Method of providing low gloss coating

Abstract

The present invention relates to a method for producing a coating from an aqueous radiation curable coating composition wherein the method comprises the following steps in sequence (1) to (4): (1) applying an aqueous radiation curable coating composition on a surface of a substrate, (2) drying the aqueous radiation curable coating composition to provide an at least partially dried coating composition, and (3) drying the at least partially dried coating composition. The present invention relates to an aqueous radiation curable coating composition comprising: (1) at least partially dried coating composition, (2) at least partially dried coating composition, (3) irradiating the at least partially dried coating composition with ultraviolet light having a wavelength of < = 220 nm under an inert atmosphere, followed by (4) irradiating with ultraviolet light having a wavelength of > = 300 nm or with an electron beam wherein the aqueous radiation curable coating composition is a dispersion comprising: (A) at least one water dispersible polyurethane (A); wherein the polyurethane (A) has a urea group (-NH-CO-NH-) concentration of at least 0.1 milliequivalents per gram of polyurethane (A) and at most 2.6 milliequivalents per gram of polyurethane (A), and the polyurethane (A) is substantially free of radiation-curable ethylenically unsaturated bonds, (B) at least one radiation-curable diluent (B) having a molar mass of less than 750 g / mol and having an acrylate functionality of 2 to 5, and (C) water and optionally an organic solvent, whereby the optional organic solvent is present in an amount of at most 30% by weight, based on the total amount of water and organic solvent, where the amount of (A) is 30 to 85% by weight, and the amount of (B) is 15 to 70% by weight, based on the total amount of (A) and (B).

Description

[0001] The present invention relates to the field of waterborne radiation-curable polyurethane coating compositions having low gloss. The present invention also relates to a process for producing low gloss coatings from waterborne radiation-curable coating compositions.

[0002] Aqueous radiation-curable polyurethane dispersions (PUDs) are widely used in the production of materials such as coatings, inks and / or adhesives. After applying the aqueous radiation-curable polyurethane dispersion on a substrate, the dispersion is dried to obtain an at least partially dried coating composition, and then the at least partially dried coating composition is irradiated with ultraviolet light of a wavelength ≥ 300 nm or with an electron beam to obtain a radiation-cured coating. Such radiation-cured coatings exhibit very good properties on many substrates such as wood, plastics, concrete, metals, glass and / or textiles. The structure and functionality of radiation-curable polyurethane dispersions are known to control factors such as cure speed, degree of crosslinking and the final properties of the coating (especially properties such as flexibility, hardness, adhesion, scratch resistance and / or chemical resistance).

[0003] "Low gloss" surfaces give products a highly sought-after aesthetic effect, especially in the wooden furniture, flooring and wall covering industries, as they can create a very natural look, which helps to emphasize the materiality of the article even more. Currently, the creation of matt surfaces usually involves the use of coating products whose formulations contain matting agents made of organic and / or inorganic substances, which, by positioning themselves on the coating surface and / or appearing on the coating surface, are able to act on the degree of reflection of light to give the observer the visual perception of a low gloss surface. However, the use of matting agents leads to a deterioration of the surface properties of the coating, as they do not participate in the crosslinking and polymerization processes so that the stain resistance is significantly reduced. In addition, matting agents tend to migrate to the coating surface after application, so that the matting agents may be lost upon mechanical deformation, such as caused by scratching, so that the gloss increases.

[0004] The use of matting agents also seriously reduces the tolerance to typical household chemicals such as coffee, red wine and mustard. The long-term effect of these household chemicals at least leads to a reduction in the quality of the coating and may even lead to its complete destruction. Silicon dioxide-based compounds are the main matting agents used. Usually, silicon dioxide-based matting agents are porous, as shown by their oil absorption values ​​of 100-500 ml / 100 g. The disadvantage of using this type of matting agent in coating formulations is that it not only deteriorates the quality of the final coating, but also leads to undesirable coloring of the exposed coating area, because especially colored household stains such as coffee, red wine and mustard (part of DIN1B) are easily absorbed by porous silica, and because these stains contain organic dyes, this can lead to undesirable coloring of the exposed coating area.

[0005] It is an object of the present invention to provide a process for obtaining low-gloss coatings from aqueous radiation-curable polyurethane dispersions without having to use matting agents.

[0006] According to the present invention, there is provided a method for producing a coating, wherein the method comprises the following steps in the order (1) to (4):

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

[0008] (2) drying the aqueous radiation-curable coating composition to provide an at least partially dried coating composition,

[0009] (3) irradiating the at least partially dried coating composition with ultraviolet light having a wavelength of ≤220 nm under an inert atmosphere, and then

[0010] (4) Irradiation with ultraviolet light with a wavelength of ≥300nm or electron beam,

[0011] The aqueous radiation-curable coating composition is a dispersion comprising:

[0012] (A) at least one water-dispersible polyurethane (A), wherein the polyurethane (A) has a concentration of urea groups (—NH—CO—NH—) of at least 0.1 milliequivalents per gram of polyurethane (A) and at most 2.6 milliequivalents per gram of polyurethane (A), and the polyurethane (A) is substantially free of radiation-curable ethylenically unsaturated bonds,

[0013] (B) at least one radiation-curable diluent (B) having a molar mass of less than 750 g / mol and having an acrylate functionality of 2 to 5, and

[0014] (C) water and optionally an organic solvent, whereby the optional organic solvent is present in an amount of up to 30% by weight, based on the total amount of water and organic solvent,

[0015] The amount of (A) is 30 to 85% by weight, and the amount of (B) is 15 to 70% by weight, based on the total amount of (A) and (B).

[0016] It has surprisingly been found that the process of the present invention, which comprises pre-treating the coating composition with UV light of wavelength ≤ 220 nm (also further referred to as excimer irradiation step), enables obtaining low gloss coatings from aqueous radiation-curable polyurethane dispersions as defined herein, without the use of matting agents, and this is achieved while the aqueous dispersible polyurethane is substantially free of radiation-curable ethylenically unsaturated bonds. More particularly, with the process of the present invention, coatings having a gloss measured at 20° angular geometry of less than 10 gloss units, and preferably a gloss measured at 60° angular geometry of less than 40 gloss units (further referred to as low gloss), and more preferably a gloss measured at 60° angular geometry of less than 30 gloss units can be obtained. The aqueous radiation-curable coating composition according to the present invention allows obtaining a difference in gloss measured at 60° angular geometry of at least 40 gloss units, preferably at least 50 gloss units, more preferably at least 60 gloss units. It has furthermore surprisingly been found that the process of the invention enables low gloss coatings to be obtained from aqueous radiation curable polyurethane dispersions as defined herein without the use of matting agents, while at the same time improving the coffee, red wine and / or mustard resistance of the coating compared to when the dispersion contains a matting agent.

[0017] Another advantage of the present invention is that no matting agent needs to be handled, which is advantageous because matting agents have a large surface area and contain a large proportion of small dust-forming particles that may pose an exposure and explosion hazard. Another advantage of not having to use matting agents to obtain low-gloss coatings is that coating compositions with less or no sedimentation and thus improved storage stability can be achieved. Another advantage of the process of the present invention is that coatings with significantly higher smoothness can be obtained compared to when the coating contains matting particles. Another advantage of the process of the present invention is that coatings with good intercoat adhesion to subsequent coatings can be obtained.

[0018] WO-A-2013 / 092521 describes a method for producing uniform matte coatings on flat surfaces based on so-called 100% radiation-curable coating compositions. In this method, first, a 100% radiation-curable coating composition containing a low molecular weight radiation-curable oligomer as a binder and optionally one or more reactive diluents to reduce the viscosity is applied to the surface of a flat substrate using a spiral scraper. This wet paint layer is then irradiated with a wavelength of 200 to 420 nm and a radiation dose of 25 to 120 mJ / cm 2The coating composition is then irradiated with ultraviolet light to cause partial gelation of the coating composition. The coating thus obtained is then irradiated with ultraviolet light from an excimer lamp having a wavelength of 120nm to 230nm under an inert gas, followed by final curing using a conventional UV emitter. A 100% radiation-curable coating composition refers to a coating composition having a solid content of 100% by weight. A 100% radiation-curable coating composition refers to a homogeneous system having only one phase, while an aqueous radiation-curable polyurethane coating composition as defined herein is a dispersion having at least two phases, wherein one phase contains discrete particles (colloidally dispersed particles) distributed throughout an aqueous medium, the particles being a dispersed phase, and the aqueous medium being a continuous phase. WO-A-2013 / 092521 does not teach that a low gloss coating can be obtained from an aqueous coating composition, let alone an aqueous radiation-curable polyurethane dispersion as defined herein, and does not mention the stain resistance of the cured coating.

[0019] Another disadvantage of the method described in WO-A-2013 / 092521 is that the viscosity of the 100% radiation-curable coating composition is generally high, so that some application techniques, such as spraying, are difficult or impossible to use to apply the coating composition to the substrate. Spraying application can be advantageously used to apply the coating composition to substrates with more complex shapes, such as furniture or decorative frames. The viscosity of the 100% radiation-curable coating composition can be reduced by adding a monofunctional diluent with a low molecular weight, so that a viscosity that allows the radiation-curable coating composition to be deposited on the substrate by spraying can be obtained. However, applying a 100% radiation-curable coating composition by spraying inherently results in a coating having a high coating thickness.

[0020] Another advantage of using an aqueous radiation curable polyurethane dispersion as defined herein is that the viscosity can be controlled by adjusting the solids content with water so that with the process of the present invention the coating can be easily applied by spraying even at low coating thicknesses, e.g. 25 micrometers wet coating thickness.

[0021] Another advantage of the fact that aqueous radiation curable polyurethane dispersions as defined herein are easier to apply by spraying is that the process of the invention also enables low gloss coatings to be obtained on articles of more complex shapes, such as decorative frames, with a more uniform gloss of the coated article.

[0022] Another advantage of using an aqueous radiation curable coating composition as defined herein is that low gloss can be imparted to coatings having relatively low thicknesses (e.g., coating thicknesses of 50 microns or even less) using the process of the present invention. Another advantage of the present invention is that the gloss of the coating can be adjusted with the residual water and / or organic solvent content present in the at least partially dried coating composition.

[0023] Furthermore, it has surprisingly been found that with the coating composition as claimed, low gloss coatings can be obtained in only 2 irradiation steps (i.e. steps (3) and (4)), in particular for coatings with a wet thickness (before drying) of at most 300 microns, or at most 250 microns, or at most 200 microns or at most 175 microns, in particular at most 150 microns, more in particular at most 125 microns, more in particular at most 100 microns, and more in particular at most 75 microns. WO-A-2013 / 092521 teaches that an additional partial gelling irradiation step is required before the excimer irradiation step (step (3) of the method of the invention) and the final curing step (step (4) of the method of the invention), and thus WO-A-2013 / 092521 teaches that three irradiation steps are required to obtain a low gloss / matt coating with a homogeneous surface structure, see in particular Table 2.

