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 a radiation curable coating composition wherein the method comprises the steps of: (1) applying a radiation curable coating composition on a substrate, (2) irradiating the radiation curable coating composition from step (1) 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 (3) completing the curing of the coating from step (2) with actinic radiation, thereby securing the partially cured surface layer having a reduced gloss and providing a cured coating having a low gloss surface, where steps (2) and (3) are carried out in air; and wherein the radiation curable coating composition comprises one or more acrylate functional oligomers (A) and one or more acrylate functional diluents (B).

Description

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

[0002] "Low-gloss" surfaces confer a much sought-after aesthetic effect on products, especially in the wooden furniture, flooring and wallcovering industries, as they can produce a very natural appearance that helps to highlight more the materiality of the article. Currently, the generation of matte surfaces often involves the use of coating products containing matting agents made of organic and / or inorganic substances, which are able to act on the degree of light reflection by positioning themselves 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 results in the deterioration of the surface properties of the coating, as they do not participate in the crosslinking and polymerization processes and they cause a significant reduction in the tolerance to chemical reagents. In addition, the incorporation of these matting agents in the formulation of coating products significantly affects the rheology, modifying their viscosity to the extent that high concentrations of such matting agents cannot be used without adversely altering the "application" characteristics of the coating product.

[0003] Certain classes of surface coatings are radiation-curable coating compositions that are polymerizable by electron beam or by ultraviolet radiation (UV). Typically, the crosslinking mechanism involves the use of a photochemical source or an ultraviolet radiation lamp (UV). A surface coating cured by UV lamp induction may contain solvents, water, and other coalescing substances in its formulation, or when its viscosity is adjusted by adding a reactive diluent, it is characterized by a 100% solids content. The absence of volatile compounds such as water or volatile organic solvents results in only a slight reduction in the applied coating thickness of a coating system with a 100% solids content during curing. This slight shrinkage makes it more difficult to produce a low-gloss surface by adding a conventional matting agent to the coating formulation. Excimer lamp technology for pretreating radiation-curable coating formulations with high-energy radiation of very short wavelengths ≤230 nm under an inert gas (preferably using a 172 nm excimer lamp) to produce a low-gloss, usually deep matte coating is also known, as described, for example, in US9073082B2 and in the review article "Low-gloss UV curable coatings: Light mechanisms, formulations and processes - A Review" by Calvez et al., Progress in Organic Coatings 171 (2022). The effect achieved by this pretreatment with short-wave UV light is a photochemically induced microfolding at the coating surface, where the mechanism is thought to be that the very thin skin layer of the coating cured by very short wavelength light swells from the underlying liquid and forms a microfolded structure at the surface. This microfolding is responsible for the low-gloss or matte surface. The very short wavelength excimer light at ≤230 nm penetrates into the very thin skin layer and directly breaks the C═C or C═O double bonds bearing the photoinitiator free radicals with its high photon energy. The coating composition below the folded surface is then fully cured using a conventional UV emitter such as, for example, a mercury medium-pressure emitter or an electron beam emitter.

[0004] A disadvantage of pretreating radiation-curable coating formulations with excimer radiation is that this must be carried out under an inert gas atmosphere, such as, for example, under nitrogen, and thus requires an inert gas curing apparatus. Nitrogen or other inert gases (such as argon) are expensive. In addition, making an industrial curing production line completely airtight is a challenge, and nitrogen leakage into the environment around the curing production line may thus occur, making the process even more expensive and potentially affecting worker safety, as this may result in an excessive nitrogen concentration in the environment around the curing production line.

[0005] The object of the present invention is to provide a method for preparing a low-gloss coating surface by irradiating a radiation-curable coating composition without having to use a matting agent and without having to use an inert gas atmosphere during the irradiation process.

[0006] According to the present invention, there is provided a method for preparing a cured coating having a low gloss surface from a radiation-curable coating composition, wherein the method comprises the following steps:

[0007] (1) applying a radiation-curable coating composition onto a substrate,

[0008] (2) irradiating the radiation-curable coating composition from step (1) with UV light having a wavelength substantially in the wavelength range of 231 to 280 nm, to provide a coating of a partially cured surface layer having a reduced glossiness,

[0009] then

[0010] (3) completing the curing of the coating from step (2) with actinic radiation, thereby fixing the partially cured surface layer having a reduced glossiness and providing a cured coating having a low gloss surface,

[0011] wherein steps (2) and (3) are carried out in air; and

[0012] wherein the radiation-curable coating composition comprises one or more acrylate-functional oligomers (A) and one or more acrylate-functional diluents (B).

[0013] It has surprisingly been found that the method of the present invention allows for the preparation of a low gloss coating surface without having to use an inert gas curing apparatus in the UV radiation method. Another advantage of the method of the present invention is that it allows for the preparation of a low gloss coating surface without having to use a matting agent and thereby without adversely affecting the stain resistance of the coating.

[0014] In excimer lamp technology as described, for example, in US9073082B2, light of very short wavelengths ≤230 nm is the reason for the need to use inert gases to avoid strong O2 absorption in air. However, such very short wavelengths with a very thin penetration depth are also considered to be the cause of generating a micro-folded surface structure resulting in a matte coating surface. DE 10 2017008353B3 describes a method for adjusting the amplitude and frequency of micro-folds during the photochemical matting of a radiation-curable coating, in which the coating is irradiated with short-wave monochromatic radiation from a low-pressure mercury lamp having emission lines at 185 and 254 nm in order to increase only the viscosity on the coating surface, and subsequently the coating is microstructured using an excimer emitter in an inert gas atmosphere with emission lines in the range of 172 to 222 nm, and subsequently the microstructured coating is cured by means of UV or electron beam curing. Surprisingly, the present inventors have found a method for preparing a low-gloss coating surface by UV radiation of a radiation-curable coating composition without having to use an inert gas atmosphere during the UV radiation, wherein the step of generating the low-gloss surface is carried out by forming a micro-folded surface structure using UV light having a wavelength essentially above 230 nm and below or equal to 280 nm under atmospheric conditions, such lamp types being commonly used for disinfection and sterilization purposes.

[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 indicating x to y, it means including x and y and all intermediate values.

[0016] The method of the present invention optionally includes an additional radiation curing step before step (2), i.e., before the step of irradiating with UV light having a wavelength essentially above 230 nm and below or equal to 280 nm. In such an additional radiation curing step, the radiation-curable coating composition from step (1) is pre-cured by irradiating with a radiation dose that causes partial curing of the coating composition from step (1) to a pre-gel or near-gel point state. Accordingly, the method of the present invention comprises the following steps:

[0017] (1) Applying a radiation-curable coating composition on a substrate,

[0018] (1b) Optionally pre-curing the radiation-curable coating composition from step (1) by irradiating with light to provide a partially cured coating,

[0019] (2) Irradiating the radiation-curable coating composition from step (1) or the partially cured coating from step (1b) (when present) with UV light having a wavelength essentially in the range of 231 to 280 nm to provide a coating having a partially cured surface layer with reduced glossiness,

[0020] Then

[0021] (3) Curing the coating from step (2) with actinic radiation, thereby fixing the partially cured surface layer with reduced gloss and providing a cured coating with a low gloss surface,

[0022] wherein steps (2) and (3) are carried out in air.

