Aqueous coating composition

Abstract

The invention relates to an aqueous coating composition comprising a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB and at least one crosslinker X, wherein DA comprises a vinyl oligomer OLA and at least one vinyl polymer PA, said vinyl oligomer OLA and optionally said at least one vinyl polymer PA comprising pendant functional groups which are reactive with the functional groups of the at least one crosslinker X, and pendant olefinically unsaturated functional groups which are crosslinkable by a free radical process; DB comprises a vinyl oligomer OLB and at least one vinyl polymer PB, said vinyl oligomer OLB and / or optionally said at least one vinyl polymer PB comprising pendant functional groups which are reactive with the functional groups of the at least one crosslinker X; the invention also relates to a process for the preparation of said crosslinkable oligomer-stabilized vinyl organic polymer dispersion. The invention also relates to the use of said coating composition for coating a wooden substrate.

Description

Technical Field

[0001] This invention relates to an aqueous coating composition comprising a first crosslinkable oligomer-stabilized vinyl polymer dispersion, a second crosslinkable oligomer-stabilized vinyl polymer dispersion, and at least one (carbonyl reactive) crosslinking agent; it also relates to a method for preparing the aqueous coating composition, and to a coated substrate coated with the coating composition. Background Technology

[0002] Due to increasingly stringent regulations regarding the permissible levels of volatile organic compounds (VOCs) in coatings, significant efforts have been made to minimize the use of organic cosolvents in waterborne coatings based on vinyl monomer-based waterborne binders. However, in waterborne coatings using vinyl polymers as the primary binder, the final hardness of the cured film is limited by the amount of organic cosolvent in the coating formulation. For some coating applications, a minimum hardness is required, such as when high anti-blocking properties or high scratch resistance are important. The hardness of the final coating can be improved by introducing a crosslinking mechanism into the coating. Coating compositions that are crosslinked under photochemical radiation have been known for some time. In industrial practice, the photochemical radiation used is primarily ultraviolet (UV) or electron beam (EB) radiation. To sufficiently reduce viscosity for application to surfaces, known compositions invariably contain low molecular weight diluents with olefinic functional groups. These diluents are known to be irritating or toxic, thus creating a clear need for developing waterborne binders that can be cured by UV, visible, or EB radiation without requiring olefinic unsaturated diluents, yet still have sufficiently low viscosity for application by conventional methods.

[0003] U.S. Patent 4,107,013 discloses a UV-curable waterborne coating comprising a vinyl polymer dispersion having a so-called "core-shell" morphology and 5-35% of an emulsified low molecular weight radiation crosslinking agent, wherein the vinyl polymer dispersion has a shell of a bifunctional monomer containing unreacted allyl groups. The presence of the low molecular weight radiation crosslinking agent poses a serious problem for the safe use of such coatings.

[0004] US Patent 4,244,850 discloses an air-curing waterborne coating composition comprising olefinically unsaturated resin particles, an emulsion of a metal desiccant salt, and a water-immiscible organic solvent. The unsaturated resin is formed from 1-20 wt% of a monoolefinically unsaturated monomer having carboxyl or 1,2-epoxy functional groups, wherein a portion of the carboxyl or 1,2-epoxy functional groups has reacted with the 1,2-epoxy or carboxyl functional groups, respectively, to provide unsaturated sites on the resin particles. The resin is not neutralized prior to functionalization. The presence of a large number of unsaturated monomers in the coating composition also poses a health threat to personnel applying the coating.

[0005] European patent application EP330246 discloses a curable aqueous dispersion formed by first polymerizing an organophosphate or phosphonate compound or a mixture thereof with a (meth)acrylate derivative or another unsaturated compound or a styrene derivative, and then adding an olefinically unsaturated epoxy-containing monomer. In this case, the presence of the olefinically unsaturated monomer also poses a health and safety risk.

[0006] US Patent 4,925,893 discloses an oxidatively and radiation-curable dispersion of vinylidene chloride / vinyl chloride / 2-ethylhexyl acrylate copolymer, which has residual unsaturation by adding at least 5 wt% of a gel moiety formed by a polyfunctional monomer in the early stage of polymerization and adding a low-reactive polyfunctional compound (e.g. diallyl phthalate) in the later stage of polymerization.

[0007] European patent application EP442653 discloses the preparation of polymers containing vinyl functional groups. An amine-functionalized vinyl copolymer dispersion is formed by reacting a carboxyl-functionalized copolymer dispersion with aziridine (e.g., ethyleneimine or acrylamide). The amine-functionalized latex is then reacted with a material having both an enol carbonyl group and another functional group (e.g., 2-(acetylacetoxy)ethyl methacrylate) to obtain a methacrylate-functionalized polymer.

[0008] European patent application EP0602763 describes a multi-stage polymer dispersion formed from a first-stage polymer and a second-stage polymer having β-unsaturated carbonyl functional groups (allowing for curing by UV radiation). The weight ratio of the first-stage polymer to the second-stage polymer is about 20:80 to 70:30. For the first-stage polymer, a hydrophobic monomer is preferred. The second-stage polymer contains about 30-60 wt% of at least one comonomer containing an acidic functional group. The acidic functional group is partially neutralized by a base and reacted with a mono-olefinic unsaturated epoxide. Preferably, the first-stage polymer contains about 10 wt%, preferably about 1-5 wt%, of a crosslinking comonomer (allyl methacrylate). A problem associated with this synthetic route is that the dispersion is not very stable, resulting in coarse particles and a wide particle size distribution. The resulting polymer dispersion is difficult to filter, and the membrane cast from it has a dull and gritty appearance. Due to the instability, the maximum solids content achievable in the final dispersion is lower than expected, typically below about 30 wt%. Without being limited by interpretation, it is believed that significant aqueous-phase polymerization occurs during the synthesis of carboxyl-functionalized second-stage polymers in existing technological processes. Aqueous-phase polymerization leads to the formation of water-soluble, non-adsorbent high-molecular-weight polymers, which may result in dispersion instability and consequently flocculation. Furthermore, it has been found that carboxyl-functionalized second-stage polymers swell upon the addition of neutralizing alkali. This causes a sharp increase in dispersion viscosity. Following the reaction of the carboxyl group with the mono-olefinic unsaturated epoxide, the acid value of the second-stage polymer decreases again. This has been found to further destabilize the polymer dispersion.

[0009] European patent application EP 3892682A1 describes a coating composition based on a blend of a self-crosslinking anionic oligomer (a polyethylene moiety with methoxyl-terminated ends), an oligomer-stabilized carbonyl functional polymer dispersion, an aqueous polymer of an N-vinylpyrrolidone-co-ethyl acrylate copolymer, and an oligomer-stabilized self-crosslinking polymer dispersion. More specifically, EP 3892682A1 describes an aqueous vinyl polymer dispersion comprising:

[0010] - An aqueous dispersion of a vinyl polymer P1 comprising 5-25 wt% of an olefinically unsaturated monomer containing a polyethylene glycol or monoalkoxy polyethylene glycol moiety, characterized in that the number average molecular weight (Mn) is 2,000-120,000 g / mol.

[0011] - An aqueous dispersion of vinyl polymer P2, comprising 25-95 wt% of an olefinic unsaturated monomer selected from N-vinylamide, characterized by a number-average molecular weight (Mn) of 1,000-50,000 g / mol.

[0012] - A film-forming vinyl polymer P3 in the form of an aqueous dispersion, comprising 20-60 wt% of a water-dispersible crosslinkable vinyl oligomer OL and 40-80 wt% of a high molecular weight vinyl polymer P4.

[0013] The crosslinking agents used in EP 3892682A1 include diamines or polyamines and dicarboxylic acid hydrazides or polycarboxylic acid hydrazides (e.g., adipic acid dihydrazides). Coatings based on the aqueous dispersions described in EP 3892682A1 have improved open times; however, EP 3892682A1 does not mention rapid drying properties (i.e., EP 3892682A1 neither discloses nor implies coatings with rapid drying properties).

[0014] Patent application WO 2020 / 178378 A1 describes coatings comprising blends of oligomer-stabilized dispersions and surfactant-stabilized polymer dispersions. More specifically, WO 2020 / 178378 A1 describes an aqueous vinyl polymer dispersion comprising:

[0015] -70-97.5 wt% of a crosslinkable oligomer-stabilized dispersion PD1, wherein PD1 comprises 20-60 wt% of a water-soluble or water-dispersible crosslinkable oligomer OL and 40-80 wt% of at least one high molecular weight vinyl polymer P1.

[0016] -2-29.5 wt% of a dispersion of at least one non-oligomer-stabilized vinyl polymer P2; and

[0017] -0.5-28 wt% of at least one crosslinking agent X, which can react with the functional groups of OL and optionally with the functional groups of P1 and / or P2.

[0018] Coatings based on the aqueous dispersions described in WO 2020 / 178378 A1 exhibit better viscosity stability compared to coatings based solely on dispersions stabilized by oligomers.

[0019] Patent application WO 2009 / 007232 A1 describes a method for preparing an aqueous coating composition comprising cationic vinyl oligomers, the method comprising the following steps:

[0020] I. Preparation of cationic vinyl oligomers by solution polymerization or bulk polymerization

[0021] II. The cationic vinyl oligomer is dispersed in an aqueous medium and nonionic amine functional groups are included.

[0022] The cationic vinyl oligomer dispersions of WO 2009 / 007232 A1 can be used as the sole stabilizer for second-phase emulsion polymerization to prepare vinyl polymers in the presence of cationic vinyl oligomers. Coatings containing cationic oligomers as described in WO 2009 / 007232 A1 exhibit good tannin-stain sealing properties.

[0023] European Patent EP1758961B1 describes a multi-stage vinyl polymer dispersion comprising an acrylic oligomer having carboxylic acid and carbonyl functional groups, wherein core particles composed of olefinically unsaturated monomers are polymerized in the presence of the oligomer. In a next step, a portion of the carboxylic acid groups of the oligomer are reacted with an olefinically unsaturated monoepoxide to introduce (meth)acryloyl functional groups. When the resin composition according to EP1758961B1 is used on dimensionally unstable substrates (e.g., wood exterior finishes, deck stains, etc.), the high crosslinking density may cause the coating to fail due to cracking or peeling.

[0024] While not questioning the advantages of existing technology systems, it is evident that there remains a need for waterborne coating compositions with reduced health and safety risks, which contain stable dispersions and provide clear varnishes for external wood applications and wood staining coatings with improved performance compared to existing technology coating systems.

[0025] Purpose of the invention

[0026] The present invention aims to provide a water-based coating composition that does not have the limitations of current existing coating systems.

[0027] The object of this invention is to provide an aqueous coating composition comprising a stable dispersion having a low minimum film-forming temperature (MFFT) and providing an external coating on a wood (or wood-based) substrate with high hardness and good chemical resistance (particularly early water resistance and gloss retention). Invention Overview

[0029] This invention discloses an aqueous coating composition comprising a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, and at least one (carbonyl reactive) crosslinking agent X, wherein:

[0030] -DA comprises a vinyl oligomer OLA and at least one vinyl polymer PA, wherein the vinyl oligomer OLA and optionally the at least one vinyl polymer PA comprise chain-side (carbonyl) functional groups reactable with (carbonyl-reactive) functional groups of at least one (carbonyl-reactive) crosslinking agent X, and chain-side olefinically unsaturated functional groups crosslinkable via (photochemical radiation-induced) radical processes; and

[0031] -DB comprises a vinyl oligomer OLB and at least one vinyl polymer PB, wherein the vinyl oligomer OLB and optionally the at least one vinyl polymer PB comprise chain-side (carbonyl) functional groups that can react with the (carbonyl) functional groups of at least one (carbonyl-reactive) crosslinking agent X.

