Method for producing low gloss coated surface by radiation curing

Abstract

The present invention relates to a method of preparing a cured coating having a low gloss surface from an aqueous radiation curable coating composition wherein the method comprises the steps of (1) applying an aqueous radiation curable coating composition on a substrate, (2) drying the aqueous radiation curable coating composition, providing an at least partially dried coating composition, and (3) curing the at least partially dried coating composition. (3) irradiating the at least partially dried coating composition from step (2) with UV light having a wavelength substantially in the range of 231 to 280 nm, providing a coating of a partially cured surface layer having a reduced gloss, followed by (4) completing the curing of the coating from step (3) with actinic radiation, step (3) and step (4) are carried out in the air, and wherein the aqueous, radiation curable coating composition comprises at least one polymer, at least one reactive diluent and water, whereby a partially cured surface layer having a reduced gloss is fixed and a cured coating having a low gloss surface is provided, where step (3) and step (4) are carried out in the air, and where the aqueous, radiation curable coating composition comprises at least one polymer, at least one reactive diluent and water.

Description

[0001] The present invention relates to a method for preparing a low-gloss coating surface from an aqueous coating composition.

[0002] Aqueous coating compositions are widely used in the coating industry. However, generally, after the aqueous coating composition dries, a glossy surface is obtained. A "low-gloss" surface imparts a highly sought-after aesthetic effect to products, especially in the wooden furniture, flooring, and wallcovering industries, as they can produce a very natural appearance, which helps to more prominently highlight the materiality of the article. Currently, the production of matte surfaces often involves the use of a coating product whose formulation contains a matting agent made of organic and / or inorganic substances, which can act on the degree of light reflection by positioning itself on and / or floating on the coated surface, giving the observer the visual sensation of a low-gloss surface. However, the use of matting agents leads to the deterioration of the coating surface properties because they do not participate in the polymerization process. In addition, matting agents tend to migrate to the coating surface after application, and thus the matting agents may be lost during mechanical deformation, such as caused by scratching, resulting in an increase in gloss.

[0003] The object of the present invention is to provide a method for obtaining a low-gloss coating from an aqueous coating composition without having to use a matting agent.

[0004] The object of the present invention is to provide a method for preparing a low-gloss coating surface by irradiating an aqueous, radiation-curable coating composition without having to use a matting agent and without having to use an inert gas atmosphere during the radiation process.

[0005] According to the present invention, there is provided a method for preparing a cured coating having a low-gloss surface from an aqueous, radiation-curable coating composition, wherein the method comprises the following steps:

[0006] (1) applying an aqueous, radiation-curable coating composition onto a substrate,

[0007] (2) drying the aqueous, radiation-curable coating composition to provide at least partially dried coating composition,

[0008] (3) irradiating the at least partially dried coating composition from step (2) with UV light having a wavelength substantially in the range of 231 to 280 nm to provide a coating having a partially cured surface layer with reduced gloss,

[0009] Then

[0010] (4) completing the curing of the coating from step (3) with actinic radiation, thereby fixing the partially cured surface layer with reduced gloss and providing a cured coating having a low-gloss surface,

[0011] Among them, steps (3) and (4) are carried out in air.

[0012] Wherein the aqueous, radiation-curable coating composition comprises at least one polymer, at least one reactive diluent and water.

[0013] It has surprisingly been found that the process of the present invention allows for the preparation of a low-gloss coating surface without the need to use a matting agent. And thus a low-gloss coating surface is prepared without adversely affecting the stain resistance of the coating.

[0014] Furthermore, it has surprisingly been found that curing can be carried out in air, and thus the process of the present invention can be carried out without the need to use an inert gas curing device in a UV radiation process. This is advantageous because inert gases such as nitrogen and argon are expensive, and in addition, making an industrial curing production line completely airtight is a challenge, and thus there may be a loss of inert gas into the environment around the curing production line, making the process even more expensive and potentially affecting worker safety as it may lead to an excessive concentration of inert gas in the environment around the curing production line.

[0015] For all upper and / or lower limits of any ranges given herein, unless specifically stated otherwise, the boundary values are included within the given ranges. Thus, when specifying x to y, it means including x and y and all intermediate values.

[0016] The process of the present invention optionally includes an additional radiation curing step before step (3), i.e., before the step of irradiating with UV light having a wavelength essentially higher than 230 nm and lower than or equal to 280 nm. In such an additional radiation curing step, the radiation-curable coating composition from step (2) is pre-cured by irradiating with a radiation dose that causes partial curing of the coating composition from step (2) to a pre-gel or near-gel point state. Thus, the process of the present invention comprises the following steps:

[0017] (1) Applying an aqueous, radiation-curable coating composition onto a substrate,

[0018] (2) Drying the aqueous, radiation-curable coating composition to provide at least a partially dried coating composition,

[0019] (2a) Optionally pre-curing the radiation-curable coating composition from step (2) by irradiating with light to provide a partially cured coating,

[0020] (3) Irradiating the at least partially dried coating composition from step (2) or the partially cured coating from step (2a) (when present) with UV light having a wavelength essentially in the range of 231 to 280 nm to provide a coating having a surface layer with reduced glossiness and being partially cured,

[0021] Next

[0022] (4) Curing the coating from step (3) with actinic radiation, thereby fixing the partially cured surface layer having a reduced gloss and providing a cured coating having a low gloss surface,

[0023] wherein steps (3) and (4) are carried out in air.

[0024] In step (1) of the process of the present invention, an aqueous, radiation-curable coating composition is applied to a substrate by methods known to those skilled in the art, such as, for example, knife coating, brush coating, roll coating, spray coating. The coating composition is applied to the substrate at a coating thickness of preferably 5 to 300 μm, more preferably 15 to 175 μm, more preferably 20 to 150 μm, more preferably 25 to 125 μm.

[0025] In step (2) of the process of the present invention, the drying of the aqueous, radiation-curable coating composition applied to the substrate is preferably achieved at a temperature above 30 °C to evaporate water and optionally organic solvents and other volatile compounds, obtaining an at least partially dried coating composition. The term "drying" means the loss of water and (if present) organic solvents and other volatile compounds from the aqueous coating composition by evaporation until preferably at least 80% by weight of the water is removed.

[0026] The skin curing step (3) of the method of the present invention is carried out by irradiating at least partially dried coating composition from step (2) or partially cured coating from step (2a) (when present) with UV light having a wavelength substantially in the range of 231 to 280 nm, providing a coating with a partially cured surface layer having reduced gloss. The expression "UV light having a wavelength substantially in the wavelength range of X to Y (such as 231 to 280 nm)" means that at least 60%, preferably at least 70%, of the actinic radiation power of the applied radiation source is in the wavelength range of X to Y (such as 231 to 280 nm). Since oxygen absorbs at wavelengths ≤ 230 nm, leading to the formation of ozone, in the present invention, it is preferred to minimize the emission at wavelengths ≤ 230 nm (i.e., preferably at most 10%, more preferably at most 5%, even more preferably at most 2%, and even more preferably at most 1% of the radiation power of the radiation source applied in step (3) emits light at wavelengths ≤ 230 nm), or more preferably there is no such emission. Therefore, it is also preferred that at least 60%, more preferably at least 70%, even more preferably at least 80% of the radiation power of the applied radiation source emitted in the wavelength range of 200 nm to 390 nm is in the wavelength range of X to Y (such as 231 to 280 nm). Even more preferably, at least 70%, more preferably at least 80%, even more preferably at least 90% of the radiation power of the applied radiation source emitted in the wavelength range of 231 to 390 nm is in the wavelength range of X to Y (such as 231 to 280 nm).

[0027] The irradiation in step (3) is preferably carried out with UV light having a wavelength substantially in the range of 241 to 280 nm, more preferably in the range of 241 to 270 nm, even more preferably in the range of 244 to 265 nm, or preferably in the range of 251 to 280 nm, more preferably in the range of 251 to 260 nm.

[0028] The UV light applied in step (3) preferably has a UV radiation dose in the range of 2 to 200 mJ / cm 2 range, preferably having at least 3 mJ / cm 2 、or at least 4 mJ / cm 2 、or at least 5 mJ / cm 2 radiation dose, and preferably having at most 90 mJ / cm 2 、preferably at most 80 mJ / cm 2 、or at most 70 mJ / cm 2 、or at most 60 mJ / cm 2 、or at most 50 mJ / cm 2 、or at most 40 mJ / cm 2 radiation dose.

[0029] A radiation source suitable for emitting light in a specified wavelength range can be selected by calculating the percentage of light emitted in the specified wavelength region from the spectral profile of the radiation source available from the radiation source supplier. The spectral irradiance can be expressed as the irradiance power in W / nm or W / 10nm, or as the spectral irradiance in W / m 2 / nm or on a relative scale. The spectral curve is a display of how the radiation output is distributed over the electromagnetic spectrum.

[0030] Radiation sources suitable for emitting UV light in the specified wavelength range in step (3) of the method of the present invention are, for example, low-pressure mercury vapor lamps, or UVC LED lamps with peak wavelengths in the range of 231 to 280 nm, such as peak wavelengths of 240 nm, or 245 nm, or 250 nm, or 255 nm, or 260 nm, or 265 nm, or 270 nm or 275 nm, or excimer lamps with peak wavelengths in the range of 231 to 280 nm, such as 248 nm (KrF*) or 253 nm (XeI*) or 259 nm (Cl2*). For example, a suitable low-pressure mercury vapor lamp that can be used in step (3) of the present invention is the Premium P2035 UV disinfection lamp system from Heraeus Noblelight, which has a main narrow emission peak at 254 nm with a full width at half maximum of 2 nm; it can be calculated from the spectral curve that in the wavelength range of 200 to 390 nm, 91% of the irradiation power is emitted in the wavelength range of 231 nm to 280 nm, more specifically 251 nm to 260 nm.

[0031] Another radiation source suitable for emitting UV light in the specified wavelength range in step (3) is used in combination with an optical bandpass filter having a maximum transmittance in the wavelength range of 241 nm to 270 nm, preferably an optical bandpass filter having a maximum transmittance in the wavelength range of 251 to 260 nm, such as an optical bandpass filter having a maximum transmittance at 254 nm. A suitable bandpass filter is, for example, the 254 nm, 10 nm FWHM, First Surface UV bandpass filter from Edmund Optics Ltd. Suitable medium-pressure mercury vapor lamps for use in combination with such an optical bandpass filter are, for example, the Fusion H lamp and Fusion H+ lamp from Heraeus Noblelight. By multiplying the spectral curve of the Fusion H bulb or H+ bulb provided by the lamp supplier by the % transmittance spectrum of the bandpass filter provided by the filter supplier, it can be calculated that when the Fusion H bulb or H+ bulb is used with this filter, 100% of the UV irradiation power is emitted in the wavelength range of 231 nm to 280 nm.

[0032] The skin curing step (3) is preferably carried out using at most 6 lamps. Therefore, the skin curing step (3) is preferably carried out using 1 lamp, or 2 lamps, or 3 lamps, or 4 lamps, or 5 lamps, or 6 lamps. Preferably, each lamp has a width that covers the entire width of the substrate so as to form a uniform gloss over the entire surface. These lamps can be in one or more lamp units. Different lamp units can be provided such that the irradiance from a single lamp unit can vary. For example, the earlier lamp units can be set at a lower irradiance to form a fine multiple pattern, and the later lamp units with further skin curing have a higher amplitude to further reduce the gloss. Those skilled in the art will understand that when multiple lamps are used, the surface texture, i.e., the gloss, can be further adjusted by changing the distance and irradiance of different lamps.

[0033] Preferably, the irradiance from each lamp unit in the skin curing step (3) is at least 5 mW / cm 2 , more preferably at least 10 mW / cm 2 , even more preferably at least 15 mW / cm 2 , even more preferably at least 20 mW / cm 2 , even more preferably at least 25 mW / cm 2 , even more preferably at least 30 mW / cm 2 ; and the irradiance from each lamp unit in the skin curing step (3) is preferably at most 500 mW / cm 2 , more preferably at most 300 mW / cm 2 , even more preferably at most 200 mW / cm 2 .

[0034] The irradiation in the skin curing step (3) is carried out under atmospheric conditions, i.e., in air, in other words, not under inert gas conditions and / or not in an atmosphere with reduced oxygen.

[0035] After step (3), a surface wrinkled pattern is formed at the coating surface. Without wishing to be bound by any theory, it is believed that the surface wrinkled pattern is formed by microfolding of the coating skin layer, and the microfolding pattern preferably has a random microscopic pattern of peaks and valleys, and the average spacing between adjacent peaks and / or valleys is shorter than 100 μm. By changing the radiation dose in step (3) and / or optional step (2a), the microfolding pattern, such as the spacing between adjacent peaks and / or valleys, can be further adjusted, and it is believed that by doing so, the gloss level and / or surface texture can be further adjusted.

[0036] Step (4) of the process according to the invention is carried out by irradiating the partially cured surface layer with actinic radiation to complete the curing of the coating, thereby providing a cured coating with a low-gloss surface. Curing of coatings by actinic radiation, such as, for example, UV light or electron beam radiation, is known in the industry. Actinic radiation is understood to mean electromagnetic, ionizing radiation, in particular electron beams, UV light and visible light. The irradiation in step (4) is preferably carried out with an electron beam or UV light having a significant emission at wavelengths > 280 nm. More preferably, the irradiation in step (4) is carried out with UV light, wherein at least 40% of the actinic radiation power of the applied radiation source is provided by UV light having a wavelength higher than 280 nm. Also preferably, in the radiation power of the applied radiation source emitted in the wavelength range from 200 to 390 nm, at least 40% is emitted at wavelengths > 280 nm; and also preferably, in the radiation power of the applied radiation source emitted in the wavelength range from 231 to 390 nm, at least 40%, more preferably at least 50%, is emitted at wavelengths > 280 nm.

[0037] The light applied in step (4) preferably has a radiation dose of 150 to 2500 mJ / cm 2 2, more preferably having at least 200 mJ / cm 2 2, or at least 250 mJ / cm 2 2, or at least 300 mJ / cm 2 2. The upper limit of the radiation dose in step (4) is not critical, but is generally at most 2250 mJ / cm 2 2, or at most 2000 mJ / cm 2 2.

[0038] Radiation sources suitable for step (4) are, for example, LED lamps or broadband UV lamps having a peak wavelength in the range from 350 to 450 nm, such as medium-pressure mercury vapor lamps. Preferably, the irradiation in the final curing step (4) is carried out with UV light emitted from a broadband UV lamp. Examples of broadband UV lamps suitable for step (4) are medium-pressure mercury vapor arc lamps or microwave-powered lamps, such as, for example, the Fusion H lamp and the Fusion H+ lamp available from Heraeus Noblelight.

[0039] For example, according to the spectral curve of the FusionH bulb 13mm 10-inch lamp with a broadband spectrum, it can be calculated that, for example, in the wavelength range of 200 to 450 nm, only 28% of the emitted light has a wavelength of 231 to 280 nm, and 62% is emitted at a wavelength > 280 nm. This shows the key difference from the UV light used in step (3). For an LED lamp with a single peak in the wavelength range of 350 nm to 450 nm, 0% of the actinic light has a wavelength of 231 to 280 nm, and 100% is emitted at a wavelength > 280 nm, which shows the key difference from the UV light used in step (3).

[0040] The irradiation in step (4) is carried out under atmospheric conditions, that is, in air, in other words, not under inert gas conditions and / or not in an atmosphere with reduced oxygen.

[0041] In optional step (2a), some of the reactive ethylenically unsaturated double bonds of the curable compounds of the radiation-curable coating composition polymerize in the uncured coatinglayer obtained in step (2), such that the coating is partially cured to a pre-gel or near-gel point state. This process is also called pre-curing. The optional pre-curing step (2a) is preferably carried out by irradiating the radiation-curable coating composition from step (2) with light having a significant emission at a wavelength > 280 nm. More preferably, the irradiation in step (2a) is carried out with light in which at least 40% of the actinic radiation power of the applied radiation source is provided by light having a wavelength higher than 280 nm. More preferably, the optional pre-curing step (2a) is preferably carried out by irradiating the radiation-curable coating composition from step (2) with light having a significant emission at a wavelength > 320 nm. Even more preferably, the irradiation in step (2a) is carried out with UV light in which at least 40%, more preferably at least 50%, even more preferably at least 60%, even more preferably at least 80%, and even more preferably 100% of the actinic radiation power of the applied radiation source is provided by light having a wavelength higher than 320 nm.