[0023] In step (1) of the method of the present invention, a radiation-curable coating composition is applied to a substrate by a method 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 with a coating thickness of preferably 5 to 300 μm, more preferably 15 to 175 μm, more preferably 20 to 150 μm, more preferably 20 to 125 μm.

[0024] The skin curing step (2) of the method of the present invention is carried out by irradiating the radiation-curable coating composition from step (1) or the partially cured coating (when present) from step (1b) with UV light having a wavelength substantially in the range of 231 to 280 nm, providing a coating of a partially cured surface layer with 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, resulting in 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 (2) emits light at wavelengths ≤ 230 nm), or more preferably there is even 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).

[0025] The irradiation in step (2) 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.

[0026] The UV light applied in step (2) preferably has an energy in the range of 2 to 200 mJ / cm 2A range of UV radiation doses, 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 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.

[0027] 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 / 10 nm, or as the spectral irradiance in W / m 2 / nm or expressed on a relative scale. The spectral curve is a display of how the radiation output is distributed over the electromagnetic spectrum.

[0028] A radiation source suitable for emitting UV light substantially in the specified wavelength range in step (2) of the method of the present invention is, for example, a low-pressure mercury vapor lamp, or a UVC LED lamp with a peak wavelength in the range of 231 to 280 nm, such as a peak wavelength 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 an excimer lamp with a peak wavelength 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 (2) of the present invention is the Premium P2035 UV disinfection lamp system available 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 in the wavelength range of 251 nm to 260 nm.

[0029] Another radiation source suitable for emitting UV light in the specified wavelength range in step (2) 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 the Fusion H+ lamp available 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.

[0030] The skin curing step (2) is preferably carried out using up to 6 lamps. Therefore, the skin curing step (2) 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 on 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, an earlier lamp unit is set at a lower irradiance to form a fine multiple pattern, and a later lamp unit with further skin curing has a higher amplitude to further reduce the gloss. Those skilled in the art will understand that when using multiple lamps, the surface texture, i.e., the gloss, can be further adjusted by changing the distance and irradiance of different lamps.

[0031] Preferably, the irradiance from each lamp unit in the skin curing step (2) 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 (2) is preferably at most 500 mW / cm 2 , more preferably at most 300 mW / cm 2 , even more preferably at most 200 mW / cm2 。

[0032] The irradiation in the skin curing step (2) 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.

[0033] After step (2), a surface wrinkling pattern is formed at the coating surface. Without wishing to be bound by any theory, it is believed that the surface wrinkling 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 varying the radiation dose in step (2) and / or optional step (1b), 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.

[0034] Step (3) of the method of the present 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 the coating with actinic radiation (such as, for example, UV light or electron beam radiation) is known in the industry. Actinic radiation is understood to be electromagnetic, ionizing radiation, particularly electron beam, UV light, and visible light. The irradiation in step (3) is preferably carried out with an electron beam or UV light having a significant emission at a wavelength > 280 nm. More preferably, the irradiation in step (3) 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, at least 40% of the radiation power of the applied radiation source emitted in the wavelength range of 200 to 390 nm is emitted at a wavelength > 280 nm; and also preferably, at least 40%, more preferably at least 50% of the radiation power of the applied radiation source emitted in the wavelength range of 231 to 390 nm is emitted at a wavelength > 280 nm.

[0035] The light applied in step (3) preferably has a radiation dose of 150 to 2500 mJ / cm 2 , more 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 . The upper limit of the radiation dose in step (3) is not critical, but is usually at most 2250 mJ / cm 2 , or at most 2000 mJ / cm 2 .

[0036] The radiation source suitable for step (3) is, for example, an LED lamp with a peak wavelength in the range of 350 to 450 nm or a broadband UV lamp, such as a medium-pressure mercury vapor lamp. Preferably, the irradiation in the final curing step (3) is carried out with UV light emitted from a broadband UV lamp. Examples of broadband UV lamps suitable for step (3) 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.

[0037] For example, according to the spectral curve of the Fusion H bulb 13 mm 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 wavelengths > 280 nm. This shows a key difference from the UV light used in step (2). 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 wavelengths > 280 nm, which shows a key difference from the UV light used in step (2).

[0038] The irradiation in 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.

[0039] In optional step (1b), some of the reactive ethylenically unsaturated double bonds of the curable compounds of the radiation-curable coating composition polymerize in the uncured coating layer obtained in step (1), so 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 (1b) is preferably carried out by irradiating the radiation-curable coating composition from step (1) with light having a significant emission at wavelengths > 280 nm. More preferably, the irradiation in step (1b) is carried out with light in which at least 40% of the actinic radiation power of the applied radiation source is provided by light with a wavelength higher than 280 nm. More preferably, the optional pre-curing step (1b) is preferably carried out by irradiating the radiation-curable coating composition from step (1) with light having a significant emission at wavelengths > 320 nm. Even more preferably, the irradiation in step (1b) 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.

[0040] When present, the light applied in step (1b) preferably has a radiation dose in the range of 1 to 200 mJ / cm 2 and preferably has at least 2 mJ / cm2 or at least 3 mJ / cm 2 of radiation dose, and preferably having 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.

[0041] The radiation source suitable for step (1b) 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 (1b) is carried out with light emitted from an LED lamp having a peak wavelength higher than 320 nm, such as, for example, 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.

[0042] The irradiation in the optional pre-curing step (1b) 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.

[0043] The method of the present invention is preferably carried out under atmospheric conditions, i.e., in air.

[0044] Those skilled in the art will understand that for the optional pre-curing step (1b), 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 above 350 nm, such as a suitable LED lamp with a peak wavelength above 350 nm, in the pre-curing step (1b), while for the complete curing step (3), 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.

[0045] The radiation dose as defined herein is the radiation dose of light emitted in the wavelength range of 200 to 390 nm.

[0046] The method of the present invention allows to obtain a surface coating with low gloss, and the gloss level can be controlled by adjusting the dosage conditions in step (2) and / or optional step 1(b). 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.

[0047] The coating composition used in the method of the present invention is radiation-curable. Radiation-curable means that radiation is required to initiate the crosslinking of the composition. The coating composition for use in the method of the present invention contains ethylenically unsaturated (C═C) bond functionality, which can be crosslinked by free radical polymerization preferably in combination with the presence of a photoinitiating system under the influence of radiation. The radiation-curable coating composition as used in the present invention comprises (A) one or more radiation-curable acrylate-functional oligomers, and (B) one or more radiation-curable acrylate-functional diluents (also referred to as reactive diluents).