[0032] Preferred embodiments of the present invention disclose one or more of the following features:

[0033] ● Vinyl oligomers OLA and OLB are characterized by:

[0034] - The number-average molecular weight Mn is 500-50,000 g / mol, preferably 2,500-25,000 g / mol, and more preferably 5,000-15,000 g / mol;

[0035] - The calculated glass transition temperature Tg of the oligomer backbone (calculated using the Fox equation) is 10-150°C, preferably 20-125°C, more preferably 25-115°C;

[0036] ● At least one vinyl polymer, PA and PB, is characterized by:

[0037] - The number-average molecular weight Mn is greater than 60,000 g / mol, preferably greater than 80,000 g / mol, and more preferably greater than 100,000 g / mol;

[0038] The calculated glass transition temperature Tg of the polymer backbone (calculated using the Fox equation) is -70 to 50°C, preferably -45 to 45°C, and more preferably -25 to 40°C.

[0039] The calculated glass transition temperatures (Tg) of PA and PB are at least 25°C, preferably at least 35°C, and more preferably at least 40°C lower than the glass transition temperatures of the main chains of the vinyl oligomers OLA and OLB, respectively.

[0040] ● The first crosslinkable oligomer-stabilized vinyl polymer dispersion DA comprises 20-60 wt% of a combination of PA and OLA based on the total weight of DA, wherein the combination of PA and OLA comprises at least 35 wt% and at most 75 wt% of OLA based on the combined weight of PA and OLA (100 wt%).

[0041] ● The second crosslinkable oligomer-stabilized vinyl polymer dispersion DB comprises 20-60 wt% of a combination of PB and OLB based on the total weight of DB, wherein the combination of PB and OLB comprises at least 35 wt% and at most 75 wt% of OLB based on the combined weight of PB and OLB (100 wt%).

[0042] ● The waterborne coating composition comprises 25-50 wt% of a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA and 50-75 wt% of a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, based on a total weight of 100 wt% DA and DB.

[0043] ● The (carbonyl) functional group in any vinyl oligomer OLA and OLB and optionally any vinyl polymer PA and PB that can react with at least one (carbonyl reactive) crosslinker X is a chain-side (carbonyl) functional group of the type of ketone, aldehyde or acetyl acetyl.

[0044] ● At least one (carbonyl reactive) crosslinking agent X contains a (carbonyl reactive) functional group selected from primary amines, secondary amines, hydrazines, acyl hydrazides, hydrazones, and mixtures thereof;

[0045] ● The ratio of (carbonyl) functional groups of vinyl oligomers OLA and OLB, and optionally at least one vinyl polymer PA and PB, to the carbonyl reactive functional groups of at least one (carbonyl reactive) crosslinking agent X is 0.5-10, preferably 0.75-5, more preferably 0.95-2.5;

[0046] ● The vinyl oligomer chains of OLA and OLB are polymer products of the following substances:

[0047] -1-45wt% of at least one acid-functionalized olefinic unsaturated monomer M1, preferably M2 different from M1.

[0048] -0.5-20wt% of at least one olefinic unsaturated monomer M2 having a crosslinking functional group during film formation,

[0049] -50-98.5 wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0050] -0-8wt% of at least one surfactant M5 containing an olefinic unsaturated group;

[0051] in

[0052] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 polymerized is at least partially converted to its salt, wherein the degree of neutralization is 0.2-0.8; and

[0053] in:

[0054] - In the case of vinyl oligomer OLA, the carboxylic acid group of at least one acid-functional olefinic unsaturated monomer M1 polymerized is at least partially converted into an olefinic unsaturated side group by reacting with a bifunctional compound M6, M6 comprising an olefinic unsaturated ((meth)acryloyl) group and a group that can react with the carboxylic acid, wherein the conversion degree is 0.2-0.8.

[0055] ● The vinyl polymer chains of PA and PB are polymerization products of the following substances:

[0056] -0-5wt% of at least one acid-functionalized olefinic unsaturated monomer M1, preferably M2 different from M1.

[0057] -0-10wt% of at least one olefinic unsaturated monomer M2 having a crosslinking functional group during film formation.

[0058] -80-100wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0059] -0.1-5wt% of at least one polyfunctional olefinic unsaturated monomer M4 used to impart gel content;

[0060] in:

[0061] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 is at least partially converted to a salt; and

[0062] - One or more vinyl polymers PA are different from one or more vinyl polymers PB.

[0063] The aqueous coating composition of the present invention, disclosed in one or even a more preferred embodiment, comprises 25-50 wt% of a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, 50-75 wt% of a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, at least one (carbonyl reactive) crosslinking agent X, and at least one photoinitiator, based on a total weight of 100 wt% of DA and DB, wherein:

[0064] -DA comprises 20-60 wt% of a combination of vinyl oligomer OLA and at least one vinyl polymer PA based on the total weight of DA, wherein the PA and OLA combination comprises at least 35 wt% and at most 75 wt% OLA based on the combined weight of PA and OLA (100 wt%), and

[0065] -DB comprises 20-60 wt% of a combination of vinyl oligomers (OLB) and at least one vinyl polymer (PB) based on the total weight of DB, wherein the PB and OLB combination comprises at least 35 wt% and at most 75 wt% of OLB based on the combined weight of PB and OLB (100 wt%).

[0066] in:

[0067] - The vinyl oligomer chains of OLA and OLB are polymerization products of the following substances:

[0068] -1-45wt% of at least one acid-functionalized olefinic unsaturated monomer M1

[0069] -0.5-20 wt% of at least one olefinic unsaturated monomer M2 having a carbonyl functional group that crosslinks during film formation, preferably M2 is different from M1.

[0070] -50-98.5 wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0071] -0-8wt% of at least one surfactant M5 containing an olefinically unsaturated group; and

[0072] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 polymerized is at least partially converted to its salt, wherein the degree of neutralization is 0.2-0.8; and

[0073] - For the vinyl oligomer OLA, the carboxylic acid group of at least one acid-functionalized olefinically unsaturated monomer M1 polymerized is at least partially converted to an olefinically unsaturated side group by reacting with a bifunctional compound M6, M6 comprising an olefinically unsaturated group and a group reactive to the carboxylic acid, wherein the degree of conversion is 0.2-0.8; and

[0074] in:

[0075] - The vinyl polymer chains of PA and PB are polymerization products of the following substances:

[0076] -0-5wt% of at least one acid-functionalized olefinic unsaturated monomer M1

[0077] -0-10 wt% of at least one olefinic unsaturated monomer M2, having a (carbonyl) functional group that crosslinks upon film formation, preferably M2 is different from M1.

[0078] -80-100wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0079] -0.1-5 wt% of at least one polyfunctional olefinic unsaturated monomer M4 for imparting gel content; and

[0080] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 is at least partially converted to a salt; and

[0081] - One or more vinyl polymers PA differ from one or more vinyl polymers PB; and

[0082] in:

[0083] The vinyl oligomer OLA and optionally at least one vinyl polymer PA comprise:

[0084] - A chain-side functional group (from M2) that can react with at least one functional group of a (carbonyl reactive) crosslinking agent X, and

[0085] - Chains with side-attached olefinic unsaturated ((meth)acryloyl) functional groups (from M6) that can be crosslinked via (photochemical radiation-induced) radical processes; and

[0086] Vinyl oligomer OLB and optionally at least one vinyl polymer PB contain a chain-side (carbonyl) functional group from M2 that can react with the functional group of at least one (carbonyl reactive) crosslinking agent X, said (carbonyl reactive) crosslinking agent X having functional groups that can react with the carbonyl functional groups of vinyl oligomers OLA and OLB and optionally at least one vinyl polymer PA and PB.

[0087] This invention also discloses a method for preparing a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, the method comprising the following steps:

[0088] a. To prepare an aqueous emulsion or solution of a vinyl oligomer OLB comprising a carboxylic acid-functionalized monomer, wherein the amount of the carboxylic acid-functionalized monomer is sufficient to impart water solubility or water dispersibility to the vinyl oligomer OLB.

[0089] b. Neutralize the vinyl oligomer OLB at least partially with an alkali.

[0090] c. Add a monomer mixture to at least partially neutralized vinyl oligomer OLB (formed in the preceding steps) and emulsion polymerize the monomer mixture to form a vinyl polymer PB dispersion with lower hydrophilicity than vinyl oligomer OLB, thereby forming a mixture of vinyl polymer PB and vinyl oligomer OLB.

[0091] This invention also discloses a method for preparing a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, the method comprising the following steps:

[0092] a. To prepare an aqueous emulsion or solution of a vinyl oligomer OLA precursor comprising a carboxylic acid-functionalized monomer, wherein the amount of the carboxylic acid-functionalized monomer is sufficient to impart water solubility or water dispersibility to the vinyl oligomer OLA precursor.

[0093] b. Neutralize the vinyl oligomer OLA precursor at least partially with a base.

[0094] c. Add a monomer mixture to at least partially neutralized vinyl oligomer OLA precursor (formed in the previous step) and emulsion polymerize the monomer mixture to form a vinyl polymer PA dispersion with lower hydrophilicity than the vinyl oligomer OLA precursor.

[0095] d. Reacting the carboxylic acid groups (formed) in the vinyl oligomer OLA precursor with a bifunctional compound comprising an olefinically unsaturated ((meth)acryloyl) group and a group capable of reacting with the carboxylic acid groups (formed) in the vinyl oligomer OLA precursor, thereby at least partially converting the carboxylic acid groups of the vinyl oligomer OLA precursor into olefinically unsaturated ((meth)acryloyl) groups, thereby forming a mixture of vinyl polymer PA and vinyl oligomer OLA.

[0096] The present invention also relates to the use of the waterborne coating composition for coating wood (or wood-based) substrates selected from medium-density fiberboard (MDF), high-density fiberboard (HDF), particleboard, oriented strand board (OSB), solid wood, and composite materials, such as wood-plastic composites (WPC). The present invention also relates to a coated article comprising a wood (or wood-based) substrate at least partially coated with the waterborne coating composition. Invention Details

[0098] In this invention, it has been found that aqueous coating compositions comprising a first crosslinkable oligomer-stabilized vinyl polymer dispersion, a second crosslinkable oligomer-stabilized vinyl polymer dispersion, and at least one crosslinking agent can obtain a stable coating system that provides a crosslinked coating with both improved hardness and excellent water resistance. More specifically, it has been found that aqueous coating compositions comprising a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, and at least one carbonyl reactive crosslinking agent X can obtain a stable coating system that provides a crosslinked coating with both improved hardness and excellent water resistance.

[0099] In the context of this invention, "carbonyl reactive crosslinking agent" refers to a crosslinking agent containing functional groups that are capable of or readily react with carbonyl functional groups, i.e., a crosslinking agent that forms covalent bonds between molecules by targeting carbonyl functional groups.

[0100] In the context of this invention, "oligomer-stabilized vinyl polymer dispersion" refers to a dispersion of at least one vinyl polymer in an aqueous medium containing a vinyl oligomer. The oligomer-stabilized vinyl polymer dispersion is obtained by free radical emulsion copolymerization of an olefinic unsaturated monomer in an aqueous medium in the presence of the vinyl oligomer.