[0024] The aqueous radiation-curable coating composition used in the process of the present invention is a dispersion comprising:

[0025] (A) at least one water-dispersible polyurethane (A), wherein the polyurethane (A) has a concentration of urea groups (—NH—CO—NH—) of at least 0.1 milliequivalents per gram of polyurethane (A) and at most 2.6 milliequivalents per gram of polyurethane (A), and the polyurethane (A) is substantially free of radiation-curable ethylenically unsaturated bonds,

[0026] (B) at least one radiation-curable diluent (B) having a molar mass of less than 750 g / mol and having an acrylate functionality of 2 to 5, and

[0027] (C) water and optionally an organic solvent, whereby the optional organic solvent is present in an amount of up to 30% by weight, based on the total amount of water and organic solvent,

[0028] The amount of (A) is 30 to 85% by weight, and the amount of (B) is 15 to 70% by weight, based on the total amount of (A) and (B).

[0029] A dispersion is a system having at least two phases, one of which contains discrete particles (colloidally dispersed particles) distributed throughout a bulk substance, the particles being the dispersed phase, and the bulk substance being the continuous phase. The continuous phase of an aqueous dispersion is provided at least in part by water. Preferably, the continuous phase of the dispersion of the present invention comprises at least 75% by weight, more preferably at least 80% by weight of water (relative to the continuous phase).

[0030] The aqueous coating composition used in the method of the present invention is radiation curable. Radiation curable means that radiation is required to initiate crosslinking of the dispersion. The aqueous coating composition used in the method of the present invention contains ethylenically unsaturated (C=C) bond functional groups, which can crosslink by free radical polymerization under the influence of radiation in combination with the presence of a (photo)initiator.

[0031] As used herein, the acrylate functionality of a compound is the number of acrylate functional groups per molecule of the compound.

[0032] The acrylate functional group has the formula:

[0033] CH2=CH-C(O)O-

[0034] For all upper and / or lower limits of any range given herein, unless otherwise specifically stated, the boundary values ​​are included in the given range. Thus, when reference is made to x to y, x and y and all intermediate values ​​are included.

[0035] Water-dispersible polyurethane (A)

[0036] The aqueous radiation-curable coating composition used in the process of the present invention comprises the polyurethane (A) in dispersed form, ie the composition comprises dispersed particles of the polyurethane (A).

[0037] The urea group (-NH-CO-NH-) concentration of the polyurethane (A) is at least 0.1 and at most 2.6 milliequivalents / gram of polyurethane (A). It has surprisingly been found that the use of a polyurethane (A) having a urea bond concentration of more than 2.6 milliequivalents / gram of polyurethane (A) in a process comprising steps (1) to (4) does not result in a low gloss coating. The polyurethane (A) preferably has a urea group content of at most 2.3 milliequivalents (meq) / g (A), more preferably at most 2.1 meq / g (A), even more preferably at most 1.9 meq / g (A), even more preferably at most 1.7 meq / g (A), even more preferably at most 1.5 meq / g (A), most preferably at most 1.3 meq / g (A), and preferably at least 0.2 meq / g (A), more preferably at least 0.3 meq / g (A), even more preferably at least 0.4 meq / g (A). The urea group (-NH-CO-NH-) concentration of the polyurethane (A) is determined by calculation as further described herein.

[0038] Methods for preparing polyurethanes are known in the art and are described, for example, in G. Oertel, Polyurethane Handbook, 2nd edition, published by Carl Hanser, 1994. Typically, an isocyanate-terminated polyurethane prepolymer is first formed and then chain extended, preferably with a nitrogen-containing compound.

[0039] The polyurethane (A) is preferably prepared by the reaction of at least the following components, and the polyurethane (A) is more preferably prepared by the reaction of the following components:

[0040] (A1) at least one polyisocyanate,

[0041] (A2) at least one isocyanate-reactive compound containing at least one salt group capable of rendering the polyurethane (A) dispersible in water and / or a functional group convertible into a salt group capable of rendering the polyurethane (A) dispersible in water, preferably an acid functional group,

[0042] (A3) optionally, at least one isocyanate-reactive compound containing at least one nonionic group capable of making the polyurethane (A) dispersible in water,

[0043] (A4) at least one isocyanate-reactive polyol different from (A2) and (A3) having an OH number of 25 to 225 mg KOH / g solids,

[0044] (A5) optionally, at least one isocyanate-reactive polyol different from (A2) and (A3) having an OH value of more than 225 mg KOH / g solid and less than 1850 mg KOH / g solid, and

[0045] (A6) water and / or at least one nitrogen-containing chain extender compound.

[0046] Preferred isocyanate-reactive groups are hydroxyl groups.

[0047] Component (A1)

[0048] At least one polyisocyanate is used as component (A1). The at least one polyisocyanate used according to the present invention is preferably selected from diisocyanates having the general formula Y(NCO)2, wherein Y is a C4-12 divalent aliphatic hydrocarbon group, i.e. an aliphatic diisocyanate compound, a C6-15 divalent alicyclic hydrocarbon group, i.e. an alicyclic diisocyanate compound, a C6-15 divalent aromatic hydrocarbon group, i.e. an aromatic diisocyanate compound, or a C7-15 divalent araliphatic hydrocarbon group, i.e. an araliphatic diisocyanate compound.

[0049] Examples of suitable organic difunctional isocyanates (component (A1)) include ethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate, dicyclohexylmethane diisocyanate (HMDI), such as 4,4'-dicyclohexylmethane diisocyanate (4,4'-H 12The preferred organic difunctional isocyanates are IPDI, HMDI and HDI. Mixtures of organic difunctional isocyanates may also be used.

[0050] Typically, the amount of component (A1) is 5 to 55% by weight, preferably 10 to 45% by weight, most preferably 15 to 40% by weight, based on the weight of the polyurethane (A).

[0051] Component (A2)

[0052] As component (A2), at least one isocyanate-reactive compound is used which contains at least one salt group, preferably a salt of an acidic group, which makes the polyurethane (A) dispersible in water and / or at least one functional group, preferably an acidic group, which can be converted into a salt group, preferably an acidic group, which makes the polyurethane (A) dispersible in water by reaction with a neutralizing agent.

[0053] Typically, the amount of component (A2) is 1 to 15% by weight, preferably 2 to 12% by weight, and even more preferably 3 to 10% by weight, based on the weight of polyurethane (A).

[0054] According to the present invention, the acidic group is preferably selected from a carboxylic acid group, a sulfonic acid group and / or a phosphoric acid group. Component (A2) is preferably a compound having two or more hydroxyl groups and / or two or more amino groups. Preferably, at least one compound having two or more hydroxyl groups is used as component (A2). A combination of at least one compound containing a carboxylic acid group and at least one compound containing a sulfonic acid group can be used. Preferred components (A2) are dihydroxy alkanoic acids and diamine sulfonates.

[0055] Preferably, at least one compound containing carboxylic acid groups is used as component (A2).

[0056] In the case where component (A2) contains at least one functional group that can be converted into a salt group by reaction with a neutralizing agent, the neutralizing agent for deprotonating (neutralizing) the functional group (preferably a carboxylic acid group, a sulfonic acid group and / or a phosphoric acid group, more preferably a carboxylic acid group) is preferably selected from ammonia, (tertiary) amines, metal hydroxides and any mixtures thereof. Suitable tertiary amines include triethylamine and N,N-dimethylethanolamine. Suitable metal hydroxides include alkali metal hydroxides, such as lithium hydroxide, sodium hydroxide and potassium hydroxide. Preferably, at least 30 mol%, more preferably at least 50 mol%, and most preferably at least 70 mol% of the total molar amount of the neutralizing agent is an alkali metal hydroxide, preferably selected from lithium hydroxide, sodium hydroxide, potassium hydroxide and any mixtures thereof. Preferably, the neutralizing agent for deprotonating (neutralizing) the carboxylic acid group, the sulfonic acid group and / or the phosphoric acid group is an alkali metal hydroxide. As used herein, the neutralizing agent (if any) is not regarded as a component from which the structural units of the polyurethane (A) are derived. Therefore, the calculation of the weight of polyurethane (A) does not take into account the amount of neutralizing agent (if any) used to prepare polyurethane (A).

[0057] In one embodiment of the present invention, component (A2) comprises or consists essentially of or consists of at least one diamine sulfonate. In this embodiment, the isocyanate-terminated polyurethane prepolymer is generally first formed by reaction of components (A1) and (A4) and optionally (A3) and optionally (A5), and then further reacted with the diamine sulfonate (A2) and water and optionally a nitrogen-containing chain extender compound (A6). A preferred diamine sulfonate is the sodium salt of 2-[(2-aminoethyl)amino]ethanesulfonic acid.

[0058] In a preferred embodiment of the present invention, component (A2) comprises or consists essentially of or consists of at least one dihydroxyalkanoic acid. In this embodiment, the isocyanate-terminated polyurethane prepolymer is usually first formed by reaction of components (A1), (A2) and (A4) and optionally (A3) and optionally (A5), and then chain extended with water and / or nitrogen-containing chain extender compounds (A6).

[0059] Preferred dihydroxyalkanoic acid is α,α-dimethylolpropionic acid and / or α,α-dimethylolbutanoic acid. More preferably, the dihydroxyalkanoic acid is α,α-dimethylolpropionic acid.

[0060] The amount of acidic groups present in polyurethane (A) is preferably such that the acid value of polyurethane (A) is 5 to 50, more preferably 10 to 40, still more preferably 15 to 30 mg KOH / g polyurethane (A) solid.

[0061] As used herein, acid value is determined according to the following formula:

[0062] AV [mgKOH / g solid] = (the sum of the acid groups present in the polyurethane (A) (in moles) / the total weight of the polyurethane (A)) * 56.1 * 1000.

[0063] Component (A3)

[0064] Optionally, at least one isocyanate-reactive compound containing at least one nonionic group which makes the polyurethane (A) dispersible in water is used as component (A3).

[0065] The polyurethane (A) may be further stabilized in dispersion by nonionic functional groups incorporated into the polyurethane (A). Thus, the polyurethane (A) may be at least partially nonionic stabilized by chemically incorporating nonionic groups into the polyurethane (A) to provide at least a portion of the hydrophilicity required to enable the polyurethane (A) to be stably dispersed in an aqueous dispersion medium. A preferred nonionic water-dispersing group is polyethylene oxide.

[0066] Preferred component (A3) is a polyethylene glycol having at least 5 ethylene oxide repeating units, preferably at least 10, more preferably at least 15 ethylene oxide repeating units, and preferably up to 120, more preferably up to 80, and even more preferably up to 40 ethylene oxide repeating units. More preferred component (A3) is a polyethylene glycol having 10 to 60, and preferably 15 to 30 ethylene oxide repeating units.

[0067] Non-limiting examples of suitable components (A3) include Ymer available from Perstorp TM N120 and MPEG750.

[0068] In the case of using component (A3) to prepare polyurethane (A), the amount of component (A3) is generally 1 to 15% by weight, preferably 1 to 12% by weight, most preferably 1 to 5% by weight, based on the weight of polyurethane (A).