[0048] In one embodiment of the present invention, the radiation-curable coating composition used in the method of the present invention contains at least 20% by weight, or at least 30% by weight, or at least 40% by weight, or at least 50% by weight of water and non-polymerizable volatile compounds based on the weight of the radiation-curable coating composition of the present invention. In this embodiment, the method preferably includes a drying step before the skin curing step (2). In another preferred embodiment of the present invention, the radiation-curable coating composition used in the method of the present invention is 100% radiation-curable. A 100% radiation-curable coating composition means a coating composition that is substantially free of water and non-polymerizable volatile compounds. As used herein, substantially free of water and non-polymerizable volatile compounds means that the composition contains less than 20% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, more preferably less than 3% by weight, more preferably less than 1% by weight of water and non-polymerizable volatile compounds based on the weight of the radiation-curable coating composition of the present invention. Non-polymerizable volatile compounds are compounds that do not have reactive double bonds and have an initial boiling point of less than or equal to 250 °C measured at a standard atmospheric pressure of 101.3 kPa.

[0049] Acrylate-functional oligomer

[0050] One or more acrylate-functional oligomers (also referred to as "acrylate-functionalized oligomers") are preferably selected from polyether acrylate oligomers, urethane acrylate oligomers, epoxy acrylate oligomers, polyester acrylate oligomers, and any mixtures thereof.

[0051] Exemplary polyester acrylate oligomers include the reaction product of acrylic acid with a hydroxyl-terminated polyester polyol. The reaction process can be carried out such that all or substantially all of the hydroxyl groups of the polyester polyol have been acrylated, particularly in the case where the polyester polyol is bifunctional. The polyester polyol can be prepared by the polycondensation reaction of a polyhydroxy-functional component (particularly a diol) and a polycarboxylic acid-functional compound (particularly a dicarboxylic acid and an acid anhydride). The polyhydroxy-functional component and the polycarboxylic acid-functional component can each have a linear aliphatic, branched aliphatic, cycloaliphatic, or aromatic structure and can be used alone or as a mixture.

[0052] Examples of suitable epoxy acrylate oligomers include the reaction product of acrylic acid with an epoxy resin (a polyglycidyl ether or ester). The epoxy resin can be particularly selected from bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol 6 diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexane-1,4-dioxane, bis(3,4-epoxycyclohexylmethyl) adipate, vinylcyclohexene oxide, 4-vinylcyclohexene oxide, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, methylene bis(3,4-epoxycyclohexane), dicyclopentadiene diepoxide, bis(3,4-epoxycyclohexylmethyl) ether of ethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate), 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polyglycidyl ethers of polyether polyols obtained by adding one or more alkylene oxides to aliphatic polyols such as ethylene glycol, propylene glycol, and glycerol, diglycidyl esters of aliphatic long-chain dibasic acids, monoglycidyl ethers of higher aliphatic alcohols, monoglycidyl ethers of phenol, cresol, butylphenol, or polyether alcohols obtained by adding alkylene oxides to these compounds, glycidyl esters of higher fatty acids, epoxidized soybean oil, epoxy butyl stearate, epoxy octyl stearate, epoxidized linseed oil, epoxidized polybutadiene, and the like.

[0053] Suitable polyether acrylate oligomers include, but are not limited to, the condensation reaction products of acrylic acid with polyether alcohols, where the polyether alcohols are polyether polyols (such as polyethylene glycol, polypropylene glycol, or polytetramethylene glycol). Suitable polyether alcohols can be straight-chain or branched-chain materials containing ether bonds and terminal hydroxyl groups. The polyether alcohols can be prepared by the ring-opening polymerization of cyclic ethers such as tetrahydrofuran or alkylene oxides (e.g., ethylene oxide and / or propylene oxide) with starter molecules. Suitable starter molecules include water, polyhydroxy-functional materials, polyester polyols, and amines.

[0054] The urethane acrylate oligomers suitable for the radiation-curable coating compositions of the present invention include urethanes based on aliphatic, cycloaliphatic, and / or aromatic polyester polyols and / or aliphatic, cycloaliphatic, and / or aromatic polyether polyols and aliphatic, cycloaliphatic, and / or aromatic diisocyanates and terminated with acrylate end groups. The polyurethane acrylate oligomers can be prepared by reacting aliphatic, cycloaliphatic, and / or aromatic polyisocyanates (e.g., diisocyanates, triisocyanates) with polyester polyols, polyether polyols, polycarbonate polyols, polycaprolactone polyols, polyorganosiloxane polyols (e.g., polydimethylsiloxane polyols), or polybutadiene polyols (e.g., polybutadiene polyols) or combinations thereof terminated with OH groups to form isocyanate-functionalized oligomers, which are then reacted with hydroxy-functionalized acrylates such as hydroxyethyl acrylate or hydroxyethyl methacrylate to provide terminal acrylate groups. For example, the polyurethane acrylate oligomers can contain two, three, four, or more acrylate functional groups per molecule. As is known in the art, other addition sequences can also be implemented to prepare the urethane acrylate oligomers. For example, the hydroxy-functionalized acrylate can first be reacted with the polyisocyanate to obtain an isocyanate-functionalized acrylate, which can then be reacted with polyester polyols, polyether polyols, polycarbonate polyols, polycaprolactone polyols, polydimethylsiloxane polyols, polybutadiene polyols, or combinations thereof terminated with OH groups. In yet another embodiment, the polyisocyanate can first be reacted with a polyol (including any of the aforementioned types of polyols) to obtain an isocyanate-functionalized polyol, which is then reacted with the hydroxy-functionalized acrylate to obtain a polyurethane acrylate. Alternatively, all components can be combined and reacted simultaneously.

[0055] Preferably, the acrylate-functional oligomer is selected from acrylate-functional urethane oligomers (also known as "urethane acrylate oligomers", "polyurethane acrylate oligomers" or "carbamate acrylate oligomers"), acrylate-functional epoxy oligomers (also known as "epoxy acrylate oligomers") and acrylate-functional polyester oligomers (also known as "polyester acrylate oligomers") and mixtures thereof. More preferably, the acrylate-functional oligomer is selected from acrylate-functional urethane oligomers (also known as "urethane acrylate oligomers"), acrylate-functional polyester oligomers (also known as "polyester acrylate oligomers") and mixtures thereof.

[0056] The acrylate-functional oligomer is preferably an aliphatic acrylate-functional oligomer, i.e., free of aromatic groups.

[0057] Preferred urethane acrylate oligomers are aliphatic urethane acrylate oligomers. More preferred urethane acrylate oligomers are urethane acrylate oligomers based on aliphatic polyesters, urethane acrylate oligomers based on aliphatic polyethers, and urethane acrylate oligomers based on aliphatic polyester / polyethers. Most preferred urethane acrylate oligomers are urethane acrylate oligomers based on aliphatic polyethers.

[0058] One or more acrylate-functional oligomers preferably have an average weight per acrylate functionality (WPA) of at most 5000 g / mol, more preferably at most 4000 g / mol, even more preferably at most 3000 g / mol, even more preferably at most 2000 g / mol, even more preferably at most 1500 g / mol as determined by 1 1H NMR as used herein. The WPA of the one or more acrylate-functional oligomers is preferably at least 170 g / mol, more preferably at least 180 g / mol, even more preferably at least 200 g / mol, and even more preferably at least 210 g / mol.

[0059] The WPA of the acrylate-functional oligomer is determined via 1 1H-NMR spectroscopy according to the following method. More specifically, the WPA of the acrylate-functional oligomer is calculated according to the following equation:

[0060]

[0061] wherein,

[0062] W pyr is the weight of pyrazine (internal standard),

[0063] W 树脂is the weight, W, of the acrylate-functional oligomer pyr and W 树脂 are expressed in the same units.