[0101] In this article, "aqueous medium" refers to 70-100 wt% water and 0-30 wt% water-miscible compounds (e.g., alcohols, glycols, glycol ethers, glycol esters, etc.) based on the weight of the aqueous medium (100%).

[0102] In this article, "aqueous" compositions, solutions, emulsions or dispersions refer to particles dispersed in an aqueous medium.

[0103] In the context of this invention, "crosslinkable oligomer-stabilized vinyl polymer dispersion" means that the vinyl oligomer and optionally the vinyl polymer contain reactive functional groups that enable the formation of a network, and more specifically, that the vinyl oligomer and optionally the vinyl polymer contain carbonyl reactive functional groups that enable the formation of a polymer network.

[0104] In the context of this invention, "carbonyl reactive functional group" refers to a functional group that is capable of or readily reacts with a carbonyl functional group, i.e., forming covalent bonds between molecules by targeting the carbonyl functional group.

[0105] To distinguish between oligomers and polymers in this application, the definition given by IUPAC (IUPAC, Compendium of Chemical Terminology, 2nd ed. (the Gold Book), compiled by ADMcNaught and A. Wilkinson, Blackwell Scientific Publications, Oxford (1997)) can be used. Oligomers are polymer molecules with a medium relative molecular mass whose structure essentially comprises a small number of units derived from molecules with a lower relative molecular mass. According to the invention, the number-average molecular weight of oligomers is 500-50,000 g / mol. Since the average molecular weight of repeating units is about 100 g / mol, the number of repeating units in the oligomer is 5-500. Considering that conventional emulsion copolymers have 10 6 Or the number-average molecular weight of 10,000 repeating units, so the standard of “medium relative molecular mass” applies to the definition of “oligomer” in this article.

[0106] In the context of this invention, "olefinic unsaturated monomer" or "vinyl monomer" refers to a monomer having at least one carbon-carbon double bond capable of free radical polymerization. The prefix "(meth)acryloyl" used to name compounds of this invention includes "acryloyl" and "methacryloyl", and refers to compounds containing at least one CH2=CHCOO- group or CH2=CCH3COO- group, mixtures thereof, and mixtures of such compounds.

[0107] The aqueous coating composition of the present invention comprises a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, and at least one crosslinking agent X, wherein:

[0108] -DA comprises a vinyl oligomer OLA and at least one vinyl polymer PA, wherein the vinyl oligomer OLA and optionally the at least one vinyl polymer PA comprise:

[0109] - Chain-side functional groups that can react with functional groups of at least one crosslinking agent X, and

[0110] - Chain-side alkene unsaturated functional groups that can be cross-linked via free radical processes; and

[0111] -DB comprises a vinyl oligomer OLB and at least one vinyl polymer PB, wherein the vinyl oligomer OLB and optionally the at least one vinyl polymer PB comprise chain-side functional groups capable of reacting with functional groups of at least one crosslinking agent X.

[0112] More specifically, the waterborne coating composition of the present invention comprises a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, and at least one carbonyl reactive crosslinking agent X, wherein:

[0113] -DA comprises a vinyl oligomer OLA and at least one vinyl polymer PA, wherein the vinyl oligomer OLA and optionally the at least one vinyl polymer PA comprise:

[0114] - A chain-side carbonyl functional group that can react with the functional group of at least one carbonyl reactive crosslinking agent X, and

[0115] - Chains with side-attached olefinic unsaturated (meth)acryloyl functional groups that can be crosslinked via free radical processes; and

[0116] -DB comprises a vinyl oligomer OLB and at least one vinyl polymer PB, wherein the vinyl oligomer OLB and optionally the at least one vinyl polymer PB contain chain-side carbonyl functional groups that can react with the functional groups of at least one carbonyl reactive crosslinking agent X.

[0117] In the context of this invention, "first crosslinkable oligomer-stabilized vinyl polymer dispersion DA" refers to an oligomer-stabilized vinyl polymer dispersion comprising a carbonyl functional group for crosslinking with a carbonyl reactive crosslinking agent X and a side-mounted (meth)acryloyl functional group for crosslinking via a photochemical radiation-induced free radical polymerization process. "Second crosslinkable oligomer-stabilized vinyl polymer dispersion DB" refers to an oligomer-stabilized vinyl polymer dispersion comprising a carbonyl functional group for crosslinking with a carbonyl reactive crosslinking agent X.

[0118] In the context of this invention, "chain-side functional group" refers to a functional group attached to the oligomer and / or polymer backbone, also known as a side group, which is capable of reacting with the functional group of crosslinking agent X. More specifically, "chain-side carbonyl functional group" refers to a carbonyl functional group attached to the oligomer and / or polymer backbone, which is capable of reacting with the functional group of (carbonyl reactive) crosslinking agent X.

[0119] As is well known to those skilled in the art, a "carbonyl functional group" refers to a functional group with the formula C=O, that is, a functional group composed of an oxygen atom bonded to a carbon atom via a double bond. The carbon atom is divalent and is usually written as (R1)(R2)C=O, or described as formula (I): When both R1 and R2 in formula (I) are carbon-containing substituents, formula (I) is called a ketone group. When R1 is a carbon-containing substituent and R2 is a hydrogen atom (H), formula (I) is called an aldehyde group. When R1 is a carbon-containing substituent and R2 is CH2-(C=O)-R3, where R3 is a carbon-containing substituent, formula (I) is called an acetoacetyl group (or two carbonyl functional groups linked by an activated methylene group).

[0120] In the context of this invention, a "chain-side olefin unsaturated functional group" refers to an olefin unsaturated ((meth)acryloyl) functional group attached to the backbone of the oligomer and optionally the polymer, also known as a side group, capable of reacting with other chain-side olefin unsaturated functional groups of the same or different oligomers and optionally the polymer. This reaction is a free radical polymerization reaction induced by photochemical radiation in the presence of a photoinitiator.

[0121] Preferably, the vinyl oligomer chains of OLA and OLB are polymerization products of the following substances:

[0122] -1-45wt% of at least one acid-functionalized olefinic unsaturated monomer M1

[0123] -0.5-20 wt% of at least one olefinic unsaturated monomer M2 having a crosslinking functional group during film formation, preferably M2 is different from M1.

[0124] -50-98.5 wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0125] -0-8wt% of at least one surfactant M5 containing an olefinic unsaturated group;

[0126] in:

[0127] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 polymerized is at least partially converted to its salt, wherein the degree of neutralization is 0.2-0.8; and

[0128] in:

[0129] - For the vinyl oligomer OLA, the carboxylic acid group of at least one acid-functional olefinic unsaturated monomer M1 is at least partially converted into an olefinic unsaturated side group by reacting with a bifunctional compound M6, M6 comprising an olefinic unsaturated ((meth)acryloyl) group and a group that can react with the carboxylic acid, wherein the degree of conversion is 0.2-0.8.

[0130] More preferably, the vinyl oligomers OLA and OLB comprise:

[0131] 1) 1-45 wt% of at least one acid-functionalized olefinic unsaturated monomer M1,

[0132] 2) 0.5-20 wt% of at least one olefinic unsaturated monomer M2, different from M1, having a (carbonyl) functional group that crosslinks during film formation.

[0133] 3) 50-98.5 wt% of at least one olefinic unsaturated monomer M3, different from M1 and M2.

[0134] 4) 0-1 wt% of at least one polyfunctional olefinic unsaturated monomer M4 used for pre-crosslinking to impart gel content.

[0135] 5) 0-8 wt% of at least one surfactant M5 containing an olefinically unsaturated group, and

[0136] 6) Chain transfer agents used to control the molecular weight of oligomers.

[0137] in:

[0138] The sum of -1) to 6) is 100wt%.

[0139] - The carboxylic acid group of at least one acid-functionalized olefinic unsaturated monomer M1 is at least partially converted to a salt, wherein the degree of neutralization is 0.2-0.8, and

[0140] - For the vinyl oligomer OLA, the carboxylic acid group of at least one acid-functionalized olefinically unsaturated monomer M1 polymerized is at least partially converted to an olefinically unsaturated ((meth)acryloyl) side group by reacting with a bifunctional compound M6, M6 comprising an olefinically unsaturated ((meth)acryloyl) group and a group (such as an ethylene oxide group) reactive to the carboxylic acid, wherein the degree of conversion is 0.2-0.8, and

[0141] - After partial conversion to salt, and in the special case of OLA, after partial conversion to salt and conversion to olefinic unsaturated ((meth)acryloyl) side groups, the acid value of the vinyl oligomer is at least 45 mg KOH / g, more preferably at least 50 mg KOH / g, and most preferably at least 55 mg KOH / g.

[0142] In the context of this invention, "oligomer backbone" refers to the backbone of an oligomer, namely, a sequence of monomer units interconnected by -CC- bonds, generated by copolymerization of M1, M2, M3, optional M4, and optional M5.

[0143] The acid groups of the vinyl oligomer are at least partially converted to salts by adding a base. Preferably, the carboxylic acid groups of the vinyl oligomer are converted only to the extent required for its dissolution or emulsification. Preferably, the degree of neutralization is less than 1. The "degree of neutralization" is defined as the ratio of the concentration of the carboxylate groups to the initial concentration of the carboxylic acid groups. The degree of neutralization is preferably less than 0.8, more preferably less than 0.6, and even more preferably less than 0.4. Given the desired dissolution or emulsification, the degree of neutralization is preferably at least 0.2.

[0144] The base used is preferably a volatile base, most preferably ammonia. Other possible bases include volatile amines such as aminomethylpropanol, dimethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, triethylamine, diisopropylethylamine, or monoethanolamine. Optionally, blends of different volatile bases can be used. The advantage of using a volatile base is that, after the film dries and cures, the salt groups convert back to free carboxylic acid groups, thereby imparting better water resistance to the coating.

[0145] The acid groups of the vinyl oligomer OLA precursor are at least partially converted into olefinically unsaturated side groups by reaction with the bifunctional compound M6. The "conversion" of the carboxylic acid groups is defined as the ratio of the molar concentration of functional groups in M6 that can react with the carboxylic acid groups of the vinyl oligomer to the molar concentration of the initial carboxylic acid groups in the vinyl oligomer. A conversion of less than 1 is desirable because it would compromise the stability of DA. In most cases, the conversion is at least 0.5, preferably at least 0.80, and most preferably at least 0.9.

[0146] The bifunctional compound M6, comprising an olefinically unsaturated ((meth)acryloyl) group and a group capable of reacting with a carboxylic acid, is preferably an olefinically unsaturated monoepoxide. More specifically, the bifunctional compound M6 comprising an olefinically unsaturated ((meth)acryloyl) group and a group capable of reacting with a carboxylic acid is preferably an olefinically unsaturated monoepoxide, including glycidyl (meth)acrylate, allyl glycidyl ether, glycidyl cinnamate, glycidyl crotonate, glycidyl itaconic acid, norbornene glycidyl ether, etc. This conversion is carried out in the presence of a catalyst suitable for an epoxide-carboxylic acid reaction (preferably a phase transfer catalyst).

[0147] Examples of phase transfer catalysts that can be used for modification are tetra-n-butylammonium hydroxide, methyltributylammonium hydroxide, or benzyltriethylammonium hydroxide.

[0148] Given the toxicity of unreacted M6, the conversion of the monoepoxide M6 must achieve a high conversion rate. Therefore, the conversion rate of M6 should be at least 95%, more preferably 99%, and most preferably greater than 99.5%.