[0069] Component (A4)

[0070] Use at least one OH value with 25 to 225mgKOH / g solid and be different from the isocyanate reactive compound of (A2) and (A3) as component (A4).Preferred component (A4) is the polyol that can be selected from any polyol chemical category that can be used for polyurethane synthesis.Especially, polyol can be polyester polyol, polyesteramide polyol, polyether polyol, polythioether polyol, polycarbonate polyol, polyacetal polyol, polyvinyl polyol and / or polysiloxane polyol.Preferably polyester polyol, polyether polyol and polycarbonate polyol.Preferably, the OH value of component (A4) is in the range of 35 to 190mgKOH / g solid, more preferably in the range of 45 to 125mgKOH / g solid.The OH value is provided by the supplier and can be measured by the titration of the alcohol of known mass according to ASTM D4274, and is expressed as mgKOH / g.

[0071] Typically, the amount of component (A4) is 20 to 80% by weight, preferably 30 to 70% by weight, more preferably 35 to 65% by weight, based on the weight of polyurethane (A).

[0072] Component (A5)

[0073] Optionally, at least one isocyanate-reactive compound having an OH number of more than 225 mg KOH / g solid and less than 1850 mg KOH / g solid and different from (A2) and (A3) is used as component (A5).

[0074] Examples of suitable components (A5) include neopentyl glycol (NPG), cyclohexanedimethanol (CHDM), butanediol, hexanediol and trimethylolpropane.

[0075] In the case of using component (A5) to prepare polyurethane (A), the amount of component (A5) is generally 0.5 to 10% by weight, preferably 1 to 8% by weight, most preferably 2 to 6% by weight, based on the weight of polyurethane (A).

[0076] Component (A6)

[0077] As chain extender component (A6) water and / or at least one nitrogen-containing chain extender compound are used.

[0078] For water chain extension, two NCO groups will form one urea bond. First, the NCO group reacts with water to form an unstable carbamic acid intermediate, which decomposes into CO2 and an amine group, which will then react with another NCO group to form a urea group. However, water chain extension is very slow compared to chain extension using nitrogen-containing chain extenders. Therefore, if a nitrogen-containing chain extender compound is applied, the calculation for the urea group concentration assumes that the isocyanate groups of the polyurethane prepolymer react first with the nitrogen-containing chain extender and during and / or after dispersion, the isocyanate groups still present on the polyurethane prepolymer react with water to form urea groups.

[0079] Examples of suitable nitrogen-containing chain extenders include amino alcohols, primary or secondary diamines or polyamines (including compounds containing primary and secondary amino groups), hydrazines and substituted hydrazines. Examples of such chain extender compounds useful herein include 2-(methylamino)ethylamine, aminoethylethanolamine, aminoethylpiperazine, diethylenetriamine and alkylenediamines such as ethylenediamine and 1,6-hexamethylenediamine, and cyclic amines such as isophoronediamine. The following compounds may also be useful: hydrazine, azines such as acetone azines, substituted hydrazines such as dimethylhydrazine, 1,6-hexamethylene-bishydrazines, carbon dihydrazides, hydrazides of dicarboxylic acids such as adipic acid dihydrazides, oxalic acid dihydrazides and isophthalic acid dihydrazides, hydrazides made by reacting lactones with hydrazides, bis-semi-carbazides and bis-hydrazide carbonates of diols. Water-soluble nitrogen-containing chain extenders are preferred.

[0080] Preferably, the nitrogen-containing chain extender compound is selected from the group consisting of amino alcohols, primary or secondary diamines, hydrazines, substituted hydrazines, substituted hydrazides, and any mixtures thereof.

[0081] When the chain extender is not water, such as hydrazine, it can be added to the aqueous dispersion of the isocyanate-terminated polyurethane prepolymer, or alternatively it can already be present in the aqueous medium when the isocyanate-terminated polyurethane prepolymer is dispersed in the aqueous medium. Chain extension can be carried out at a convenient temperature of about 5°C to 95°C, or more preferably about 10°C to 60°C.

[0082] If used, the total amount of nitrogen-containing chain extender compounds used should be such that the ratio of active hydrogens in the chain extender to isocyanate groups in the polyurethane prepolymer is preferably 0.1:1 to 2:1, more preferably 0.6:1 to 1.4:1, and especially preferably 0.8 to 1.2.

[0083] Preferably, component (A6) is water or water and at least one NH x (where x is 1 or 2) functionality, more preferably having 2 NH x More preferably, component (A6) comprises at least one NH containing chain extender having 2 or 3 NHx (where x is 1 or 2) functionality, more preferably having 2 NH x More preferably, component (A6) is water and at least one NH containing chain extender having 2 or 3 NH x (where x is 1 or 2) functionality, more preferably having 2 NH x The functional nitrogen-containing chain extender is selected from diamines and / or dihydrazides, wherein for hydrazides, the NH group attached to the carbonyl group is not considered as a chain extender.

[0084] The concentration of radiation-curable ethylenically unsaturated bonds (also referred to as C=C bond concentration) of the polyurethane (A) present in the aqueous radiation-curable coating composition used in the present invention is less than 0.25 meq / g polyurethane (A), preferably less than 0.2 milliequivalents / g polyurethane (A), more preferably less than 0.1 milliequivalents / g polyurethane (A), more preferably less than 0.05 milliequivalents / g polyurethane (A), more preferably less than 0.01 milliequivalents / g polyurethane. As used herein, the amount of radiation-curable ethylenically unsaturated bonds in the polyurethane (A) is determined by adding all radiation-curable C=C functionalities of the components from which the structural units of the polyurethane (A) are derived. As used herein, the expression " / g polyurethane (A)" is determined by the total weight of the components used to prepare the polyurethane from which the structural units of the polyurethane are derived. Most preferably, the polyurethane (A) contains no radiation-curable ethylenically unsaturated bonds.

[0085] Radiation curable diluent (B)

[0086] The aqueous radiation-curable coating composition comprises at least one radiation-curable diluent (B) having a molar mass of less than 750 g / mol and having an acrylate functionality of 2 to 5. The molar mass of the radiation-curable diluent (B) is calculated from its corresponding molecular formula, which indicates the number of atoms of each type in the radiation-curable diluent. Thus, the molar mass of (B) is the calculated molar mass obtained by adding the atomic masses of all atoms present in the structural formula of the compound.

[0087] 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 radiation curable diluent (B) is selected from:

[0088] With the corresponding molecular formula C 24 H 34O9 and its corresponding di(trimethylolpropane)tetraacrylate (di-TMPTA) with a molar mass of 467 g / mol,

[0089] With the corresponding molecular formula C 21 H 32 O8 and its corresponding di(trimethylolpropane) triacrylate (di-TMP3A) with a molar mass of 412 g / mol,

[0090] di(trimethylolpropane) triacrylate containing an alkoxy group,

[0091] With the corresponding molecular formula C 21 H 32 O9 and its corresponding glyceryl propoxy triacrylate (GPTA) with a molar mass of 428 g / mol,

[0092] Glyceryl propoxy triacrylate containing an additional alkoxy group,

[0093] With the corresponding molecular formula C 17 H 20 O8 and its corresponding pentaerythritol tetraacrylate (PET4A) with a molar mass of 352 g / mol,

[0094] Pentaerythritol tetraacrylate containing an alkoxy group,

[0095] With the corresponding molecular formula C 14 H 18 O7 and its corresponding pentaerythritol triacrylate (PET3A) with a molar mass of 298 g / mol,

[0096] Pentaerythritol triacrylate containing an alkoxy group,

[0097] With the corresponding molecular formula C 15 H 20 O6 and its corresponding trimethylolpropane triacrylate (TMPTA) with a molar mass of 296 g / mol,

[0098] trimethylolpropane triacrylate containing an alkoxy group,

[0099] With the corresponding molecular formula C 12 H 18 O5 and its corresponding dipropylene glycol diacrylate (DPGDA) with a molar mass of 242 g / mol,

[0100] Dipropylene glycol diacrylate containing an additional alkoxy group,

[0101] and any mixture thereof.

[0102] In case the radiation-curable diluent (B) comprises (additional) alkoxy groups, the maximum number of alkoxy groups is such that the molar mass remains below 750 g / mol.

[0103] In a more 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. %, most preferably at least 50 wt. %, more preferably at least 60 wt. %, more preferably at least 70 wt. %, more preferably at least 80 wt. %, more preferably at least 90 wt. %, and most preferably 100 wt. % of the radiation curable diluent (B) is selected from:

[0104] With the corresponding molecular formula C 24 H 34 O9 and its corresponding di(trimethylolpropane)tetraacrylate (di-TMPTA) with a molar mass of 467 g / mol,

[0105] With the corresponding molecular formula C 21 H 32 O8 and its corresponding di(trimethylolpropane) triacrylate (di-TMP3A) with a molar mass of 412 g / mol,

[0106] di(trimethylolpropane) triacrylate containing an alkoxy group,

[0107] With the corresponding molecular formula C 21 H 32 O9 and its corresponding glyceryl propoxy triacrylate (GPTA) with a molar mass of 428 g / mol,

[0108] Glyceryl propoxy triacrylate containing an additional alkoxy group,

[0109] With the corresponding molecular formula C 15 H 20 O6 and its corresponding trimethylolpropane triacrylate (TMPTA) with a molar mass of 296 g / mol,

[0110] trimethylolpropane triacrylate containing an alkoxy group,

[0111] With the corresponding molecular formula C 12 H 18 O5 and its corresponding dipropylene glycol diacrylate (DPGDA) with a molar mass of 242 g / mol,

[0112] Dipropylene glycol diacrylate (DPGDA) containing an additional alkoxy group,

[0113] and any mixture thereof.

[0114] Preferably, at least one radiation-curable diluent (B) has an acrylate functionality of 2 or 3, since this can advantageously lead to a more pronounced matting effect. The radiation-curable diluent (B) having an acrylate functionality of 2 is preferably selected from dipropylene glycol diacrylate (DPGDA) (having the corresponding molecular formula C 12 H 18 O5 and its corresponding molar mass 242g / mol); dipropylene glycol diacrylate containing additional alkoxy groups, preferably propoxy groups; and any mixture thereof.

[0115] The radiation-curable diluent (B) having an acrylate functionality of 3 is preferably selected from glyceryl propoxy triacrylate (GPTA) (having the corresponding molecular formula C 21 H 32 O9 and its corresponding molar mass 428g / mol); glyceryl propoxy triacrylate containing an additional alkoxy group, preferably a propoxy group; trimethylolpropane triacrylate (TMPTA) (having the corresponding molecular formula C 15 H 20 O6 and its corresponding molar mass 296g / mol); trimethylolpropane triacrylate containing alkoxy groups, preferably propoxy groups; having the corresponding molecular formula C 21 H 32 O8 and its corresponding di(trimethylolpropane) triacrylate (di-TMP3A) with a molar mass of 412 g / mol, di(trimethylolpropane) triacrylate containing an alkoxy group, preferably a propoxy group; pentaerythritol triacrylate (PET3A) (having the corresponding molecular formula C 14 H 18 O7 and its corresponding molar mass 298g / mol); pentaerythritol triacrylate containing alkoxy groups, preferably propoxy groups; and any mixtures thereof. The radiation-curable diluent (B) having an acrylate functionality of 2 or 3 preferably contains alkoxy groups, preferably propoxy groups (-C3H6O-).

