4) UV irradiation is preferred, preferably with a wavelength of from 300 to 420 nm and preferably with a radiation dose of from 100 to 2000 mJ/cm ² , more preferably from 150 to 1500 mJ/cm ² . High- and medium-pressure mercury vapour lamps can in particular be used as UV radiation sources, wherein the mercury vapour can be doped with further elements such as gallium or iron. Step (4) can optionally also be performed in an inert gas atmosphere. In case UV irradiation is applied in step (4), the radiation-curable coating composition comprises a photo-initiator. If the radiation curable coating composition of the invention comprise one or more photo-initiators, they are included in an amount sufficient to obtain the desired cure response. Typically, the one or more photo-initiators are included in amounts in a range of from 0.1 to 5% by weight of the entire coating composition. Preferably, the one or more photo-initiators are present in an amount, relative to the entire weight of the coating composition, of from 0.25 wt.% to 4 wt.%, more preferably from 0.5 wt.% to 3.5 wt.% and even more preferably from 0.5 wt.% to 3 wt.%. A photoinitiator is a compound that chemically changes due to the action of light or the synergy between the action of light and the electronic excitation of a sensitizing dye to produce at least one of a radical, an acid, and a base. Well-known types of photoinitiators include cationic photoinitiators and free-radical photoinitiators. According to an embodiment of the present invention, the photoinitiator is a free-radical photoinitiator.

In an embodiment, the photoinitiator compound includes, consists of, or consists essentially of one or more acylphosphine oxide photoinitiators. Acylphosphine oxide photoinitiators are known, and are disclosed in, for example, U.S. Pat. Nos. 4324744, 4737593, 5942290, 5534559, 6020529, 6486228, and 6486226. Preferred types of acylphosphine oxide photoinitiators for use in the photoinitiator compound include bisacylphosphine oxides (BAPO) or monoacylphosphine oxides (MAPO). More specifically, examples include 2,4,6- trimethylbenzoylethoxyphenylphosphine oxide (CAS# 84434-11-7) or 2,4,6- trimethylbenzoyldiphenylphosphine oxide (CAS# 127090-72-6). In a preferred embodiment, the photoinitiator compound may also optionally comprise, consist of, or consist essentially of a-hydroxy ketone photoinitiators. For instance, suitable a-hydroxy ketone photoinitiators are a-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2- methyl-1 -phenylpropanone, 2-hydroxy-2-methyl-1-(4-isopropylphenyl)propanone, 2-hydroxy- 2-methyl-1-(4-dodecylphenyl)propanone, 2-Hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)- benzyl]-phenyl}-2-methyl-propan-1 -one and 2-hydroxy-2-methyl-1 -[(2- hydroxyethoxy)phenyl]propanone.

In another embodiment, the photoinitiator compound includes, consists of, or consists essentially of: a-aminoketones, such as 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)- 1 -propanone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-but anone, 2-(4- methylbenzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1 -butanone or 2-benzyl-2- (dimethylamino)-1-[3,4-dimethoxyphenyl]-1-butanone; benzophenones, such as benzophenone, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, 2- methylbenzophenone, 2-methoxycarbonylbenzophenone, 4,4’-bis(chloromethyl)- benzophenone, 4-chlorobenzophenone, 4-phenylbenzophenone, 4,4’-bis(dimethylamino)- benzophenone, 4,4’-bis(diethylamino)benzophenone, methyl2-benzoylbenzoate, 3,3’- dimethyl-4-methoxybenzophenone, 4-(4-methylphenylthio)benzophenone, 2,4,6-trimethyl-4’- phenyl-benzophenone or 3-methyl-4’-phenyl-benzophenone; ketal compounds, for example 2,2-dimethoxy-1,2-diphenyl-ethanone; and monomeric or dimeric phenylglyoxylic acid esters, such as methylphenylglyoxylic acid ester, 5,5’-oxo-di(ethyleneoxydicarbonylphenyl) or 1,2-(benzoylcarboxy)ethane.

Yet further suitable photoinitiators for use in the photoinitiator compound include oxime esters, such as those disclosed in U.S. Pat. No.6, 596, 445. Still another class of suitable photoinitiators for use in the photoinitiator compound include, for example, phenyl glyoxalates, for example those disclosed in U.S. Pat. No. 6,048,660.