[0149] Typically, at the end of the formation of vinyl polymer PA in an aqueous medium containing a vinyl oligomer OLA precursor with a carboxylic acid group, the carboxylic acid group of the vinyl oligomer OLA precursor is at least partially converted to a side-mounted olefin unsaturated ((meth)acryloyl) group by reacting it with M6. That is, the at least partial conversion is carried out on a blend of vinyl polymer PA and carboxylic acid functional vinyl oligomer OLA precursor.

[0150] In the context of this invention, "vinyl oligomer OLA precursor" refers to a vinyl oligomer obtained by polymerization of M1, M2, M3, and optionally M4 and M5.

[0151] Preferably, the vinyl polymer chains of PA and PB are polymerization products of the following substances:

[0152] -0-5wt% of at least one acid-functionalized olefinic unsaturated monomer M1

[0153] -0-10 wt% of at least one olefinic unsaturated monomer M2 having a crosslinking functional group during film formation, preferably M2 is different from M1.

[0154] -80-100wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0155] -0.1-5wt% of at least one polyfunctional olefinic unsaturated monomer M4 used to impart gel content;

[0156] in:

[0157] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 is at least partially converted to a salt; and

[0158] - One or more vinyl polymers PA are different from one or more vinyl polymers PB.

[0159] More preferably, the vinyl polymers PA and PB comprise:

[0160] 1) 0-5 wt% of at least one acid-functionalized olefinic unsaturated monomer M1,

[0161] 2) 0-10 wt% of at least one olefinic unsaturated monomer M2, different from M1, having a (carbonyl) functional group that crosslinks during film formation.

[0162] 3) 80-100 wt% of at least one olefinic unsaturated monomer M3, different from M1 and M2.

[0163] 4) 0.1-5 wt% of at least one polyfunctional olefinic unsaturated monomer M4 used for pre-crosslinking to impart gel content.

[0164] 5) 0-8 wt% of at least one surfactant M5 containing an olefinically unsaturated group, and

[0165] 6) Optional chain transfer agent for controlling polymer molecular weight,

[0166] in:

[0167] The sum of -1) to 6) is 100wt%.

[0168] - The carboxylic acid group (if present) of at least one acid-functionalized olefinic unsaturated monomer M1 polymerized is at least partially converted to a salt, wherein the degree of neutralization is 0.2-0.8, and

[0169] - Vinyl polymer PA is different from vinyl polymer PB.

[0170] In the context of this invention, "polymer backbone" refers to the backbone of a polymer, namely, a sequence of monomer units interconnected by -CC- bonds, generated by copolymerization of M3, M4, optional M1, optional M2 and optional M5.

[0171] The first crosslinkable oligomer-stabilized dispersion DA may contain more than one vinyl polymer PA. The second crosslinkable oligomer-stabilized vinyl dispersion DB may also contain more than one vinyl polymer PB.

[0172] Preferably, the first crosslinkable oligomer-stabilized vinyl polymer dispersion DA comprises 20-60 wt%, preferably 30-50 wt%, of a combination of PA and OLA based on the total weight of DA, said combination of PA and OLA comprising at least 35 wt%, preferably at least 40 wt%, more preferably at least 45 wt%, most preferably at least 50 wt%, and at most 75 wt%, preferably at most 70 wt%, more preferably at most 65 wt%, and most preferably at most 60 wt%, of OLA based on the combined (or total) weight (of 100 wt%) of PA and OLA, wherein the weight of OLA includes the total weight of M1, M2, M3, chain transfer agent, M6, optional M4, and optional M5, and wherein the weight of PA includes the total weight of M3, M4, optional M1, optional M2, optional M5, and optional chain transfer agent.

[0173] In this specification, "combined PA and OLA" refers to PA and OLA that form or have formed a polymer network (i.e., PA and OLA are linked (or connected) to form a polymer network). PA and OLA may be interconnected, for example, through carbon-carbon double bonds (C=C) or through hydrazone crosslinking. "Combined weight of PA and OLA" refers to the total weight of PA and OLA when combined, that is, the total weight of PA and OLA when they are linked and form a polymer network.

[0174] The first crosslinkable oligomer-stabilized vinyl polymer dispersion DA is preferably prepared by a method comprising the following steps:

[0175] a. To prepare an aqueous emulsion or solution of a vinyl oligomer OLA precursor comprising a carboxylic acid-functionalized monomer, wherein the amount of the carboxylic acid-functionalized monomer is sufficient to impart water solubility or water dispersibility to the vinyl oligomer OLA precursor.

[0176] b. Neutralize the vinyl oligomer OLA precursor at least partially with a base.

[0177] c. Add a monomer mixture to at least partially neutralized vinyl oligomer OLA precursor (formed in the previous step) and emulsion polymerize the monomer mixture to form a vinyl polymer PA dispersion with lower hydrophilicity than the vinyl oligomer OLA precursor, and

[0178] d. Reacting the carboxylic acid groups (formed) in the vinyl oligomer OLA precursor with a bifunctional compound comprising an olefinically unsaturated ((meth)acryloyl) group and a group capable of reacting with the carboxylic acid groups (formed) in the vinyl oligomer OLA precursor, thereby at least partially converting the carboxylic acid groups of the vinyl oligomer OLA precursor into olefinically unsaturated ((meth)acryloyl) groups, thereby forming a mixture of vinyl polymer PA and vinyl oligomer OLA.

[0179] Preferably, the second crosslinkable oligomer-stabilized vinyl polymer dispersion DB comprises 20-60 wt%, preferably 30-50 wt%, of a combination of PB and OLB based on the total weight of DB, wherein the combination of PB and OLB comprises at least 35 wt%, preferably at least 40 wt%, more preferably at least 45 wt%, most preferably at least 50 wt%, and at most 75 wt%, preferably at most 70 wt%, more preferably at most 65 wt%, and most preferably at most 60 wt%, of OLB based on the combined (or total) weight of PB and OLB (100 wt%), wherein the weight of OLB includes the total weight of M1, M2, M3, chain transfer agent, optional M4, and optional M5, and wherein the weight of PB includes the total weight of M3, M4, optional M1, optional M2, optional M5, and optional chain transfer agent.

[0180] In this specification, "combined PB and OLB" means that PB and OLB form or have formed a polymer network (i.e., PB and OLB are connected (or linked) to form a polymer network). PB and OLB can be interconnected, for example, through carbon-carbon double bonds (C=C) or through hydrazone crosslinking. "Combined weight of PB and OLB" refers to the total weight of PA and OLA when combined, i.e., the total weight of PB and OLB when they are connected and form a polymer network.

[0181] The second crosslinkable oligomer-stabilized vinyl polymer dispersion DB is preferably prepared by a method comprising the following steps:

[0182] a. To prepare an aqueous emulsion or solution of a vinyl oligomer OLB comprising a carboxylic acid-functionalized monomer, wherein the amount of the carboxylic acid-functionalized monomer is sufficient to impart water solubility or water dispersibility to the vinyl oligomer OLB.

[0183] b. Neutralize the vinyl oligomer OLB at least partially with an alkali, and

[0184] c. Add a monomer mixture to at least partially neutralized vinyl oligomer OLB (formed in the preceding steps) and emulsion polymerize the monomer mixture to form a vinyl polymer PB dispersion with lower hydrophilicity than vinyl oligomer OLB, thereby forming a mixture of vinyl polymer PB and vinyl oligomer OLB.

[0185] Preferably, the waterborne coating composition of the present invention comprises 25-50 wt% of a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA and 50-75 wt% of a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB based on a total weight of 100 wt% DA and DB.

[0186] Preferably, the acid-functionalized olefinic unsaturated monomer M1 is selected from carboxylic acid-functionalized monomers, such as acrylic acid, methacrylic acid, maleic acid or its half-ester, fumaric acid or its half-ester, citacic acid or its half-ester, itaconic acid or its half-ester, mucoacic acid and its half-ester, and mixtures thereof. These monomers can be produced from petrochemical feedstocks. Alternatively, they can be derived from renewable feedstocks. Bio-based acrylic acid can be produced from glycerol or hydroxypropionic acid, hydroxypropionic acid derivatives, or mixtures thereof. Itaconic acid is obtained through the fermentation of sugars, and bio-based methacrylic acid can be derived from itaconic acid.

[0187] In the context of this specification, "renewable raw material" means a naturally renewable resource that will be replenished through natural reproduction or other cyclical processes (within a finite timescale on a human timescale) to replace portions depleted by use and consumption. Substances or mixtures of substances obtained from such renewable raw materials should have a bio-based carbon content greater than 20 wt% based on the total carbon content of the substance or mixture, determined using American Standard ASTM D6866-20 or European Standard EN16785-1.

[0188] As used herein, “bio-based compounds” or “bio-based monomers” (or “bio-derived monomers”) refer to compounds or monomers derived from or made from renewable raw materials, such as biomass or plant-based sources. Biomass is biologically derived material, excluding materials embedded in strata and / or petrified; it typically originates from plant materials and animal waste.

[0189] Other acid-functionalized monomers that do not contain a carboxylic acid group may be, for example, sulfate or sulfonic acid monomers. Non-limiting examples include 2-acrylamido-2-methylpropanesulfonic acid or its base, ammonium, or amine salts, as well as the sodium salt of the adduct of allyl glycidyl ether and sodium bisulfite, 2-sulfoethyl methacrylate, or 1-(allyloxy)-2-hydroxypropane-1-sulfonic acid. Phosphate or phosphonate-functionalized monomers may also be used. Non-limiting examples of such monomers are monoacryloyloxyethyl phosphate, SIPOMER® PAM-100 and SIPOMER® PAM-200 (both from Solvay Novecare), 10-methacryloyloxydecyl phosphate dihydrogen ester (Kuraray), dimethyl (2-methacryloyloxyethyl) phosphonate and dimethyl (2-methacryloyloxypropyl) phosphonate, or ethyl 2-[4-(dihydroxyphosphoryl)-2-oxabutyl]acrylate.

[0190] The acid-functional olefinic unsaturated monomer M1 is more preferably selected from carboxylic acid-functional monomers, even more preferably selected from acrylic acid, methacrylic acid, itaconic acid, mucoacic acid and mixtures thereof, and most preferably selected from acrylic acid, methacrylic acid and mixtures thereof.

[0191] The olefinic unsaturated monomer M2, having a (carbonyl) functional group that crosslinks during film formation, can be ketone, aldehyde, or acetoacetyl-functionalized. Examples of monomers with a carbonyl functional group include acrolein, methacrolein, crotonaldehyde, 4-vinylbenzaldehyde, and vinylalkyl ketones having 4-7 carbon atoms (e.g., methyl vinyl ketone). Other examples include acrylamidoneopentaldehyde, methacrylamidoneopentaldehyde, 3-acrylamidomethylanisaldehyde, diacetone acrylate and diacetone methacrylate, and ketone-containing amides (e.g., diacetone acrylamide). Examples of (carbonyl-functionalized) monomers having an acetoacetoxy functional group are acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, acetoacetoxyethyl methacrylate, acetoacetoxypropyl acrylate, allyl acetoacetate, acetoacetaminoethyl methacrylate, and acetoacetoxybutyl acrylate.

[0192] Preferably, the (carbonyl-functional) monomer M2 is selected from acetyl acetoxyethyl methacrylate, diacetone acrylamide, and mixtures thereof.