[0116] Preferably, the composition further comprises at least one radiation-curable diluent (B) having an acrylate functionality of 4 or 5, since this advantageously leads to further improved chemical resistance. The radiation-curable diluent (B) having an acrylate functionality of 4 is preferably selected from di(trimethylolpropane) tetraacrylate (di-TMPTA) (having the corresponding molecular formula C 24 H 34 O9 and its corresponding molar mass 467g / mol); pentaerythritol tetraacrylate (PET4A) (with the corresponding molecular formula C 17 H 20 O8 and its corresponding molar mass 352g / mol); pentaerythritol tetraacrylate containing alkoxy groups, preferably propoxy groups; and any mixture thereof.

[0117] The radiation-curable diluent (B) having an acrylate functionality of 5 is preferably a diluent having the corresponding formula C 25 H 32 O 12 and dipentaerythritol pentaacrylate (DPPA) with a corresponding molar mass of 525 g / mol.

[0118] In a preferred embodiment, the aqueous radiation curable coating composition used in the process of the present invention comprises at least two radiation curable diluents (B), and the radiation curable diluents (B) present in the aqueous radiation curable coating composition have 2 to 4, preferably 2 to 3, diluents according to the formula The average acrylate functionality of k is the molar mass M present in the aqueous radiation curable coating composition k And has acrylate functionality f k Preferably, the aqueous radiation curable coating composition used in the process of the present invention comprises a monofunctional diluent in an amount of less than 7 wt %, more preferably less than 5 wt %, more preferably less than 3 wt %, and more preferably less than 1 wt %, and especially preferably less than 0.5 wt %, relative to the weight of the entire aqueous radiation curable coating composition.

[0119] The aqueous radiation curable coating composition used in the process may further comprise an acrylate diluent having a molar mass as defined for the (B) compound present in the radiation curable coating composition (i.e. below 750 g / mol) but having an acrylate functionality different from that defined for (B), for example having an acrylate functionality of 6. However, such an acrylate diluent may only be present in the aqueous radiation curable coating composition in an amount such that the average acrylate functionality of the acrylate diluent having a molar mass as defined for (B) (i.e. below 750 g / mol) is preferably from 2 to 5, more preferably from 2 to 4, even more preferably from 2 to 3.

[0120] Preferably, the aqueous radiation curable coating composition used in the process comprises a monofunctional diluent in an amount of less than 7 wt.-%, more preferably less than 5 wt.-%, more preferably less than 3 wt.-%, more preferably less than 1 wt.-%, most preferably less than 0.5 wt.-% relative to the weight of the entire aqueous radiation curable coating composition.

[0121] In an even more 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. %, most preferably at least 50 wt. %, more preferably at least 60 wt. %, more preferably at least 70 wt. %, more preferably at least 80 wt. %, more preferably at least 90 wt. %, and most preferably 100 wt. % of the radiation curable diluent (B) is a mixture of:

[0122] (1) di(trimethylolpropane) tetraacrylate (di-TMPTA) and / or a corresponding compound of formula C 17 H 20 O8 and its corresponding pentaerythritol tetraacrylate (PET4A) with a molar mass of 352 g / mol and / or pentaerythritol tetraacrylate containing an alkoxy group,

[0123] and

[0124] (2) Glyceryl propoxy triacrylate (GPTA) and / or glyceryl propoxy triacrylate containing additional alkoxy groups, preferably propoxy groups, and / or dipropylene glycol diacrylate (DPGDA) and / or dipropylene glycol diacrylate containing additional alkoxy groups, preferably propoxy groups.

[0125] In the present invention, the water-dispersible polyurethane (A) and the radiation-curable diluent (B) together preferably have a weight average molecular weight M of at least 15,000 g / mol, more preferably at least 20,000 g / mol, and even more preferably at least 30,000 g / mol. w The water-dispersible polyurethane (A) and the radiation-curable diluent (B) together preferably have a z-average molecular weight M of at least 25,000 g / mol, preferably at least 40,000 g / mol, more preferably at least 60,000 g / mol, more preferably at least 110,000 g / mol. z , and may even be higher than the highest z-average molecular weight measurable using the method used herein for determining weight average molecular weight. w and z-average molecular weight M z Determined as further described herein.

[0126] The amounts of (A) and (B) in the aqueous radiation-curable coating composition can vary within wide ranges, since water and optionally organic solvents can be used to adopt the viscosity and to adjust the layer thickness of the applied coating. Preferably, the amount of (A) is 35 to 80% by weight and the amount of (B) is 20 to 65% by weight, based on the total amount of (A) and (B), more preferably, the amount of (A) is 40 to 80% by weight and the amount of (B) is 20 to 60% by weight.

[0127] The total amount of (A) and (B) is preferably 10 to 60 wt%, more preferably 15 to 50 wt%, more preferably 15 to 45 wt%, even more preferably 20 to 40 wt%, even more preferably 25 to 35 wt%, based on the total weight of the aqueous radiation curable coating composition.

[0128] The optional organic solvent is at most 30 wt %, preferably at most 25 wt %, more preferably at most 20 wt %, more preferably at most 15 wt %, more preferably at most 10 wt %, more preferably at most 5 wt %, more preferably at most 1 wt %, wherein the amount of the organic solvent is based on the total amount of water and the organic solvent present in the aqueous radiation-curable coating composition. Suitable organic solvents are solvents that are inert to the functional groups present in the coating composition. Suitable solvents are, for example, hydrocarbons, alcohols, ketones and esters, such as cosolvents that also have a coalescing agent function, such as 1-methyl-2-pyrrolidone, glycols and glycol ethers, such as alkyl ethers of butyl diglycol, dipropylene glycol methyl ether, acetone, methyl ethyl ketone and glycol acetate or mixtures thereof. Most preferably, the aqueous radiation-curable coating composition is substantially free of organic solvents, i.e. preferably, organic solvents are not intentionally added to the aqueous radiation-curable coating composition (i.e., a small amount of organic solvents may be present in the additive for preparing the composition).

[0129] The total amount of the biobased carbon content in (A) and (B) relative to the total mass of carbon in (A) and (B), measured by method B according to standard ASTM D6866-12, is preferably at least 5% by weight, more preferably at least 10% by weight, more preferably at least 20% by weight, more preferably at least 30% by weight, most preferably at least 40% by weight relative to the total weight of (A) and (B).

[0130] The viscosity of the dispersion consisting of (A), (B) and (C) and containing 10 to 60 wt. % of (A) and (B), relative to the total amount of (A), (B) and (C), is preferably 10 to 1000 mPa.s, or 10 to 800 mPa.s, or 10 to 500 mPa.s. The viscosity is determined as further described herein.

[0131] The z-average particle size of the dispersion consisting of (A), (B) and (C) is preferably from 20 to 1000 nm, more preferably from 25 to 500 nm, even more preferably from 25 to 250 nm, and most preferably from 30 to 200 nm, whereby the z-average particle size is determined as further described herein.

[0132] The aqueous radiation-curable coating composition used in the method of the present invention is preferably substantially free of tin and / or substantially free of tertiary amines. As used herein, substantially free of tin means that the radiation-curable coating composition contains preferably up to 50 ppm (relative to the aqueous radiation-curable coating composition), more preferably up to 10 ppm, more preferably up to 5 ppm, and more preferably up to 2 ppm of tin, and more preferably, the aqueous radiation-curable coating composition used in the method of the present invention does not contain tin. As used herein, substantially free of tertiary amines means that the radiation-curable coating composition contains preferably up to 1.5 wt % (relative to the aqueous radiation-curable coating composition), more preferably up to 1 wt %, more preferably up to 0.5 wt %, and more preferably up to 0.1 wt % of tertiary amines, such as triethylamine, and more preferably, the aqueous radiation-curable coating composition used in the method of the present invention does not contain tertiary amines.

[0133] The coating composition generally further contains an additive compound; that is, a collection of one or more than one individual additives having one or more than one specified structure or type. Suitable additives are, for example, light stabilizers, such as ultraviolet absorbers and reversible free radical scavengers (HALS), photosensitizers, antioxidants, degassing agents, wetting agents, emulsifiers, slip additives, waxes, inhibitors, adhesion promoters, flow control agents, film formers, rheological aids such as thickeners, flame retardants, corrosion inhibitors, waxes, desiccants and biocides. One or more of the above additives may be used in any suitable amount in the coating composition used in the method of the present invention, and may be selected individually or in combination of one or more types listed herein. In a preferred embodiment, the additive compound is present in an amount of about 0% to 40% by weight, or 0% to 30% by weight, or 0% to 20% by weight, or 0% to 10% by weight, or 0% to 5% by weight, or 0.01% to 40% by weight, or 0.01% to 30% by weight, or 0.01% to 20% by weight, or 0.01% to 10% by weight, or 0.01% to 5% by weight, or 0.1% to 2% by weight, relative to the total weight of the coating composition. According to another embodiment, the additive compound is present in an amount of 1% to 40% by weight, or 1% to 30% by weight, or 1% to 20% by weight, or 1% to 10% by weight, or 1% to 5% by weight, relative to the weight of the entire radiation curable composition. Another advantage of the present invention is that the coating composition can also be colored without significantly complicating the application of the coating composition on the substrate. The coating composition then contains at least one pigment. Titanium dioxide (TiO2) is considered in the art to be a commercially important white pigment. Despite the porous nature of this type of pigment, it has surprisingly been found that the presence of this type of pigment in a coating composition as defined herein hardly impairs the coffee, red wine and / or mustard resistance of the coating, or only deteriorates it to such an extent that the resistance to coffee, red wine and / or mustard remains at an acceptable level.

[0134] The coating composition may also contain one or more inorganic fillers. The coating composition may also contain external matting agents with an additional matting effect, but this is not preferred. Suitable external matting agents are, for example, inorganic silica or organic waxes. The maximum amount of external matting agent is preferably at most 1.5 wt. %, more preferably at most 1 wt. %, and most preferably at most 0.5 wt. %, relative to the total weight of the coating composition.

[0135] The present invention further relates to a process for preparing the aqueous radiation-curable coating composition used in the process of the present invention.

[0136] The method for preparing the aqueous radiation-curable coating composition used in the method of the present invention comprises preparing an aqueous radiation-curable dispersion of particles comprising polyurethane (A), wherein at least a portion of the radiation-curable diluent (B) may be present during the preparation of the dispersion and / or at least a portion of the radiation-curable diluent (B) may be added after the preparation of the dispersion.