[0042] When present, the light applied in step (2a) preferably has a radiation dose in the range of 1 to 200 mJ / cm 2 preferably having a radiation dose of at least 2 mJ / cm 2 or at least 3 mJ / cm 2 and preferably having a radiation dose of at most 90 mJ / cm 2 or at most 80 mJ / cm 2 or at most 70 mJ / cm 2 or at most 60 mJ / cm 2 or at most 50 mJ / cm 2 or at most 40 mJ / cm 2, or at most 30 mJ / cm 2 , or at most 20 mJ / cm 2 of radiation dose.

[0043] The radiation source suitable for step (2a) is, for example, a broadband UV lamp, such as a medium-pressure mercury vapor lamp or an LED lamp with a peak wavelength in the range of 350 to 400 nm. Suitable medium-pressure mercury vapor lamps are, for example, arc lamps or microwave-powered lamps, such as the Fusion H lamp and the Fusion H+ lamp available from Heraeus Noblelight. Preferably, the irradiation in step (2a) is carried out with light emitted from an LED lamp having a peak wavelength higher than 320 nm, such as, for example, light having a peak wavelength of 350 nm, or 355 nm, or 360 nm, or 365 nm, or 370 nm, or 375 nm, or 380 nm, or 385 nm, or 390 nm, or 395 nm.

[0044] The irradiation in the optional pre-curing step (2a) is preferably carried out under atmospheric conditions, i.e., in air, in other words, not under inert gas conditions and / or not in an atmosphere with reduced oxygen.

[0045] The method of the present invention is preferably carried out under atmospheric conditions, i.e., in air.

[0046] Those skilled in the art will understand that for the optional pre-curing step (2a), in which only the pre-gel or near-gel point state of the coating should be achieved, it is preferred to use light having a significant emission with a wavelength higher than 350 nm, such as a suitable LED lamp with a peak wavelength higher than 350 nm, while for the complete curing step (4), preferably, UV light having a significant emission in the wavelength range of 281 to 390 nm is preferred, such as a broadband medium-pressure mercury vapor lamp. This again illustrates the difference in the lamps most suitable for each step.

[0047] The radiation dose as defined herein is the radiation dose of light emitted in the wavelength range of 200 to 390 nm.

[0048] The method of the present invention allows to obtain a surface coating with low gloss, and thus the gloss level can be controlled by adjusting the dose conditions in step (3) and / or the optional step (2a). The gloss of the cured coating surface measured at a 60° geometric angle is less than or equal to 52 gloss units, preferably in the range of 1 to 50 gloss units, or 4 to 40 gloss units, or 4 to 30 gloss units, or 4 to 20 gloss units, or 4 to 10 gloss units; and / or the gloss of the cured coating surface measured at an 85° geometric angle is less than or equal to 60 gloss units, preferably in the range of 1 to 60 gloss units, or 5 to 40 gloss units, or 5 to 30 gloss units.

[0049] The aqueous coating composition used in the method of the present invention is radiation-curable. Radiation-curable means that radiation is required to initiate crosslinking of the composition. The aqueous, radiation-curable coating composition for use in the method of the present invention contains ethylenically unsaturated (C═C) bond functionality which, preferably in combination with the presence of a photoinitiating system under the influence of radiation, can be crosslinked by free radical polymerization. The aqueous, radiation-curable coating composition as used in the present invention comprises (A) at least one polymer, and (B) at least one radiation-curable diluent (also referred to as a reactive diluent), and (C) water.

[0050] The acrylate functionality has the following formula:

[0051] CH2═CH-C(O)O-

[0052] As used herein, the acrylate functionality of a compound is the number of acrylate functional groups per molecule of the compound.

[0053] A dispersion is a system having at least two phases, where one phase contains discrete particles (colloidally dispersed particles) distributed throughout the bulk material, the particles being the dispersed phase and the bulk material being the continuous phase. The continuous phase of the aqueous dispersion is provided at least in part by water. Preferably, the continuous phase of the dispersion of the present invention comprises at least 75% by weight, more preferably at least 80% by weight, of water (relative to the continuous phase).

[0054] The aqueous, radiation-curable coating composition comprises at least one polymer, at least one reactive diluent and water. The at least one polymer is preferably selected from polyurethanes, radiation-curable polyurethanes, vinyl polymers, polyesters, polyurethane-vinyl polymer hybrids and any mixtures thereof.

[0055] Preferably, the aqueous, radiation-curable coating composition used in the method of the present invention is a dispersion which comprises:

[0056] (A) particles comprising at least one water-dispersed polymer, preferably selected from polyurethanes, radiation-curable polyurethanes, vinyl polymers, polyesters, polyurethane-vinyl polymer hybrids and any mixtures thereof, and

[0057] (B) at least one radiation-curable diluent (B) having a molar mass of less than 800 g / mol and an acrylate functionality of from 1 to 6, and

[0058] (C) water and optionally an organic solvent, where the optional organic solvent is present in an amount of up to 30% by weight based on the total amount of water and organic solvent,

[0059] Based on the total amount of (A) and (B), the amount of (A) is 30 to 95% by weight, and the amount of (B) is 5 to 70% by weight.

[0060] In a preferred embodiment of the present invention, the aqueous, radiation-curable coating composition comprises at least one non-radiation-curable polyurethane, at least one reactive diluent, and water. In another preferred embodiment of the present invention, the aqueous, radiation-curable coating composition comprises at least one radiation-curable polyurethane, at least one reactive diluent, and water. In these preferred embodiments, the aqueous, radiation-curable coating composition used in the method of the present invention preferably comprises polyurethane (AA) in a dispersed form, i.e., the composition preferably comprises dispersed particles of polyurethane (AA). Optionally, polyurethane (AA) is radiation-curable.

[0061] Water-dispersible polyurethane (AA)

[0062] The ureido (-NH-CO-NH-) concentration of polyurethane (AA) is preferably at most 2.6 meq per gram of polyurethane (AA). Polyurethane (A) preferably has a ureido content of at most 1.3 meq per gram of (AA), and preferably at least 0.05 meq per gram of (AA), most preferably at least 0.2 meq / g per gram of (AA).

[0063] If polyurethane (AA) is free-radically polymerizable (radiation-curable), the concentration of curable ethylenically unsaturated bonds (also referred to as C═C bond concentration) of polyurethane (AA) present in the aqueous, radiation-curable coating composition of the present invention is preferably at least 0.25 meq per gram of polyurethane (AA), preferably at least 0.4 meq per gram of polyurethane (AA), more preferably at least 0.6 meq per gram of polyurethane (AA), and preferably at most 4.5 meq per gram of polyurethane (AA), more preferably at most 3.5 meq per gram of polyurethane (AA), and most preferably at most 2.5 meq per gram of polyurethane (AA).

[0064] As used herein, the amount of radiation-curable ethylenically unsaturated bonds in polyurethane (AA) is determined by adding up all the radiation-curable C═C functionalities of the components of the structural units (building blocks) that give rise to polyurethane (AA). As used herein, the expression per gram of polyurethane (AA) is determined by the total weight amount of the components used to prepare the polyurethane, from which the structural units of the polyurethane are derived.

[0065] The radiation-curable vinyl bonds in polyurethane (AA), i.e., C═C bonds, are preferably selected from (meth)acryloyl and allyl, more preferably (meth)acryloyl, and most preferably acryloyl.

[0066] Processes for preparing polyurethanes are known in the art and are described, for example, in the second edition of the "Polyurethane Handbook" by G. Oertel, published by Carl Hanser in 1994. Generally, an isocyanate-terminated polyurethane prepolymer is first formed, which is subsequently preferably chain-extended with a nitrogen-containing compound.

[0067] The polyurethane (AA) is preferably prepared by the reaction of at least the following components:

[0068] (AA1) at least one polyisocyanate,

[0069] (AA2) at least one isocyanate-reactive compound which contains at least one salt group capable of rendering the polyurethane (AA) dispersible in water and / or a functional group which can be converted into a salt group capable of rendering the polyurethane (A) dispersible in water,

[0070] (AA3) optionally at least one isocyanate-reactive compound containing at least one nonionic group which is capable of rendering the polyurethane (AA) dispersible in water,

[0071] (AA4) optionally at least one isocyanate-reactive compound containing a radiation-curable ethylenically unsaturated group,

[0072] (AA5) at least one isocyanate-reactive polyol other than (AA2), (AA3) and (AA4), having an OH value of 25 - 225 mg KOH / g solids,

[0073] (AA6) optionally at least one isocyanate-reactive polyol other than (AA2), (AA3) and (AA4), having an OH value higher than 225 mg KOH / g solids and lower than 1850 mg KOH / g solids, and

[0074] (AA7) water and / or at least one nitrogen-containing chain extender compound.

[0075] The preferred isocyanate-reactive group is a hydroxyl group.

[0076] Component (AA1)

[0077] At least one polyisocyanate is used as component (AA1). The at least one polyisocyanate used according to the invention is preferably selected from diisocyanates having the general formula Y(NCO)2, where Y is a C4-12 divalent aliphatic hydrocarbon radical, i.e. an aliphatic diisocyanate compound, a C6-15 divalent cycloaliphatic hydrocarbon radical, i.e. a cycloaliphatic diisocyanate compound, a C6-C15 divalent aromatic hydrocarbon radical, i.e. an aromatic diisocyanate compound, or a C7-15 divalent araliphatic hydrocarbon radical, i.e. an araliphatic diisocyanate compound.

[0078] Suitable organic diisocyanates (examples of component (AA1) include: ethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate, dicyclohexylmethane diisocyanate (HMDI), such as 4,4'-dicyclohexylmethane diisocyanate (4,4'-H 12 MDI), p-xylylene diisocyanate, p-tetramethylxylylene diisocyanate (p-TMXDI) and its meta-isomer (m-TMXDI), 1,4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hydrogenated 2,4-toluene diisocyanate, hydrogenated 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate, 3(4)-isocyanatomethyl-1-methylcyclohexyl isocyanate (IMCI) and 1,5-naphthalene diisocyanate. Preferred organic difunctional isocyanates are IPDI, HMDI and HDI. Mixtures of organic difunctional isocyanates can also be used.

[0079] Generally, based on the weight of the polyurethane (AA), the amount of component (AA1) is 5 to 55% by weight, preferably 10 to 45% by weight, and most preferably 15 to 40% by weight.

[0080] Component (AA2)

[0081] At least one isocyanate-reactive compound is used as component (AA2), and the isocyanate-reactive compound contains at least one salt group, preferably a salt of an acidic group, which can render the polyurethane (AA) dispersible in water, and / or at least one functional group, preferably an acidic group, which can be converted into a salt group capable of rendering the polyurethane (AA) dispersible in water by reaction with a neutralizing agent.

[0082] Generally, based on the weight of the polyurethane (AA), the amount of component (AA2) is 1 to 15% by weight, preferably 2 to 12% by weight, and even more preferably 3 to 10% by weight.

[0083] According to the present invention, the acidic group is preferably selected from carboxylic acid groups, sulfonic acid groups and / or phosphoric acid groups. Component (AA2) is preferably a compound having two or more hydroxyl groups and / or two or more amino groups. It is preferred to use at least one compound having two or more hydroxyl groups as component (AA2). A combination of at least one carboxylic acid group-containing compound and at least one sulfonic acid group-containing compound can be used. Preferred components (AA2) are dihydroxyalkanoic acids and diamine sulfonates.

[0084] Preferably, at least one carboxylic acid group-containing compound is used as component (AA2).

[0085] If component (AA2) contains at least one functional group that can be converted into a salt group by reaction with a neutralizing agent, the neutralizing agent for deprotonating (neutralizing) the functional group (preferably carboxylic acid group, sulfonic acid group and / or phosphoric acid group, more preferably carboxylic acid group) is preferably selected from ammonia, (tertiary) amines, metal hydroxides and any mixture thereof. Suitable tertiary amines include triethylamine and N,N-dimethylethanolamine. Suitable metal hydroxides include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide. Preferably, at least 30 mol%, more preferably at least 50 mol% and most preferably at least 70 mol% of the total molar amount of the neutralizing agent is an alkali metal hydroxide, preferably selected from lithium hydroxide, sodium hydroxide, potassium hydroxide and any mixture thereof. Preferably, the neutralizing agent for deprotonating (neutralizing) the carboxylic acid group, sulfonic acid group and / or phosphoric acid group is an alkali metal hydroxide. As used herein, the neutralizing agent (if any) should not be regarded as a component that produces the structural unit of polyurethane (AA). Therefore, when calculating the weight of polyurethane (AA), the amount of the neutralizing agent (if any) used in the preparation of polyurethane (AA) is not considered.

[0086] In one embodiment of the present invention, component (AA2) comprises a diamine sulfonate or consists essentially of at least one diamine sulfonate. In this embodiment, usually an isocyanate-terminated polyurethane prepolymer is first formed by the reaction of components (AA1) and (AA5) and optionally (AA4) and optionally (AAR) and optionally (AA6), and then further reacted with a diamine sulfonate (AA2) and water and optionally a nitrogen chain extender compound (AA7). The preferred diamine sulfonate is the sodium salt of 2-[(2-aminoethyl)amino]ethanesulfonic acid.

[0087] In a preferred embodiment of the present invention, component (AA2) comprises a dihydroxyalkanoic acid or consists essentially of at least one dihydroxyalkanoic acid. In this embodiment, usually an isocyanate-terminated polyurethane prepolymer is first formed by the reaction of components (AA1), (AA2) and (AA5) and optionally (AA4) and optionally (AAR) and optionally (AA6), and then chain-extended with water and / or a nitrogen chain extender compound (AA7).

[0088] Preferred dihydroxyalkanoic acids are α,α-dihydroxymethylpropionic acid and / or α,α-dihydroxymethylbutyric acid. More preferably, the dihydroxyalkanoic acid is α,α-dihydroxymethylpropionic acid.

[0089] Generally, the amount of acidic groups present in the polyurethane (AA) is preferably such that the acid value of the polyurethane (AA) is in the range of 5 to 50, more preferably 10 to 40 mg KOH / g of polyurethane (AA) solids, and even more preferably 15 to 30 mg KOH / g of polyurethane (AA) solids.

[0090] Component (AA3)

[0091] Optionally, at least one isocyanate-reactive compound containing at least one nonionic group is used as component (AA3), and the nonionic group can render the polyurethane (AA) dispersible in water.

[0092] By incorporating nonionic functional groups into the polyurethane (AA), the polyurethane (AA) in the dispersion can be further stabilized. Thus, by chemically incorporating nonionic groups into the polyurethane (AA), the polyurethane (AA) can be at least partially nonionically stabilized to provide at least a portion of the required hydrophilicity to enable the polyurethane (AA) to be stably dispersed in an aqueous dispersion medium. Preferred nonionic aqueous dispersion groups are polyethylene oxide groups.

[0093] Preferred component (AA3) is polyethylene glycol having at least 5 ethylene oxide repeat units, preferably at least 10, more preferably at least 15 ethylene oxide repeat units, and preferably at most 120, more preferably at most 80 and even more preferably at most 40 ethylene oxide repeat units. More preferred component (AA3) is polyethylene glycol having 10 to 60, and preferably 15 to 30 ethylene oxide repeat units.

[0094] Non-limiting examples of suitable component (AA3) include Ymer TM N120 and MPEG750 available from Perstorp.

[0095] If component (AA3) is used to prepare the polyurethane (AA), based on the weight of the polyurethane (AA), the amount of component (AA3) is generally 1 to 25% by weight, preferably 1 to 15% by weight, more preferably 1 to 12% by weight, and most preferably 1 to 5% by weight.