[0193] Monomer M3 may include, but is not limited to, vinyl monomers such as styrene, α-methylstyrene (or other styrene derivatives, such as tert-butylstyrene, vinyltoluene, o-, m-, and p-methylstyrene, o-, m-, and p-ethylstyrene), acrylonitrile, methacrylonitrile, vinyl halides (e.g., vinyl chloride), vinylidene halides (e.g., vinylidene chloride), vinyl esters (e.g., vinyl acetate, vinyl propionate, vinyl laurate); and neodecanoate, such as VEOVA™ 9 and VEOVA™ 10 (VEOVA™ is Hexion...). (Trademark of Inc.), heterocyclic vinyl compounds; alkyl esters of olefinically unsaturated dicarboxylic acids, such as di-n-butyl maleate and di-n-butyl fumarate; itaconic esters, such as dimethyl itaconic acid or dibutyl itaconic acid, especially acrylic and methacrylate esters of the formula CH=CR1-COOR2, wherein R1 is H or methyl, and R2 is optionally substituted C1-C20, more preferably C1-C8 alkyl, cycloalkyl, aryl, or (alkyl)aryl, examples being methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, isopropyl (meth)acrylate, propyl (meth)acrylate (all isomers), and hydroxyalkyl (meth)acrylate esters (e.g., hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and their modified analogues, such as TONE™ M-100 (TONE™ is Dow (A trademark of Chemical). Polyethylene glycol or monoalkoxyethylene glycol modified (meth)acrylates, such as ethyl triethylene glycol methacrylate, methoxy polyethylene glycol 350 methacrylate, methoxy polyethylene glycol 750 methacrylate, methoxy polyethylene glycol 1000 methacrylate, methoxy polyethylene glycol 2000 methacrylate, and methoxy polyethylene glycol 5000 methacrylate (all supplied by Evonik under the trade name VISIOMER® and by BASF under the trademark BISOMER®). Acrylamide and... N-substituted compounds of methacrylamide, such as N-tert-butylacrylamide, N-tert-hexylacrylamide, N-tert-octylacrylamide, N-(1,5-dimethyl-1-ethyl)hexylacrylamide, N-(1,1-dimethyl-2-phenyl)ethylacrylamide, N-cyclohexylacrylamide, N-(1-methylbutyl)acrylamide, N-ethylacrylamide, N-ethylhexylacrylamide, N-butylmethacrylamide, and N-cyclohexylmethacrylamide. Monomer M3 may also include adhesion-promoting monomers. These monomers typically contain amino, urea, or N-heterocyclic groups.Examples of such monomers are dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, 3-dimethylamino-2,2-dimethylpropyl-1-(meth)acrylate, N-dimethylaminomethyl (meth)acrylamide, N-(4-morpholinylmethyl)(meth)acrylamide, 1-vinylimidazolium, and N-vinylpyrrolidone. Another type is N-alkylazacyclobutane (meth)acrylates, such as N-cyclohexylazacyclobutane methacrylate or N-isopropylazacyclobutane methacrylate. Compounds having a pyrrolidine, piperidine, morpholine, piperazine, imidazole, pyrrolidine-2-one, or imidazoline-2-one (ethyleneurea) ring may also be mentioned. In this case, urea-functionalized monomers are preferred, such as N-(2-methacryloyloxyethyl)ethylidene, 1-[2-[[3-(allyloxy)-2-hydroxypropyl]amino]ethyl]imidazolidine-2-one and 2-ethylidene urea ethyl methacrylate.

[0194] M3 monomers can be produced from petrochemical feedstocks. Alternatively, they can be derived from renewable feedstocks such as bio-based acrylic acid and methacrylic acid. The alkanols used in the (ester)exchange reactions can also be bio-derived. Non-limiting examples of such monomers are VISIOMER® Terra C13-MA, VISIOMER® Terra C17.4-MA (available from Evonik), n-octyl acrylate, and isobornyl methacrylate.

[0195] Another source of M3 monomers can be recycled monomers, such as recycled methyl methacrylate (MMA) or recycled styrene. These can be obtained by high-temperature pyrolysis (i.e., pyrolysis at temperatures above their upper limit) of waste polymethyl methacrylate or polystyrene. The resulting recycled monomers can be used directly without removing any impurities present in the pyrolysis products. Alternatively, the pyrolysis products can be further purified (e.g., by distillation) or even converted, for example, by transesterification of recycled methyl methacrylate with an alcohol other than methanol to other monomers.

[0196] In addition, dienes (e.g., 1,3-butadiene or isoprene or mixtures thereof) and vinyl esters (e.g., vinyl acetate, vinyl alkyl esters or derivatives thereof or mixtures thereof) may also be used in the M3 monomer composition.

[0197] Preferably, monomer M3 (M3 is different from M1 and M2) is selected from vinyl monomers, (meth)acrylates of the formula CH=CR1-C(O)OR2 (wherein R1 is H or methyl, and R2 is an optionally substituted C1-C20 alkyl, cycloalkyl, aryl, or (alkyl)aryl), and mixtures thereof. More specifically, monomer M3 is each independently selected from vinyl monomers (particularly styrene), acrylic and methacrylates of the formula CH=CR1-C(O)OR2 (wherein R1 is H or methyl, and R2 is an optionally substituted C1-C20, more preferably C1-C8 alkyl, cycloalkyl, aryl, or (alkyl)aryl), and mixtures thereof.

[0198] Monomer M4 is typically selected from polyfunctional monomers having two or more olefinically unsaturated groups per molecule, and can be present in monomer compositions of OLA, OLB, PA, and / or PB. Examples of such monomers are 1,3-butadiene, isoprene, divinylbenzene, triallyl cyanurate, vinyl or allyl acrylates or methacrylates, glycol diacrylates and glycol dimethacrylates, and methylenebisacrylamide or methylenebismethylacrylamide (or mixtures thereof). The use of polyfunctional monomers in emulsion polymerization will result in an increase in the molecular weight of the polymer or partial crosslinking during polymerization.

[0199] Monomers M1, M2, M3, and M4 can be derived from petrochemical feedstocks or can be wholly or partially derived from biomass. If biomass-derived monomers are used, the bio-based carbon content of the polymer can be determined by radiocarbon analysis according to European standard EN 16785-1 (or American standard ASTM D6866-20).

[0200] Crosslinkable vinyl oligomers OLA and OLB preferably have a (calculated) glass transition temperature (Tg) of 10-150°C, more preferably 20-125°C, and most preferably 25-115°C (calculated using the Fox equation).

[0201] The vinyl polymers PA and PB (polymer backbones) preferably have a (calculated) glass transition temperature (Tg) of -70 to 50°C, more preferably -45 to 45°C, and most preferably -25 to 40°C (calculated using the Fox equation). The (calculated) Tg of each vinyl polymer PA and PB is preferably at least 25°C, more preferably at least 40°C, lower than the Tg of the vinyl oligomers OLA and OLB (backbone), respectively.

[0202] In this paper, the (calculated) Tg of vinyl oligomers OLA and OLB and vinyl polymers PA and PB refers to the calculated glass transition temperature, which is well known as the temperature at which the polymer transitions from a glassy, ​​brittle state to a rubbery state. Tg values ​​are calculated using the well-known Fox equation (TG Fox, Bull. Am. Phys. Soc. 1, 123 (1956)), which is well-known in the art and is expressed by the following equation:

[0203] 1 / Tg = W1 / Tg(1) + W2 / Tg(2) + W3 / Tg(3) + ….

[0204] Where W1, W2, W3, etc., are the weight fractions of comonomers (1), (2), and (3), respectively, and Tg(1), Tg(2), and Tg(3) are the glass transition temperatures of their respective homopolymers. The glass transition values ​​of the homopolymers are calculated using the values ​​given in the Polymer Handbook, 4th edition (editors: J. Brandrup, E.H.M.G., EA. Grulke, John Wiley & Sons, Inc., 1999). Tg calculated in Kelvin can be easily converted to Celsius.

[0205] If the oligomer backbone (i.e., the sequence of monomer units interconnected by -CC- bonds) is subsequently modified by a covalent reaction with its functional groups (e.g., -COOH groups), the calculated Fox Tg refers to the Tg value of the respective oligomer OLA and optional OLB precursor.

[0206] The glass transition temperature (Tg) values ​​for OLA, OLB, PA, and PB reported in this specification are those calculated using the Fox equation described above (referred to as calculated glass transition temperature, or calculated Tg).

[0207] The preferred number-average molecular weight (Mn) of crosslinkable vinyl oligomers OLA and OLB is 500-50,000 g / mol, more preferably 2,500-25,000 g / mol, and most preferably 5,000-15,000 g / mol.

[0208] The preferred number-average molecular weight (Mn) of crosslinkable vinyl polymers PA and PB is greater than 60,000 g / mol, more preferably greater than 80,000 g / mol, and most preferably greater than 100,000 g / mol.

[0209] The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of vinyl oligomers OLA and OLB, and vinyl polymers PA and PB, were determined by gel permeation chromatography (GPC) according to ISO 13885-1:2008, ASTM D 3536, and ASTM D 3593. The formula for number-average molecular weight is: Mn = ΣNi.Mi / ΣNi, where Mn is the number-average molecular weight, Σ is the summation of all species, Ni is the number of molecules of species i, and Mi is the molar mass of species i.

[0210] Methods for influencing molecular weight to achieve a desired number-average molecular weight in emulsion polymerization are well known to those skilled in the art. Molecular weight control can be achieved by using chain transfer agents (e.g., thiols and halogenated hydrocarbons). Suitable thiols include n-dodecyl thiols, n-octyl thiols, tert-dodecyl thiols, mercaptoethanol, isooctyl thioglycanate, C2-C8 mercaptocarboxylic acids and their esters (e.g., 3-mercaptopropionic acid and 2-mercaptopropionic acid).

[0211] Crosslinkable vinyl oligomers OLA and OLB precursors can be prepared by any known technique and can include the direct synthesis of oligomers in an aqueous process, i.e., in the presence of water (e.g., by emulsion polymerization, suspension polymerization, microsuspension polymerization, or microemulsion polymerization), or by solution polymerization (where the solvent can be water and / or any organic solvent that is miscible with water or is removed by distillation after the vinyl oligomer has been transferred to water).

[0212] When the oligomer is a vinyl macromonomer, it can be prepared by a variety of methods, including but not limited to the use of reversible addition-fragmentation chain transfer (RAFT) agents, the use of catalytic chain transfer agents, such as cobalt chain transfer agents. As described in US 2007 / 0043156 and US 6,872,789, α-methylstyrene dimers or oligomers of α-methylstyrene dimers can also be used. Another method for synthesizing oligomers with well-defined molecular weights is using diarylethene (e.g., diphenylethylene) or high-temperature methods.

[0213] Most preferably, the vinyl oligomers OLA and OLB precursors are prepared via aqueous free radical emulsion polymerization. This method is described in *Chemistry and Technology of Emulsion Polymerisation*, Editor AM van Herk, (2005), Blackwell Publishing Ltd. The free radical polymerization can be carried out using either batch or semi-continuous polymerization processes.

[0214] In this document, "aqueous free radical emulsion polymerization method" refers to a method using an aqueous medium (or carried out in an aqueous medium) containing more than 70 wt% water based on the total weight of the aqueous medium (100 wt%), preferably more than 80 wt%, more preferably more than 90 wt%, even more preferably more than 95 wt%, and most preferably 100 wt% water.