[0137] In a preferred embodiment of the present invention in which component (A2) comprises at least one dihydroxyalkanoic acid or consists essentially of at least one dihydroxyalkanoic acid or consists of at least one dihydroxyalkanoic acid, the process for preparing an aqueous radiation-curable coating composition comprising a water-dispersible polyurethane (A) preferably comprises

[0138] I. reacting components (A1), (A2) and (A4) and optionally (A3) and optionally (A5) to obtain a polyurethane prepolymer,

[0139] (a) blending a polyurethane prepolymer with an aqueous phase comprising a neutralizing agent and preferably comprising a nitrogen-containing chain extender compound (A6) to obtain a dispersion, or (b.1) neutralizing the polyurethane prepolymer by adding a neutralizing agent to the polyurethane prepolymer, and subsequently (b.2) adding the neutralized polyurethane prepolymer to water preferably comprising a nitrogen-containing chain extender compound (A6) to obtain a dispersion, or (b.2′) adding water preferably comprising a nitrogen-containing chain extender compound (A6) to the neutralized polyurethane prepolymer to obtain a dispersion, or (b.2″) adding the neutralized polyurethane prepolymer to water to obtain a dispersion, and then adding the nitrogen-containing chain extender compound (A6) to the dispersion, thereby

[0140] Step I can be carried out in the presence of at least a portion of the radiation-curable diluent (B); and / or at least a portion of the radiation-curable diluent (B) can be added after step I and before step II.(a) or before and / or after step II.(b.1), and / or at least a portion of the radiation-curable diluent (B) can be added after step II.(a) or after step II.(b.2) or after step II.(b.2'). Therefore, step I can also be carried out in the absence of a radiation-curable diluent (B). Any of the aforementioned steps can be carried out in the presence of a temporary solvent such as acetone or MEK removed from the aqueous polyurethane (A) dispersion.

[0141] In a preferred embodiment of the present invention in which component (A2) comprises at least one diamine sulfonate or consists essentially of at least one diamine sulfonate or consists of at least one diamine sulfonate, the process for preparing an aqueous radiation-curable coating composition comprising a water-dispersible polyurethane (A) preferably comprises

[0142] I. reacting components (A1), (A4) and optionally (A3) and optionally (A5) to obtain a polyurethane prepolymer,

[0143] II. (II.1) adding a polyurethane prepolymer to water containing a diamine sulfonate (A2) and preferably a nitrogen-containing chain extender compound (A6) to obtain a dispersion, or (II.1') adding water containing a diamine sulfonate (A2) and preferably a nitrogen-containing chain extender compound (A6) and optionally further adding water to the polyurethane prepolymer to obtain a dispersion, thereby

[0144] Step I can be carried out in the presence of at least a portion of the radiation-curable diluent (B); and / or at least a portion of the radiation-curable diluent (B) can be added after step I and before step II, and / or at least a portion of the radiation-curable diluent (B) can be added after step II. Therefore, step I can also be carried out in the absence of a radiation-curable diluent (B).

[0145] In the case where step I is carried out in the presence of a radiation-curable diluent (B), the amount of the radiation-curable diluent (B) containing isocyanate-reactive groups is selected so that the ethylenically unsaturated bond concentration of the polyurethane (A) is less than 0.25 meq / g polyurethane (A), preferably less than 0.2 milliequivalents / g polyurethane (A), more preferably less than 0.1 milliequivalents / g polyurethane (A), more preferably less than 0.05 milliequivalents / g polyurethane (A), more preferably less than 0.01 milliequivalents / g polyurethane (A), and most preferably so that the polyurethane (A) does not contain radiation-curable vinyl bonds. In the case where step I is carried out in the presence of a radiation-curable diluent (B), the radiation-curable diluent is preferably selected from glyceryl propoxy triacrylate, dipropylene glycol diacrylate, trimethylolpropane triacrylate, alkoxylated forms of any of the foregoing substances, and any mixtures thereof. Any of the foregoing steps can be carried out in the presence of a temporary solvent such as acetone or MEK removed from the aqueous polyurethane (A) dispersion.

[0146] The method of the present invention optionally includes a pre-curing step (2a). Carrying out the pre-curing step (2a) may be beneficial to improve adhesion, in particular to improve inter-coat adhesion. In this optional step (2a), pre-curing of the at least partially dried coating composition is achieved to provide an at least partially cured coating composition. In the optional step (2a), some reactive ethylenically unsaturated double bonds of the curable compound are polymerized in the uncured coating so that the coating is partially cured but not yet fully cured. This process is also referred to as pre-curing.

[0147] Therefore, the method of the present invention comprises the following steps in the order (1), (2), (2a), (3), (4) and (5):

[0148] (1) applying an aqueous radiation-curable coating composition onto a surface of a substrate,

[0149] (2) drying the aqueous radiation-curable coating composition to provide an at least partially dried coating composition,

[0150] (2a) optionally by irradiating with ultraviolet light having a wavelength of 300 to 450 nm, preferably 300 to 420 nm, at a dose of 20 to 200 mJ / cm 2 The radiation dose is preferably 30 to 100 mJ / cm 2 irradiating the at least partially dried coating composition with a radiation dose of 1000 Å to pre-cure the at least partially dried coating composition to provide an at least partially cured coating composition,

[0151] (3) irradiating the at least partially dried coating composition or the at least partially cured coating composition with ultraviolet light having a wavelength of ≤220 nm, preferably a wavelength of ≥120 nm, more preferably ≥150 nm, and particularly preferably 172 nm or 195 nm under an inert atmosphere, and then

[0152] (4) Irradiation with ultraviolet light of wavelength ≥ 300 nm or electron beam.

[0153] In step (1) of the method of the present invention, the aqueous radiation-curable coating composition is applied to the substrate by methods known to those skilled in the art (e.g., knife coating, brush coating, roller coating, spray coating). The coating composition is applied to the substrate in a coating thickness (before drying) of preferably 5 to 300 microns, more preferably 15 to 175 microns, more preferably 20 to 150 microns, more preferably 25 to 125 microns.

[0154] In step (2) of the process of the present invention, the drying of the aqueous radiation curable coating composition applied to the substrate is generally carried out at a temperature above 30° C. to evaporate water and optionally organic solvents and other volatile compounds to provide an at least partially dried coating composition. The term "drying" refers to the loss of water and, if present, organic solvents and other volatile compounds, such as neutralizing agent amines, from the aqueous coating composition by evaporation to such an extent that preferably at least 80% by weight of the water is removed.

[0155] The irradiation in the optional pre-curing step (2a) is preferably carried out under atmospheric conditions, in other words not under inert gas conditions and / or not in an oxygen-reduced atmosphere. Suitable radiation sources for the ultraviolet light in the specified wavelength range in step (2a) are UV-A emitting radiation sources (e.g. fluorescent tubes, LED lamps), high-pressure or medium-pressure mercury vapor lamps (wherein the mercury vapor can be modified by doping with other elements such as gallium or iron), pulsed lamps (so-called UV flash lamps) or halogen lamps. In a preferred embodiment of the present invention, the process is carried out without step (2a), i.e. the curing of the radiation-curable coating composition is carried out in only two irradiation steps, i.e. steps (3) and (4)).

[0156] A suitable radiation source for step (3) is an excimer ultraviolet lamp, which emits ultraviolet light with a wavelength of ≤220 nm, preferably ≥120 nm, more preferably ≥150 nm, and particularly preferably 172 nm or 195 nm. The radiation dose used in step (3) is generally in the range of 0.1 to 150 mJ / cm 2 , preferably 1 to 100 mJ / cm 2 , more preferably 1 to 20 mJ / cm 2 , more preferably 2 to 15 mJ / cm 2 In order to improve the inter-coat adhesion to the subsequent coating, the radiation dose used in step (3) is preferably 2 to 10 mJ / cm 2 , more preferably 2 to 8 mJ / cm 2 , even more preferably 2.5 to 6 mJ / cm 2 . Step (3) must be carried out in an inert gas atmosphere. An inert gas atmosphere is understood to mean an essentially oxygen-free atmosphere, i.e. an atmosphere containing less than 0.5% by volume of oxygen, preferably less than 0.1% by volume of oxygen, and particularly preferably less than 0.05% by volume of oxygen. Typically, an inert gas atmosphere is achieved by purging the area exposed to UV radiation with an inert gas stream. An inert gas atmosphere prevents unwanted ozone formation on the one hand, and prevents the polymerization of the paint layer from being inhibited on the other hand. Examples of inert gases are nitrogen, carbon dioxide, combustion gases, helium, neon or argon. Particularly preferably, nitrogen is used. This nitrogen should contain only very small amounts of foreign gases, such as oxygen, preferably with a purity grade of <300 ppm oxygen.

[0157] In step (4) of the method of the present invention, the coating obtained in step (3) is irradiated with ultraviolet light having a wavelength ≥ (higher than or equal to) 300 nm or with electron beams to achieve a major or preferably complete polymerization of the radiation curable compounds of the coating composition, so that the coating is preferably completely cured. In the case of applying electron beam irradiation (150 to 300 kV) in step (4), a dose of 10 to 100 kGy, preferably 20 to 50 kGy, is generally applied. In step (4), ultraviolet irradiation is preferred, preferably with a wavelength of 300 to 420 nm and preferably with a power of 100 to 2000 mJ / cm 2 , more preferably 150 to 1500 mJ / cm 2 The radiation dose of the present invention can be 0.1 to 5% by weight of the total coating composition. Preferably, the one or more photoinitiators are present in an amount of 0.25% to 4% by weight, more preferably 0.5% to 3.5% by weight, and even more preferably 0.5% to 3% by weight, relative to the total weight of the coating composition.

[0158] Photoinitiator is a compound that chemically changes to produce at least one of free radicals, acids and bases due to the action of light or the synergistic effect between the action of light and the electronic excitation of the sensitizing dye. Known photoinitiator types include cationic photoinitiators and free radical photoinitiators. According to one embodiment of the present invention, the photoinitiator is a free radical photoinitiator.

[0159] In one embodiment, the photoinitiator compound includes, consists of, or consists essentially of one or more acylphosphine oxide photoinitiators. Acylphosphine oxide photoinitiators are known and disclosed, for example, in U.S. Pat. Nos. 4,324,744, 4,737,593, 5,942,290, 5,534,559, 6,020,529, 6,486,228, and 6,486,226. Preferred types of acylphosphine oxide photoinitiators for the photoinitiator compound include bisacylphosphine oxide (BAPO) or monoacylphosphine oxide (MAPO). More specifically, examples include 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (CAS#84434-11-7) or 2,4,6-trimethylbenzoyldiphenylphosphine oxide (CAS#127090-72-6).

[0160] In a preferred embodiment, the photoinitiator compound may also optionally comprise, consist of, or consist essentially of an α-hydroxyketone photoinitiator. For example, suitable α-hydroxyketone photoinitiators are α-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropanone, 2-hydroxy-2-methyl-1-(4-isopropylphenyl)propanone, 2-hydroxy-2-methyl-1-(4-dodecylphenyl)propanone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one, and 2-hydroxy-2-methyl-1-[(2-hydroxyethoxy)phenyl]propanone.