[0064] MW pyr is the molecular weight of pyrazine (= 80 Da) (internal standard).

[0065] A pyr is the peak area of the methine protons attached to the aromatic ring of pyrazine, and

[0066] N pyr is the number of methine protons of pyrazine equal to 4.

[0067] A C＝C is the peak area of the methine protons (...-CH=...) of the carbon-carbon double bond moiety (...>C=C<...) present.

[0068] N C＝C is the number of methine protons (...-CH=...) attached to the carbon-carbon double bond moiety (...>C=C<...) present.

[0069] The peak areas of the methine protons of pyrazine and the methine protons are determined as follows: A 75 mg sample of the acrylate-functional oligomer is diluted in 1 mL of deuterated chloroform containing a known amount (mg) of pyrazine as an internal standard at 25 °C in order to perform 1 1H-NMR spectroscopy. Subsequently, the 1H-NMR spectrum of the acrylate-functional oligomer sample is recorded at 25 °C on a 400 MHz BRUKER NMR spectrometer. 1 Subsequently, the chemical shifts (ppm) of the methine protons of pyrazine and the methine protons of A C＝C are identified. Subsequently, using suitable commercially available software for analyzing 1 1H-NMR spectra, such as the ACD / Spectrus Processor software provided by ACD / Labs, the peak areas of the methine protons of pyrazine and A C＝C are determined and these values are used in the above equation to calculate WPA.

[0070] The one or more acrylate-functional oligomers preferably have an acrylate functionality of from 2 to 14, more preferably from 2 to 12, even more preferably less than 10. The radiation-curable coating composition used in the present invention may also comprise an acrylate-functional oligomer having a functionality of 1. The average acrylate functionality of the acrylate-functional oligomers present in the radiation-curable coating composition is preferably in the range from 2 to 6. As used herein, the average wherein w kis the amount in grams of an acrylate-functional oligomer present in a radiation-curable coating composition having a number-average molecular weight M k and having an acrylate functionality f k .

[0071] The one or more acrylate-functional oligomers preferably have a number-average molecular weight M higher than 1000 g / mol, more preferably higher than 1100 g / mol, more preferably higher than 1200 g / mol, even more preferably higher than 1300 g / mol and preferably lower than 10000 g / mol, more preferably lower than 7500 g / mol, even more preferably lower than 5000 g / mol, where the number-average molecular weight M is determined using triple detection size exclusion chromatography n . n

[0072] The one or more acrylate-functional oligomers are present in the radiation-curable coating composition in an amount of at least 20% by weight, more preferably at least 25% by weight, more preferably at least 30% by weight and preferably up to 80% by weight, even more preferably up to 75% by weight, even more preferably up to 70% by weight, even more preferably up to 65% by weight, even more preferably up to 60% by weight, where the amount is given relative to the total weight of the acrylate-functional oligomers and acrylate-functional diluents present in the radiation-curable coating composition

[0073] Acrylate-functional diluent

[0074] 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

[0075] As used herein, "reactive" refers to the ability to undergo 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 groups or functional groups are polymerizable groups, more preferably such reactive groups or functional groups are ethylenically unsaturated polymerizable groups. The acrylate groups of the reactive diluent are capable of (co)polymerizing with the acrylate groups of the acrylate-functional oligomer

[0076] The acrylate functionality has the formula

[0077] CH2=CH-C(O)O-

[0078] As used herein, the acrylate functionality of a compound is the number of acrylate functional groups per molecule of the compound

[0079] ​One or more acrylate-functional diluents present in the radiation-curable coating composition preferably have from 1 to 6 acrylate groups, i.e., an acrylate functionality of from 1 to 6. More preferably, the one or more acrylate-functional diluents have an acrylate functionality of from 1 to 5, even more preferably from 1 to 4. Preferably, at least one of the acrylate-functional diluents present in the radiation-curable coating composition has an acrylate functionality of 2 or 3. In a preferred embodiment, the 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 where w k is the amount in grams of acrylate-functional diluent present in the radiation-curable coating composition having a molar mass M k and having a functionality f k .

[0080] Preferably, the radiation-curable coating composition used in the method of the present invention comprises 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, based on the weight of the entire radiation-curable coating composition.

[0081] The one or more acrylate-functional 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 750 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.

[0082] Preferably, the one or more reactive diluents are aliphatic reactive diluents, i.e., free of aromatic groups. Preferred examples of acrylate functional 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).

[0083] Preferably, at least one reactive diluent (B) has an acrylate functionality of 2 or 3. The reactive diluent (B) with 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.

[0084] The reactive diluent (B) with an acrylate functionality of 3 is preferably selected from glycidyl propoxylate triacrylate (GPTA), trimethylolpropane triacrylate (TMPTA), di(trimethylolpropane) triacrylate (di - TMP3A), pentaerythritol triacrylate (PET3A), and pentaerythritol triacrylate, including their alkoxylated forms, preferably propoxylated forms, and any mixture thereof.

[0085] In a preferred embodiment of the present invention, at least 10 wt%, preferably at least 20 wt%, more preferably at least 30 wt%, more preferably at least 40 wt%, more preferably at least 50 wt%, more preferably at least 60 wt%, more preferably at least 70 wt%, more preferably at least 80 wt%, more preferably at least 90 wt%, and most preferably 100 wt% of the acrylate functional 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 mixture thereof.

[0086] The one or more acrylate-functional diluents are preferably present in the radiation-curable coating composition in an amount of at least 20% by weight, more preferably at least 25% by weight, even more preferably at least 30% by weight, even more preferably at least 35% by weight, even more preferably at least 40% by weight, and preferably in an amount of at most 80% by weight, even more preferably at most 75% by weight, even more preferably at most 70% by weight, where the amount is given relative to the total weight of the acrylate-functional oligomer and acrylate-functional diluent present in the radiation-curable coating composition.

[0087] Relative to the entire radiation-curable coating composition, the total amount of the one or more acrylate-functional oligomers and the one or more acrylate-functional diluents present in the radiation-curable coating composition is at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight.

[0088] The radiation-curable coating composition for use in the present invention preferably comprises a photoinitiating system comprising (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.

[0089] 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.

[0090] A redox active compound is a compound that can be oxidized or reduced by the excited state of a photo-redox active compound.

[0091] 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, π-π* transitions can occur in the photo-redox active compound. This short-lived excited state can now undergo a redox 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 only form 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 (3) or an optional pre-curing step (1b), where irradiation is carried out with light having a significant emission at wavelengths >280 nm, it is speculated that n-π* transitions may now occur. These longer-lived excited states may generate initiating radicals via α-cleavage reactions, hydrogen abstraction reactions, and via redox 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, resulting in 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.

[0092] The one or more photo-redox active compounds preferably have a 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 onium salts such as, for example, iodonium 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.

[0093]

[0094] In embodiments of the 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-).

[0095] More preferably, the 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, which is prone to form 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).