In another embodiment, the photoinitiator compound may comprise, consist of, or consist essentially of one or more alkyl-, aryl-, or acyl- substituted compounds not mentioned above herein.

According to another embodiment, the composition may contain a photoinitiator that is an alkyl-, aryl-, or acyl- substituted compound. In an embodiment the alkyl-, aryl-, or acylsubstituted photoinitiator possesses or is centered around an atom in the Carbon (Group 14) group. In such instance, upon excitation (via absorption of radiation) the Group 14 atom present in the photoinitiator compound forms a radical. Such compound may therefore produce a radical possessing or centered upon an atom selected from the group consisting of silicon, germanium, tin, and lead. In an embodiment, the alkyl-, aryl-, or acyl-substituted photoinitiator is an acylgermanium compound. Such photoinitiators are described in, US9708442. Known specific acylgermanium photoinitiators include benzoyl trimethyl germane (BTG), tetracylgermanium, or bis acyl germanoyl (commercially available as Ivocerin® from Ivoclar Vivadent AG, 9494 Schaan/Liechtenstein).

Photoinitiators may be employed singularly or in combination of one or more as a blend. Suitable photoinitiator blends are for example disclosed in U.S. Pat. No. 6,020,528 and U.S. Pat. App. No. 60/498,848. According to an embodiment, the photoinitiator compound includes a photoinitiator blend of, for example, bis(2,4,6-trimethylbenzoyl) phenyl phosphine oxide (CAS# 162881-26-7) and 2, 4, 6, -trimethylbenzoylethoxyphenylphosphine oxide (CAS# 84434-11-7) in ratios by weight of about 1:11 , 1 :10, 1 :9, 1 :8 or 1 :7.

Another especially suitable photoinitiator blend is a mixture of bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide, 2, 4, 6, -trimethylbenzoylethoxyphenylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1 -propanone (CAS# 7473-98-5) in weight ratios of for instance about 3:1:15 or 3:1 :16 or 4:1 :15 or 4:1:16. Another suitable photoinitiator blend is a mixture of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and 2-hydroxy-2-methyl-1- phenyl-1 -propanone in weight ratios of for instance about 1 :3, 1 :4 or 1 :5.

One or more of the aforementioned photoinitiators can be employed for use in the photoinitiator compound in compositions according to the present invention in any suitable amount and may be chosen singly or in combination of one or more of the types enumerated herein. In a preferred embodiment, the photoinitiator compound comprises, consists of, or consists essentially of free-radical photoinitiators, preferably of the a-cleavage type.

Suitable substrates for the process according to the invention are for example mineral substrates such as fiber cement board, wood, wood containing materials, paper including cardboard, textile, leather, metal, thermoplastic polymer, thermosets, ceramic, glass. Suitable thermoplastic polymers are for example polyvinylchloride PVC, polymethylmethacrylate PMMA, acrylonitrile-butadiene-styrene ABS, polycarbonate, polypropylene PP, polyethylene PE, polyamide PA, polyethylene terephthalate PET and polystyrene PS. Suitable thermosets are for example linoleum, epoxy, melamine, novolac, and urea-formaldehyde.

The substrate is optionally pre-treated and/or optionally pre-coated. For example, thermoplastic plastic films can be treated with corona discharges before application or pre- coated with a primer. Mineral building materials are also usually provided with a primer before the coating composition is applied.

The coating obtained in the process of the invention can advantageously be used in a floor or wall covering or in automotive interior or on furniture.

With the process of the invention, low gloss coatings can advantageously be obtained with a dry thickness of at least 2 micron, or of at least 3 micron, or of at least 4 micron, and of at most 100 micron, or of at most 75 micron, or of at most 50 micron.

The present invention further relates to the aqueous, radiation-curable coating composition as described herein above. The present invention further relates to a coated substrate that is obtained by coating a substrate with the process as described herein above.

The present invention is now illustrated by reference to the following examples. Unless otherwise specified, all parts, percentages and ratios are on a weight basis.