[0161] In another embodiment, the photoinitiator compound comprises, consists of, or consists essentially of: 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; benzophenones, such as benzophenone, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, 2-methylbenzophenone, 2-methoxycarbonyldi ... benzophenone, 4,4'-bis(chloromethyl)-benzophenone, 4-chlorobenzophenone, 4-phenylbenzophenone, 4,4'-bis(dimethylamino)-benzophenone, 4,4'-bis(diethylamino)benzophenone, 2-benzoylbenzoic acid methyl ester, 3,3'-dimethyl-4-methoxybenzophenone, 4-(4-methylphenylthio)benzophenone, 2,4,6-trimethyl-4'-phenyl-benzophenone or 3-methyl-4'-phenyl-benzophenone; ketal compounds, for example 2,2-dimethoxy-1,2-diphenyl-ethanone; and monomeric or dimeric benzoylformates, such as methylbenzoylformate, 5,5'-oxy-bis(ethyleneoxydicarbonylphenyl) or 1,2-(benzoylcarboxy)ethane.

[0162] Other suitable photoinitiators for use in the photoinitiator compound include oxime esters, such as those disclosed in US Pat. No. 6,596,445. Yet another class of suitable photoinitiators for use in the photoinitiator compound include, for example, phenyl glyoxylates, such as those disclosed in US Pat. No. 6,048,660.

[0163] In another embodiment, the photoinitiator compound may comprise, consist of, or consist essentially of one or more alkyl-, aryl-, or acyl-substituted compounds not mentioned above.

[0164] According to another embodiment, the composition may contain a photoinitiator that is an alkyl-, aryl- or acyl-substituted compound. In one embodiment, the alkyl-, aryl- or acyl-substituted photoinitiator has or is centered on an atom in the carbon group (Group 14). In this case, upon excitation (by absorbing radiation), the Group 14 atoms present in the photoinitiator compound form free radicals. Such compounds can therefore produce free radicals having or being centered on an atom selected from silicon, germanium, tin and lead. In one embodiment, the alkyl-, aryl- or acyl-substituted photoinitiator is an acylgermanium compound. Such photoinitiators are described in US9708442 assigned to DSMIPAssets B.V. Specific acylgermanium photoinitiators known include benzoyltrimethylgermane (BTG), tetraacylgermane or bisacylgermane (available as Commercially available from Ivoclar Vivadent AG, 9494 Schaan / Liechtenstein).

[0165] Photoinitiators can be used alone or in combination as a blend. Suitable photoinitiator blends are disclosed, for example, in U.S. Patent No. 6,020,528 and U.S. Patent Application No. 60 / 498,848. According to one embodiment, the photoinitiator compound includes, for example, a photoinitiator blend of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (CAS#162881-26-7) and 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (CAS#84434-11-7) in a weight ratio of about 1:11, 1:10, 1:9, 1:8 or 1:7.

[0166] Another particularly suitable photoinitiator blend is a mixture of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone (CAS#7473-98-5), for example, in a weight ratio of about 3:1:15 or 3:1:16 or 4:1:15 or 4:1:16. Another suitable photoinitiator blend is a mixture of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-1-propanone, for example, in a weight ratio of about 1:3, 1:4 or 1:5.

[0167] One or more of the above-mentioned photoinitiators may be used in any suitable amount in the photoinitiator compound of the composition used in the method according to the invention and may be selected individually or in combination of one or more types listed herein. In a preferred embodiment, the photoinitiator compound comprises, consists of or consists essentially of a free radical photoinitiator, which is preferably of the α-cleavage type.

[0168] Suitable substrates for the method according to the invention are, for example, mineral substrates, such as fiber cement boards, wood, wood-containing materials, paper (including cardboard), textiles, 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, novolac resins, polyesters and urea-formaldehyde.

[0169] The substrate is optionally pretreated and / or optionally precoated. For example, a thermoplastic film may be treated with a corona discharge or precoated with a primer prior to application. Mineral building materials are also typically provided with a primer prior to application of the coating composition.

[0170] The coatings obtained in the process of the invention can advantageously be used for floor or wall coverings or for automotive interiors or furniture.

[0171] The present invention further relates to an aqueous radiation curable coating composition as described above and for use in the process of the present invention.The present invention further relates to a coated substrate obtained by coating a substrate with a process as described above.

[0172] The invention will now be illustrated with reference to the following examples. Unless otherwise indicated, all parts, percentages and ratios are by weight.

[0173] Measurement method

[0174] Average particle size PS:

[0175] The intensity average particle size, z-average, was determined by photon correlation spectroscopy using a Malvern Zetasizer Nano ZS. The sample was diluted in demineralized water to a concentration of approximately 0.1 g dispersion / liter. The measurement temperature was 25°C. The laser incident angle was 173°. The laser wavelength was 633 nm.

[0176] pH

[0177] The pH was measured using a Metrohm pH meter.

[0178] Solid content

[0179] The solids content of the dispersions was measured on a HB43-S halogen moisture analyzer from Mettler Toledo at a temperature of 75°C.

[0180] Viscosity

[0181] Viscosity was measured using a Brookfield LV (spindle 2 at 60 rpm, room temperature).

[0182] Number average molecular weight, weight average molecular weight, z average molecular weight and molecular weight distribution

[0183] The number average molecular weight, weight average molecular weight, z average molecular weight and molecular weight distribution were determined by size exclusion chromatography at 40°C using three silica-modified 7μm PFG columns on a Waters Alliance 2695 LC system with a Waters 2410 DRI detector and a Waters 2996 PDA detector. Hexafluoroisopropanol (HFIP) and PTFA 0.1% were used as eluents with a flow rate of 0.8 mL / min. The samples were dissolved in the eluent using a concentration of 5 mg polymer / mL solvent. The solubility was judged with a laser pen after stabilization for 24 hours at room temperature; if any scattering was visible, the sample was first filtered using a 0.45μm PTFE filter and 150μl of the sample solution was injected. M was calculated using 11 narrow polymethyl methacrylate standards from 645 to 1.677.000Da supplied by Agilent. W (weight average molecular weight), M z (z-average molecular weight) and MWD (molecular weight distribution) results.

[0184] Generally, a series of average molecular weights can be defined by the following equation: M = ∑N i M n+1 / ∑N i M i n , from which: n = 0, we get M = M n ; n = 1 gives M = Mw, n = 2 gives M = M z Higher average values ​​are increasingly sensitive to high molecular weight polymers. i The molecular weight is M i The number of molecules.

[0185] Glossiness

[0186] Gloss is measured in the drawdown direction according to ISO 2813 and is expressed in gloss units (GU).

[0187] Stain resistance

[0188] Coffee, red wine and mustard tolerance were determined colorimetrically using an eXact standard handheld spectrophotometer from X-rite and are reported in Tables 5 and 6. For coffee, the spots were exposed for 1 hour, 6 hours and rated after 24 hours. For red wine and mustard, the spots were exposed for 6 hours and rated after 24 hours. a- and b-values ​​were measured according to ISO7724. Coffee and mustard tolerance was determined by Δb values, where Δb value = b (分别在咖啡暴露6小时和1小时或芥末暴露6小时后并在24小时后评级) –b (暴露前) A higher Δb value indicates a greater color change caused by staining, and therefore poor stain resistance. Red wine resistance is determined using the Δa value colorimetrically, where Δa value = a (在红酒暴露6小时后并在24小时后评级) -a (暴露前) A higher Δa value indicates a greater color change caused by staining, and therefore poor stain resistance. The a* axis is relative to the green-red color opposition, with negative values ​​tending toward green and positive values ​​tending toward red. The b* axis represents the blue-yellow color opposition, with negative numbers tending toward blue and positive numbers tending toward yellow.

[0189] Method for calculating the urea content in polyurethane (A)

[0190] As known to the person skilled in the art, the concentration of urea bonds in the polyurethane (A) in meq / g solids is determined by calculation according to the formula given below.

[0191] Urea content PU(A)=(((total NCO-total OH-total NH x )*ED*(AF CE / AH CE ))+((Total NCO-Total OH-Total NH x )*(1-ED)*0,5)+total NH x )*1000 / W PU(A)

[0192] in

[0193] Total NCO: the number of NCO groups in moles originating from component (A1),

[0194] Total OH: number of alcohol groups in moles from components (A2) to (A5),

[0195] Total NH x : The molar amount of amine (NH x , where x = 1 or 2) the total number of groups,

[0196] W PU(A) : the total weight of polyurethane (A) [components (A1) to (A6)] in grams,

[0197] ED: chain extension degree: the molar ratio of active hydrogen in the nitrogen-containing chain extender (A6) to the theoretical residual isocyanate groups in the polyurethane prepolymer (= total NCO-total OH-total NH x ),

[0198] AH CE : The number of active hydrogen atoms in the nitrogen-containing chain extender (A6), where each NH x (where x = 1 or 2) The functionality is counted as one active hydrogen, except for hydrazides where the NH group attached to the carbonyl is not considered a chain extending group.

[0199] AF CE : NH of nitrogen-containing chain extender (A6) x A functionality where x = 1 or 2 and where for hydrazide, the NH group attached to the carbonyl group is not considered a chain extending group.

[0200] We illustrate this calculation with the following theoretical example.

[0201] Calculation of the urea group content in the polyurethane (A) for theoretical examples I to VI

[0202]

[0203]

[0204]

[0205] Method for calculating dry film thickness

[0206] The dry film thickness is calculated by multiplying the wet film thickness by the solids content of the formulation used.

[0207] DFT = WFT * solid content / 100

[0208] in

[0209] DFT: Dry film thickness in μm

[0210] WFT: wet film thickness in μm

[0211] Solid content (wt%): total weight of all solid compounds present in a formulation divided by (total weight of the formulation*100).