[0096] Suitable redox active compounds are preferably selected from aliphatic amines, aromatic amines, thioethers, thiols and any mixtures thereof. For reasons of stability, the amine is preferably a tertiary amine, otherwise they can undergo a Michael addition reaction with the radiation-curable groups present in the radiation-curable coating composition, thereby forming a tertiary amine. 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 lower 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 of 1), Agisyn TM 008 (acrylate functionality of 2), both of which can also act as reactive diluents, Agisyn TM 701 and Agisyn TM 703 (acrylate functionality of 4), both of which can also act as acrylate-functional oligomers, 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.

[0097] When UV irradiation is applied in the final curing step (3), the photoinitiating system optionally further comprises another photoactive compound beside the photo-redox active compound. A photoactive compound refers to a compound that can generate free radicals when irradiated with light having a wavelength of substantially >280 nm.

[0098] 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 glyoxylate, for example, those disclosed in U.S. Patent No. 6,048,660.

[0099] 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.

[0100] The photoinitiating system is preferably present in the 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 radiation-curable coating composition. Preferably, the one or more photo-redox active compounds and redox active compounds are present in the 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, and 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 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 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 radiation-curable coating composition by 4 (i.e., the number of mercapto groups present in pentaerythritol tetrakis(mercaptoacetate)).

[0101] 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 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 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 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 thus redox - active. In this case, the amount of the redox active compound can be as high as 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 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%.

[0102] The radiation-curable coating composition generally further contains additive compounds; that is, a collection of one or more individual additives having one or more specified structures or types. 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-forming agents, 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 combinations of one or more of the 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% relative to the total weight of the coating composition; 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%. 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% relative to 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 pigments. The coating composition can also contain one or more inorganic fillers.

[0103] The coating composition can also contain one or more solvents. Suitable solvents are inert with respect to the functional groups present in the coating composition from the time they are added until the end of the process. Examples of suitable solvents are hydrocarbons, alcohols, ketones, and esters, such as toluene, xylene, isooctane, acetone, butanone, methyl isobutyl ketone, ethyl acetate, butyl acetate, tetrahydrofuran, dimethylacetamide, dimethylformamide. The coating composition is preferably a 100% radiation-curable coating composition as defined hereinafter.

[0104] 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.

[0105] The radiation-curable coating composition used in the method of the present invention is preferably 100% radiation-curable. A 100% radiation-curable coating composition means a coating composition that is substantially free of water and non-polymerizable volatile compounds. As used herein, substantially free of water and non-polymerizable volatile compounds means that the composition contains less than 20% by weight, preferably less than 10% by weight, more preferably less than 5% by weight, more preferably less than 3% by weight, more preferably less than 1% by weight of water and non-polymerizable volatile compounds, based on the weight of the radiation-curable coating composition of the present invention. Non-polymerizable volatile compounds are compounds that do not have reactive double bonds and have an initial boiling point of less than or equal to 250 °C measured at a standard atmospheric pressure of 101.3 kPa.

[0106] The present invention further relates to a radiation-curable coating composition as described above.

[0107] 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 of plastic, paper and metal substrates, by the method as described above.

[0108] Substrates suitable for the method according to the present invention are, for example, inorganic substrates such as fiber cement boards, wood, wood-containing materials, paper (including cardboard), fabrics, leather, metals, 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.

[0109] The substrate is optionally pretreated and / or optionally pre-coated. For example, a thermoplastic plastic film can be treated by corona discharge before application, or pre-coated with a primer. Mineral building materials are also usually provided with a primer before applying the coating composition.

[0110] The coating obtained by the method of the present invention can advantageously be used for floor or wall coverings or automotive interiors or furniture or window frames or facade panels.

[0111] The present invention is further defined by a set of exemplary embodiments listed below. Unless otherwise stated herein or if technically clearly infeasible to a 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.

[0112] [1] A method for preparing a cured coating having a low-gloss surface from a radiation-curable coating composition, wherein the method comprises the following steps:

[0113] (1) Apply a radiation-curable coating composition on a substrate,

[0114] (2) Irradiate the radiation-curable coating composition from step (1) with UV light having a wavelength substantially in the range of 231 to 280 nm, to provide a coating with a partially cured surface layer having reduced gloss,

[0115] Then

[0116] (3) Complete the curing of the coating from step (2) with actinic radiation, thereby fixing the partially cured surface layer having reduced gloss and providing a cured coating with a low gloss surface,

[0117] where steps (2) and (3) are carried out in air; and

[0118] wherein the radiation-curable coating composition comprises one or more acrylate-functional oligomers (A) and one or more acrylate-functional diluents (B).

[0119] [2] The method according to embodiment [1], wherein the irradiation in step (2) is carried out with UV light having a wavelength substantially 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.

[0120] [3] The method according to embodiment [1] or [2], wherein the UV light having a wavelength substantially in the 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.

[0121] [4] The method according to any one of the foregoing embodiments, wherein the UV light applied in step (2) has a UV radiation dose in the range of 2 to 200 mJ / cm 2 , preferably having a radiation dose of at least 3 mJ / cm 2 , or at least 4 mJ / cm 2 , or at least 5 mJ / cm 2 , and preferably having a radiation dose of 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 .

[0122] [5] The method according to any of the foregoing embodiments, wherein the epidermis curing step is carried out with one or more lamp units, and wherein the irradiance from each lamp unit in the epidermis curing step (2) 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 epidermis curing step (2) 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 .

[0123] [6] The method according to any of the foregoing embodiments, wherein the UV light applied in step (2) comes 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.

[0124] [7] The method according to any of the foregoing embodiments, wherein the irradiation in step (2) 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 combined with an optical band-pass filter having a maximum transmittance in the wavelength range of 241 nm to 270 nm, preferably in the wavelength range of 251 to 260 nm.

[0125] [8] The method according to any of the foregoing embodiments, wherein the irradiation in the curing step (3) is carried out with an electron beam or with light having 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.

[0126] [9]A method according to any 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%, and even more preferably 0% of the radiation power of the radiation source applied in step (2) emits light at a wavelength of ≤ 230 nm; and / or wherein, among the radiation power of the radiation source applied in step (2) 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, among the radiation power of the radiation source applied in step (2) 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.

[0127]

[10] A method according to any of the foregoing embodiments, wherein the light applied in step (3) 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 .

[0128]

[11] A method according to any of the foregoing embodiments, wherein the irradiation in step (3) is carried out with a broadband UV lamp.

[0129]

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

[0130] (1) Applying a radiation-curable coating composition on a substrate,

[0131] (1b) Optionally pre-curing the radiation-curable coating composition from step (1) by irradiating with light to provide a partially cured coating,

[0132] (2) Irradiating the radiation-curable coating composition from step (1) or the partially cured coating from step (1b) 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 glossiness,

[0133] Then

[0134] (3) Curing the coating from step (2) with actinic radiation, thereby fixing the partially cured surface layer with reduced gloss and providing a cured coating with a low gloss surface, and

[0135] wherein steps (2) and (3) are carried out in air.

[0136]

[13] The method according to embodiment

[12] , wherein the irradiation in step (1b) is carried out with 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.