[0096] Component (AA4)

[0097] If the polyurethane (AA) is free-radically polymerizable (radiation-curable), at least one isocyanate-reactive compound containing a radiation-curable ethylenically unsaturated group is used as component (AA4). Component (AA4) is preferably selected from compounds containing at least one isocyanate-reactive group and at least one (meth)acryloyl functional group, preferably at least one acryloyl functional group. Examples of suitable components (AA4) are as follows: polyester acrylate, epoxy acrylate, polyether acrylate (such as polypropyleneglycolacrylate and polyethylene glycol acrylate), hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxy-functionalized (poly)caprolactone acrylate, trimethylolpropane di(meth)acrylate and its polyethoxylated and polypropoxylated equivalents, pentaerythritol tri(meth)acrylate and its polyethoxylated and polypropoxylated equivalents, bis-trimethylolpropane tri(meth)acrylate and its polyethoxylated and polypropoxylated equivalents. Such exemplary components (AA4) can be used alone or, alternatively, in combination of two or more. Preferred components (AA4) are selected from hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate and any mixture thereof, and / or trimethylolpropane di(meth)acrylate, pentaerythritol tri(meth)acrylate, bis-trimethylolpropane tri(meth)acrylate and their polyethoxylated and polypropoxylated equivalents, and any mixture thereof. More preferred components (AA4) are selected from hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate and any mixture thereof and / or trimethylolpropane diacrylate, pentaerythritol triacrylate, bis-trimethylolpropane triacrylate and their polyethoxylated and polypropoxylated equivalents, and any mixture thereof.

[0098] If the polyurethane (AA) is free-radically polymerizable (radiation-curable), the amount of component (AA4) is preferably selected such that the concentration of radiation-curable ethylenically unsaturated bonds in the polyurethane (AA) is at least 0.25 meq per gram of polyurethane (AA), preferably at least 0.4 meq per gram of polyurethane (AA), more preferably at least 0.6 meq per gram of polyurethane (AA), and preferably at most 4.5 meq per gram of polyurethane (AA), more preferably at most 3.5 meq per gram of polyurethane (A), and most preferably at most 2.5 meq per gram of polyurethane (AA).

[0099] Component (AA5)

[0100] Use at least one isocyanate-reactive compound having an OH value of 25 to 225 mg KOH / g solid and different from (AA2), (AA3) and (AA4) as component (AA5). Preferred component (AA5) is a polyol, which can be selected from polyols of any chemical type available in polyurethane synthesis. In particular, the polyol can be a polyester polyol, a polyesteramide polyol, a polyether polyol, a polysulfide polyol, a polycarbonate polyol, a polyacetal polyol, a polyvinyl polyol and / or a polysiloxane polyol. Polyester polyols, polyether polyols and polycarbonate polyols are preferred. The OH value of component (AA5) is preferably 45 to 125 mg KOH / g solid.

[0101] Generally, based on the weight of the polyurethane (AA), the amount of component (AA5) is 10 to 80% by weight, preferably 20 to 70% by weight, more preferably 25 to 65% by weight, and even more preferably 25 to 60% by weight.

[0102] Component (AA6)

[0103] Optionally, use at least one isocyanate-reactive compound having an OH value higher than 225 mg KOH / g solid and lower than 1850 mg KOH / g solid and different from (AA2), (AA3) and (AA4) as component (AA6).

[0104] Examples of suitable component (AA6) include neopentyl glycol (NPG), cyclohexanedimethanol (CHDM), butanediol, hexanediol and trimethylolpropane.

[0105] If component (AA6) is used to prepare polyurethane (AA), based on the weight of the polyurethane (AA), the amount of component (AA6) is generally 0.5 to 10% by weight, preferably 0.5 to 8% by weight, more preferably 0.5 to 6% by weight, and most preferably 0.5 to 4% by weight.

[0106] Component (AA7)

[0107] Use water and / or at least one nitrogen-containing chain extender compound as the chain extender component (AA7).

[0108] For water chain extension, two NCO groups will form a urea bond. First, one NCO group reacts with water to form an unstable carbamic acid intermediate, which decomposes into CO2 and an amino group, and then this amino group reacts with another NCO group to form a ureido group. However, compared with chain extension using nitrogen-containing chain extenders, water chain extension is very slow. Therefore, if a nitrogen-containing chain extender compound is used, when calculating the concentration of ureido groups, it should be assumed that the isocyanate groups of the polyurethane prepolymer first react with the nitrogen-containing chain extender, and during and / or after dispersion, the isocyanate groups remaining on the polyurethane prepolymer react with water to form ureido groups.

[0109] Examples of suitable nitrogen-containing chain extenders include amino alcohols, primary or secondary diamines or polyamines (including compounds containing primary and secondary amino groups), hydrazine and substituted hydrazines. Examples of such chain extender compounds available herein include 2-(methylamino)ethylamine, aminoethyl ethanolamine, aminoethyl piperazine, diethylenetriamine and alkylene diamines (such as ethylenediamine and 1,6-hexanediamine), and cyclic amines (such as isophorone diamine). In addition, compounds such as hydrazine, azines (such as acetone azine), substituted hydrazines (such as, for example, dimethylhydrazine, 1,6-hexamethylenedihydrazine), carbohydrazide, dicarboxylic acid hydrazides (such as adipic dihydrazide, oxalic dihydrazide and isophthalic dihydrazide), hydrazides formed by the reaction of lactones with hydrazine, bis-semi-carbazide and bis-acylhydrazide carbonates of glycols may also be useful. Water-soluble nitrogen-containing chain extenders are preferred.

[0110] Preferably, the nitrogen-containing chain extender compound is selected from amino alcohols, primary or secondary diamines, hydrazine, substituted hydrazines, substituted hydrazides and any mixtures thereof.

[0111] When the chain extender is other than water, for example hydrazine, it can be added to the aqueous dispersion of the isocyanate-terminated polyurethane prepolymer, or alternatively, when the isocyanate-terminated polyurethane prepolymer is dispersed in an aqueous medium, the chain extender can also already be present in the aqueous medium. The chain extension can be carried out at a suitable temperature of about 5 °C to 95 °C, or more preferably about 10 °C to 60 °C.

[0112] If used, the total amount of the nitrogen-containing chain extender compound used should be such that the ratio of active hydrogen in the chain extender to the isocyanate groups in the polyurethane prepolymer is preferably in the range of 0.1:1 to 2:1, more preferably 0.6:1 to 1.4:1, and particularly preferably 0.8 to 1.2.

[0113] Preferably, component (AA7) is water, or water and at least one NH x (where x is 1 or 2) having a functionality of 2 or 3, more preferably NH xA nitrogen-containing chain extender with a functionality of 2, wherein for hydrazide, the NH group connected to the carbonyl group is not regarded as a chain-extending group. More preferably, component (AA7) comprises at least one NH x (where x is 1 or 2) having a functionality of 2 or 3, more preferably NH x A nitrogen-containing chain extender with a functionality of 2, wherein for hydrazide, the NH group connected to the carbonyl group is not regarded as a chain-extending group. Even more preferably, component (AA7) is water and at least one NH x (where x is 1 or 2) having a functionality of 2 or 3, more preferably NH x A nitrogen-containing chain extender with a functionality of 2, wherein for hydrazide, the NH group connected to the carbonyl group is not regarded as a chain-extending group. The nitrogen-containing chain extender is preferably selected from diamines and / or dihydrazides.

[0114] In the present invention, the water-dispersible polyurethane (AA) preferably has a weight-average molecular weight M w determined by size exclusion chromatography of at least 15,000 g / mol, more preferably at least 20,000 g / mol, and even more preferably at least 30,000 g / mol.

[0115] In another preferred embodiment of the present invention, the aqueous, radiation-curable coating composition comprises a vinyl polymer system, at least one reactive diluent, and water.

[0116] Vinyl polymer system (AB)

[0117] In this preferred embodiment, the aqueous, radiation-curable coating composition used in the method of the present invention preferably comprises the vinyl polymer system (AB) in a dispersed form, that is, the composition preferably comprises dispersed particles of the vinyl polymer system (AB). The vinyl polymer system (AB) comprises one or more vinyl polymers, and its glass transition temperature T g is preferably less than or equal to 77 °C, and based on the amount of the polymer system (AB), its amount is at least 50% by weight, preferably at least 65% by weight. The glass transition temperature T g is measured by differential scanning calorimetry.

[0118] Therefore, in the vinyl polymer system (AB), the amount of the vinyl polymer with a glass transition temperature T g less than or equal to 77 °C is 50 to 100% by weight, preferably 65 to 100% by weight; and in the vinyl polymer system (AB), the amount of the vinyl polymer with a glass transition temperature T g higher than 77 °C that is allowed to be present is 0 to 50% by weight, preferably 0 to 35% by weight.

[0119] The theoretical acid value of the vinyl polymer system (AB) present in the aqueous, radiation-curable coating composition used in the present invention is preferably from 5 to 105 mg KOH / g (AB).

[0120] The vinyl polymer system (AB) present in the aqueous, radiation-curable coating composition used in the present invention is substantially free of radiation-curable ethylenically unsaturated bonds.

[0121] As used herein, vinyl polymers generally refer to polymers derived from the addition polymerization (usually by free radical methods) of at least one ethylenically unsaturated monomer. Thus, vinyl monomers as used herein refer to ethylenically unsaturated monomers.

[0122] At least one vinyl polymer in the vinyl polymer system (AB) is preferably obtained by solution polymerization, emulsion polymerization or suspension polymerization. If the vinyl polymer is obtained by solution polymerization, the solvent used (preferably a volatile solvent) is removed during and / or after emulsification of the vinyl polymer. Preferably, the method for preparing at least one vinyl polymer is free of organic solvents. Thus, at least one vinyl polymer is preferably obtained by emulsion polymerization or suspension polymerization. Most preferably, at least one vinyl polymer is obtained by emulsion polymerization, preferably at least one vinyl polymer is obtained by an aqueous emulsion polymerization method. Such an aqueous emulsion polymerization method is itself well known in the art and need not be described in great detail. Suffice it to say that such a method involves polymerizing monomers in an aqueous medium and using a free radical yielding initiator for the polymerization and using (usually) appropriate heating (e.g., 30 to 120 °C) and agitation (stirring). The aqueous emulsion polymerization can be effected using one or more conventional emulsifiers (which are surfactants). Anionic, nonionic, anionic-nonionic surfactants, as well as combinations of the three types, can be used; cationic surfactants can also be used.

[0123] If at least one vinyl polymer is prepared via emulsion polymerization, free radical polymerization is carried out using a free radical initiator, appropriate heating, and agitation (stirring) to obtain the vinyl polymer. The polymerization can use conventional free radical initiators [such as hydrogen peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, persulfates (such as ammonium, potassium, and sodium persulfates); redox systems can be used; combinations such as tert-butyl hydroperoxide, isoascorbic acid, and FeEDTA can be used; the amount of the initiator or initiator system is usually 0.05% to 3% based on the total weight of the monomers charged. The molecular weight of the vinyl polymer can be controlled by using well-known chain transfer agents. Preferred chain transfer agents can include thiols and alkyl halides. More preferably, the chain transfer agent is selected from lauryl mercaptan, 3-mercaptopropionic acid, i-octylthioglycolate, mercaptoethanol, carbon tetrabromide, or tribromomethane. Most preferably, the chain transfer agent is a thiol selected from lauryl mercaptan, 3-mercaptopropionic acid, i-octylthioglycolate, and mercaptoethanol.

[0124] The polymerization of vinyl monomers to form a polymer system (AB) can be carried out in different ways. It is conceivable to use a straight emulsion with only one monomer feed; sequential polymerization to obtain a phase-separated particle morphology; and use of an oligomer-polymer emulsion, where preferably one of the polymer phases contains significantly more acid functionality than the other phases.

[0125] The polymer system can have a phase-separated particle morphology obtained by polymerizing at least a first monomer feed and a different second monomer feed. The polymer system (AB) preferably contains at least two vinyl polymers. If the polymer system (AB) contains at least two vinyl polymers, then preferably, the glass transition temperatures (T g ) of the at least two vinyl polymers differ by at least 20 °C and preferably by at most 200 °C. In one embodiment of the present invention, the polymer system (AB) contains at least two vinyl polymers with different acid values, where the acid value of one vinyl polymer is at least 13 mg KOH / g of vinyl polymer, and the acid value of at least one other vinyl polymer is preferably not more than 13 mg KOH / g of vinyl polymer.

[0126] The emulsion polymerization for preparing at least one vinyl polymer can be carried out using an "integrated" batch method (i.e., a method in which all the materials to be used are present in the polymerization medium at the start of polymerization) or a semi-batch process (in which one or more materials to be used (usually at least one monomer) are fed entirely or partially into the polymerization medium during polymerization). Online mixing of two or more of the materials used can also be employed.

[0127] The pH of the final polymer emulsion containing the polymer system (AB) is preferably between 5 and 9, more preferably between 7 and 9. In the case of the emulsion polymerization method, ammonia, organic amines or inorganic bases are preferably used during monomer feeding or at the end of polymerization to increase the pH. Preferred bases are ammonia, dimethylethanolamine and hydroxide salts of lithium, sodium or potassium. The most preferred base is ammonia.

[0128] The weight-average molecular weight M of the vinyl polymer system (AB) w is preferably at least 5,000 g / mol, more preferably at least 10,000 g / mol, even more preferably at least 20,000 g / mol, and even more preferably at least 30,000 g / mol. The upper limit of the weight-average molecular weight is not critical, but is preferably at most 1,000,000 g / mol, more preferably at most 500,000 g / mol, and even more preferably at most 250,000 g / mol. The weight-average molecular weight M w is determined by size exclusion chromatography (SEC).

[0129] The vinyl polymer in the vinyl polymer system (AB) is preferably a (meth)acrylic polymer. As used herein, the term (meth)acrylic polymer refers to a polymer obtained by polymerizing at least one polymer precursor containing acrylate (-HC=CHC(=O)O-) and / or methacrylate (-HC=C(CH3)C(=O)O-) moieties, and the resulting polymer contains

[0130] -(CH2-CHC(=O)O-)- and / or -(CH2-C(CH3)C(=O)O-)- moieties. The (meth)acrylic polymer may contain other moieties, including arylalkylene such as styrene, but in one embodiment of the present invention, the composition is preferably substantially free of arylalkylene.

[0131] The polymer system (AB) preferably comprises

[0132] (AB1) a carboxylic acid functional ethylenically unsaturated monomer, and

[0133] (AB2) an ethylenically unsaturated monomer, different from (A1).

[0134] The monomer (AB1) is preferably selected from itaconic acid, itaconic anhydride, monoalkyl itaconate, monoaryl itaconate, acrylic acid, methacrylic acid, β-carboxyethyl acrylate, and combinations thereof. More preferably, the monomer (AB1) is acrylic acid and / or methacrylic acid, and most preferably, the monomer (A1) is methacrylic acid.

[0135] The monomer (AB2) is preferably selected from acrylates, methacrylates, arylalkylene, itaconates, and any mixtures thereof. Preferably, at least 30 wt%, more preferably at least 40 wt%, more preferably at least 50 wt%, more preferably at least 60 wt%, and even more preferably at least 70 wt% of the total amount of the monomer (AB2) is selected from methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, styrene, and mixtures of two or more of the said monomers. Preferably, at least 30 wt%, more preferably at least 40 wt%, more preferably at least 50 wt%, more preferably at least 60 wt%, and even more preferably at least 70 wt% of the total amount of the monomer (AB2) is selected from methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, and mixtures of two or more of the said monomers.

[0136] In a preferred embodiment of the present invention, the aqueous, radiation-curable coating composition comprises at least one polyurethane-vinyl polymer hybrid, at least one reactive diluent, and water.

[0137] Polyurethane-vinyl polymer hybrid (AC)

[0138] At least one hybrid (AC) of at least one polyurethane and at least one vinyl polymer is obtained by free radical polymerization of one or more vinyl monomers in the presence of at least one polyurethane, preferably in the presence of at least one water-dispersible polyurethane, as described hereinafter.

[0139] After the free radical polymerization of the vinyl monomers, a reactive diluent (B) is added to obtain the vinyl polymer of the polyurethane-vinyl polymer hybrid. The polyurethane is preferably prepared in the presence of at least a portion of one or more vinyl monomers used to prepare the vinyl polymer.

[0140] The vinyl polymer is advantageously formed in situ by polymerizing one or more vinyl monomers in the presence of a preformed aqueous polyurethane dispersion.

[0141] A polyurethane-vinyl polymer hybrid refers to preparing a vinyl polymer by free radical polymerization of vinyl monomers in the presence of a polyurethane, forming an aqueous dispersion of the polyurethane resin, and polymerizing one or more vinyl monomers to form a vinyl polymer such that the vinyl polymer is in-situ incorporated into the aqueous dispersion by polymerizing the vinyl monomers used to form the vinyl polymer in the presence of the polyurethane resin. The vinyl monomers are added before, during, and / or after preparing the polyurethane, and the vinyl monomers are polymerized by adding a free radical initiator in the presence of the polyurethane.