[0212] Components and abbreviations used :

[0213] IPDI = isophorone diisocyanate available from Covestro

[0214] HDI = Hexane diisocyanate available from Covestro

[0215] W = DesW = HMDI = dicyclohexylmethane diisocyanate available from Covestro

[0216] DMPA = dimethylolpropionic acid available from Perstorppolyols

[0217] PPG2000 = polypropylene glycol available from BASF, OH value = 56 mgKOH / g

[0218] pTHF1000 = polytetramethylene glycol available from BASF, OH value = 112.5 mg KOH / g

[0219] pTHF650 = polytetramethylene glycol available from BASF, OH value = 173 mg KOH / g

[0220] Ymer TM N120 = nonionic diol available from Perstorp, OH value = 110 mg KOH / g

[0221] CHDM = 1,4-cyclohexanedimethanol available from Eastman

[0222] NPG = neopentyl glycol available from Perstorp

[0223] TEA = triethylamine from Arkema

[0224] DPGDA = dipropylene glycol diacrylate available from Covestro

[0225] GPTA = propoxylated (3) glyceryl triacrylate available from Covestro

[0226] TMPTA = trimethylolpropane triacrylate available from Covestro

[0227] DiTMPTA = ditrimethylolpropane tetraacrylate available from Covestro

[0228] Agisyn TM 2020 = Partially acrylated epoxidized soybean oil available from Covestro

[0229] Agisyn TM 2830L = dipentaerythritol hexaacrylate available from Covestro

[0230] EGDMA = ethylene glycol dimethacrylate available from Covestro

[0231] BHT = Butylated hydroxytoluene available from Brenntag

[0232] Hydrazine = Hydrazine hydrate available from Arkema (16%)

[0233] Vestamin A-95 = Sodium N-(2-aminoethyl)aminoethanesulfonate (51% w / w aqueous solution)

[0234] EDA = ethylenediamine available from Caldic

[0235] Bismuth ND = bismuth neodecanoate catalyst available from Reaxis

[0236] Omnirad500 = photoinitiator available from IGM

[0237] Omnirad1173 = Photoinitiator from IGM

[0238] BYK346 = surfactant available from BYK (45% solids content)

[0239] Butyl glycol = solvent available from Aldrich

[0240] Airex902W = defoamer available from Evonik (24% solids)

[0241] GelL75N = rheology modifier available from Borchers (50% solids)

[0242] TS100 = Silica matting agent from Evonik

[0243] Example 1: Preparation of polyurethane resin dispersion (PUDEx1)

[0244] A 1000 cm 3 The flask was charged with components DMPA (15.0 g), PPG2000 (169.2 g) and IPDI (65.1 g). The reaction was heated to 50° C. Then 0.08 g of bismuth neodecanoate was added. After the exotherm was complete, the reaction was maintained at 90° C. for 120 minutes. The NCO content of the resulting isocyanate-terminated prepolymer was 2.93% (theoretically 3.29%). The prepolymer was cooled to 80° C., and DPGDA (167.8 g), BHT (0.17 g) and TEA (11.3 g) were added and mixed at 50-60° C. for 10 minutes.

[0245] A dispersion of the resulting isocyanate-terminated prepolymer was made by feeding 285.8 g of the resulting prepolymer mixture into deionized water (505.7 g) over 45 minutes.

[0246] The dispersion temperature was controlled between 25 and 30° C. Hydrazine (10.4 g) was added after the feed was complete.

[0247] Example 2-7: Preparation of polyurethane resin dispersion (PUDEx.2–PUDEx.7)

[0248] For Examples 2, 3, 4, 5 and 7, the process described for Example 1 was repeated using the components and amounts as specified in Table 1a, except that the radiation-curable diluent (TMPTA in Example 2, GPTA in Example 3 and DPGDA in Examples 4, 5 and 7) was charged to the reactor at the beginning of the prepolymer reaction along with the other components (polyisocyanate, dispersed diol, nonionic diol (if used) and polyol).

[0249] For Example 6, the process described for Example 1 was repeated using the components and amounts as specified in Table 1a, except that DPGDA was charged to the reactor at the beginning of the prepolymer reaction along with the other components (polyisocyanate, DMPA and polyol) and DiTMPTA (instead of DPGDA) was added to the prepolymer after it had cooled.

[0250] Comparative experiment 1: Preparation of polyurethane resin dispersion (PUDCEx1)

[0251] A 1000 cm 3 The flask was charged with components DMPA (24.9 g), PPG2000 (282.1 g) and IPDI (108.6 g). The reaction was heated to 50°C. 0.08 g of bismuth neodecanoate was then added. After the exotherm was complete, the reaction was held at 90°C for 120 minutes. The NCO content of the resulting isocyanate-terminated prepolymer was 2.74% (theoretical 3.29%). The prepolymer was cooled to 80°C and TEA (18.8 g) was added.

[0252] A dispersion of the resulting isocyanate-terminated prepolymer was prepared by feeding 289 g of the resulting prepolymer mixture into deionized water (492.5 g) over 45 minutes.

[0253] The dispersion temperature was controlled between 25 and 30° C. Hydrazine (16.3 g) was added after the feed was complete.

[0254] Comparative Experiment 2-6: Preparation of Polyurethane Resin Dispersions (PUDCEx.2–PUDCEx.6)

[0255] For comparative experiments 2-6, the method described for comparative experiment 1 was repeated with the components and amounts as specified in Table 1b, except that the radiation-curable diluent added after the prepolymer was cooled and before dispersion was also applied. For comparative experiments 5-6, the method described for comparative experiment 1 was repeated with the components and amounts as specified in Table 1b, except that the radiation-curable diluent (DPGDA) was charged to the reactor at the beginning of the prepolymer reaction together with the other components (i.e., polyisocyanate, dispersing diol and polyol).

[0256] Tables 1a and 1b specify the components and their amounts used to prepare the polyurethane resin dispersions of Examples 1 to 7 and Comparative Experiments 1 to 6. Unless otherwise stated, the amounts of the various components are expressed in grams.

[0257] The properties of the resulting compositions are shown in Table 2.

[0258] Table 1a-1 : Composition of PUD Examples 1-7 - Preparation of Prepolymer Mixtures

[0259]

[0260]

[0261] Table 1a-2 : Composition of PUD Examples 1-7 - Dispersion Step

[0262]

[0263] Table 1b-1 : Composition of PUDs of Comparative Experiments 1-6 – Preparation of Prepolymer Mixtures

[0264]

[0265] Table 1b-2 : Composition of PUD in Comparative Experiments 1-6 – Dispersion Step

[0266]

[0267] Table 2 :Specification

[0268]

[0269]

[0270]

[0271] Preparation of formulations

[0272] The PUDs of Examples 1-7 and Comparative Experiments 1-6 were formulated as shown in Table 3. The ingredients listed in Table 3 were added to a PE jar and (Orange Line, ATP Engineering B.V.) and mix thoroughly.

[0273] Table 3 Formulations without and with matting agent from PUD Examples 1-7 and from PUD Comparative Experiments 1-6

[0274]

[0275]

[0276]

[0277] Application of formulation

[0278] The coating composition thus obtained was applied to a Leneta card (2CLeneta Inc) using a 125 μm wire rod applicator. The coated card was dried in an oven at 50° C. for 10 minutes at an air speed of 1.2 m / s. The dried composition thus obtained was then cured, and the curing conditions are shown in Tables 4-6. In Table 7, 125, 75, 50 and 25 μm wire rod applicators were used, respectively.

[0279] Curing of the dried coating composition

[0280] Excimer / UV curing:

[0281] Immediately after drying (within 20 seconds), the formulation was cured on a UVio curing rig equipped with 2 lamps at a conveyor speed of 15 m / min. The first lamp was an Excirad 172 lamp (IOT GmbH, a xenon-based excimer lamp generating 172 nm light), under which a nitrogen atmosphere (O2 level <50 ppm detected with an IOT online detector) was used at 11.4 mJ / cm 2 The curing was carried out with a radiation dose of 1000 mJ / cm (except for formulation 4c) (measured with Tinytracker 172, IOT GmbH). The next curing step was carried out with a second lamp, which was a LightHammer 10 Mark III (Heraeus Holding, Hg-doped UV lamp) equipped with an H-bulb operating at 50% power, which generated UV light with a wavelength of ≥315 nm, with a total dose of 181 mJ / cm as measured with a PowerPuck II (EIT Inc). 2 ).

[0282] Conventional UV atmospheric curing (Conv UVcure atmosph):

[0283] Immediately after drying (within 20 seconds), the formulation was cured on a UVio curing unit with a conveyor speed of 15 m / min. The total dose was 181 mJ / cm2 as measured with a Power Puck II (EIT Inc) by a Light Hammer 10 Mark III (Heraeus Holding, Hg-doped UV lamp) equipped with an H-bulb operating at 50% power. 2 ) The curing step is carried out in air.

[0284] Conventional UV inert atmosphere curing (Conv UVcure inert):

[0285] Immediately after drying (within 20 seconds), the formulation was cured on a UVio curing unit with a conveyor speed of 15 m / min. The total dose was 181 mJ / cm2 as measured with a Power Puck II (EIT Inc) by a Light Hammer 10 Mark III (Heraeus Holding, Hg-doped UV lamp) equipped with an H-bulb operating at 50% power. 2 ) The curing step is carried out under an inert atmosphere.

[0286] Testing of Cured Coatings

[0287] The gloss and coffee, red wine and mustard resistance of the cured coatings were determined as described above. The measured gloss values ​​are reported in Tables 4 and 6. The coffee, red wine and mustard resistance are reported in Tables 4 and 5.

[0288] Table 4 : measured gloss values ​​of formulations without matting agent and cured with excimer / UV curing; gloss values ​​of formulations with matting agent and cured with conventional UV curing under atmospheric conditions; colorimetrically measured stain resistance of formulations without matting agent and cured with excimer / UV curing, and colorimetrically measured stain resistance of formulations with matting agent and cured with conventional UV curing under atmospheric conditions (ConvUVatmosph) and conventional UV curing under inert conditions (ConvUVinert), respectively

[0289]

[0290] Figure 1Shows coated test cards obtained by the excimer / UV curing method according to the method of the present invention for formulation 4a containing the PUD of Example 4 but without a matting agent (upper test card) and by conventional UV curing under atmospheric conditions for formulation 4b containing the PUD of Example 4 and a matting agent (bottom test card);

[0291] From left to right: coffee [6 hours], red wine [6 hours], and coffee [1 hour] stains.

[0292] Table 5 : Colorimetric stain resistance of formulations without matting agent and cured with excimer / UV curing (Δb for coffee and mustard and Δa for red wine)

[0293]

[0294]

[0295] Table 6 : Gloss values ​​measured for formulations without matting agent after combined excimer / UV curing and conventional UV curing under atmospheric conditions

[0296]

[0297] Coating formulation 4c was applied to Leneta cards (2C Leneta Inc) using a 125 μm wire bar applicator. The coated cards were dried in an oven at 50°C at an air velocity of 1.2 m / s for 10 minutes. The dried composition thus obtained was subsequently cured according to the above curing conditions, except that the radiation dose of the Excirad 172 lamp was 4.0 mJ / cm 2 Instead of 11.4mJ / cm 2 After 1 hour, a second layer of coating formulation 4c was applied over the first coating using a 125 μm wire bar applicator without further treatment of the first layer (eg sanding), and the same drying and curing conditions were applied.

[0298] After the second coat is cured, the intercoat adhesion is tested by using a nail. The nail is placed on the coating with a certain force as described below and moved over the coating for a distance of approximately 5 cm. A score of "-" is given when the second coat is easily peeled off from the first coat under a small / mild force; a score of "+ / -" is given when the second coat is peeled off from the first coat when a moderate force is applied; and a score of "+" is given when the second coat is not peeled off from the first coat even when a high force is applied.

[0299] When the coating does not peel off after applying high force using the fingernail test, repeat the test with a stainless steel scraper with a non-bent blade width of 8 mm instead of the fingernail. The scraper is held at a 45 degree angle and moved over the coating a distance of approximately 5 cm with a force as described above for the fingernail test. The same scoring as for the fingernail test is used.

[0300] Table 7 reports the nail and scraper test scores and the gloss values ​​measured for the cured coatings obtained from formulation 4c.