[0137]

[14] The method according to embodiment

[12] or

[13] , wherein when present, the light applied in step (1b) 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 .

[0138]

[15] The method according to any one of embodiments

[12] to

[14] , wherein when present, the irradiation in step (1b) is carried out with an LED lamp having a peak wavelength in the range of 350 to 450 nm.

[0139]

[16] The method according to any one of embodiments

[12] to

[15] , wherein when present, step (1b) is carried out in air.

[0140]

[17] The method according to any of the foregoing embodiments, wherein a micro-folded pattern is formed at the coating surface after step (2), having a random microscopic pattern of peaks and valleys, 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.

[0141]

[18] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers are selected from polyether acrylate oligomers, polyester acrylate oligomers, epoxy acrylate oligomers, urethane acrylate oligomers, and any mixtures thereof.

[0142]

[19] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers are selected from polyester acrylate oligomers, urethane acrylate oligomers, and any mixtures thereof.

[0143]

[20] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers are aliphatic acrylate-functional oligomers.

[0144]

[21] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers are aliphatic polyester acrylate oligomers or aliphatic urethane acrylate oligomers.

[0145]

[22] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers are urethane acrylate oligomers based on aliphatic polyethers.

[0146]

[23] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers have a number-average molecular weight Mn higher than 1000 g / mol, more preferably higher than 1100 g / mol, more preferably higher than 1200 g / mol, even more preferably higher than 1300 g / mol and preferably lower than 10000 g / mol, more preferably lower than 7500 g / mol, even more preferably lower than 5000 g / mol, n wherein the number-average molecular weight Mn is determined as described in the specification. n .

[0147]

[24] The method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers have an acrylate functionality of 2 to 14, more preferably 2 to 12, even more preferably less than 10.

[0148]

[25] The method according to any one of the foregoing embodiments, wherein the average acrylate functionality of the acrylate-functional oligomer present in the radiation-curable coating composition is preferably in the range of 2 to 6, and the average where w k is the amount in grams of the acrylate-functional oligomer present in the radiation-curable coating composition having a number-average molecular weight M k and an acrylate functionality f k .

[0149]

[26] The method according to any one of the foregoing embodiments, wherein one or more of the acrylate-functional oligomers have an average weight per acrylate functionality (WPA) of at most 5000 g / mol, more preferably at most 4000 g / mol, even more preferably at most 3000 g / mol, even more preferably at most 2000 g / mol, even more preferably at most 1500 g / mol, and preferably at least 170 g / mol, more preferably at least 180 g / mol, even more preferably at least 200 g / mol, and even more preferably at least 210 g / mol, where WPA is determined as described in the specification.

[0150]

[27] The method according to any one of the foregoing embodiments, wherein one or more of the acrylate-functional diluents 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 750 g / mol, even more preferably lower than 700 g / mol, even more preferably lower than 650 g / mol.

[0151]

[28] The method according to any one of the foregoing embodiments, wherein one or more of the acrylate-functional diluents have an acrylate functionality of 1 to 6, more preferably 1 to 5, even more preferably 1 to 4.

[0152]

[29] A method according to any of the foregoing embodiments, wherein at least one of the acrylate functional 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 mixtures 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 mixtures thereof; and / or the amount of the monofunctional diluent present in the radiation-curable coating composition, relative to the weight of the entire 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.

[0153]

[30] A method according to any of the foregoing embodiments, wherein the radiation-curable coating composition comprises at least two acrylate functional diluents having different acrylate functionalities, 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 4, more preferably at most 3.

[0154]

[31] A method according to any of the foregoing embodiments, wherein the one or more acrylate functional diluents are aliphatic; and / or 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 acrylate functional 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.

[0155]

[32] A method according to any of the foregoing embodiments, wherein the one or more acrylate functional oligomers are aliphatic and the one or more acrylate functional diluents are aliphatic.

[0156]

[33] A method according to any of the foregoing embodiments, wherein the one or more acrylate-functional oligomers are present in the radiation-curable coating composition in an amount of at least 20% by weight, more preferably at least 25% by weight, more preferably at least 30% by weight, and preferably up to 80% by weight, even more preferably up to 75% by weight, even more preferably up to 70% by weight, even more preferably up to 65% by weight, even more preferably up to 60% by weight; and the one or more acrylate-functional diluents are present in the radiation-curable coating composition in an amount of at least 20% by weight, more preferably at least 25% by weight, even more preferably at least 30% by weight, even more preferably at least 35% by weight, even more preferably at least 40% by weight, and preferably up to 80% by weight, even more preferably up to 75% by weight, even more preferably up to 70% by weight, wherein the amounts are given relative to the total weight of the acrylate-functional oligomers and acrylate-functional diluents present in the radiation-curable coating composition.

[0157]

[34] A method according to any of the foregoing embodiments, wherein the total amount of the one or more acrylate-functional oligomers and the one or more acrylate-functional diluents is at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, relative to the entire radiation-curable coating composition.

[0158]

[35] A method according to any of the foregoing embodiments, wherein the radiation-curable coating composition is 100% radiation-curable.

[0159]

[36] A method according to any of the foregoing embodiments, wherein the 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.

[0160]

[37] A method according to embodiment

[36] , 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.

[0161]

[38] A method according to embodiment

[36] , wherein the irradiation in step (2) 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.

[0162]

[39] The method according to any one of embodiments

[36] to

[38] , 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.

[0163]

[40] The method according to any one of embodiments

[36] to

[39] , 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.

[0164]

[41] The method according to any one of embodiments

[36] to

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

[0165]

[42] The method according to any one of embodiments

[36] to

[41] , 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.

[0166]

[43] The method according to any one of embodiments

[36] to

[42] , wherein the photo - initiator system is present in the 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 40% by weight, more preferably at most 35% by weight, more preferably at most 30% by weight, even more preferably at most 25% by weight, wherein the amount is given relative to the radiation - curable coating composition.

[0167]

[44] The method according to any one of embodiments

[36] to

[43] , wherein the one or more photo - redox active compounds are present in the 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 amount is given relative to the radiation - curable coating composition.

[0168]

[45] A method according to any one of embodiments

[36] to

[44] , wherein the one or more redox-active compounds are present in the 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 radiation-curable coating composition.

[0169]

[46] A method according to any one of embodiments

[36] to

[45] , wherein the one or more photo-redox-active compounds and redox-active compounds are present in the radiation-curable coating composition in an amount such 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.

[0170]

[47] A method according to any one of the preceding 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 from 1 to 50 gloss units, or from 4 to 40 gloss units, or from 4 to 30 gloss units, or from 4 to 20 gloss units, or from 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 from 1 to 60 gloss units, or from 5 to 40 gloss units, or from 5 to 30 gloss units.

[0171]

[48] A method according to any one of embodiments

[32] to

[47] , wherein the gloss of the cured coating surface measured at a 60° geometric angle is in the range from 4 to 40 gloss units, or from 4 to 30 gloss units, or from 4 to 20 gloss units, or from 4 to 10 gloss units.

[0172]

[49] A radiation-curable coating composition as defined in any one of the preceding embodiments.

[0173]

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

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

[0174]

[51] A coated substrate according to embodiment

[50] , 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.