[0215] Free radical emulsion polymerization typically requires the use of free radical-generating initiators to initiate the polymerization. Suitable free radical-generating initiators include inorganic peroxides (e.g., K, Na, or ammonium salts of persulfate), hydrogen peroxide or percarbonate, organic peroxides (e.g., acyl peroxides, including, for example, benzoyl peroxide), alkyl hydroperoxides (e.g., tert-butyl hydroperoxide and cumene hydroperoxide), dialkyl peroxides (e.g., di-tert-butyl peroxide), peroxide esters (e.g., tert-butyl perbenzoate, etc.); mixtures may also be used. Peroxides are advantageously used in certain cases in combination with suitable reducing agents (redox systems, such as Na or K metabisulfite or bisulfite, isoascorbic acid). Metal compounds such as Fe-EDTA (EDTA is ethylenediaminetetraacetic acid) can also be used as part of a redox initiator system. Azo-functionalized initiators such as azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile) (ANBN), and 4,4'-azobis(4-cyanopentanoic acid) can also be used. Initiator systems partitioned between the aqueous and organic phases can be used, such as combinations of tert-butyl hydroperoxide, isoascorbic acid, and Fe-EDTA. The amount of initiator or initiator system used is conventional, for example, in the range of 0.05-6 wt% based on the total vinyl monomers used. Preferred initiators for the preparation of crosslinkable oligomers OLA and OLB include ammonium persulfate, sodium persulfate, potassium persulfate, azobisisobutyronitrile, and / or 4,4'-azobis(4-cyanopentanoic acid). The most preferred initiators for the preparation of crosslinkable oligomer precursors OLA and OLB include redox systems and persulfates as described above. An additional amount of initiator may be added at the end of the polymerization process to help remove any remaining residual vinyl monomers.

[0216] If crosslinkable vinyl oligomers OLA and OLB precursors are prepared via emulsion polymerization, surfactants can be used to stabilize the vinyl copolymers in water (even if they are self-dispersible). Suitable surfactants are either ionic or nonionic. Examples of anionic emulsifiers are potassium laurate, potassium stearate, potassium oleate, sodium decyl sulfate, sodium dodecyl sulfate, and sodium rosinate. Examples of nonionic emulsifiers are linear and branched alkyl and alkylaryl polyethylene glycol ethers and sulfides, linear and branched alkyl and alkylaryl polyethylene glycol ethers and sulfides, alkylphenoxy poly(ethyleneoxy)ethanol such as an adduct of 1 mole of nonylphenol with 5-50 moles of ethylene oxide, or alkali metal or ammonium salts of sulfuric or phosphoric acid of said adducts.

[0217] Surfactants containing olefinically unsaturated groups that can participate in free radical polymerization can also be used. Suitable polymerizable surfactants include those of formula M... + The half-ester of maleic anhydride of -OOC-CH=CHCOOR, where R is a C6-C22 alkyl group and M is a C6-C22 alkyl group. + Yes + K + Li + NH4 +Alternatively, protonated amines or quaternary amines may be used. Polyoxyethylene alkylphenyl ethers with olefinically unsaturated bonds, sold under the trade name NOIGEN® RN (supplied by Montello, Inc.), such as NOIGEN® RN-10, NOIGEN® RN-20, NOIGEN® RN-30, NOIGEN® RN-40, and NOIGEN® RN-5065, or their sulfates, sold under the trade name HITENOL® BC (supplied by Montello, Inc.), such as HITENOL® BC-10, HITENOL® BC-1025, HITENOL® BC-20, HITENOL® BC-2020, and HITENOL® BC-30, may also be used. MAXEMUL™ 6106 (available from Cargill Industrial Specialties), which has both phosphonate and ethoxy hydrophilic properties, and a nominal C18 alkyl chain with acrylate reactive groups, may also be used. Other representative phosphate-containing reactive surfactants suitable for such reactions include, but are not limited to, MAXEMUL™ 6112, MAXEMUL™ 5011, and MAXEMUL™ 5010 (all available from Cargill Industrial Specialties). Alternative reactive surfactants suitable for various embodiments of the invention include sodium allyl hydroxypropyl sulfonate (available from Solvay, trade name SIPOMER™ COPS-1), the ADEKA REASOAP® SR / ER series such as ADEKA REASOAP® ER-10, ER-20, ER-30, and ER-40, AKEDA REASOAP® SR-10, SR-20, and SR-30 (all available from ADEKA Corporation), and allyl sulfosuccinate derivatives such as TREM™ LT-40 (sodium dodecyl allyl sulfosuccinate, available from Henkel).

[0218] The amount of surfactant used in the synthesis of oligomer OLA and OLB precursors is preferably 0-15 wt%, more preferably 0-8 wt%, still more preferably 0-5 wt%, particularly 0.1-3 wt%, and most preferably 0.2-2 wt%.

[0219] Preferably, the vinyl polymers PA and PB are prepared by an aqueous method in the presence of oligomer precursors OLA and OLB. Prior to the polymerization of the monomers constituting the vinyl polymers PA and PB, the carboxylic acid groups contained in the main chain of the oligomers (precursors) can be (partially) neutralized by adding a base, thereby partially or completely solubilizing the crosslinkable oligomer precursors OLA or OLB. The degree of neutralization of the acid functional groups is preferably 0.6, more preferably 0.7, and most preferably 0.8. Most preferably, the vinyl polymers PA and PB are prepared by an aqueous emulsion polymerization method.

[0220] Preferably, at least one vinyl polymer PA and PB are prepared by emulsion copolymerization of a mixture of olefinically unsaturated monomers in the presence of at least partially neutralized vinyl oligomer precursors OLA and OLB. During the neutralization of the carboxylic acid groups on the OLA and OLB vinyl oligomer precursors, the oligomer particles initially swell with water until the particles appear to be completely dissolved, indicating that the refractive index of the swollen particles has become the same as that of water. Since particle size can still be measured using dynamic light scattering, we believe (but not limited to theory) that the oligomer chains in OLA and OLB have formed micelles, which will serve as polymerization sites for subsequent emulsion polymerization. At least one vinyl polymer PA and PB are characterized by their significantly lower hydrophilicity than that of the vinyl oligomer precursors OLA and OLB. Hydrophilicity can be quantified by acid value or the concentration of acid-functionalized monomers. When both the vinyl oligomer precursor and the vinyl polymer contain carboxylic acid-functionalized monomers, the vinyl polymer contains significantly fewer carboxylic acid-functionalized monomers than the vinyl oligomer precursor. The difference in hydrophilicity is necessary to obtain a particle morphology in which the vinyl oligomer precursor remains on the periphery of the polymer particles during and after the polymerization of the vinyl polymer. Preferably, the vinyl oligomer precursor contains 10-45 wt% of a carboxylic acid functionalized monomer, and the vinyl polymer contains less than 5 wt% of a carboxylic acid functionalized monomer.

[0221] Methods for preparing vinyl polymers PA and PB can be carried out in various modes, including but not limited to: one-time polymerization of all oligomers OLA and OLB and monomer M3 and optionally M1 and / or M2 and / or M4; preloading oligomers OLA or OLB into a reactor and then adding monomers or individual monomers or mixtures of monomers (which may be the same or different) (or vice versa) in one or more stages and / or using gradient feeding techniques; adding oligomers OLA and individual monomers into the reactor (optionally preloaded together with some oligomers); preparing polymers by adding individual monomers to oligomers OLA or OLB simultaneously added to the reactor (optionally preloaded together with some oligomers); or continuously adding one of oligomers OLA or OLB and a mixture of individual monomers into the reactor.

[0222] At the end of the formation of vinyl polymer PA in an aqueous medium containing a vinyl oligomer OLA precursor containing a carboxylic acid group, the carboxylic acid group of the vinyl oligomer OLA precursor is at least partially converted into a side-hanging olefin unsaturated ((meth)acryloyl) group by reacting with M6.

[0223] The crosslinkable waterborne coating composition is preferably prepared by blending a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA with a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB and at least one (carbonyl reactive) crosslinking agent X.

[0224] The blending ratio of DA to DB is 50:50, preferably 35:65, and more preferably 25:75.

[0225] Before or after blending, a (carbonyl reactive) crosslinker that reacts with the M2 (carbonyl) functional group can be added to DA and optionally DB.

[0226] Preferably, the equivalence ratio of the (carbonyl) functional groups of the vinyl oligomers OLA and OLB, and optionally at least one vinyl polymer PA and PB, to the (carbonyl) reactive functional groups of at least one (carbonyl reactive) crosslinking agent X is 0.5-10, more preferably 0.75-5, and more preferably 0.95-2.5. More specifically, the amount of (carbonyl reactive) crosslinking agent is preferably such that the equivalence ratio of the functional groups provided by monomer M2 in oligomer OLA and optionally by monomer M2 in vinyl oligomer OLB, vinyl polymer PA, and vinyl polymer PB to the crosslinking agent functional groups is 0.5-10, more preferably 0.75-5, and most preferably 0.95-2.5.

[0227] The type of at least one (carbonyl reactive) crosslinking agent X depends on the choice of functional group of the olefin unsaturated monomer M2.

[0228] Preferably, the functional group in any vinyl oligomer OLA and OLB, and optionally any vinyl polymer PA and PB, that can react with at least one (carbonyl reactive) crosslinker X is a chain-side (carbonyl) functional group of the ketone, aldehyde, or acetyl group type.

[0229] Preferably, at least one (carbonyl reactive) crosslinker X, having a (carbonyl) functional group that can react with the vinyl oligomers OLA and OLB and optionally at least one vinyl polymer PA and PB, comprises a (carbonyl reactive) functional group selected from primary amines, secondary amines, hydrazides, acyl hydrazides, hydrazones, and mixtures thereof.

[0230] More specifically, the (carbonyl-reactive) crosslinking agent X, which reacts with the (carbonyl) functional group of monomer M2 in OLA and optionally OLB, vinyl polymer PA and vinyl polymer PB, is preferably a diamine or polyamine or dihydrazide or polyhydrazide or a mixture thereof. Examples of diamines are aliphatic or alicyclic amines having 2-10 primary and / or secondary amino groups and 2-100 carbon atoms. Suitable polyfunctional amines include, but are not limited to, hexamethylenediamine, 2-methylpentamethylenediamine, 1,3-diaminopentane, dodecanediamine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, p-phenylenediamine, 3-methylpiperidine, isophoronediamine, bis(hexamethylenetriamine), diethylenetriamine, and combinations thereof. Other suitable polyfunctional amines include those containing ethylene oxide and propylene oxide adducts, such as Huntsman Chemical Company's "JEFFAMINE®" series D, ED and T.

[0231] Examples of dihydrazides include, but are not limited to, dihydrazides of carbonate, dihydrazides of oxalate, dihydrazides of malonate, dihydrazides of succinate, dihydrazides of glutarate, dihydrazides of adipate, dihydrazides of sebacic acid, dihydrazides of maleate, dihydrazides of fumarate, dihydrazides of itaconic acid, dihydrazides of phthalate, or dihydrazides of terephthalate. Alternatively, the crosslinking agent may be a water-soluble aliphatic dihydrazide, such as ethylene-1,2-dihydrazide, propylene-1,3-dihydrazide, and butyl-1,4-dihydrazide, or a polyamine, such as isophorone diamine or 4,7-dioxane-1,10-diamine. Adipate dihydrazide is most preferred.