[0301] Table 7

[0302]

[0303] Table 8 :Effect of layer thickness on gloss value

[0304]

[0305] With the process of the invention, low gloss coatings can be obtained at very low dry film thicknesses, even low gloss coatings with a dry film thickness of 7 microns can be obtained, whereas when the formulation contains a matting agent (Formulation 9b) and the formulation is cured with conventional UV curing, no suitable films with such low dry film thicknesses can be obtained.

[0306] Comparative Experiment 7-13

[0307] A representative set of commercially available water-based UV-curable coating dispersions as specified in Table 9 was applied to Leneta cards (2CLeneta Inc) using a 125 μm wire bar applicator. The coated cards were dried in an oven at 50° C. at an air speed of 1.2 m / s for 10 minutes. The dried composition thus obtained was subsequently cured using conventional UV atmospheric curing and excimer / UV curing as described above. The measured gloss values ​​are reported in Table 9. The commercially available water-based UV-curable coating compositions as shown in Table 9 have different compositions from the water-based radiation-curable coating compositions of the present invention.

[0308] Table 9 : Gloss values ​​of a representative set of commercially available waterborne UV-curable coating compositions after conventional UV curing and combined excimer / UV curing under atmospheric conditions

[0309]

[0310] Table 9 shows that this representative set of commercially available waterborne UV curable compositions did not give a matte coating when subjected to excimer / UV curing.

Claims

1. A method for producing a coating from an aqueous radiation-curable coating composition, wherein the method comprises the following steps in the order (1) to (4): (1) applying an aqueous radiation-curable coating composition onto a surface of a substrate, (2) drying the aqueous radiation-curable coating composition to provide an at least partially dried coating composition, (3) irradiating the at least partially dried coating composition with ultraviolet light having a wavelength of ≤220 nm under an inert atmosphere, and then (4) Irradiation with ultraviolet light with a wavelength of ≥300nm or electron beam, The aqueous radiation-curable coating composition is a dispersion comprising: (A) at least one water-dispersible polyurethane (A), wherein the polyurethane (A) has a concentration of urea groups (—NH—CO—NH—) of at least 0.1 milliequivalents per gram of polyurethane (A) and at most 2.6 milliequivalents per gram of polyurethane (A), and the polyurethane (A) is substantially free of radiation-curable ethylenically unsaturated bonds, (B) at least one radiation-curable diluent (B) having a molar mass of less than 750 g / mol and having an acrylate functionality of 2 to 5, and (C) water and optionally an organic solvent, whereby the optional organic solvent is present in an amount of up to 30% by weight, based on the total amount of water and organic solvent, in The amount of (A) is 30 to 85% by weight, and the amount of (B) is 15 to 70% by weight, based on the total amount of (A) and (B).

2. The method according to claim 1, wherein the polyurethane (A) has a urea group content of at most 2.3 milliequivalents (meq) / g(A), more preferably at most 2.1 meq / g(A), more preferably at most 1.9 meq / g(A), more preferably at most 1.7 meq / g(A), more preferably at most 1.5 meq / g(A), more preferably at most 1.3 meq / g(A), and preferably at least 0.2 meq / g(A), more preferably at least 0.3 meq / g(A), and even more preferably at least 0.4 meq / g(A).

3. The process according to any one of claims 1 to 2, wherein (A) and (B) together have a z-average molecular weight M of at least 25,000 g / mol, preferably at least 40,000 g / mol, more preferably at least 60,000 g / mol, most preferably at least 110,000 g / mol. z , so the z-average molecular weight M z Assayed as described in the instructions. 4 . The process according to claim 1 , wherein at least one radiation-curable diluent (B) has an acrylate functionality of 2 to 3. 5 .

5. The method according to any one of the preceding claims, wherein the aqueous radiation curable coating composition comprises at least two radiation curable diluents (B), and the radiation curable diluents (B) present in the aqueous radiation curable coating composition have 2 to 4, preferably 2 to 3, dilutions according to the formula The average acrylate functionality of k is the molar mass M present in the aqueous radiation curable coating composition k And has acrylate functionality f k The amount of acrylate diluent (B) in g.

6. The process according to any one of claims 1 to 3, wherein at least 10 wt. %, preferably at least 20 wt. %, more preferably at least 30 wt. %, more preferably at least 40 wt. %, more preferably at least 50 wt. %, more preferably at least 60 wt. %, more preferably at least 70 wt. %, more preferably at least 80 wt. %, more preferably at least 90 wt. %, and most preferably 100 wt. % of the radiation curable diluent (B) is selected from: With the corresponding molecular formula C 24 H 34 O9 and its corresponding di(trimethylolpropane)tetraacrylate (di-TMPTA) with a molar mass of 467 g / mol, With the corresponding molecular formula C 21 H 32 O8 and its corresponding di(trimethylolpropane) triacrylate (di-TMP3A) with a molar mass of 412 g / mol, di(trimethylolpropane) triacrylate containing an alkoxy group, With the corresponding molecular formula C 21 H 32 O9 and its corresponding glyceryl propoxy triacrylate (GPTA) with a molar mass of 428 g / mol, Glyceryl propoxy triacrylate containing an additional alkoxy group, With the corresponding molecular formula C 17 H 20 O8 and its corresponding pentaerythritol tetraacrylate (PET4A) with a molar mass of 352 g / mol, Pentaerythritol tetraacrylate containing an alkoxy group, With the corresponding molecular formula C 14 H 18 O7 and its corresponding pentaerythritol triacrylate (PET3A) with a molar mass of 298 g / mol, Pentaerythritol triacrylate containing an alkoxy group, With the corresponding molecular formula C 15 H 20 O6 and its corresponding trimethylolpropane triacrylate (TMPTA) with a molar mass of 296 g / mol, trimethylolpropane triacrylate containing an alkoxy group, With the corresponding molecular formula C 12 H 18 O5 and its corresponding dipropylene glycol diacrylate (DPGDA) with a molar mass of 242 g / mol, Dipropylene glycol diacrylate containing an additional alkoxy group, and any mixture thereof.

7. The method according to any one of claims 1 to 3, wherein at least 10 wt %, preferably at least 20 wt %, more preferably at least 30 wt %, more preferably at least 40 wt %, most preferably at least 50 wt %, more preferably at least 60 wt %, more preferably at least 70 wt %, more preferably at least 80 wt %, more preferably at least 90 wt %, and most preferably 100 wt % of the radiation curable diluent (B) is a mixture of: (1) di(trimethylolpropane) tetraacrylate (di-TMPTA) and / or a corresponding compound of formula C 17 H 20 O8 and its corresponding pentaerythritol tetraacrylate (PET4A) with a molar mass of 352 g / mol and / or pentaerythritol tetraacrylate containing an alkoxy group, and (2) Glyceryl propoxy triacrylate (GPTA) and / or glyceryl propoxy triacrylate containing additional alkoxy groups, preferably propoxy groups, and / or dipropylene glycol diacrylate (DPGDA) and / or dipropylene glycol diacrylate containing additional alkoxy groups, preferably propoxy groups.

8. The method according to any one of the preceding claims, wherein the amount of (A) is 35 to 80 wt % and the amount of (B) is 20 to 65 wt %, more preferably, the amount of (A) is 40 to 80 wt % and the amount of (B) is 20 to 60 wt %, based on the total amount of (A) and (B).

9. A method according to any one of the preceding claims, wherein The total amount of (A) and (B) is 10 to 60 wt%, preferably 15 to 50 wt%, more preferably 15 to 45 wt%, even more preferably 20 to 40 wt%, even more preferably 25 to 35 wt%, based on the total weight of the aqueous radiation curable coating composition.

10. The method according to any one of the preceding claims, wherein the optional organic solvent is present in an amount of up to 25 wt.-%, preferably in an amount of up to 20 wt.-%, preferably in an amount of up to 15 wt.-%, preferably in an amount of up to 10 wt.-%, more preferably in an amount of up to 5 wt.-%, more preferably in an amount of up to 1 wt.-%, wherein the amount of organic solvent is given based on the total amount of water and organic solvent present in the aqueous radiation curable coating composition.

11. The method according to any one of the preceding claims, wherein the polyurethane (A) is the reaction product of at least the following components: (A1) at least one polyisocyanate, (A2) at least one isocyanate-reactive compound containing at least one salt group capable of rendering the polyurethane (A) dispersible in water and / or at least one functional group which can be converted into a salt group capable of rendering the polyurethane (A) dispersible in water, (A3) optionally, at least one isocyanate-reactive compound containing at least one nonionic group capable of making the polyurethane (A) dispersible in water, (A4) at least one isocyanate-reactive polyol different from (A2) and (A3) having an OH number of 25 to 225 mg KOH / g solids, (A5) optionally, at least one isocyanate-reactive polyol different from (A2) and (A3) having an OH value of more than 225 mg KOH / g solid and less than 1850 mg KOH / g solid, and (A6) water and / or at least one nitrogen-containing chain extender compound. 12 . The process according to claim 11 , wherein the isocyanate-reactive polyol (A4) has an OH value of 35 to 190 mg KOH / g solid, more preferably 45 to 125 mg KOH / g solid.

13. The method according to claim 11 or 12, wherein the polyurethane (A) comprises the isocyanate-reactive polyol (A4) in an amount of 20 to 80% by weight, preferably 30 to 70% by weight, even more preferably 35 to 65% by weight, based on the total amount of compounds (A1) to (A6).

14. The method according to any one of the preceding claims, wherein the polyurethane (A) comprises at least one NH x (wherein x is 1 or 2) a nitrogen-containing chain extender having a functionality of 15. The method according to any one of the preceding claims, wherein the polyurethane (A) has an acid value of 5 to 50, more preferably 10 to 40, even more preferably 15 to 30 mg KOH / g polyurethane (A) solids.

16. The method according to any one of claims 1 to 15, wherein the polyurethane (A) has a radiation-curable ethylenically unsaturated bond concentration of less than 0.2 milliequivalents (meq) / g polyurethane (A), preferably less than 0.1 meq / g polyurethane (A), more preferably less than 0.05 meq / g polyurethane (A), more preferably less than 0.01 meq / g polyurethane (A).

17. The method according to any one of the preceding claims, wherein the dispersion consisting of (A), (B) and (C) has a z-average particle size of 20 to 1000 nm, preferably 25 to 500 nm, more preferably 25 to 250 nm, and most preferably 30 to 200 nm, whereby the z-average particle size is determined by the method as described in the description.

18. A method according to any preceding claim, wherein the coating has a dry thickness of at least 2 microns, or at least 3 microns, or at least 4 microns, and at most 100 microns, or at most 75 microns, or at most 50 microns.

19. The method according to any one of the preceding claims, wherein the irradiation in step (3) is carried out by an excimer UV lamp, preferably with UV light having a wavelength ≥120 nm, more preferably ≥150 nm, and particularly preferably 172 nm or 195 nm.

20. The method according to any one of the preceding claims, wherein UV radiation is applied in step (4) and the aqueous radiation curable coating composition comprises one or more photoinitiators.

21. An aqueous radiation curable coating composition as defined in any one of claims 1 to 17.

22. A coated substrate, wherein the coated substrate is obtained by the method according to any one of claims 1 to 20.

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