[0142] - The weight ratio of the polyurethane to the vinyl polymer present in the vinyl polymer hybrid (AC) ranges from 25:75 to 95:5, preferably from 30:70 to 90:10, more preferably from 40:60 to 88:12, more preferably from 50:50 to 85:15, more preferably from 65:35 to 80:20.

[0143] The theoretical acid value of the polyurethane-vinyl polymer hybrid (AC) preferably ranges from 3 to 45 mg KOH / g of the hybrid (AC), preferably from 4 to 40 mg KOH / g of the hybrid (A), more preferably from 5 to 35 mg KOH / g of the hybrid (AC), more preferably from 6 to 28 mg KOH / g of the hybrid (AC).

[0144] The polyurethane portion (AC-PU) of the hybrid (AC)

[0145] The ureido (-NH-CO-NH-) concentration of the polyurethane (AC-PU) is preferably at least 0.1 and at most 1.9 milliequivalents per gram of polyurethane. The ureido content of the polyurethane (AC-PU) is preferably at most 0.9 meq per gram of polyurethane and preferably at least 0.2 meq per gram of polyurethane, more preferably at least 0.4 meq per gram of polyurethane.

[0146] The polyurethane (AC-PU) is preferably prepared by reacting at least the following components:

[0147] (AA1) At least one polyisocyanate,

[0148] (AA2) At least one isocyanate-reactive compound containing at least one salt group capable of rendering the polyurethane dispersible in water and / or a functional group that can be converted into a salt group capable of rendering the polyurethane dispersible in water, preferably an acid functional group,

[0149] (AA3) Optionally at least one isocyanate-reactive compound containing at least one nonionic group capable of rendering the polyurethane dispersible in water,

[0150] (AA5) At least one isocyanate-reactive polyol other than (AA2) and (AA3), having an OH value of 25 to 225 mg KOH / g solids,

[0151] (AA6) Optionally, at least one isocyanate-reactive polyol other than (AA2) and (AA3), having an OH value higher than 225 mg KOH / g solids and lower than 1850 mg KOH / g solids, and

[0152] (AA7) Water and / or at least one nitrogen-containing chain extender compound,

[0153] wherein the types and amounts of components (AA1), (AA2), (AA3), (AA5), (AA6) and (AA7) are as described above.

[0154] Preferred isocyanate-reactive groups are hydroxyl groups.

[0155] Vinyl polymer (AC-VP) of the polymer blend

[0156] The vinyl polymer (AC-VP) of the blend is obtained by polymerizing vinyl monomers using a conventional free-radical generating initiator system. Suitable initiators are as described above.

[0157] Preferably at least 80% by weight, more preferably at least 95% by weight and most preferably 100% by weight of the total weight of the vinyl monomers used are α,β-mono-unsaturated vinyl monomers.

[0158] Examples of vinyl monomers include, but are not limited to, 1,3-butadiene, isoprene; trifluoro ethyl (meth)acrylate (TFEMA); dimethylaminoethyl (meth)acrylate (DMAEMA); styrene, α-methylstyrene, (meth)acrylamide and (meth)acrylonitrile; vinyl halides such as vinyl chloride; vinylidene dihalides such as vinylidene dichloride; vinyl ethers; vinyl esters such as vinyl acetate, vinyl propionate, vinyl laurate; vinyl esters of versatic acids such as VeoVa9 and VeoVa10 (VeoVa is a trademark of Resolution); heterocyclic vinyl compounds; alkyl esters of monoethylenically unsaturated dicarboxylic acids such as dibutyl maleate and dibutyl fumarate; dialkyl itaconates, such as dimethyl itaconate, diethyl itaconate, dibutyl itaconate, and especially esters of acrylic acid and methacrylic acid of the formula CH2=CR 4 -COOR 5 where R 4 is H or methyl, and R 5is an optionally substituted alkyl group having 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, or a cycloalkyl group having 3 to 20 carbon atoms, more preferably 3 to 6 carbon atoms. Examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), octyl (meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate, and n-propyl (meth)acrylate. Preferred formula CH2=CR 4 -COOR 5 monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), octyl (meth)acrylate (all isomers), ethylhexyl acrylate (all isomers), and isobornyl (meth)acrylate.

[0159] The vinyl monomer may include a vinyl monomer having a functional group (such as a crosslinking group and / or a water-dispersible group). Such a functional group can be directly introduced into the vinyl polymer by radical polymerization, or alternatively, a functional group can be introduced by the reaction of a reactive vinyl monomer, which then reacts with a reactive compound having the desired functional group. Examples of suitable vinyl monomers providing a crosslinking group include acrylic acid and methacrylic acid monomers having at least one free carboxyl group or hydroxyl group, epoxy group, acetoacetoxy group, or carbonyl group, such as acrylic acid, methacrylic acid, glycidyl acrylate, glycidyl methacrylate, acetoacetoxyethyl methacrylate, allyl methacrylate, tetraethylene glycol dimethacrylate, divinylbenzene, and diacetone acrylamide.

[0160] Vinyl monomers providing an ionic or potentially ionic water-dispersible group that can be used as additional vinyl monomers include, but are not limited to, (meth)acrylic acid, itaconic acid, maleic acid, citraconic acid, and styrenesulfonic acid.

[0161] Vinyl monomers providing a nonionic water-dispersible group include alkoxypolyethylene glycol (meth)acrylate, the number-average molecular weight of which is preferably 140 to 3000, and such can also be used. Commercially available examples of such monomers include ω-methoxypolyethylene glycol (meth)acrylate. The calculated glass transition temperature T of at least one vinyl polymer in the admixture (AC) g is preferably -55 °C to 115 °C, more preferably 45 °C to 115 °C.

[0162] As used herein, the glass transition temperature is determined by calculation using the Fox equation. Therefore, the T of a copolymer having "n" comonomers g(in Kelvin) given by the weight fraction W of each comonomer type and the T g ’s (in Kelvin) of the homopolymers derived from each comonomer (e.g., as listed in J. Brandrup, E. H. Immergut, Polymer Handbook, 4th Edition, p. VI 193), and calculated according to the following formula:

[0163]

[0164] Calculated T g (in Kelvin) can be easily converted to °C. In the total amount of vinyl monomers used to prepare the vinyl polymer, preferably at least 30% by weight, more preferably at least 70% by weight, are selected from methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, styrene, and mixtures of two or more of said monomers.

[0165] The vinyl polymer (AC-VP) of the admixture preferably has a theoretical acid value of 0 to 10 mg KOH / g of vinyl polymer solid, more preferably less than 3 mg KOH / g of vinyl polymer solid.

[0166] The polyurethane-vinyl polymer admixture (AC) present in the aqueous, radiation-curable coating composition of the present invention is substantially free of radiation-curable ethylenically unsaturated bonds.

[0167] In another preferred embodiment of the present invention, the aqueous, radiation-curable coating composition comprises at least one polyester, at least one reactive diluent, and water. In this preferred embodiment, the aqueous, radiation-curable coating composition used in the method of the present invention preferably comprises the polyester (AD) in dispersed form, i.e., the composition preferably comprises dispersed particles of the polyester (AD).

[0168] Water-dispersible polyester (AD)

[0169] The glass transition temperature T g (measured by differential scanning calorimetry) of the at least one water-dispersible polyester (AD) is preferably less than or equal to 70 °C. The glass transition temperature T g of the at least one water-dispersible polyester (AD) is preferably at least -50 °C, more preferably at least -10 °C.

[0170] Generally, the acid value AV of the at least one water-dispersible polyester (AD) is preferably less than or equal to 100 mg KOH / g of polyester (AD), preferably at most 70 mg KOH / g of polyester (AD). The acid value of the at least one water-dispersible polyester (AD) is preferably at least 0.2 mg KOH / g of polyester (AD), more preferably at least 0.5 mg KOH / g of polyester (AD).

[0171] The OH value range of the at least one aqueous dispersible polyester (AD) can be from 0 to 250 mg KOH / g polyester (AD). Preferably, the OH value of the at least one aqueous dispersible polyester (AD) is preferably at most 150 mg KOH / g polyester (AD), and preferably at least 1 mg KOH / g polyester (AD).

[0172] The at least one aqueous dispersible polyester (AD) preferably has a number average molecular weight Mn of at least 1000 g / mol, preferably at least 2500 g / mol, and preferably at most 15000 g / mol, more preferably at most 11000 g / mol n (measured by size exclusion chromatography (SEC)).

[0173] Preferably, the at least one aqueous dispersible polyester (AD) is amorphous. Amorphous herein means that the melting enthalpy (ΔHm) of the polyester (measured by differential scanning calorimetry as further described herein) is less than 40 J / g. More preferably, the at least one aqueous dispersible polyester (AD) is completely amorphous, i.e., does not have a melting temperature (Tm) measured by differential scanning calorimetry.

[0174] In this specification, the term "polycondensation" refers to condensation polymerization, as this type of polymerization is known to any ordinary skilled person in the art, and refers to one or both of the following: a) poly-esterification, and b) polytransesterification, as each of a) and b) is known to any ordinary skilled person in the art.

[0175] The aqueous dispersible polyester (AD) is obtained by the following method

[0176] (1) preparing a polyester, and

[0177] (2) dispersing the polyester in water.

[0178] The polyester can be prepared by polycondensation and / or bulk synthesis including a single or multiple reaction steps in the presence of a solvent (such as xylene as an azeotrope). Preferably, the polyester according to the present invention is prepared by a bulk synthesis polycondensation reaction.

[0179] The polycondensation is generally carried out under a nitrogen atmosphere at a temperature usually in the range of 160 to 260 °C. Catalysts such as dibutyltin oxide, butyl chlorotin dihydroxide, butyltin acid or tetrabutyl titanate and antioxidants such as phosphorous acid, tris(nonylphenyl) phosphite or triphenyl phosphite can be added as additives. During the reaction, water is removed and preferably removed by distillation. The desired degree of esterification can be achieved by azeotropic distillation and / or vacuum distillation.

[0180] The resulting polyester is then dispersed to obtain a water-dispersible polyester (AD).

[0181] Generally, polyesters need to contain ionic groups to be dispersed in an aqueous medium.

[0182] One way to obtain ionic groups is to neutralize the carboxyl groups of the polyester with a neutralizing agent. Suitable neutralizing agents include, but are not limited to, ammonia, dimethylethanolamine, triethylamine, aminomethylpropanol, tributylamine, sodium hydroxide, and potassium hydroxide. The neutralizing agent can be added directly to the polyester followed by the addition of water, or first dissolved in the aqueous medium and then added to the polyester. The polyester can also be added to the neutralizing agent aqueous medium.

[0183] Another way is to incorporate carboxylic acids containing ionic functional groups (such as sodium 5-(sulfo)isophthalate and lithium 5-(sulfo)isophthalate) into the main chain of the polyester. In this case, no neutralizing agent needs to be added, and a polyester dispersion can be obtained by simply adding water.

[0184] Sometimes isopropanol, 2-butanol, 2-butoxyethanol, acetone, or methyl ethyl ketone or 2-(2-butoxyethoxy)ethanol can be used as a co-solvent to simplify the dispersion process.

[0185] An aqueous (waterborne) dispersion or emulsion of the polyester can also be obtained by using at least one external surfactant in an aqueous medium. The method and the surfactants that can be used are known to those skilled in the art. A surfactant mixture is preferably used, and a combination of anionic and nonionic surfactant systems is more preferred.

[0186] Examples of surfactant systems that can be used to emulsify polyesters are described in US2003-144397 (1CI) and 'Emulsification and Polymerization of Alkyd Resins' by Jan W. Gooch, Springer, first edition, December 1, 2001 (ISBN 0306467178), and the contents of both are incorporated herein by reference.

[0187] Another way to obtain an aqueous dispersion of polyester is to use a solvent-assisted method, in which the polyester is first dissolved in a low-boiling solvent (such as acetone or methyl ethyl ketone). After the polyester is dissolved, the required amount of water can be added to the solution, and then the organic solvent is removed by vacuum distillation.

[0188] The temperature during the dispersion process can range from 20 to 90 °C, preferably from 40 to 60 °C.

[0189] The solid content of the dispersion can generally range from 10% to 60%, preferably from 20% to 50%, more preferably from 25% to 50%.

[0190] The polyesters suitable for use in the radiation-curable coating compositions of the present invention include polyesters that do not contain radiation-curable ethylenically unsaturated groups and polyesters that contain radiation-curable ethylenically unsaturated groups. If the polyester contains radiation-curable ethylenically unsaturated groups, the polyester preferably has an average weight per radiation-curable ethylenic unsaturation (WPU) of from 500 to 5000 g / mol.

[0191] Preferably, the polyester is prepared by polycondensation of at least the following components:

[0192] (AD1) at least one difunctional acid, and

[0193] (AD2) at least one difunctional alcohol, and

[0194] (AD3) optionally at least one difunctional acid other than (A2) that contains at least one salt group capable of dispersing the polyester in water,

[0195] (AD4) optionally at least one monofunctional acid,

[0196] (AD5) optionally at least one trifunctional or higher-functional acid, and

[0197] (AD6) optionally at least one trifunctional or higher-functional alcohol,

[0198] wherein the total amount of components (AD1) and (AD2) used to prepare the polyester (AD) is from 20 to 100% by weight, more preferably from 30 to 100% by weight, and the total amount of components (AD3), (AD4), (AD5) and (AD6) used to prepare the polyester (AD) is from 0 to 80% by weight, more preferably from 0 to 70% by weight.

[0199] Examples of the difunctional carboxylic acids (AD1) used to prepare 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, 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.

[0200] Examples of difunctional alcohols (AD2) for preparing polyesters 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.

[0201] Examples of difunctional carboxylic acids (AD3) containing at least one salt group capable of rendering the polyester dispersible in water include 5 - (sulfonic acid group) isophthalate salts, such as metal (Na + , Li + , K + , Mg ++ , Ca ++ , Cu ++ , Fe ++ or Fe +++ ) salts and / or ammonium salts. Preferred 5 - (sulfonic acid group) isophthalate salts are sodium 5 - (sulfonic acid group) isophthalate and / or lithium 5 - (sulfonic acid group) isophthalate.

[0202] Examples of trifunctional or higher - functional carboxylic acids (AD5) for preparing polyesters include, but are not limited to, trimellitic acid (anhydride), citric acid (anhydride), pyromellitic acid (anhydride), and mixtures thereof.

[0203] Examples of trifunctional or polyfunctional alcohols (AD6) for preparing polyesters include, but are not limited to, trimethylolpropane, trimethylolethane, glycerol, pentaerythritol, bis(trimethylolpropane) ether, xylitol, dipentaerythritol, sorbitol, and mixtures thereof.

[0204] More preferably, the polyester is prepared by polycondensation of at least the following components:

[0205] (AD1) at least one difunctional acid, including terephthalic acid, isophthalic acid, phthalic acid, adipic acid, and any mixture thereof, and

[0206] (AD2)At least one bifunctional alcohol, including diethylene glycol, ethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, and any mixture thereof, and

[0207] (AD3)Optionally, at least one bifunctional acid other than (A2) that contains at least one salt group capable of rendering the polyester dispersible in water and includes one or more 5-(sulfonic acid group) isophthalates,

[0208] (AD4)Optionally, at least one monofunctional acid, including benzoic acid, soybean oil fatty acid, tall oil fatty acid, soybean oil, tall oil, and any mixture thereof,

[0209] (A5)Optionally, at least one trifunctional or higher-functional acid, including trimellitic anhydride, citric acid, and any mixture thereof, and

[0210] (A6)Optionally, at least one trifunctional or higher-functional alcohol, including glycerol, trimethylolpropane, pentaerythritol, and any mixture thereof,

[0211] wherein the total amount of components (AD1) and (AD2) used to prepare polyester (A) is 20 to 100% by weight, more preferably 30 to 100% by weight, and the total amount of components (AD3), (AD4), (AD5), and (AD6) used to prepare polyester (AD) is 0 to 80% by weight, more preferably 0 to 70% by weight.