Measurement methods

Average particle size PS:

The intensity average particle size, z-average, has been determined by photon correlation spectroscopy using a Malvern Zetasizer Nano ZS. Samples are diluted in demineralized water to a concentration of approximately 0.1 g dispersion/liter. Measurement temperature 25°C. Angle of laser light incidence 173°. Laser wavelength 633 nm.

£H

The pH was measured using a Metrohm pH meter.

Solids

The solid content of the dispersion was measured on a HB43-S halogen moisture analyzer from Mettler Toledo at a temperature of 160°C.

Viscosity

The viscosity was determined using a RheolabQC machine from Anton Paar at a temperature of 23 °C and a shear rate of 100 s’ ¹ .

Gloss

The gloss is determined according to ISO2813 in the direction of the drawdown and is expressed in gloss units (GU). Glass transition temperature (Tg) (inflection point), crystallization temperature (Tc), melting temperature (Tm) and melting enthalphy (AHm)

The glass transition temperature (Tg) (inflection point), the crystallization temperature (Tc), the melting temperature (Tm) and the melting enthalpy (AHm) were measured via Differential Scanning Calorimetry (DSC) on a Mettler Toledo, TA DSC821 apparatus, in N2 atmosphere as described herein after: A sample of 10 mg was placed in the DSC apparatus. The sample was brought to 25° C. In the first heating curve, the sample was heated to 150° C. with a heating rate of 5° C./min. The sample was kept at 150° C. for 1 min. The sample was subsequently cooled to -50° C. with a cooling rate of 5° C./min, resulting in a cooling curve. After reaching -50° C. The sample was immediately heated to 150° C with a heating rate of 5° C./min, affording a second heating curve. The Tg was measured from the cooling curve (150° C. to -50° C., cooling rate 5° C./min) whereas the Tm and AHm were determined from the second heating curve (-50° C. to 150° C., heating rate of 5° C./min).

Stain resistances

The coffee, red wine and mustard resistances were determined colorimetric using an eXact Standard Handheld Spectrophotometer from X-rite and are reported in Tables 5 and 6. For coffee, the spot exposure time was 1 hr resp. 6 hr and was rated after 24hrs. For red wine and mustard, the spot exposure time was 6 hr and was rated after 24hrs The a- and b- values were measured according to ISO 7724. The coffee and mustard resistances were determined by Ab value where Ab-value — b(after resp 6 and 1 hr coffee exposure or 6 hr mustard exposure and rated after 24 hours) - before exposure). A higher Ab value indicates larger colour change due to staining, therefore worse stain resistance performance. The red wine resistance was determined COlOrimetriC using Aa value where Aa-value — afgfter 6 hr red wine exposure and rated after 24 hours) a(before exposure). A higher Aa value indicates larger colour change due to staining, therefore worse stain resistance performance. The a* axis is relative to the green-red opponent colours, with negative values toward green and positive values toward red. The b*axis represents the blue-yellow opponents, with negative numbers toward blue and positive toward yellow. Method to calculate the dry film thickness

The dry film thickness is calculated by multiplying the wet film thickness times the solids content of the formulation used.

DFT = WFT* solids content/100

Where

DFT: dry film thickness in pm

WFT: wet film thickness in pm

Solids content (wt.%): total weight of all solid compounds present in formulation divided by (total weight of the formulation *100).

Components and abbreviations used:

DPGDA = Agisyn™ 2833, dipropyleneglycoldiacrylate, available from Covestro

GPTA = Agisyn™ 2837, propoxylated(3)glycerol triacrylate available from Covestro EGDMA = ethyleneglycoldimethacrylate available from Covestro

DPHA = Agisyn™ 2830L, dipentaerythritolhexaacrylate available from Covestro Omnirad 500 = photoinitiator available from IGM

BYK 346 = Surfactant available from BYK (45% solids)

TEGO® Airex 902W = defoamer available from Evonik (24% solids)

Borchi® Gel L 75 N = Rheology modifier available from Borchers (50% solids) Acematt® TS 100 = silica matting agent from Evonik

Materials

Isophthalic acid, Phthalic anhydride, Adipic acid, Neopentyl glycol, Diethylene glycol, 1,4- Cyclohexanedimethanol, Glycerol, Pentaerythritol, DYTEK A (2-methylpentane-1,5-diamine), maleic anhydride, tert-butylhydroquinone, trimellitic anhydride, dimethylethanolamine, Lithium Hydroxide Monohydrate, Tetra Butoxy Titanate (Titanium (IV) butoxide), distearyl pentaerythritol diphosphate, butylglycol, Xylene and Methyl Ethyl Ketone were obtained from Sigma Aldrich. Soybean oil fatty acids were bought from Oleon.