[0175] The present invention will now be described with reference to the following examples. Unless otherwise specifically stated, all parts, percentages, and ratios are by weight.

[0176] Synthetic aliphatic acrylate-functional polyester resin (Resin 1)

[0177] Step 1: Synthesis of hydroxy-functional polyester

[0178] Charge 558.2 g of diethylene glycol, 253.6 g of trimethylolpropane, 645.8 g of adipic acid, 0.2 g of butyltin acid, and 1.4 g of distearylpentaerythritol phosphite into a reactor equipped with a stirrer, a Vigreux column with a distillation device, a temperature measuring device, and an inert gas inlet. Slowly heat the reaction mixture with stirring to 230 °C and maintain at this temperature until the distillation of water stops. Remove the Vigreux column, lower the temperature to 200 °C and slowly apply a vacuum (100 mbar). Keep the mixture under reduced pressure until the acid value reaches a value below 4 mg KOH / g of resin. Release the vacuum with nitrogen gas and cool the mixture to below 80 °C and discharge. The resulting polyester has an acid value of 2.8 mg KOH / g and a hydroxyl value of 297 mg KOH / g.

[0179] Step 2: Acrylation of the hydroxy-functional polyester

[0180] Charge 625 g of OH-functional polyester, 230 g of acrylic acid, 150 g of methylcyclohexane, 4.9 g of methanesulfonic acid, 0.65 g of distearylpentaerythritol phosphite, and 2.35 g of p-methoxyphenol into a reactor equipped with a Dean Stark apparatus, a temperature measuring device, and an (inert) air inlet. Slowly heat the reaction mixture to 90 °C and remove water via an azeotropic distillation process at a temperature of 90 - 100 °C until the acid value reaches a value below 20 mg KOH / g of resin. Next, lower the temperature to 95 °C and distill the solvent under reduced pressure until a solids content of >99% is reached. After releasing the vacuum, add 8.6 g of trimethylolpropane oxetane and cool the mixture to below 80 °C and discharge.

[0181] The resulting acrylate-functional aliphatic polyester has an acid value of 11.3 mg KOH / g. In Table 1, this acrylate-functional aliphatic polyester is referred to as Resin 1.

[0182] Preparation of coating composition

[0183] Add the components listed in Table 1 in the amounts listed in Table 1 (amounts in weight %, based on the weight of the coating composition) to a container and mix well for 2 minutes at 3500 rpm using a high-speed mixer (DAC 150.1FV, Hauschield GmbH).

[0184] Table 1 : Coating Compositions F1 - F6

[0185]

[0186]

[0187] Application of coating composition (Step (1))

[0188] Unless otherwise stated, the coating compositions F1 - F6 were applied onto the white part of a Leneta card (2C Leneta Inc) using a 24μm wire rod applicator (#3Kbar, RK Printcoat Instruments Ltd). For another thickness, i.e., 100μm, 6Kbar was applied.

[0189] Examples 1-10 (curing the coating composition using a low-pressure mercury vapor lamp) and Comparative Experiments C1-C3 (see Table 2)

[0190] The coating composition was cured immediately after application (within 20 seconds) on a UVio curing rig equipped with a conveyor belt with multiple lamps.

[0191] A 395nm LED (Heraeus Noblelight UV4003, with an intensity (at the emission window) of 14W / cm 2 ) was used for optional pre - curing (optional step (1b)).

[0192] A Heraeus 2 Premium P2035 UV disinfection system (low - pressure mercury vapor lamp, main emission peak at 254nm (>90%), irradiance measured by UV Power II at 32mW / cm 2 ) was used to irradiate the applied radiation - curable coating composition with UV light, or in the case of pre - cured application, the pre - cured radiation - curable coating composition (epidermal curing step (step (2))).

[0193] Subsequently, a medium - pressure mercury vapor lamp (Heraeus Noblelight 10 MARK III H bulb, 600W / in) was used to irradiate the epidermally cured coating composition (step (3)).

[0194] Unless otherwise stated, all curing was carried out in air, and the irradiation doses of UV - A, UV - B, and UV - C light were measured by UV Power Determined by II (EIT Inc), where typical EIT optical responses are given for UVA (320 - 390 nm), UVB (280 nm - 320 nm), and UVC (250 - 260 nm).

[0195] Examples 1 - 5 and Comparative Experiments C2 - C3 all used coating composition F1, where the curing conditions were different. Example 1 and Comparative Experiment C1 were carried out in air and in N2 respectively under the same skin curing conditions, both reaching a similar low gloss level, indicating that surprisingly inerting is not required.

[0196] In the comparative experiments, C2 without pre - curing and C3 with pre - curing were compared with Example 1 and Example 3 respectively. For the skin curing step (step (2)), a medium - pressure mercury vapor lamp Heraeus Noblelight 10 MARKIII H bulbs, 600 W / in was used, and its power was reduced so that the UV - C dose in the comparative experiments was the same as that in Example 1 and Example 3. Using a medium - pressure mercury vapor lamp H bulb that emits less than 50% of its light with wavelengths between 231 and 280 nm produced a high - gloss coating with a flat coating surface (i.e., without a micro - folded structure).

[0197] In Example 1, 2, and 3 and Comparative Experiment C2, micrographs of the cured coatings were taken.

[0198] Figure 1 : Example 1

[0199] Figure 2 : Example 2

[0200] Figure 3 : Example 3

[0201] Figure 4 : Comparative Experiment C2

[0202] Comparing Figure 1 with Figure 2 showed that the gloss value and surface texture can be adjusted by changing the skin curing radiation dose. A finer micro - folded pattern with a shorter distance between adjacent peaks or valleys was obtained in Example 2 (distance of about 52 μm in Example 2 and about 60 μm in Example 1).

[0203] Comparing Figure 1 with Figure 3 showed that the gloss value and surface texture can also be adjusted by performing pre - curing (while keeping the skin curing radiation dose the same). Compared with Example 1, a finer micro - folded pattern with a shorter distance between adjacent peaks or valleys was obtained in Example 3 (distance of about 34 μm).

[0204] Figure 4 It shows that for Comparative Experiment C2, when the skin curing step is carried out with UV light, a flat surface is obtained, and a small part of the UV light has a wavelength in the range of 231 to 280 nm. For Comparative Experiment C3, a flat surface similar to that of Comparative Experiment C1 in Figure 4 is obtained, resulting in a high gloss surface.

[0205] Examples 6 - 8 use coatings with different oligomers. Examples 9 - 10 use coatings with different diluents. All examples achieved a gloss level of less than 60 at 60° and 85°. Coatings with aliphatic oligomers and aliphatic monomers achieved a 60° gloss level of less than 10 and an 85° gloss level of less than 15 for coating compositions F1, F2, and F5, and a 60° gloss level of less than 25 and an 85° gloss level of less than 35 for coating composition F4; while coatings with aromatic oligomers or aromatic monomers (F3, F6) achieved a gloss level of only 40 - 60 at 60° and 85°.