[0212] Even more preferably, the polyester is prepared by polycondensation of at least the following components:

[0213] (AD1)At least one bifunctional acid, including terephthalic acid, isophthalic acid, phthalic acid, adipic acid, and any mixture thereof, and

[0214] (AD2)At least one bifunctional alcohol, including diethylene glycol, ethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, and any mixture thereof,

[0215] (AD3)At least one bifunctional acid other than (A2) that contains at least one salt group capable of rendering the polyester dispersible in water, preferably one or more 5-(sulfonic acid group) isophthalates, and

[0216] (AD4)Optionally, at least one monofunctional acid, including benzoic acid, soybean oil fatty acid, tall oil fatty acid, soybean oil, tall oil, and any mixture thereof,

[0217] (AD5) Optionally at least one trifunctional or higher-functional acid, including trimellitic anhydride, citric acid and any mixture thereof, and

[0218] (AD6) Optionally at least one trifunctional or higher-functional alcohol, including glycerol, trimethylolpropane, pentaerythritol and any mixture thereof,

[0219] wherein the total amount of components (AD1) and (AD2) for preparing the polyester (AD) is 30 to 99% by weight, the amount of component (AD3) is 1 to 10% by weight, and the total amount of components (AD4), (AD5) and (AD6) for preparing the polyester (A) is 0 to 69% by weight.

[0220] Reactive diluent (B)

[0221] As used herein, "diluent" refers to a substance that reduces the viscosity of the larger composition into which it is incorporated or with which it is associated.

[0222] As used herein, "reactive" refers to the ability to form a chemical reaction, preferably a polymerization reaction, with another molecule. Thus, a reactive compound will be referred to as having at least one reactive group or functional group. Preferably, such reactive group or functional group is a polymerizable group, more preferably such reactive group or functional group is an ethylenically unsaturated polymerizable group, and even more preferably is an acrylate group.

[0223] As used herein, the acrylate functionality of a compound is the number of acrylate functional groups per molecule of the compound.

[0224] One or more reactive diluents (also referred to as radiation-curable diluents) present in the aqueous, radiation-curable coating composition preferably have 1 to 6 acrylate groups, i.e., have an acrylate functionality of 1 to 6. More preferably, the one or more acrylate-functional diluents have an acrylate functionality of 1 to 5, even more preferably 1 to 4, and even more preferably 2 to 4. Preferably, at least one of the acrylate-functional diluents present in the aqueous, radiation-curable coating composition has an acrylate functionality of 2 or 3. In a preferred embodiment, the aqueous, radiation-curable coating composition comprises at least two reactive diluent monomers having different functionalities. The average functionality of the at least two reactive diluent monomers having different functionalities is preferably at least 1.1, more preferably at least 1.2, and preferably at most 4, more preferably at most 3. As used herein, the at least two reactive diluent monomers having different functionalities where w k is having a molar mass M k and having a functionality f kThe amount of acrylate-functional diluent, in grams, present in the aqueous, radiation-curable coating composition.

[0225] Preferably, the aqueous, radiation-curable coating composition used in the process of the present invention contains a monofunctional diluent in an amount of less than 50% by weight, more preferably less than 30% by weight, more preferably less than 10% by weight, and more preferably less than 5% by weight, and particularly preferably less than 3% by weight, relative to the weight of the entire aqueous, radiation-curable coating composition.

[0226] The one or more reactive diluents preferably have a molar mass higher than 125 g / mol, more preferably higher than 150 g / mol, more preferably higher than 175 g / mol, even more preferably higher than 200 g / mol and preferably lower than 800 g / mol, more preferably lower than 650 g / mol, more preferably lower than 700 g / mol, even more preferably lower than 650 g / mol. The molar mass is the calculated molar mass obtained by adding up the atomic masses of all the atoms present in the chemical structure of the compound.

[0227] Preferably, the one or more reactive diluents are aliphatic reactive diluents, i.e., those without aromatic groups. Preferred examples of aliphatic reactive diluents are lauryl acrylate, isobornyl acrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, isodecyl acrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate (DPGDA), triethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane diacrylate, trimethylolpropane triacrylate (TMPTA), di(trimethylolpropane) triacrylate (di-TMP3A), and pentaerythritol tetraacrylate (PET4A), di(trimethylolpropane) tetraacrylate (di-TMPTA), glycidyl propoxylate triacrylate (GPTA), pentaerythritol triacrylate (PET3A).

[0228] In a preferred embodiment of the present invention, at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight, more preferably at least 40% by weight, more preferably at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight, and most preferably 100% by weight of the reactive diluent (B) is selected from: di(trimethylolpropane) tetraacrylate (di-TMPTA), di(trimethylolpropane) triacrylate (di-TMP3A), glycerol triacrylate, pentaerythritol tetraacrylate (PET4A), pentaerythritol triacrylate (PET3A), trimethylolpropane triacrylate (TMPTA), dipropylene glycol diacrylate (DPGDA), and their alkoxylated, preferably propoxylated, forms, and any mixtures thereof.

[0229] Preferably, at least one reactive diluent (B) has an acrylate functionality of 2 or 3. The reactive diluent (B) having an acrylate functionality of 2 is preferably selected from dipropylene glycol diacrylate (DPGDA), dipropylene glycol diacrylate containing additional alkoxy groups (preferably propoxy groups), and any mixture thereof.

[0230] The reactive diluent (B) having an acrylate functionality of 3 is preferably selected from glycerol propoxylate triacrylate (GPTA), trimethylolpropane triacrylate (TMPTA), di(trimethylolpropane) triacrylate (di-TMP3A), pentaerythritol triacrylate (PET3A), and pentaerythritol triacrylate, including their alkoxylated forms, and any mixture thereof. The reactive diluent (B) having an acrylate functionality of 2 or 3 preferably contains alkoxy groups, preferably propoxy groups (-C3H6O-).

[0231] Preferably, the composition further comprises at least one reactive diluent (B) having an acrylate functionality of 4 or 5, as this can advantageously lead to further improvement in chemical resistance. The reactive diluent (B) having an acrylate functionality of 4 is preferably selected from di(trimethylolpropane) tetraacrylate (di-TMPA), pentaerythritol tetraacrylate (PET4A), pentaerythritol tetraacrylate containing alkoxy groups (preferably propoxy groups); and any mixture thereof.

[0232] The reactive diluent (B) having an acrylate functionality of 5 is preferably dipentaerythritol pentaacrylate (DPPA).

[0233] In an even more preferred embodiment of the present invention, at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight, more preferably at least 40% by weight, most preferably at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight, and most preferably 100% by weight of the reactive diluent (B) is a mixture of:

[0234] (1) di(trimethylolpropane) tetraacrylate (di-TMPTA) and / or pentaerythritol tetraacrylate (PET4A) and / or pentaerythritol tetraacrylate containing alkoxy groups, and

[0235] (2) glycerol propoxylate triacrylate (GPTA) and / or glycerol propoxylate triacrylate containing additional alkoxy groups (preferably propoxy groups) and / or dipropylene glycol diacrylate (DPGDA) and / or dipropylene glycol diacrylate containing additional alkoxy groups (preferably propoxy groups).

[0236] The amounts of one or more polymers and one or more reactive diluents in the aqueous, radiation-curable coating composition can vary within a wide range because water and optionally organic solvents can be used to adjust the viscosity and the layer thickness of the applied coating. Preferably, based on the total amount of one or more polymers and one or more reactive diluents, the amount of one or more polymers is 35 to 80% by weight, and the amount of one or more reactive diluents is 20 to 65% by weight. More preferably, the amount of one or more polymers is 40 to 80% by weight, and the amount of one or more reactive diluents is 20 to 60% by weight.

[0237] Based on the total weight of the aqueous, radiation-curable coating composition, the total amount of one or more polymers and one or more reactive diluents is preferably 10 to 60% by weight, more preferably 15 to 50% by weight, more preferably 15 to 45% by weight, even more preferably 20 to 40% by weight, and even more preferably 25 to 35% by weight.

[0238] The optional organic solvent is present in an amount of up to 30% by weight, preferably up to 25% by weight, more preferably up to 20% by weight, more preferably up to 15% by weight, more preferably up to 10% by weight, more preferably up to 5% by weight, and more preferably up to 1% by weight, where the amount of the 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 that are inert with respect to the functional groups present in the coating composition. Suitable solvents are, for example, hydrocarbons, alcohols, ketones, and esters, such as co-solvents that also have a coalescent function, such as 1-methyl-2-pyrrolidone, diols, and ethylene glycol ethers, such as alkyl ethers of butanediol, dipropylene glycol methyl ether, acetone, methyl ethyl ketone, and ethylene glycol acetate, or mixtures thereof. Most preferably, the aqueous, radiation-curable coating composition is substantially free of organic solvents, i.e., organic solvents are preferably not deliberately added (i.e., small amounts of organic solvents may be present in the additives used to prepare the composition) to the aqueous, radiation-curable coating composition.

[0239] Relative to the total amount of (A), (B), and (C), the viscosity of the dispersion consisting of (A), (B), and (C) and containing 10 to 60% by weight of (A) and (B) is preferably 10 to 1000 mPa·s or 10 to 800 mPa·s or 10 to 500 mPa·s.

[0240] The z-average particle size of the dispersion consisting of (A), (B), and (C) is preferably 20 - 1000 nm, more preferably 25 - 500 nm, even more preferably 25 - 250 nm, and most preferably 30 - 200 nm.

[0241] The aqueous, radiation-curable coating composition used in the present invention preferably comprises a photoinitiating system, which comprises (i) at least one compound comprising at least one photo-redox active group (also referred to as a photo-redox active compound) and (ii) at least one compound comprising at least one redox active group (also referred to as a redox active compound). In one embodiment of the present invention, the photo-redox active group and the redox active group are present in the same molecule. In another and preferred embodiment, the photo-redox active group and the redox active group are present in separate molecules. In another preferred embodiment, a part of the photo-redox active group and a part of the redox active group are present in the same molecule, and the remaining part of the photo-redox active group and the remaining part of the redox active group are present in separate molecules.

[0242] A photo-redox active compound is a compound that generates an excited state after absorbing light in the wavelength range of 231 to 280 nm, and when in the excited state, it is capable of oxidizing or reducing a redox active compound.

[0243] A redox active compound is a compound that can be oxidized or reduced by the excited state of a photo-redox active compound.

[0244] Without wishing to be bound by any theory, the inventors hypothesize that upon irradiation with light in the wavelength region of 231 to 280 nm, a π-π* transition can occur in the photo-redox active compound. This short-lived excited state can now undergo an oxidation-reduction reaction with the redox active compound (which reaction can be described by the Rehm-Weller equation) to generate one or more initiating radicals determined by the photo-redox active compound and the redox active compound. Due to the low penetration depth of light in the wavelength region of 231 to 280 nm, these radicals will form only at the surface, resulting in a partially cured thin skin, and subsequently monomers diffuse into the thin skin, generating microfolds, resulting in a reduced gloss. For the final curing step (4) or an optional pre-curing step (2a), where irradiation is carried out with light having significant emission at wavelengths > 280 nm, it is speculated that an n-π* transition may now occur. These longer-lived excited states may generate initiating radicals via α-cleavage reactions, hydrogen abstraction reactions, and via oxidation-reduction reactions. Due to the higher penetration depth of the light used, this may result in the formation of radicals throughout the depth of the coating, leading to at least partial curing (pre-curing) or complete curing of the coating. In the case of curing via electron beam, initiating radicals are generated by the interaction of accelerated electrons with the material throughout the depth of the coating.

[0245] The one or more photo-redox active compounds preferably have peak absorbance in the wavelength range of 231 to 280 nm, more preferably in the wavelength range of 241 to 280 nm, even more preferably in the wavelength range of 241 to 270 nm, even more preferably in the wavelength range of 244 to 265 nm, or preferably in the wavelength range of 251 to 280 nm, more preferably in the wavelength range of 251 to 260 nm. Examples of suitable photo-redox active compounds are salts such as, for example, iodine and sulfonium salts; and / or organometallic compounds such as metallocene compounds, for example titanocene compounds; and / or compounds containing at least one aryl ketone moiety, such as aromatic ketones and / or aromatic α-hydroxy ketones; and / or keto esters. Preferred photo-redox active compounds are compounds containing at least one (preferably one or two) aryl ketone moieties having the following structural formula (1), wherein the aromatic ring may optionally be substituted by one or more C1-C9 hydrocarbon groups (preferably C1-C9 alkyl groups), one or more halogens, one or more ether groups and / or one or more ester groups.

[0246]

[0247] In embodiments of the present invention in which at least a portion of the photo-redox active group and at least a portion of the redox active group are present in the same molecule, the aryl ketone moiety is, for example, substituted by a thioether or a dialkylamino group (such as (H3C)2-N-).

[0248] More preferred photo-redox active compounds are aromatic ketones and aromatic α-hydroxy ketones, because these compounds having strong absorption at the π-π* transition contribute to obtaining a very thin skin layer that is prone to forming microfolds, providing a very low gloss level. Examples of (substituted) aromatic ketones are benzophenone, methyl 2-benzoylbenzoate (CAS No 606-28-0), 4-methylbenzophenone (CAS No 134-84-9). Examples of aromatic α-hydroxy ketones are Omnirad 1173 (CAS No. 7473-98-5) and Omnirad 127 (CAS No 474510-57-1).

[0249] Suitable redox-active compounds are preferably selected from aliphatic amines, aromatic amines, thioethers, thiols and any mixtures thereof. For reasons of stability, the amines are preferably tertiary amines, otherwise they can undergo a Michael addition reaction with the radiation-curable groups present in the radiation-curable coating composition, thereby forming tertiary amines. More preferably, the one or more redox-active compounds are aliphatic tertiary amines. Preferably, the redox-active compound is acrylate-functional, i.e., contains one, preferably two or more acrylate groups. Without wishing to be bound by any theory, the inventors speculate that when the acrylate groups of the acrylate-functional redox-active compound in the skin layer of the coating react, diffusion of the compound from the underlying layer occurs, thereby increasing the active concentration of the redox-active compound in the skin. Examples of suitable acrylate-functional amines are Agisyn TM 002 (acrylate functionality 1), Agisyn TM 008 (acrylate functionality 2), both of which can also act as reactive diluents, Agisyn TM 701 and Agisyn TM 703 (acrylate functionality 4), both of which can also act as acrylate-functional oligomers and are available from Covestro AG. Examples of suitable acrylate-functional thioethers are BDT-1006, BDT-1015, BDT-4330 and XDT-1018, available from Bomar. The acrylate functionality of the redox-active compound is considered beneficial to the surface properties of the final cured coating, such as stain resistance and abrasion resistance. The most preferred redox-active compounds are aliphatic tertiary amines having at least one acrylate functional group, preferably two or more acrylate functional groups.

[0250] When UV irradiation is applied in the final curing step (4), the photoinitiating system optionally further comprises another photoactive compound beside the photo-redox-active compound. A photoactive compound is a compound that is capable of generating free radicals when irradiated with light having a wavelength of essentially >280 nm.

[0251] Examples of suitable photoactive compounds, including examples of suitable photoredox active compounds, include but are not limited to bisacylphosphine oxides such as, for example, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (CAS#162881-26-7) or bis(2,4,6-trimethylbenzoyl)-(2,4-bis-pentyloxyphenyl)phosphine oxide; monoacylphosphine oxides such as, for example, 2,4,6-trimethylbenzoyl ethoxyphenylphosphine oxide (CAS#84434-11-7) or 2,4,6-trimethylbenzoyl diphenylphosphine oxide (CAS#127090-72-6); ketals such as 2,2-dimethoxy-1,2-diphenylethan-1-one (CAS#24650-42-8); benzophenones such as benzophenone, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, 2-methylbenzophenone, 2-methoxycarbonylbenzophenone, 4-phenylbenzophenone, 4,4'-bis(dimethylamino)-benzophenone, 4,4'-bis(diethylamino)benzophenone, methyl 2-benzoylbenzoate, 3,3'-dimethyl-4-methoxybenzophenone, 4-(4-methylphenylthio)benzophenone, 2,4,6-trimethyl-4'-phenyl-benzophenone or 3-methyl-4'-phenyl-benzophenone; α-hydroxy ketones such as α-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-hydroxy-2-methyl-1-(4-isopropylphenyl)propan-1-one, 2-hydroxy-2-methyl-1-(4-dodecylphenyl)propan-1-one, 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]propan-1-one; α-amino ketones such as 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-(4-methylbenzyl)-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone or 2-benzyl-2-(dimethylamino)-1-[3,4-dimethoxyphenyl]-1-butanone; ketal compounds such as, for example, 2,2-dimethoxy-1,2-diphenyl-ethanone; and monomeric or dimeric phenylglyoxylates such as methyl phenylglyoxylate, 5,5'-oxo-bis(ethylenedioxy dicarbonylphenyl) or 1,2-(benzoylcarboxy)ethane; oxime esters such as those disclosed in U.S. Patent No. 6,596,445; phenyl glyoxylates such as those disclosed in U.S. Patent No. 6,048,660.