[0232] More preferably, the aqueous coating composition of the present invention comprises 25-50 wt% of a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, 50-75 wt% of a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, at least one (carbonyl reactive) crosslinking agent X, and at least one photoinitiator based on a total weight of 100 wt% DA and DB, wherein:

[0233] -DA comprises 20-60 wt% of a combination of vinyl oligomer OLA and at least one vinyl polymer PA based on the total weight of DA, wherein the PA and OLA combination comprises at least 35 wt% and at most 75 wt% OLA based on the combined weight of PA and OLA (100 wt%), and

[0234] -DB comprises 20-60 wt% of a combination of vinyl oligomers (OLB) and at least one vinyl polymer (PB) based on the total weight of DB, wherein the PB and OLB combination comprises at least 35 wt% and at most 75 wt% of OLB based on the combined weight of PB and OLB (100 wt%).

[0235] in:

[0236] - The vinyl oligomer chains of OLA and OLB are polymerization products of the following substances:

[0237] -1-45wt% of at least one acid-functionalized olefinic unsaturated monomer M1

[0238] -0.5-20 wt% of at least one olefinic unsaturated monomer M2 having a carbonyl functional group that crosslinks during film formation, preferably M2 is different from M1.

[0239] -50-98.5 wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0240] -0-8wt% of at least one surfactant M5 containing an olefinically unsaturated group; and

[0241] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 polymerized is at least partially converted to its salt, wherein the degree of neutralization is 0.2-0.8; and

[0242] - For the vinyl oligomer OLA, the carboxylic acid group of at least one acid-functionalized olefinically unsaturated monomer M1 polymerized is at least partially converted to an olefinically unsaturated side group by reacting with a bifunctional compound M6, M6 comprising an olefinically unsaturated group and a group reactive to the carboxylic acid, wherein the degree of conversion is 0.2-0.8; and

[0243] in:

[0244] - The vinyl polymer chains of PA and PB are polymerization products of the following substances:

[0245] -0-5wt% of at least one acid-functionalized olefinic unsaturated monomer M1

[0246] -0-10 wt% of at least one olefinic unsaturated monomer M2 having a (carbonyl) functional group that crosslinks during film formation, preferably M2 is different from M1.

[0247] -80-100wt% of at least one olefinic unsaturated monomer M3, M3 being different from M1 and M2, and

[0248] -0.1-5 wt% of at least one polyfunctional olefinic unsaturated monomer M4 for imparting gel content; and

[0249] - The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 is at least partially converted to a salt; and

[0250] - One or more vinyl polymers PA differ from one or more vinyl polymers PB; and

[0251] in:

[0252] The vinyl oligomer OLA and optionally at least one vinyl polymer PA comprise:

[0253] - A chain-side functional group (from M2) that can react with at least one functional group of a (carbonyl reactive) crosslinking agent X, and

[0254] - Chains with side-attached olefinic unsaturated ((meth)acryloyl) functional groups (from M6) that can be crosslinked via (photochemical radiation-induced) radical processes; and

[0255] Vinyl oligomer OLB and optionally at least one vinyl polymer PB contain a chain-side (carbonyl) functional group from M2 that can react with the functional group of at least one (carbonyl reactive) crosslinking agent X, said (carbonyl reactive) crosslinking agent X having functional groups that can react with the carbonyl functional groups of vinyl oligomers OLA and OLB and optionally at least one vinyl polymer PA and PB.

[0256] It is preferred to add one or more photoinitiators to the aqueous coating compositions of the present invention, preferably photoinitiators that absorb visible light wavelengths (i.e., in the range of 380-700 nm, preferably 400-700 nm, referred to as sunlight initiators) to provide free radicals for the polymerization of methacryloyl groups in the vinyl oligomer OLA upon exposure to visible light. Non-limiting examples of sunlight initiators are lithium phenyl-2,4,6-trimethylbenzoylphosphine (LAP), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), diaryl iodonium salts and sulfonium salts, aryl alkyl ketones and benzophenones or heterocyclic aromatic ketones. A comprehensive review was published by SM Müller et al. in Chem Photo Chem (2022), 6, (2 of 12). The most preferred visible light initiator is bis(acyl)phosphine oxide, sometimes referred to as "BAPO" initiator. Examples of commercially available BAPO initiators are OMNIRAD® 819 DW (44-46% active solution of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide) from IGMresins or GENOCURE® BAPO (phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide) from Rahn AG, in 97% powder form.

[0257] The amount of one or more photoinitiators added to a coating composition depends on the pigment used; for example, adding a clear iron oxide (as is common in wood staining applications) will require a larger amount than clear wood varnish.

[0258] The waterborne coating composition preferably contains 0.1-2.0 wt%, preferably 0.3-1.7 wt%, more preferably 0.5-1.5 wt% of one or more photoinitiators. More preferably, the waterborne coating composition contains 0.1-2.0 wt%, preferably 0.3-1.7 wt%, more preferably 0.5-1.5 wt% of one or more sunlight initiators.

[0259] If desired (and less preferred), a photoinitiator with a maximum absorption value in the ultraviolet spectrum (i.e., in the range of 100-400 nm, preferably 100-380 nm) may also be added to the coating formulation.

[0260] Unbound by theory, we believe that the polymerization of olefinic unsaturated side-hanging functional groups in the vinyl polymer dispersion DA is the reason for the coating's rapid drying performance, while the formation of hydrazone crosslinks between the vinyl polymer dispersions DA and DB is the reason for the coating network's longer durability.

[0261] The waterborne coating compositions of the present invention allow for coatings with excellent decorative, protective, and mechanical properties. In particular, the waterborne coating compositions allow for coatings that provide high hardness and good chemical resistance (especially early water resistance and gloss retention). The waterborne coating compositions of the present invention have low MFFT and better application performance than those provided by current prior art.

[0262] The crosslinkable waterborne coating composition typically has a minimum film-forming temperature (MFFT) of 0-50°C, preferably 5-50°C, more preferably 5-25°C, and most preferably 5-15°C.

[0263] If desired, the aqueous compositions of the present invention may be used in combination with other aqueous polymer compositions not conforming to the present invention. Examples of such aqueous polymer compositions include water-reducible alkyd resins, alkyd emulsions, water-reducible polyesters or polyester emulsions, polyurethane dispersions, or epoxy dispersions.

[0264] The water-based coating composition may be colored or uncolored. Preferably, the water-based coating composition is formulated for use in coloring coatings for exterior wood, wherein the pigment used is a transparent iron oxide. More preferably, the water-based coating composition is used in transparent or translucent varnishes for outdoor use on wood (or wood-based) substrates. Most preferably, the water-based coating composition is used as a coating for wood decks (e.g., a deck colorant formulation for deck colorant coatings, also known as a wood coloring coating composition or wood coloring composition).

[0265] Typical deck coloring formulations consist of a binder, transparent iron oxide pigments (typically black, red, and yellow), some rheology modifiers, a coalescing agent, and additional water for viscosity adjustment. Deck coloring formulations are typically applied by roller or brush. Multiple coats are usually applied to achieve a uniform finish. The waterborne coating compositions of the present invention can also be applied to a wide variety of other substrates, including sheet metal, metal, stone, concrete, glass, fabric, leather, paper, plastics, foam, etc., by any conventional method, including brushing, roller coating, dip coating, flow coating, spraying, flexographic printing, gravure printing, inkjet printing, and any other graphic arts application methods. For these applications, the photoinitiator sometimes must be replaced with another initiator that decomposes under shorter wavelengths of ultraviolet light. Therefore, in a further embodiment of the invention, coatings, polymer films, printing inks, and / or overprinting varnishes obtainable from the waterborne coating compositions of the present invention are provided.

[0266] The waterborne coating composition of the present invention, as described above, may further comprise at least one or more conventional ingredients (or one or more additives and auxiliaries) selected from the following: pigments, dyes, emulsifiers, surfactants, plasticizers, thickeners, heat stabilizers, leveling agents, anti-cratering agents, fillers, sedimentation inhibitors, UV absorbers, antioxidants, desiccant salts, organic cosolvents, wetting agents, etc., and mixtures thereof. These ingredients may be introduced at any stage of the waterborne coating composition production process or subsequently.

[0267] Optionally, additional external crosslinking agents may be added to the aqueous coating compositions of the present invention to assist crosslinking during or after drying. Additional external crosslinking agents include solutions of polyisocyanates, amino resins such as melamine-formaldehyde and urea-formaldehyde resins, polyaziridinium, carbodiimide, epoxy resins, and transition metal salts (e.g., zinc ammonium carbonate or zirconium ammonium carbonate).

[0268] Therefore, the waterborne coating compositions of the present invention are particularly suitable for coating exterior wood (e.g., for coating decks, (garden) furniture, (garden) fences, etc.). Preferably, the waterborne coating compositions of the present invention are used to coat wood (or wood-based) substrates selected from: medium-density fiberboard (MDF), high-density fiberboard (HDF), particleboard, oriented strand board (OSB), solid wood, and composite materials (e.g., wood-plastic composites (WPC), composite materials based on blends (or made from) wood or wood-based materials (e.g., wood flour or wood fiber) with thermoplastic plastics (e.g., polyethylene, polypropylene, or polyvinyl chloride). More preferably, the waterborne coating compositions are used to coat wood (or wood-based) substrates selected from medium-density fiberboard (MDF), high-density fiberboard (HDF), particleboard, oriented strand board (OSB), and solid wood. Even more preferably, the waterborne coating compositions are used to coat wood (or wood-based) substrates made of solid wood.

[0269] The present invention also relates to a coated article comprising a wood (or wood-based) substrate at least partially coated with the water-based coating composition of the present invention.

[0270] Experimental Section

[0271] Test methods

[0272] Molecular weight and molecular weight distribution were determined using size exclusion chromatography according to ASTM D 3536 and ASTM D 3593. The size exclusion apparatus used was an Alliance system consisting of a pump, autosampler, and He-degasser (Uniflows Degasys DG-1210), equipped with a PLgel 5 μm MIXED-C 600 x 7.5 mm column and a PLgel 5 μm guard column (50 x 7.5 mm, Polymer Laboratories). The column oven (Separations Analytical Instruments) was set at 30°C. Tetrahydrofuran (THF - Extra Dry, Biosolve 206347) + 2% acetic acid (JTBaker® 6052) was used as the eluent at a flow rate of 0.8 ml / min. Carbon disulfide (JTBaker®) was used as the label. A Waters 410 refractive index detector was used. The injection volume was 100 μl, and the concentration was 1.5 mg / ml. Third-order polynomials were used, and calibration was performed using polystyrene standards (Polymer Laboratories, Easical PS-1, 2010-0501 (molecular weight range 580–8,500,000 g / mol) and Easical PS-2, 2010-0601 (molecular weight range 580–400,000 g / mol)). Empower (Waters) was used for data analysis.

[0273] The minimum film-forming temperature (MFFT) was determined using a Rhopoint MFFT-Bar 60 according to ASTM D2354-10 (2018), with a temperature range of 0–60°C. Each film was applied with a wet film thickness of 25 μm. MFFT is the lowest temperature at which the film will not crack.

[0274] Particle size was determined by dynamic light scattering using a Malvern Zetasizer Nano-S90. The Z-mean value is reported as the particle size. The Z-mean diameter is the average hydrodynamic diameter, calculated according to the international standard for dynamic light scattering, ISO 13321.

[0275] Dynamic mechanical thermal analysis (DMTA) measurements were performed on self-supporting films (60–70 μm thickness) in tensile mode using a TA Instruments Q800 DMTA. DMTA measurements were performed in single-frequency mode at a frequency of 1 Hz and a strain of 0.03% (oscillation amplitude). The temperature was varied between -80°C and 200°C at a heating rate of 5°C / min.