5-Sulfoisophthalic acid monosodium salt (“SSI PA”, >99% purity) was purchased from the Future Fuel Company.

Demineralized water was used from a MilliQ water system.

Preparation of WB Polycondensate Dispersion Example 1 Step 1. Synthesis of Polyester Resin

The sulfopolyester was prepared by a melt-phase polymerization reaction. A 2L glass reactor equipped with a mechanical stirrer, thermocouple, and a distillation set-up equipped with a Vigreux column was charged with isophthalic acid (774.1 g), 5-Sulfoisophthalic acid monosodium salt (48.3 g), neopentyl glycol (261.1 g), diethylene glycol (187.3 g), cyclohexanedimethanol (143.4 g), glycerol (8.3 g), and lithium hydroxide (0.04 g). The temperature was raised to 220°C under a N2 atmosphere. After 2h at 220°C, the Vigreux column was removed and replaced by a standard distillation set-up. Next, the temperature was raised to 250°C. At 250°C, vacuum (30 mBar) was applied slowly. The reaction progression was monitored by taking samples and measuring the (carboxylic) acid value (AV) and hydroxyl value (OHV). When the AV was lower than 20 mg KOH/g, a catalyst tetrabutoxy titanate (0.12 g, mixed with 6 g diethylene glycol) was added. The reaction then proceeded under vacuum at 250°C until the final AV and OHV specifications were reached (AV = 3 mg KOH/g, OHV = 10 mg KOH/g). The final sulfopolyester reaction mixture was discharged.

Step 2. Dispersing the Polyester Resin into Water Next, in a 2L glass reactor 300 g of the polyester resin was dissolved in methyl ethyl ketone (300 g). This solution was heated to 60 °C under stirring. When reaching 60 °C, water (900 g) was dosed slowly (30 min) into the reactor in a dropwise fashion. After finishing the water addition, vacuum was applied in order to remove the MEK after which the dispersion was discharged. If necessary, antifoaming agent was used. The resulting water dispersed polyester resin had a solid content of 30.0 wt%.

Preparation of WB Polycondensate Dispersion Example 2

The procedure from Example 1 was followed using isophthalic acid (642.9 g), SSIPA (40.0 g), neopentyl glycol (227.4 g), diethylene glycol (155.4 g), cyclohexanedimethanol (119.2 g), and LiOH (0.04 g). The procedure was followed until reaching the final specifications of AV = 1 mg KOH/ g and OHV = 15 mg KOH I g. The resulting dispersion had a solid content of 29.9 wt%.

Preparation of WB Polycondensate Dispersion Example 3

The procedure of Example 1 was followed using isophthalic acid (636.1 g), SSIPA (39.6 g), neopentyl glycol (136.1 g), diethylene glycol (153.8 g), cyclohexanedimethanol (117.9 g), DYTEK A (100.0 g) and LiOH (0.04 g). The procedure was followed until reaching the final specifications of AV = 3 mg KOH/ g and OHV = 10 mg KOH I g. The resulting dispersion had a solid content of 30.6 wt%.

Preparation of WB Polycondensate Dispersion Example 4

The sulfopolyester was prepared by a melt-phase polymerization reaction similar to Example 1 but with sequential monomer addition. A 2L glass reactor equipped with a mechanical stirrer, thermocouple, and a distillation set-up equipped with a Vigreux column was charged with 5-Sulfoisophthalic acid monosodium salt (52.0 g), neopentyl glycol (295.8 g), diethylene glycol (202.1 g), cyclohexanedimethanol (155.0 g), and lithium hydroxide (0.05 g). The temperature was raised to 220°C under a N2 atmosphere. The reaction proceeded until the acid value was lower than 2 mg KOH/g, at which point the temperature was lowered to 100°C and adipic acid (735.5 g) added. Then, the temperature was raised to 250 °C and the procedure from Example 1 was followed until reaching the final specifications of AV = 3 mg KOH/ g and OHV = 3 mg KOH I g. The resulting dispersion had a solid content of 30.4 wt%.