[0252] In the case of final curing by irradiation with light having a wavelength of > 280 nm, preferably, when irradiated with light having a wavelength of > 280 nm, the photoinitiating system is also capable of generating free radicals. Preferably, when irradiated with light having a wavelength of > 280 nm, the photo-redox active compound and the redox active compound are also capable of generating free radicals.

[0253] The photoinitiating system is preferably present in the aqueous, radiation-curable coating composition in an amount of at least 5% by weight, more preferably at least 7.5% by weight and even more preferably at least 10% by weight, and preferably in an amount of at most 45% by weight, more preferably at most 30% by weight and even more preferably at most 20% by weight, where the amounts are given relative to the aqueous, radiation-curable coating composition. Preferably, the one or more photo-redox active compounds and redox active compounds are present in the aqueous, radiation-curable coating composition in such amounts that the ratio of the molar amount of the photo-redox active groups to the molar amount of the redox active groups is from 1:4 to 4:1, more preferably from 1:3 to 3:1, even more preferably from 1:2 to 2:1. In the case of using a photo-redox active compound containing more than one photo-redox active group, the molar amount of the photo-redox active groups is calculated by multiplying the molar amount of the photo-redox active compound present in the aqueous, radiation-curable coating composition by the number of photo-redox active groups present in the photo-redox active compound. Similarly, in the case of using a redox active compound containing more than one redox active group, the molar amount of the redox active groups is calculated by multiplying the molar amount of the redox active compound present in the aqueous, radiation-curable coating composition by the number of redox active groups present in the redox active compound. For example, when pentaerythritol tetrakis(mercaptoacetate) is used as the redox active compound, the molar amount of the redox active groups is calculated by multiplying the molar amount of pentaerythritol tetrakis(mercaptoacetate) present in the aqueous, radiation-curable coating composition by 4 (i.e., the number of mercapto groups present in pentaerythritol tetrakis(mercaptoacetate)).

[0254] In embodiments where the photo - redox active group and the redox active group are present in separate molecules, the one or more photo - redox active compounds are preferably present in the aqueous, radiation - curable coating composition in an amount of at least 1 wt%, more preferably at least 2 wt%, even more preferably at least 3 wt%, even more preferably at least 4 wt%, even more preferably at least 5 wt% and preferably in an amount of at most 15 wt%, more preferably at most 12 wt%, even more preferably at most 10 wt%, even more preferably at most 9 wt%, where the amount is given relative to the radiation - curable coating composition; and / or the one or more redox active compounds are preferably present in the aqueous, radiation - curable coating composition in an amount of at least 1 wt%, more preferably at least 2 wt%, even more preferably at least 3 wt%, even more preferably at least 4 wt%, even more preferably at least 5 wt% and preferably in an amount of at most 30 wt%, more preferably at most 25 wt%, even more preferably at most 20 wt%, even more preferably at most 15 wt%, where the amount is given relative to the aqueous, radiation - curable coating composition. In the case where the redox active compound is acrylate - functional (and can thus also be used as a reactive diluent or a reactive oligomer), the upper limit of the amount of the redox active compound can be very high. For example, both the reactive diluent and the oligomer in the radiation - curable coating composition can be amine - functional and are thus redox - active. In this case, the amount of the redox active compound can be up to 95%. As used herein, a reactive diluent containing a redox active group and an oligomer containing a redox active group are considered redox active compounds herein. Thus, the amount of the reactive diluent containing a redox active group and the amount of the oligomer containing a redox active group are included in the determination of the amount of the redox active compound; the amount of the reactive diluent containing a redox active group is not included in the determination of the amount of the reactive diluent; and the amount of the oligomer containing a redox active group is not included in the determination of the amount of the oligomer. In the case where the redox active compound is acrylate - functional, the amount of the redox active compound in the aqueous, radiation - curable coating composition is also preferably at most 30 wt%, more preferably at most 25 wt%, even more preferably at most 20 wt%, even more preferably at most 15 wt%, even more preferably at most 20 wt%, even more preferably at most 10 wt%.

[0255] The aqueous, radiation-curable coating composition generally further contains additive compounds; that is, a collection of one or more than one individual additive having one or more than one specified structure or type. Suitable additives are, for example, light stabilizers such as UV absorbers and hindered amine light stabilizers (HALS), antioxidants, degassing agents, wetting agents, emulsifiers, slip additives, waxes, polymerization inhibitors, adhesion promoters, flow control agents, film formers, rheology aids such as thickeners, flame retardants, corrosion inhibitors, waxes, drying agents, and biocides. One or more of the foregoing additives can be used in the coating composition used in the method of the present invention in any suitable amount and can be selected individually or in combination of one or more types listed herein. In a preferred embodiment, the additive compound is present in an amount of about 0 wt% to 20 wt%, or 0 wt% to 10 wt%, or 0 wt% to 5 wt%; or 0.01 wt% to 20 wt%, or 0.01 wt% to 10 wt%, or 0.01 wt% to 5 wt%, or 0.1 wt% to 2 wt% based on the total weight of the coating composition. According to another embodiment, the additive compound is present in an amount of 1 wt% to 20 wt%, or 1 wt% to 10 wt%, or 1 wt% to 5 wt% based on the weight of the entire radiation-curable composition. The coating composition can also be colored. The coating composition then contains at least one pigment. Preferably, the coating composition does not contain any pigment. The coating composition can also contain one or more inorganic fillers.

[0256] The coating composition can also contain a matting agent having an additional matting effect. Suitable matting agents are, for example, silica. If included, the amount of the matting agent is generally in the range of 0.1 to 10 wt%, particularly in the range of 0.5 to 5 wt%, based on the total weight of the radiation-curable compounds in the coating composition.

[0257] The present invention further relates to an aqueous, radiation-curable coating composition as described above.

[0258] The present invention further relates to a low-gloss coated substrate obtained by coating a substrate, preferably a plastic, paper or metal substrate or any combination thereof, with the method described above.

[0259] Substrates suitable for the process according to the invention are, for example, inorganic substrates such as fibre cement boards, wood, wood-containing materials, paper (including cardboard), fabrics, leather, metal, thermoplastic polymers, thermosetting materials, ceramics, glass. Suitable thermoplastic polymers are, for example, polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene (ABS), polycarbonate, polypropylene (PP), polyethylene (PE), polyamide (PA) and polystyrene. Suitable thermosetting materials are, for example, linoleum, epoxy resins, melamine, phenolic varnishes, polyesters and urea formaldehyde.

[0260] Optionally pre-treat and / or optionally pre-coat the substrate. For example, a thermoplastic film can be treated by corona discharge or pre-coated with a primer before application. Mineral building materials are also usually primed before application of the coating composition.

[0261] The coatings obtained by the process according to the invention can advantageously be used for floor or wall coverings or automotive interiors or furniture or window frames or facade panels. By the process according to the invention, a low-gloss coating with a dry thickness of at least 1 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm and at most 100 μm, or at most 75 μm, or at most 50 μm can advantageously be obtained.

[0262] The invention is further defined by a group of exemplary embodiments listed below. Unless otherwise stated herein or if technically clearly infeasible to the person skilled in the art, any one of the embodiments, aspects and preferred features or ranges disclosed in this application can be combined in any combination.

[0263] [1] A process for preparing a cured coating having a low-gloss surface from an aqueous, radiation-curable coating composition, wherein the process comprises the following steps:

[0264] (1) applying an aqueous, radiation-curable coating composition to a substrate,

[0265] (2) drying the aqueous, radiation-curable coating composition to provide an at least partially dried coating composition,

[0266] (3) irradiating the at least partially dried coating composition from step (2) with UV light having a wavelength essentially in the wavelength range from 231 to 280 nm to provide a coating with a partially cured surface layer having a reduced gloss,

[0267] then

[0268] (4) completing the curing of the coating from step (3) with actinic radiation, thereby fixing the partially cured surface layer having a reduced gloss and providing a cured coating having a low-gloss surface,

[0269] where steps (3) and (4) are carried out in air; and

[0270] wherein the aqueous, radiation-curable coating composition comprises at least one polymer, at least one reactive diluent, and water.

[0271] [2] The method according to embodiment [1], wherein the irradiation in step (3) is carried out with UV light having a wavelength essentially in the range of 241 to 280 nm, preferably in the range of 241 to 270 nm, more preferably in the range of 244 to 265 nm, or in the range of 251 to 280 nm, preferably in the range of 251 to 260 nm.

[0272] [3] The method according to embodiment [1] or [2], wherein the UV light having a wavelength essentially in the wavelength range of X to Y means that at least 60%, preferably at least 70%, even more preferably at least 80% of the actinic radiation power of the applied radiation source is provided by UV light in the wavelength range of X to Y.

[0273] [4] The method according to any one of the foregoing embodiments, wherein the UV light applied in step (3) has a UV radiation dose in the range of 2 to 200 mJ / cm 2 , preferably having at least 3 mJ / cm 2 , or at least 4 mJ / cm 2 , or at least 5 mJ / cm 2 of radiation dose, and preferably having at most 90 mJ / cm 2 , preferably at most 90 mJ / cm 2 , more preferably at most 80 mJ / cm 2 , or at most 70 mJ / cm 2 , or at most 60 mJ / cm 2 , or at most 50 mJ / cm 2 , or at most 40 mJ / cm 2 of radiation dose.

[0274] [5] The method according to any one of the foregoing embodiments, wherein the skin curing step is carried out with one or more lamp units, wherein the irradiance from each lamp unit in the skin curing step (3) is at least 5 mW / cm 2 , more preferably at least 10 mW / cm 2 , even more preferably at least 15 mW / cm 2 , even more preferably at least 20 mW / cm 2 , even more preferably at least 25 mW / cm 2 , even more preferably at least 30 mW / cm 2; and in the skin curing step (2), the irradiance from each lamp unit is preferably at most 500 mW / cm 2 , more preferably at most 300 mW / cm 2 , even more preferably at most 200 mW / cm 2 .

[0275] [6] The method according to any one of the foregoing embodiments, wherein the UV light applied in step (3) is from 1 lamp, or 2 lamps, or 3 lamps, or 4 lamps, or 5 lamps, or at most 6 lamps, and these lamps can be in one or more lamp units.

[0276] [7] The method according to any one of the foregoing embodiments, wherein the irradiation in step (3) is carried out with a low-pressure mercury vapor lamp, or with a UVC LED lamp having a peak wavelength in the range of 231 to 280 nm, or with an excimer lamp having a peak wavelength in the range of 231 to 280 nm, or with a medium-pressure mercury vapor lamp in combination with an optical band-pass filter having a maximum transmittance in the wavelength range of 241 to 270 nm, preferably in the wavelength range of 251 to 260 nm.

[0277] [8] The method according to any one of the foregoing embodiments, wherein the irradiation in the curing step (4) is carried out with an electron beam or with light having a significant emission at wavelengths above 280 nm, preferably with UV light in which at least 40% of the actinic radiation power of the applied radiation source is provided by UV light having a wavelength above 280 nm.

[0278] [9] The method according to any one of the foregoing embodiments, wherein at most 10%, more preferably at most 5%, even more preferably at most 2%, even more preferably at most 1%, even more preferably 0% of the radiation power of the radiation source applied in step (3) emits light at wavelengths ≤ 230 nm; and / or wherein in the radiation power of the radiation source applied in step (3) that also emits in the wavelength range of 200 to 390 nm, at least 60%, more preferably at least 70%, even more preferably at least 80% is in the wavelength range of 231 to 280 nm, preferably in the range of 241 to 270 nm, more preferably in the range of 244 to 265 nm, or preferably in the range of 251 to 280 nm, more preferably in the range of 251 to 260 nm, and wherein in the radiation power of the radiation source applied in step (3) that also preferably emits in the wavelength range of 231 to 390 nm, at least 70%, more preferably at least 80%, even more preferably at least 90% is in the wavelength range of 231 to 280 nm, more preferably in the range of 241 to 270 nm, even more preferably in the range of 244 to 265 nm, or preferably in the range of 251 to 280 nm, more preferably in the range of 251 to 260 nm.

[0279]

[10] The method according to any one of the foregoing embodiments, wherein the light applied in step (4) has a radiation dose in the range of 150 to 2500 mJ / cm 2 , preferably having a radiation dose of at least 200 mJ / cm 2 , or at least 250 mJ / cm 2 , or at least 300 mJ / cm 2 , and preferably having a radiation dose of at most 2250 mJ / cm 2 , or at most 2000 mJ / cm 2 .

[0280]

[11] The method according to any one of the foregoing embodiments, wherein the irradiation in step (4) is carried out with a broadband UV lamp.

[0281]

[12] The method according to any one of the foregoing embodiments, wherein the method comprises the following steps:

[0282] (1) applying an aqueous, radiation-curable coating composition on a substrate,

[0283] (2) drying the aqueous, radiation-curable coating composition to provide at least a partially dried coating composition,

[0284] (2a) optionally pre-curing the radiation-curable coating composition from step (2) by light irradiation to provide a partially cured coating,

[0285] (3) when present, irradiating the at least partially dried coating composition from step (2) or the partially cured coating from step (2a) with UV light having a wavelength substantially in the range of 231 to 280 nm to provide a coating of a partially cured surface layer with reduced gloss,

[0286] then

[0287] (4) completing the curing of the coating from step (3) with actinic radiation, thereby fixing the partially cured surface layer with reduced gloss and providing a cured coating with a low gloss surface, and

[0288] wherein steps (3) and (4) are carried out in air.

[0289]

[13] The method according to embodiment

[12] , wherein the irradiation in step (2a) is carried out in the presence of light having a significant emission at wavelengths above 280 nm, preferably with light in which at least 40% of the actinic radiation power of the applied radiation source is provided by light having a wavelength above 280 nm, more preferably with light in which at least 40%, more preferably at least 60%, more preferably at least 80%, more preferably 100% of the actinic radiation power of the applied radiation source is provided by light having a wavelength above 320 nm.

[0290]

[14] The method according to embodiment

[12] or

[13] , wherein when present, the light applied in step (2a) has a radiation dose in the range of 1 to 200 mJ / cm 2 , preferably having a radiation dose of at least 2 mJ / cm 2 , or at least 3 mJ / cm 2 , and preferably having a radiation dose of at most 90 mJ / cm 2 , or at most 80 mJ / cm 2 , or at most 70 mJ / cm 2 , or at most 60 mJ / cm 2 , or at most 50 mJ / cm 2 , or at most 40 mJ / cm 2 , or at most 30 mJ / cm 2 , or at most 20 mJ / cm 2 .

[0291]

[15] The method according to any one of embodiments

[12] to

[14] , wherein when present, the irradiation in step (2a) is carried out with an LED lamp having a peak wavelength in the range of 350 to 450 nm.

[0292]

[16] The method according to any one of embodiments

[12] to

[15] , wherein when present, step (2a) is carried out in air.

[0293]

[17] The method according to any one of the foregoing embodiments, wherein after step (3), a micro-folded pattern, a random microscopic pattern having peaks and valleys, is formed at the coating surface, and the average spacing between adjacent peaks and / or valleys is shorter than 100 μm, preferably shorter than 80 μm, more preferably shorter than 60 μm.

[0294]

[18] The method according to any one of the foregoing embodiments, wherein the at least one polymer present in the aqueous, radiation-curable coating composition is selected from polyurethanes, radiation-curable polyurethanes, vinyl polymers, polyesters, polyurethane-vinyl polymer hybrids, and any mixtures thereof.

[0295]

[19] A method according to any of the foregoing embodiments, wherein the aqueous, radiation-curable coating composition is a dispersion comprising:

[0296] (A) particles comprising at least one water-dispersible polymer, preferably selected from polyurethanes, radiation-curable polyurethanes, vinyl polymers, polyesters, polyurethane-vinyl polymer hybrids, and any mixtures thereof, and

[0297] (B) at least one radiation-curable diluent (B) having a molar mass of less than 800 g / mol and an acrylate functionality of 1 to 6, and

[0298] (C) water and an optional organic solvent, wherein the optional organic solvent is present in an amount of up to 30% by weight, based on the total amount of water and the organic solvent,

[0299] wherein, based on the total amount of (A) and (B), the amount of (A) is 30 to 95% by weight and the amount of (B) is 5 to 70% by weight.