[0206] Without wishing to be bound by any theory, the inventors hypothesize that aromatic functional groups compete with photoinitiator absorption in the wavelength region of 231 to 280 nm and may reduce the degree of skin curing, that is, the diluent in the skin layer is not sufficiently consumed to drive the diffusion of the diluent at the lower layer into the thin skin, resulting in microfolds with a lower amplitude than that of aliphatic oligomers and / or diluents, and thus the gloss level is not as low as that of coatings with aliphatic oligomers and / or diluents.

[0207] Examples 11-12 (curing the coating composition using a band-pass filter in the skin curing step) and Comparative Experiment C4 (see Table 3)

[0208] The composition is cured immediately after application (within 20 seconds) by the following steps.

[0209] Pre - curing (step (1b)) is carried out using a 395 nm LED (Phoseon RX Fireline TM 395 LED 8W / cm 2 lamp, water - cooled with an AGT 1.7 kW cooler).

[0210] The pre - cured radiation - curable coating composition is irradiated with UV light having a wavelength essentially in the range of 231 to 280 nm by using a medium - pressure mercury vapor H + lamp (600W / in Heraeus Noblelight 10H + lamp), and the light passes through a band - pass filter (peak transmission at 254 nm, 10 nm full width at half maximum FWHM, First Surface UV band - pass filter from Edmund Optics) (skin curing step (2)).

[0211] Subsequently, the skin-cured coating composition (step (3)) was irradiated with a medium-pressure mercury vapor H+ lamp (600 W / in Heraeus Noblelight 10H+ lamp).

[0212] Unless otherwise stated, all curing was carried out in air, and the irradiation doses of UV-A, UV-B, and UV-C light were determined using a UV Power II (EIT Inc), where the typical EIT optical response is given for UVA (320 - 390 nm), UVB (280 nm - 320 nm), and UVC (250 - 260 nm).

[0213] By adjusting the pre-curing dose, Examples 11 - 12 achieved a low-gloss coating surface, where the 60° gloss was less than 15 gloss units GU, and the 85° gloss ranged from a very low level of 5 to 20 GU to a medium-low level of 20 to 60 GU.

[0214] In Comparative Experiment C4, the skin-curing step (step (2)) was carried out using a medium-pressure mercury vapor lamp, 600 W / in HeraeusNoblelight 10H+ lamp, the power of which had been reduced so that the UV-C dose in Comparative Experiment C4 was the same as in Example 11, and no band-pass filter was used. A flat surface similar to that in Figure 4 Comparative Experiment C1 was obtained, resulting in a high-gloss surface.

[0215] Testing of the cured coating composition

[0216] Gloss was measured in the drawdown direction according to ISO 2813 and expressed in gloss units (GU). The results are shown in Tables 2 and 3.

[0217] Table 2: The coating composition was cured using a low-pressure mercury vapor lamp for the skin-curing step (2) in Examples 1 - 10

[0218]

[0219] Table 3: The coating composition was cured using a band-pass filter for the skin-curing step (2) in Examples 11 - 12

[0220]

Claims

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

2. The method according to claim 1, wherein the one or more acrylate-functional oligomers are selected from polyether acrylate oligomers, polyester acrylate oligomers, epoxy acrylate oligomers, urethane acrylate oligomers, and any mixtures thereof.

3. The method according to claim 1 or 2, wherein the one or more acrylate-functional oligomers are selected from polyester acrylate oligomers, urethane acrylate oligomers, and any mixtures thereof.

4. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers are aliphatic acrylate-functional oligomers.

5. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers are aliphatic polyester acrylate oligomers or aliphatic urethane acrylate oligomers.

6. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers are urethane acrylate oligomers based on aliphatic polyethers.

7. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers have a number-average molecular weight M of higher than 1000 g / mol, more preferably higher than 1100 g / mol, more preferably higher than 1200 g / mol, even more preferably higher than 1300 g / mol and preferably lower than 10000 g / mol, more preferably lower than 7500 g / mol, even more preferably lower than 5000 g / mol n , wherein the number-average molecular weight M is determined as described in the specification n .

8. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers have an acrylate functionality of 2 to 14, more preferably 2 to 12, even more preferably less than 10.

9. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers have an average weight (WPA) per acrylate functionality of at most 5000 g / mol, more preferably at most 4000 g / mol, even more preferably at most 3000 g / mol, even more preferably at most 2000 g / mol, even more preferably at most 1500 g / mol, and preferably at least 170 g / mol, more preferably at least 180 g / mol, even more preferably at least 200 g / mol, and even more preferably at least 210 g / mol, wherein WPA is determined as described in the specification.

10. The method according to any one of the preceding claims, wherein the one or more acrylate-functional diluents 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 750 g / mol, more preferably lower than 700 g / mol, even more preferably lower than 650 g / mol.

11. The method according to any one of the preceding claims, wherein the one or more acrylate-functional diluents have an acrylate functionality of 1 to 6, more preferably 1 to 5, even more preferably 1 to 4.

12. The method according to any one of the preceding claims, wherein at least one of the acrylate-functional diluents has an acrylate functionality of 2 or 3.

13. The method according to any one of the preceding claims, wherein the radiation-curable coating composition comprises at least two acrylate-functional diluents having different acrylate functionalities, and 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 4, more preferably at most 3.

14. The method according to any one of the preceding claims, wherein the one or more acrylate-functional diluents are aliphatic.

15. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers are aliphatic and the one or more acrylate-functional diluents are aliphatic.

16. The method according to any one of the preceding claims, wherein the one or more acrylate-functional oligomers are present in the radiation-curable coating composition in an amount of at least 20% by weight, more preferably at least 25% by weight, more preferably at least 30% by weight, and preferably up to 80% by weight, even more preferably up to 75% by weight, even more preferably up to 70% by weight, even more preferably up to 65% by weight, even more preferably up to 60% by weight; and the one or more acrylate-functional diluents are present in the radiation-curable coating composition in an amount of at least 20% by weight, more preferably at least 25% by weight, even more preferably at least 30% by weight, even more preferably at least 35% by weight, even more preferably at least 40% by weight, and preferably up to 80% by weight, even more preferably up to 75% by weight, even more preferably up to 70% by weight, wherein the amounts are given relative to the total weight of the acrylate-functional oligomers and acrylate-functional diluents present in the radiation-curable coating composition.

17. The method according to any one of the preceding claims, wherein the total amount of the one or more acrylate-functional oligomers and the one or more acrylate-functional diluents is at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, relative to the entire radiation-curable coating composition.

18. The method according to any one of the preceding claims, wherein the radiation-curable coating composition is 100% radiation-curable.

19. 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.

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

21. The method according to any one of the preceding claims, wherein UV irradiation is applied in step (3), and the radiation-curable coating composition comprises a photoinitiator system comprising at least one absorption peak at a wavelength in the range of 231 to 280 nm and at least one absorption peak at a wavelength above 280 nm.

22. A radiation-curable coating composition as defined in any one of claims 1 to 21.

23. A coated substrate, wherein the coated substrate is obtained by coating a substrate with the method according to any one of claims 1 to 21, preferably a plastic, wood or metal substrate or a substrate of any combination of plastic, paper and metal.

24. The coated substrate according to claim 23, 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