Preparation of WB Polycondensate Dispersion Example 5 Step 1. Synthesis of Polyester Alkyd Resin

The polyester was prepared by reacting in a 2 L glass reactor, fitted with mechanical stirrer, nitrogen inlet, thermocouple and Dean-Stark trap, 368 grams of soybean oil fatty acids, 266 grams of pentaerythritol, 163 grams of benzoic acid, 285 grams of phthalic anhydride and a suitable amount of xylene using azeotropic water removal at 230°C until an acid value below 15 mg KOH/g was obtained. After cooling down further xylene was added to obtain a clear low viscosity liquid resin.

Step 2. Dispersing the Polyester Alkyd Resin into Water

301 grams of the solid resin from example 10 were emulsified as follows. The resin was heated to between 50-80°C and 27 grams of a 30% solution of a highly branched alcohol based surfactant combining anionic and non-ionic components and 84 grams of demineralised water were added. The mixture was neutralised with a non-amine base and was stirred until homogeneous. Demineralised water was added during 2 hours until a solids content of 53% was obtained. The emulsion showed a milky appearance and was stable.

Preparation of WB Polycondensate Dispersion Example 6

Step 1. Synthesis of Unsaturated Polyester Resin The unsaturated polyester was prepared by a melt-phase polymerization reaction between a diacid, a diol and an anhydride under an inert N2 atmosphere. Neopentyl glycol (2364.6 g) and adipic acid (2117.5 g) were added to a 6 L glass reactor equipped with a mechanical stirrer, thermocouple, and a distillation set-up with a Vigreux column. The temperature was raised slowly to 220 °C under a N2 atmosphere. The reaction progress was monitored by the measurement of acid value (AV) and hydroxyl value (OHV). When the AV was lower than 5 mg KOH/g, maleic anhydride (686.8 g) and tert-butylhydroquinone (0.69 g, calculated from 0.001 g per 1 g maleic anhydride) were added into the reactor via a solids funnel and the temperature was lowered to 190 °C. When the AV was lower than 30 mg KOH/g, tetra butoxy titanate (0.45 g, mixed with 4.50 g diethylene glycol) was added as a catalyst. After 1 hour, the Vigreux column was then removed to obtain a standard distillation set-up and vacuum was applied slowly up to 30 mBar. The reaction then proceeded under vacuum at 190 °C until the final AV and OHV specifications were reached (AV = 0-7 mg KOH/g, OHV = 25-35 mg KOH/g). The reaction mixture was discharged.

Step 2. Incorporation of Trimellitic Anhydride into the Unsaturated Polyester The linear unsaturated polyester prepared from the previous step (544.9 g) and trimellitic anhydride (TMA, 52.3 g) were added into a 1 L glass reactor equipped with a mechanical stirrer, thermocouple, and a standard distillation set-up. The temperature was raised slowly to 190 °C under a N2 atmosphere. The reaction proceeded until the final specifications were reached (AV = 62 mg KOH/g, OHV = 6 mg KOH/g). The reaction mixture was discharged. Step 3. Dispersing the Unsaturated Polyester Resin into Water

The TMA incorporated polyester (250 g) was charged into a 500 mL glass reactor and heated to 40 °C. Dimethylethanolamine (24.7 g) and water (225.3 g) were added into the reactor over a period of 30 minutes, resulting in a homogenous solution. Adjustments to the pH were performed by addition of dimethylethanolamine until a pH of 7-8 was reached. The resulting dispersion had a solids content of 43.9 wt%.