[0300]

[20] A method according to embodiment

[19] , wherein the aqueous, radiation-curable coating composition comprises dispersed particles of polyurethane (AA), wherein the polyurethane (AA) is optionally radiation-curable.

[0301]

[21] A method according to embodiment

[20] , wherein the concentration of ureido groups (-NH-CO-NH-) in the polyurethane (AA) is preferably at most 2.6 meq per gram of polyurethane (AA), preferably at most 1.3 meq per gram of (AA), and preferably at least 0.05 meq per gram of (AA), more preferably at least 0.2 meq per gram of (AA); and / or the weight-average molecular weight M w of the polyurethane (AA) determined by size-exclusion chromatography is at least 15,000 g / mol, more preferably at least 20,000 g / mol, and even more preferably at least 30,000 g / mol.

[0302]

[22] A method according to embodiment

[20] or

[21] , wherein the polyurethane (AA) is preferably prepared by the reaction of at least the following components:

[0303] (AA1) at least one polyisocyanate,

[0304] (AA2) at least one isocyanate-reactive compound containing at least one salt group capable of rendering the polyurethane (AA) dispersible in water and / or a functional group that can be converted into a salt group capable of rendering the polyurethane (A) dispersible in water,

[0305] (AA3) optionally at least one isocyanate-reactive compound containing at least one nonionic group, which can render the polyurethane (AA) dispersible in water,

[0306] (AA4) Optionally, at least one isocyanate-reactive compound containing a radiation-curable ethylenically unsaturated group

[0307] (AA5) At least one isocyanate-reactive polyol other than (AA2), (AA3), and (AA4), having an OH value of 25 to 225 mg KOH / g solids

[0308] (AA6) Optionally, at least one isocyanate-reactive polyol other than (AA2), (AA3), and (AA4), having an OH value higher than 225 mg KOH / g solids and lower than 1850 mg KOH / g solids, and

[0309] (AA7) Water and / or at least one nitrogen-containing chain extender compound

[0310] wherein the isocyanate-reactive group is preferably a hydroxyl group.

[0311]

[23] The method according to any one of embodiments

[20] -

[22] , wherein the aqueous, radiation-curable coating composition comprises dispersed particles of a vinyl polymer system (AB), wherein the vinyl polymer system (AB) is substantially free of radiation-curable ethylenically unsaturated bonds, and wherein the vinyl polymer system (AB) preferably comprises one or more vinyl polymers, the glass transition temperature T of the vinyl polymer g is preferably less than or equal to 77 °C, based on the amount of the polymer system (AB), and is at least 50% by weight, preferably at least 65% by weight.

[0312]

[24] The method according to embodiment

[23] , wherein the theoretical acid value of the vinyl polymer system (AB) present in the aqueous, radiation-curable coating composition used in the present invention is preferably 5 to 105 mg KOH / g (AB), and / or the weight-average molecular weight M of the vinyl polymer system (AB) w is preferably at least 5,000 g / mol, more preferably at least 10,000 g / mol, even more preferably at least 20,000 g / mol, even more preferably at least 30,000 g / mol, and preferably at most 1,000,000 g / mol, more preferably at most 500,000 g / mol, even more preferably at most 250,000 g / mol, wherein the weight-average molecular weight M w is determined by size exclusion chromatography (SEC).

[0313]

[25] A method according to any one of embodiments

[19] -

[24] , wherein the aqueous, radiation-curable coating composition comprises at least one admixture (AC) of at least one polyurethane and at least one vinyl polymer, the vinyl polymer being obtained by free radical polymerization of one or more vinyl monomers in the presence of at least one polyurethane, preferably in the presence of at least one water-dispersible polyurethane.

[0314]

[26] A method according to embodiment

[25] , wherein the polyurethane (AC-PU) of the admixture (AC) is prepared by the reaction of at least the following components:

[0315] (AA1) at least one polyisocyanate,

[0316] (AA2) at least one isocyanate-reactive compound containing at least one salt group capable of rendering the polyurethane dispersible in water and / or a functional group convertible to a salt group capable of rendering the polyurethane dispersible in water, preferably acid-functional,

[0317] (AA3) optionally at least one isocyanate-reactive compound containing at least one nonionic group capable of rendering the polyurethane dispersible in water,

[0318] (AA5) at least one isocyanate-reactive polyol other than (AA2) and (AA3), having an OH value of 25 to 225 mg KOH / g solids,

[0319] (AA6) optionally at least one isocyanate-reactive polyol other than (AA2) and (AA3), having an OH value higher than 225 mg KOH / g solids and lower than 1850 mg KOH / g solids, and

[0320] (AA7) water and / or at least one nitrogenous chain extender compound,

[0321] wherein the isocyanate-reactive groups are preferably hydroxyl groups.

[0322]

[27] A method according to any one of embodiments

[19] -

[26] , wherein the aqueous, radiation-curable coating composition comprises polyester (AD) discrete particles, wherein the polyester has a glass transition temperature T g , which is determined by differential scanning calorimetry, and the glass transition temperature T gLess than or equal to 70 °C, and preferably at least -50 °C, more preferably at least -10 °C; and / or the acid value AV of the polyester is less than or equal to 100 mg KOH / g polyester (AD), preferably at most 70 mg KOH / g polyester (AD), and preferably at least 0.2 mg KOH / g polyester (AD), more preferably at least 0.5 mg KOH / g polyester (AD); and / or the polyester (AD) has a number-average molecular weight M n of at least 1000 g / mol, preferably at least 2500 g / mol, and preferably at most 15000 g / mol, more preferably at most 11000 g / mol.

[0323]

[28] The method according to embodiment

[27] , wherein the polyester is prepared by polycondensation of at least the following components:

[0324] (AD1) at least one bifunctional acid, and

[0325] (AD2) at least one bifunctional alcohol, and

[0326] (AD3) optionally at least one bifunctional acid other than (A2), which contains at least one salt group capable of dispersing the polyester in water,

[0327] (AD4) optionally at least one monofunctional acid,

[0328] (AD5) optionally at least one trifunctional or higher-functional acid, and

[0329] (AD6) optionally at least one trifunctional or higher-functional alcohol,

[0330] wherein the total amount of components (AD1) and (AD2) used to prepare the polyester (AD) is 20 to 100% by weight, more preferably 30 to 100% by weight, and the total amount of components (AD3), (AD4), (AD5) and (AD6) used to prepare the polyester (AD) is 0 to 80% by weight, more preferably 0 to 70% by weight.

[0331]

[29] The method according to any of the foregoing embodiments, wherein the at least one reactive diluent has a molar mass higher than 125 g / mol, more preferably higher than 150 g / mol, more preferably higher than 175 g / mol, even more preferably higher than 200 g / mol and preferably lower than 800 g / mol, more preferably lower than 750 g / mol, even more preferably lower than 700 g / mol, even more preferably lower than 650 g / mol.

[0332]

[30] A method according to any of the foregoing embodiments, wherein the at least one reactive diluent is an acrylate-functional diluent having an acrylate functionality of 1 to 6, more preferably 1 to 4, even more preferably 2 to 4.

[0333]

[31] A method according to any of the foregoing embodiments, wherein at least one of the reactive diluents has an acrylate functionality of 2 or 3, wherein the acrylate-functional diluent having an acrylate functionality of 2 is preferably selected from dipropylene glycol diacrylate (DPGDA), dipropylene glycol diacrylate comprising additional alkoxy groups (preferably propoxy groups), and any mixture thereof, and the acrylate-functional diluent having an acrylate functionality of 3 is preferably selected from glycerol propoxylate triacrylate (GPTA), trimethylolpropane triacrylate (TMPTA), di(trimethylolpropane) triacrylate (di-TMP3A), pentaerythritol triacrylate (PET3A), and pentaerythritol tetraacrylate, including their alkoxylated forms, and any mixture thereof; and / or the amount of monofunctional diluent present in the radiation-curable coating composition relative to the weight of the entire aqueous, radiation-curable coating composition is less than 50% by weight, more preferably less than 30% by weight, more preferably less than 10% by weight, more preferably less than 5% by weight, and particularly preferably less than 3% by weight.

[0334]

[32] A method according to any of the foregoing embodiments, wherein the aqueous, radiation-curable coating composition comprises at least two reactive diluent monomers having different acrylate functionalities, wherein the average functionality of the at least two reactive diluent monomers having different functionalities is preferably at least 1.1, more preferably at least 1.2, and preferably at most 4, more preferably at most 3, wherein the at least two reactive diluent monomers having different functionalities where w k is the amount in grams of the acrylate-functional diluent present in the aqueous, radiation-curable coating composition having a molar mass M k and having a functionality f k .

[0335]

[33] A method according to any of the foregoing embodiments, wherein at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight, more preferably at least 40% by weight, more preferably at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight, and most preferably 100% by weight of the reactive diluent (B) is selected from:

[0336] Di-(trimethylolpropane) tetraacrylate (di-TMPTA), di-(trimethylolpropane) triacrylate (di-TMP3A), glycerol triacrylate, pentaerythritol tetraacrylate (PET4A), pentaerythritol triacrylate (PET3A), trimethylolpropane triacrylate (TMPTA), dipropylene glycol diacrylate (DPGDA) and alkoxylated, preferably propoxylated forms thereof, and any mixtures thereof.

[0337]

[34] The method according to any of the foregoing embodiments, wherein at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight, more preferably at least 40% by weight, most preferably at least 50% by weight, more preferably at least 60% by weight, more preferably at least 70% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight and most preferably 100% by weight of the reactive diluent (B) is a mixture of:

[0338] (1) Di-(trimethylolpropane) tetraacrylate (di-TMPTA) and / or pentaerythritol tetraacrylate (PET4A) and / or pentaerythritol tetraacrylate containing alkoxy groups, and

[0339] (2) Glycerol propoxytriacrylate (GPTA) and / or glycerol propoxytriacrylate containing additional alkoxy groups (preferably propoxy groups) and / or dipropylene glycol diacrylate (DPGDA) and / or dipropylene glycol diacrylate containing additional alkoxy groups (preferably propoxy groups).

[0340]

[35] A method according to any of the foregoing embodiments, wherein based on the total weight of the aqueous, radiation-curable coating composition, the total amount of the at least one polymer and the at least one reactive diluent is at least 10% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, even more preferably at least 25% by weight, and preferably at most 60% by weight, more preferably at most 50% by weight, more preferably at most 45% by weight, even more preferably at most 40% by weight, even more preferably at most 35% by weight; and / or based on the total weight of the aqueous, radiation-curable composition, the amount of water is at least 5% by weight, or at least 10% by weight, or at least 15% by weight, or at least 20% by weight, or at least 30% by weight, or at least 35% by weight, or at least 40% by weight, or at least 45% by weight, or at least 50% by weight, or at least 55% by weight, or at least 60% by weight, and preferably at most 85% by weight, more preferably at most 75% by weight, wherein an optional organic solvent is present in an amount of at most 30% by weight, preferably at most 25% by weight, more preferably at most 20% by weight, more preferably at most 15% by weight, more preferably at most 10% by weight, more preferably at most 5% by weight, more preferably at most 1% by weight, wherein the amount of the organic solvent is given based on the total amount of water and the organic solvent present in the aqueous, radiation-curable coating composition.

[0341]

[36] A method according to any of the foregoing embodiments, wherein based on the total amount of the one or more polymers and the one or more reactive diluents, the amount of the one or more polymers is 35 to 80% by weight, and the amount of the one or more reactive diluents is 20 to 65% by weight, more preferably, the amount of the one or more polymers is 40 to 80% by weight, and the amount of the one or more reactive diluents is 20 to 60% by weight.

[0342]

[37] A method according to any of the foregoing embodiments, wherein based on the total weight of the aqueous, radiation-curable coating composition, the total amount of the one or more polymers and the one or more reactive diluents is preferably 10 to 60% by weight, more preferably 15 to 50% by weight, more preferably 15 to 45% by weight, even more preferably 20 to 40% by weight, even more preferably 25 to 35% by weight.

[0343]

[38] A method according to any of the foregoing embodiments, wherein the aqueous, radiation-curable coating composition comprises a photoinitiating system, the photoinitiating system comprising one or more photo-redox active compounds and one or more redox active compounds.

[0344]

[39] The method according to any one of embodiments

[38] , wherein the one or more photo - redox active compounds have a peak absorbance in the wavelength range of 231 to 280 nm, preferably in the wavelength range of 241 to 280 nm, more preferably in the wavelength range of 241 to 270 nm, even more preferably in the wavelength range of 244 to 265 nm, or preferably in the wavelength range of 251 to 280 nm, more preferably in the wavelength range of 251 to 260 nm.

[0345]

[40] The method according to embodiment

[38] , wherein the irradiation in step (3) is carried out with UV light having a wavelength substantially in the range of 244 to 265 nm, and the one or more photo - redox active compounds have a peak absorption in the wavelength range of 244 to 265 nm.

[0346]

[41] The method according to any one of embodiments

[38] to

[40] , wherein the one or more photo - redox active compounds comprise at least one aryl ketone moiety, wherein the aryl of the aryl ketone moiety is optionally substituted.

[0347]

[42] The method according to any one of embodiments

[38] to

[41] , wherein the one or more redox active compounds are selected from tertiary amines, thioethers, thiols, and any mixture thereof; more preferably, the one or more redox active compounds are aliphatic tertiary amines.

[0348]

[43] The method according to any one of embodiments

[38] to

[42] , wherein the one or more redox active compounds comprise one or more acrylate functional groups.

[0349]

[44] The method according to any one of embodiments

[38] to

[43] , wherein the one or more redox active compounds are aliphatic tertiary amines having at least one acrylate functional group, preferably two or more acrylate functional groups.

[0350]

[45] The method according to any one of embodiments

[38] to

[44] , wherein the photo - initiator system is present in the aqueous, radiation - curable coating composition in an amount of at least 5 wt%, more preferably at least 7.5 wt%, and even more preferably at least 10 wt%, and preferably in an amount of at most 45 wt%, more preferably at most 40 wt%, more preferably at most 35 wt%, more preferably at most 30 wt%, even more preferably at most 25 wt%, wherein the amounts are given relative to the radiation - curable coating composition.

[0351]

[46] A method according to any one of embodiments

[38] to

[45] , wherein the one or more photo - redox active compounds are present in the aqueous, radiation - curable coating composition in an amount of at least 1% by weight, more preferably at least 2% by weight, even more preferably at least 3% by weight, even more preferably at least 4% by weight, even more preferably at least 5% by weight and in an amount of at most 15% by weight, more preferably at most 12% by weight, even more preferably at most 10% by weight, even more preferably at most 9% by weight, wherein the amounts are given relative to the aqueous, radiation - curable coating composition.

[0352]

[47] A method according to any one of embodiments

[38] to

[46] , wherein the one or more redox active compounds are present in the aqueous, radiation - curable coating composition in an amount of at least 1% by weight, more preferably at least 2% by weight, even more preferably at least 3% by weight, even more preferably at least 4% by weight, even more preferably at least 5% by weight and in an amount of at most 30% by weight, more preferably at most 25% by weight, even more preferably at most 20% by weight, even more preferably at most 15% by weight, wherein the amounts are given relative to the aqueous, radiation - curable coating composition.

[0353]

[48] A method according to any one of embodiments

[38] to

[47] , wherein the one or more photo - redox active compounds and redox active compounds are present in the aqueous, radiation - curable coating composition in such amounts that the ratio of the molar amount of the photo - redox active groups to the molar amount of the redox active groups is from 1:4 to 4:1, more preferably from 1:3 to 3:1, even more preferably from 1:2 to 2:1.

[0354]

[49] A method according to any one of the foregoing embodiments, wherein the gloss of the cured coating surface measured at a 60° geometric angle is less than or equal to 52 gloss units, preferably in the range of 1 to 50 gloss units, or 4 to 40 gloss units, or 4 to 30 gloss units, or 4 to 20 gloss units, or 4 to 10 gloss units; and / or the gloss of the cured coating surface measured at an 85° geometric angle is less than or equal to 60 gloss units, preferably in the range of 1 to 60 gloss units, or 5 to 40 gloss units, or 5 to 30 gloss units.

[0355]

[50] An aqueous, radiation - curable coating composition as defined in any one of the foregoing embodiments.