Preparation of WB Polycondensate Dispersion Example 7

The procedure of Example 6 was followed using neopentyl glycol (2370 g), adipic acid (1410 g), tetrabutoxy titanate (0.39 g, mixed with 3.90 g diethylene glycol), maleic anhydride (1170 g), and tert-butylhydroquinone (1.17 g). The final specifications of the polyester resin were AV = 63 mg KOH/g, OHV = 9 mg KOH/g and the dispersion had a solids content of 42.8 wt%. Preparation of WB Polycondensate Dispersion Example 8

Step 1. Synthesis of the High Tg Polyester Resin

High Tg polyester was prepared by a melt-phase polymerization reaction. A 2L glass reactor equipped with a mechanical stirrer, thermocouple, and a distillation set-up equipped with a Vigreux column was charged with distearyl pentaerythritol diphosphite (0.9 g), neopentyl glycol (257.4 g), ethylene glycol (100.0 g). The vessel was heated up to 150 °C until the mixture was molten. Then isophthalic acid (100.0 g,), trimellitic anhydride (47.5 g) and terephthalic acid (425,4 g,) were added and under a nitrogen flow the temperature was gradually increased to 250 °C. After completing of the reactions, the temperature is decreased to 215 °C. At 215 °C, isophthalic acid (74.5 g) is added. After completion of the reaction under atmospheric conditions, the temperature was decreased to 200 °C. At 200 °C, more reaction water was distilled off under vacuum of 50-70 mbar for 90 minutes, until the acid value of the precursor of the polyester resin was between 25 and 28 mg KOH/g; that marked the completion of the second step. For the third step the reaction trimellitic anhydride (125.9 g,) was added. The temperature was kept at 200 °C and the polyester resin was stirred at 200 °C until the acid value of the polyester resin was 104±0.5 mg KOH/g and the hydroxyl value was 1 5±0.5 mg KOH/g. Once the acid value and OH-value were reached, the polyester resin was discharged onto aluminium foil that was kept at room temperature. The properties of the isolated polyester resin were: amorphous, Mn=2780 Da, Mw= 8330 Da, Tg= 71.1 °C, AV= 103.0 mg KOH/g resin, OHV= 0.5 mg KOH/g Step 2. Dispersing the High Tg Polyester Resin into Water

The high Tg polyester resin (200 g) was charged into a 500 mL glass reactor and heated to 80°C. Dimethylethanolamine (32 g) was added slowly via pipette into the reactor. Water (268 g) was dosed into the reactor dropwise over a period of 30 minutes and stirred until a homogenous solution was obtained. The dispersion was cooled down to room temperature and adjustments to the pH were performed by addition of dimethylethanolamine until a pH of 7-8 was reached. The resulting dispersion had a solids content of 40.9 wt% and pH=7.5 Table 1 : Specifications of WB Polycondensate Dispersions Example 1 to Example 8

(abbreviated in the Table as Ex. 1 to Ex. 8)

Preparation of the UV-Curable Formulations 1a-14a based on the WB polycondensate compositions Ex. 1 - Ex. 8

The WB polycondensate compositions of Ex. 1- Ex. 8 (in Table 1) were formulated as shown in Table 2 and Table 3. The ingredients listed in Table 2 and Table 3 were added into a polyethylene (PE) jar and mixed thoroughly using a Dispermill® (OrangeLine, ATP Engineering B.V.).

Table 2: Preparation of the UV curable WB polycondensate Formulations (abbreviated as

“Form” in the Table headings) 1a-7a Table 3: Preparation of the UV curable WB polycondensate formulations (abbreviated as

“Form” in the Table headings) 8a-15a

For the matted formulation Formulations 1b-11b, 1.8 g of Acematt TS-100 was added to 100 grams of formulation Formulations 1a-11a, respectively, see Table 4.

Table 4: Formulations 1b - 9b with matting agent

Application of formulations

The so-obtained coating compositions were applied on a Leneta card (2C Leneta Inc) using a 125 pm wire rod applicator. The coated cards were dried for 10 minutes in an oven with airspeed of 1.2 m/s at 50 °C. Subseguently the so-obtained dried composition was cured, the cure conditions are indicated in Tables 5 and 7. In Table 7 resp. a 125, 75, 50, 25 and 16 pm wire rod applicator were used.

Curing of the dried coating composition

Excimer/UV cure:

Immediately (within 20 seconds) after drying the formulations were cured on a UVio curing rig with a conveyor belt speed of 15 m/min eguipped with 2 lamps. The first Lamp was an Excirad 172 lamp (IOT GmbH, xenon based excimer lamp generating 172nm light) under which the cure was performed with a radiation dose of 11.4 mJ/cm ² (determined with an ExciTrack172, IOT GmbH) in a nitrogen atmosphere (02 level < 50 ppm detected with IOT inline detector). The next cure step was performed by the second lamp being a Light Hammer 10 Mark III eguipped with a H-bulb operating @ 50% power (Heraeus Holding, Hg doped UV lamp generating UV light with wave lengths >315 nm, 181 mJ/cm ² total dose as determined with an Power Puck II (EIT Inc)).

Conventional UV cure atmospheric (Conv UV cure atmosph):

Immediately (within 20 seconds) after drying the formulations were cured on a UVio curing rig with a conveyor belt speed of 15 m/min. The cure step was performed by a Light Hammer 10 Mark III eguipped with a H-bulb operating @ 50% power (Heraeus Holding, Hg doped UV lamp generating UV light with wave lengths >315 nm , 181 mJ/cm ² total dose as determined with an Power Puck II (EIT Inc)) in air.

Conventional UV cure inert (Conv UV cure inert):

Immediately (within 20 seconds) after drying the formulations were cured on a UVio curing rig with a conveyor belt speed of 15 m/min. The cure step was performed by a Light Hammer 10 Mark III equipped with a H-bulb operating @ 50% power (Heraeus Holding, Hg doped UV lamp generating UV light with wave lengths >315 nm , 181 mJ/cm ² total dose as determined with an Power Puck II (EIT Inc)) under inert atmosphere. Testing of the cured coatings

The gloss and the coffee, red wine and mustard resistances of the cured coatings were determined as described above. The measured gloss values are reported in Table 5 and 7. The coffee, red wine and mustard resistances are reported in Table 6.

Table 5: Gloss values measured of the formulation not containing matting agent and cured with Excimer/UV cure; gloss values of the formulation containing matting agent and cured with the conventional UV cure process under atmospheric conditions; stain resistances measured colorimetric of the formulation not containing matting agent and cured with Excimer/UV cure and stain resistances measured colorimetric of the formulation containing matting agent and cured with the conventional UV cure process under atmospheric conditions (Conv UV atmosph) resp. cured with the conventional UV cure process under inert conditions (Conv UV inert)

Table 6: Stain resistances measured colorimetric (Ab for coffee and mustard and Aa for red wine) of the formulation without matting agent and cured with Excimer/UV cure.

Table 7: Gloss values measured after combined excimer/UV cure and conventional UV cure under atmospheric conditions of the formulation without matting agent.

*The film here was non-uniform matt, so gloss has been measured at different points on the film, where more than 10% of the coating film was high gloss.

**n.d. stands for “not determined” Table 8: Effect of layer thickness on gloss values for Formulation 5a and 5b

With the process of the invention, low gloss coatings can be obtained with a very low dry thickness, even low gloss coatings with a dry thickness of 4 micron could be obtained, while when the formulation contains matting agent (formulation ) and the formulation was cured with conventional UV curing, a decent film with such a low dry thickness could not be obtained.

Figure 1 shows photographs of the coated testcard obtained by the Excimer/UV curing process according to the process of the invention of the Formulation 7a containing the dispersion of Example 7 without matting agent (upper testcard) and the coated testcard obtained by conventional UV curing under atmospheric conditions of the Formulation 2b containing the dispersion of Example 7 with matting agent (bottom testcard); from left to right: Coffee [6 hrs], Red Wine [6hrs] and Coffee [1 hr] stains.

Comparative Experiments 26-32

A representative group of commercially available waterborne UV curable coating dispersions, as specified in Table 9, were applied on a Leneta card (2C Leneta Inc) using a 125 pm wire rod applicator. The coated cards were dried for 10 minutes in an oven with airspeed of 1.2 m/s at 50 °C. Subsequently the so-obtained dried composition was cured using Conventional UV cure atmospheric and Excimer/UV cure as described above. The measured gloss values are reported in Table 9. The commercially available waterborne UV curable coating compositions as indicated in Table 9 have a different composition than the aqueous, radiation-curable coating composition of the present invention.

Table 9: Gloss values measured after conventional UV cure under atmospheric conditions and combined Excimer/UV cure of a representative group of commercially available waterborne UV curable coating compositions curable dispersions, when subjected to Excimer/UV cure, do not result in matt coatings.