[0356]

[51] A coated substrate, wherein the coated substrate is obtained by coating a substrate with the method according to any one of embodiments [1] to

[49] , preferably a plastic, wood or metal substrate or a substrate of any combination of plastic, paper and metal.

[0357]

[54] The coated substrate according to embodiment

[53] , wherein the coated substrate is used as a floor covering or as a wall covering or for automotive interiors or furniture or window frames or facade panels.

[0358] The present invention will now be described with reference to the following examples. All parts, percentages, and ratios are by weight unless otherwise specifically stated.

[0359] Components and abbreviations used:

[0360] IPDI = isophorone diisocyanate, available from Covestro

[0361] DMPA = dimethylolpropionic acid, available from Perstorp Polyols

[0362] PPG2000 = polypropylene glycol, OH-value = 56 mg KOH / g, available from BASF

[0363] TEA = triethylamine, supplied by Arkema

[0364] DPGDA = dipropylene glycol diacrylate, available from Covestro

[0365] BHT = butylated hydroxytoluene, available from Brenntag

[0366] Hydrazine = hydrazine hydrate (16%), available from Arkema

[0367] Bismuth ND = bismuth neodecanoate catalyst, available from Reaxis

[0368] Omnirad 500 = photoinitiator, available from IGM Resins BV

[0369] BYK 346 = surfactant, available from BYK

[0370] Butyl glycol = solvent, available from Aldrich

[0371] Tego Airex 902W = defoamer, available from Evonik

[0372] Borchi Gel = rheology modifier, available from Borchers

[0373] UV - curable waterborne resin 1: Polyurethane resin dispersion (PUD) with reactive diluent (WB1)

[0374] Step 1: Charge the components DMPA (21.6 g), PPG2000 (244.1 g), DPGDA (240.0 g), BHT (0.24 g) and IPDI (94.0 g) into a 1000 cm 3 flask equipped with a thermometer and overhead stirrer. Heat the reaction to 50 °C. Subsequently add 0.12 g of bismuth neodecanoate. After the exotherm is complete, hold the reaction at 90 °C for 120 minutes. The NCO content of the resulting isocyanate-terminated prepolymer is 1.35% (theoretically 1.97%). Cool the prepolymer to 80 °C and add TEA (16.3 g), and mix at 50 - 60 °C for 10 minutes.

[0375] Step 2: The dispersion of the isocyanate-terminated prepolymer obtained in Step 1 is prepared by feeding 503 g of the resulting prepolymer mixture into deionized water (890 g) over 45 minutes. The dispersion temperature is controlled between 25 and 30 °C. After feeding is complete, add hydrazine (14.2 g). Dispersion WB1 is obtained.

[0376] Comparative waterborne resin A (CWBA)

[0377] Repeat Example 1, except that DPGDA is not added in the synthesis of Step 1.

[0378] Step 2: The dispersion of the isocyanate-terminated prepolymer obtained in Step 1 is prepared by feeding 289 g of the resulting prepolymer mixture into deionized water (492.5 g) over 45 minutes. The dispersion temperature is controlled between 25 and 30 °C. After feeding is complete, add hydrazine (16.3 g). Dispersion CWBA is obtained.

[0379] UV - curable waterborne resin 2: Acrylate - functional polyurethane resin dispersion with reactive diluent (WB2)

[0380] Step 1: Charge the components DMPA (14.9 g), PPG2000 (129.8 g), HEA (18.7 g), BHT (0.34 g) and IPDI (85.3 g) into a 1000 cm 3 flask equipped with a thermometer and overhead stirrer. Heat the reaction to 50 °C. Subsequently add 0.025 g of bismuth neodecanoate. After the exotherm is complete, hold the reaction at 90 °C for 120 minutes. The NCO content of the resulting isocyanate-terminated prepolymer is 3.82% (theoretically 4.31%). Cool the prepolymer to 80 °C and add DPGDA (167.4 g) and TEA (11.2 g), and mix at 50 - 60 °C for 10 minutes.

[0381] Step 2: The dispersion of the isocyanate-terminated prepolymer obtained in Step 1 was prepared by feeding 285 g of the resulting prepolymer mixture into deionized water (500 g) over 45 minutes. The dispersion temperature was controlled between 25 and 30 °C. After the feeding was completed, hydrazine (13.58 g) was added. Dispersion WB2 was obtained.

[0382] UV - curable waterborne resin 3: Polyurethane hybrid resin dispersion with reactive diluent (WB3)

[0383] Step 1: DMPA (37.4 g), PPG2000 (423.4 g) and IPDI (163.0 g) were charged into a 2000 cm 3 flask equipped with a thermometer and a overhead stirrer. The reaction was heated to 50 °C. Subsequently, 0.04 g of bismuth neodecanoate was added. After the exotherm was completed, the reaction was held at 90 °C for 120 minutes. The NCO content of the resulting isocyanate-terminated prepolymer was 3.16% (theoretically 3.29%). The prepolymer was cooled to 80 °C and TEA (28.3 g) was added, and mixed at 80 °C for 10 minutes.

[0384] Step 2: The dispersion of the isocyanate-terminated prepolymer obtained in Step 1 was prepared by feeding 500 g of the resulting prepolymer mixture into deionized water (850 g) containing 0.5 g of Tegofoamex 805 over 45 minutes. The dispersion temperature was controlled between 25 and 30 °C. After the feeding was completed, hydrazine (16% aqueous solution of 32.4 g) was added. The resulting dispersion had a solids content of 34.2 wt%.

[0385] Step 3: In a 1000 cm 3 flask, 319.1 g of the dispersion prepared in Step 2 was mixed with 43.7 g of deionized water, 21.4 g of MMA and 6.6 g of BA under a nitrogen atmosphere. After 45 minutes, tBHPO (0.8 g, 10% in water) and FeEDTA (0.08 g, 1% solution in water) were added. Subsequently, iAA acid (1%, 8.4 g) in water neutralized with ammonia was slowly fed into the PU dispersion via a dropping funnel over a 15-minute period. The resulting polyurethane-vinyl polymer hybrid dispersion had a solids content of 34.7 wt%, a pH of 7.8, and a particle size of 58 nm.

[0386] Step 4: 68 g of the dispersion obtained in Step 3 was mixed with 60 g of water and 15.8 g of DPGDA to obtain dispersion WB3.

[0387] UV - curable waterborne resin 4: Polyacrylate resin dispersion with reactive diluent (WB4)

[0388] Step 1: Charge demineralised water (656.8 g) and sodium dodecyl sulfate (19.3 g of a 30 wt% solution in water) into a 2000 cm 3 flask equipped with a thermometer, N2 inlet, and overhead stirrer. Prepare an emulsified monomer feed in a funnel by mixing deionized water (278.1 g), sodium dodecyl sulfate (28.89 g of a 30 wt% solution in water), methyl methacrylate (MMA, 539.2 g), n-butyl acrylate (n-BA, 128.1 g), acrylic acid (AA, 20.6 g), and n-dodecyl mercaptan (n-DM, 13.8 g). In another funnel, charge an initiator solution by dissolving ammonium persulfate (AP, 2.3 g) in demineralized water (68.6 g) and adjusting the pH to 7.0 - 7.5 with 25% ammonia water. Heat the reactor to 65 °C and add 10 wt% of the emulsified monomer feed, and allow the reaction temperature to increase to 75 °C. At 75 °C, add a shot of ammonium persulfate (1.2 g) dissolved in demineralized water (6.0 g), and allow it to continue the exothermic run. After mixing for 10 minutes, the reactor temperature levels off at 85 °C. Next, at a temperature of 83 - 87 °C, add the monomer feed and the initiator feed over a 150-minute period. At the end of the monomer feed, rinse the funnel holding the monomer mixture with demineralized water (7.4 g). Allow the reaction to drift to 80 °C within 15 minutes. Next, add a solution of ammonia water (4.5 g, 25%) in demineralized water (4.5 g), and allow the temperature to drift for 15 minutes. Next, cool the batch to 30 °C, and add Proxel Ultra 10 (3.6 g of a 10 wt% solution) within 10 minutes. Check the pH and adjust to 7.8 - 8.0 with ammonia water (12.5%) if necessary. Finally, filter the batch through a filter cloth to remove any condensates formed during the reaction. The solids content is 39.6%, and the particle size is 74 nm. The theoretical Tg is set at 60 °C, and the measured Tg (DSC) is 65.1 °C. The acid value is 23.4 mg KOH / g solid.

[0389] Step 2: Mix 66.5 g of the dispersion obtained in the previous step with 20 g of water and 17.6 g of DPGDA to obtain Dispersion WB4.

[0390] Formulation preparation

[0391] Add the ingredients listed in Table 1 to a PE tank and mix well using (OrangeLine, ATP Engineering BV).

[0392] Table 1 : Preparation of UV-curable aqueous coating compositions (Dispersions 1-4 and Comparative Dispersion A)

[0393]

[0394] Application and drying of the coating composition (Steps (1) and (2))

[0395] The obtained coating composition was applied onto the white part of a Leneta card (2C Leneta Inc) using a 100 μm wire rod applicator. The coated card was dried in an oven at 50 °C for 10 minutes with an air speed of 1.2 m / s. Subsequently, the obtained dried composition was cured, and the curing conditions are shown in Table 2.

[0396] Examples 1 - 8 (using a low - pressure mercury vapor lamp to cure the coating composition in the skin curing step) and Comparative Experiments CEA - CEC (see Table 2) (See Table 2)

[0397] The obtained dried coating composition was cured on a UVio curing rig equipped with a conveyor belt with multiple lamps.

[0398] using a Heraeus 2 Premium P2035 UV disinfection system (low-pressure mercury vapor lamp, main emission peak at 254 nm (>90%), irradiance measured by UV Power II 32 mW / cm to irradiate the dry radiation-curable coating composition (skin curing step (Step (3))). 2

[0399] Subsequently, the skin-cured coating composition was irradiated using a medium-pressure mercury vapor lamp (Heraeus Noblelight 10 MARK III H bulb, 600 W / in) (Step (4)).

[0400] In Comparative Experiment C (CEC), the skin curing step (Step (3)) was carried out using a medium-pressure mercury vapor lamp Heraeus Noblelight 10 MARK III H bulb, 600 W / in, the power of which had been reduced so that the UV-C dose in the comparative experiment was the same as that in Example 1. A high-gloss coating with a flat coating surface (i.e., without micro-folded structures) was produced using a medium-pressure mercury vapor lamp H bulb that emits less than 50% of its light with wavelengths between 231 and 280 nm.

[0401] Testing the cured coating composition ​

[0402] The glossiness was measured in the drawdown direction according to ISO 2813 and is expressed in glossiness units (GU). The results are shown in Table 2.

[0403] Table 2

[0404]

[0405] These results clearly show that a reduced glossiness can be obtained with various UV-curable aqueous resins using the method according to the invention, while a reduced glossiness is not obtained for non-UV-curable aqueous resins. It further shows that for step (3), most of the light should be UVC.

Claims

1. A method for preparing a cured coating having a low gloss surface from an aqueous, radiation-curable coating composition, wherein the method comprises the following steps: (1) applying an aqueous, radiation-curable coating composition onto a substrate, (2) drying the aqueous, radiation-curable coating composition to provide an at least partially dried coating composition, (3) irradiating the at least partially dried coating composition from step (2) with UV light having a wavelength substantially in the range of 231 to 280 nm to provide a coating having a partially cured surface layer with reduced gloss, wherein the UV light having a wavelength substantially in the range of 231 to 280 means that at least 60% of the actinic radiation power of the radiation source applied in step (3) is provided by UV light having a wavelength in the range of 231 to 280 nm, then (4) completing the curing of the coating from step (3) with actinic radiation, thereby fixing the partially cured surface layer with reduced gloss and providing a cured coating having a low gloss surface, wherein steps (3) and (4) are carried out in air; and wherein the aqueous, radiation-curable coating composition comprises at least one polymer, at least one reactive diluent, and water.

2. The method according to claim 1, wherein the at least one polymer is selected from polyurethanes, radiation-curable polyurethanes, vinyl polymers, polyesters, polyurethane-vinyl polymer hybrids, and any mixtures thereof.

3. The method according to any one of the preceding claims, wherein the aqueous, radiation-curable coating composition is a dispersion comprising: (A) particles comprising at least one water-dispersible polymer, preferably selected from polyurethanes, radiation-curable polyurethanes, vinyl polymers, polyesters, polyurethane-vinyl polymer hybrids, and any mixtures thereof, (B) at least one radiation-curable diluent (B) having a molar mass less than 800 g / mol and an acrylate functionality of 1 to 6, and (C) water and an optional organic solvent, wherein the optional organic solvent is present in an amount of up to 30% by weight based on the total amount of water and the organic solvent, wherein based on the total amount of (A) and (B), the amount of (A) is 30 to 95% by weight, and the amount of (B) is 5 to 70% by weight.

4. The method according to any one of the preceding claims, wherein the at least one reactive diluent has a molar mass higher than 125 g / mol, more preferably higher than 150 g / mol, more preferably higher than 175 g / mol, even more preferably higher than 200 g / mol and preferably lower than 800 g / mol, more preferably lower than 750 g / mol, even more preferably lower than 700 g / mol, even more preferably lower than 650 g / mol.

5. The method according to any one of the preceding claims, wherein the at least one reactive diluent is an acrylate-functional diluent having an acrylate functionality of 1 to 6, more preferably 1 to 4, even more preferably 2 or 3.

6. The method according to any one of the preceding claims, wherein the aqueous, radiation-curable coating composition comprises at least two acrylate-functional diluents having different acrylate functionalities, and wherein the at least two acrylate-functional diluents having different functionalities have an average acrylate functionality of at least 1.1, more preferably at least 1.2, and preferably at most 3.

5.

7. The method according to any one of the preceding claims, wherein based on the total amount of the polymer and the reactive diluent present in the aqueous, radiation-curable composition, the amount of the at least one polymer is 35 to 80% by weight, and the amount of the at least one reactive diluent is 20 to 65% by weight, more preferably, the amount of the at least one polymer is 40 to 80% by weight, and the amount of the at least one reactive diluent is 20 to 60% by weight.

8. The method according to any one of the preceding claims, wherein based on the total weight of the aqueous, radiation-curable coating composition, the total amount of the at least one polymer and the at least one reactive diluent is at least 10% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, even more preferably at least 25% by weight, and preferably at most 60% by weight, more preferably at most 50% by weight, more preferably at most 45% by weight, even more preferably at most 40% by weight, even more preferably at most 35% by weight.

9. The method according to any one of the preceding claims, wherein based on the total weight of the aqueous, radiation-curable composition, the amount of water is at least 5% by weight, or at least 10% by weight, or at least 15% by weight, or at least 20% by weight, or at least 30% by weight, or at least 35% by weight, or at least 40% by weight, or at least 45% by weight, or at least 50% by weight, or at least 55% by weight, or at least 60% by weight, and preferably at most 85% by weight, more preferably at most 75% by weight.

10. The method according to any one of the preceding claims, wherein the at least one reactive diluent is aliphatic.

11. The method according to any one of the preceding claims, wherein the at least one polymer is aliphatic.

12. The method according to any one of the preceding claims, wherein the gloss of the cured coating surface measured at a 60° geometric angle is less than or equal to 52 gloss units, preferably in the range of 1 to 50 gloss units, or 4 to 40 gloss units, or 4 to 30 gloss units, or 4 to 20 gloss units, or 4 to 10 gloss units; and / or the gloss of the cured coating surface measured at an 85° geometric angle is less than or equal to 60 gloss units, preferably in the range of 1 to 60 gloss units, or 5 to 40 gloss units, or 5 to 30 gloss units.

13. The method according to any one of the preceding claims, wherein the aqueous, radiation-curable coating composition comprises a photoinitiator system, and the photoinitiator system comprises at least one absorption peak at a wavelength in the range of 231 to 280 nm.

14. The method according to any one of the preceding claims, wherein UV irradiation is applied in step (4) and the aqueous, radiation-curable coating composition comprises a photoinitiating system which comprises at least one absorption peak at wavelengths in the range from 231 to 280 nm and at least one absorption peak at wavelengths above 280 nm.

15. A coated substrate, wherein the coated substrate is obtained by coating a substrate with the method according to any one of claims 1 to 14, preferably a plastic, wood or metal substrate or a substrate which is any combination of plastic, paper and metal.

16. The coated substrate according to claim 15, wherein the coated substrate is used as a floor covering or as a wall covering or for automotive interiors or furniture or window frames or facade panels.

Images