[0276] Simulated sunlight curing: To age the films under simulated sunlight conditions, a Q-Sun test chamber was used with a wavelength set to UV-A 340 nm and an intensity of 0.45 W / m². Testing was conducted according to the ASTM D6695 standard practice for xenon arc exposure of paints and related coatings.

[0277] pH measurements were performed according to ISO 976.

[0278] Brookfield viscosity was measured using a BROOKFIELD™ RVT viscometer at a temperature of 23 ± 1°C according to ISO 2555-1974.

[0279] Solid content determination was performed according to ISO 3251: 2008 (E).

[0280] Example

[0281] The following exemplary embodiments are for illustrative purposes only and are not intended to limit or otherwise restrict the scope of the invention.

[0282] Example 1. Synthesis of DA, a crosslinkable oligomer-stabilized vinyl polymer dispersion with methacryloyl and carbonyl functionalities.

[0283] Phase 1A: Preparation of OLA precursors with carboxyl and carbonyl functional oligomers.

[0284] Table 1: Monomers of OLA precursors

[0285]

[0286] Demineralized (or deionized) water (Aa) and emulsifier (Ab) are loaded into a jacketed 3L glass reactor purged with nitrogen (5 L / h). The emulsifier feed line is flushed with component (Ac). The reactor contents are heated to 70°C. A monomer preemulsion is prepared by adding components (Ag), (Ah), (Ai), (Aj), (Ak), (Al), (Am), (An), (Ao), and (Ap) to a mixing tank. 5% of this preemulsion is added to the reactor, and the contents are heated to 80°C. When the temperature reaches 80°C, an ammonium persulfate solution consisting of (Ad) + (Ae) is added, and the reactor is heated to 85°C. The remaining preemulsion is metered into the reactor over 60 minutes. Simultaneously, an initiator solution consisting of (Ar) + (At) is added to the reactor over 70 minutes. After the monomer preemulsion addition is complete, the mixing tank is flushed with component (Aq). The reactor is then maintained at 85°C for another 30 minutes. Then, add 80g of an aqueous solution of ammonia (25% water) over 30 minutes. Adjust the solid content of the batch to 24% with deionized water. After maintaining the batch at 85°C for 2 hours, cool the polymer dispersion to 45°C. Take samples and analyze them. The number-average molecular weight Mn is 7,550 g / mol, and the weight-average molecular weight is 16,840 g / mol.

[0287] Stage 1B. Preparation of a second vinyl polymer PA in the presence of an alkaline solution of a vinyl oligomer OLA precursor.

[0288] Table 2 shows the composition of the vinyl polymer PA polymerized in the presence of the solubilized vinyl oligomer OLA precursor in stage 1A.

[0289] Table 2: Monomers of Polymer PA

[0290]

[0291] Add 50% of the monomer mixture from Table 2 to a reactor containing the solubilized vinyl oligomer OLA precursor of Stage 1A and mix for 30 minutes. Prepare a reducing agent solution by adding 0.826 g of isoascorbic acid to 16.51 g of deionized water. Add an initiator solution of 0.182 g of tert-butyl hydroperoxide (70% water) in 16.51 g of deionized water and a Fe(II)-EDTA complex solution consisting of 2 mg of ferric sulfate heptahydrate and 5 mg of disodium ethylenediaminetetraacetate dihydrate dissolved in 16.51 g of deionized water to the reactor, followed by 10% of the reducing agent solution prepared above. An exothermic reaction occurs, raising the temperature to 55-60°C. Maintain the reactor temperature at 55-60°C. After 15 minutes, add 40% of the reducing agent solution over 30 minutes. Cool the reactor contents to 50°C. Add the remaining monomer mixture from Table 2 and mix for 20 minutes. The second initiator solution and the EDTA-Fe complex solution were added to the reactor. A 10% reducing agent solution was then added to the reactor. An exothermic reaction occurred. The batch temperature was maintained at 60-65°C. After maintaining this temperature for 15 minutes, the remaining reducing agent solution was added over 30 minutes. The batch was allowed to react at 65°C for 20 minutes. The solids content was adjusted to approximately 44%. The resulting polymer dispersion had a solids content (determined by drying the sample at 125°C for 1 hour) of 43.4% and a pH of 5.4. The particle size, measured by a Malvern Zetasizer, was 211 nm. The acid value of the polymer, determined by titration, was 151 mg KOH / g.

[0292] Stage 1C. Oligomer / polymer dispersions with carboxyl and carbonyl functionalities modified with olefinic unsaturated monoepoxide M6.

[0293] Table 3: Raw materials used for epoxy modification of the dispersion obtained after stage 1B (containing the OLA precursor and PA from stage 1A)

[0294]

[0295] 1,200 g of the polymer dispersion obtained after stage 1B was loaded into a 3 L jacketed reactor and purged with air (5 l / h). The reactor contents were heated to 80°C. Solution (Ca) was added to the reactor contents over 5–10 minutes. Then, a mixture of (Cb), (Cc), and (Cd) was added to the reactor over approximately 10 minutes. After observing a mild exothermic reaction, the reaction mixture was maintained at 80°C for 2 hours. The contents were cooled to 30°C and filtered through a 60 μm filter bag. After modification with the monoepoxide, the solid content of the vinyl polymer dispersion (dried at 125°C for 1 hour) was 40.8%, and the pH was 6.4. The viscosity at 23°C was 0.0176 mPa·s. The particle size of the modified dispersion was 215 nm. The acid value decreased to 52.0 mg KOH / g after modification. The film cast from this dispersion had a smooth and glossy appearance.

[0296] Example 2. Synthesis of a carbonyl-functionalized, crosslinkable oligomer-stabilized vinyl polymer dispersion DB.

[0297] Phase 2A: Synthesis of carboxyl and carbonyl functionalized vinyl oligomers OLB.

[0298] Crosslinkable vinyl oligomers OLB were synthesized using the same procedure as in Stage 1A of Example 1 (synthesis of OLA precursor), but with the monomer composition listed in Table 4.

[0299] Table 4: Raw Material Composition of OLB

[0300]

[0301] The number-average molecular weight (Mn) of the crosslinkable vinyl oligomer OLB is 6,580 g / mol, and the weight-average molecular weight (Mw) is 14,360 g / mol.

[0302] Phase 2B: Preparation of vinyl polymer PB in the presence of an alkaline solution of vinyl oligomer OLB.

[0303] According to the procedure of Example 1 (Phase 1B), the vinyl polymer PB was synthesized using the oligomer (OLB) of Phase 2A and monomers having the weights shown in Table 5.

[0304] Table 5: Raw materials used for vinyl polymer PB

[0305]

[0306] The weight ratio of oligomer (OLB) to polymer (PB) portion in the dispersion is approximately 1 / 1.

[0307] The dispersed oligomer-stabilized polymer dispersion has a solid content of 40.0%, a pH of 8.7, a particle size of 96 nm, and a viscosity of 128 mPa·s.

[0308] Example 3. Water-based coating composition.

[0309] A clear varnish was prepared based on a combination of vinyl dispersions DA and DB from Examples 1 and 2. A commercial reference, RESYDROL® AY 586w / 39 WA (hereinafter “AY 586”, available from Allnex Austria), was used as it is one of the benchmark binders used in wood coating staining paints. AY 586 is an oxidatively drying acrylic-modified alkyd resin, supplied in aqueous emulsion form. Its key properties are a solids content of 39% (in water) and the presence of 2.8% ethoxypropanol and 2.8% methoxypropoxypropanol.

[0310] Wood staining was prepared according to Table 6, with Examples 3.3 and 3.4 serving as comparative examples.

[0311] Table 6: Wood Staining Compositions

[0312]

[0313] Dipropylene glycol n-butyl ether. A trade name from Dow Chemical.

[0314] Transparent iron oxide pigment, purchased from Krahn Chemie Benelux.

[0315] VOC-free siloxane defoamer for water-based coatings, purchased from BYK Chemie.

[0316] 45% diacylphosphine oxide aqueous solution, BAPO type photoinitiator, purchased from IGM Resins.

[0317] The rheology modifier, a nonionic polyurethane in butyl triethylene glycol / water, was purchased from Munzing Chemie.

[0318] The wood staining coating composition was applied to glass with a wet film thickness of 125 μm. After flash drying for 10 minutes, it was cured. The Koenig hardness of different coatings was tested under different drying methods; the results are shown in Table 7.

[0319] Table 7: Drying performance (Koenig hardness) of experiments 3.1-3.5

[0320]

[0321] Interestingly, formulations based on the vinyl polymer DB appeared to exhibit the most ideal hardness development. However, the formulation consisting of 75% binder vinyl polymer dispersion DB and 25% polymer dispersion DA showed the highest hardness after 100 hours of xenon lamp irradiation. In formulations based on AY 586, no effect was observed from the presence of polymer DA. The hardness of the pure polymer DA binder nearly doubled, but the film became both hard and brittle. These results illustrate the advantages of combining vinyl polymer dispersions DA and DB.

[0322] Wood coloring compositions were prepared according to Table 8, wherein Examples 4.3 and 4.4 are comparative examples.

[0323] Table 8: Wood Staining Compositions

[0324]

[0325] The test results are shown in Table 9.

[0326] Table 9: Drying performance of experiments 4.1-4.5

[0327]

[0328] The table clearly shows the synergistic effect of the combined adhesives DA and DB, especially after UV curing.

[0329] DMTA analysis

[0330] The self-supporting films obtained by applying different coatings to a polypropylene substrate and aging were also studied by dynamic mechanical thermometry (DMTA, see test methods above). In the DMTA curves, there is always an initial transition in the region near -10°C, which can be attributed to the core particles of DA and DB (PA and PB, respectively). The tanδ peak on the right can be attributed to the crosslinked OLA and OLB, and gives the Tg of the formed network. The Tg values ​​shown in Table 10 below were determined by DMTA.

[0331] Table 10: Tg (DMTA)网络 Curing time varies depending on ambient temperature and xenon lamp irradiation. Photoinitiator (PI) OMNIRAD® 819DW

[0332]

[0333] Table 10 shows that, compared to oligomer-stabilized vinyl polymer dispersions containing only DA or DB, the coating containing DA (25%) + polymer DB (75%) + PI showed a rapid increase in Tg within the first 3 days. When the coating contained transparent iron oxide, the increase in Tg in the network appeared to be slower, possibly due to a reduction in the amount of light received by the photoinitiator.

Claims

1. A waterborne coating composition comprising a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, and at least one crosslinking agent X, wherein: DA comprises a vinyl oligomer OLA and at least one vinyl polymer PA, wherein the vinyl oligomer OLA and optionally the at least one vinyl polymer PA comprise: chain-side hanging functional groups that can react with functional groups of at least one crosslinking agent X, and chain-side hanging olefinic unsaturated functional groups that can be crosslinked via a free radical process. DB comprises a vinyl oligomer OLB and at least one vinyl polymer PB, wherein the vinyl oligomer OLB and optionally the at least one vinyl polymer PB comprise chain-side functional groups capable of reacting with functional groups of at least one crosslinking agent X.

2. The water-based coating composition according to claim 1, wherein: The vinyl oligomers OLA and OLB are characterized in that: The number-average molecular weight Mn is 500-50,000 g / mol, preferably 2,500-25,000 g / mol, and more preferably 5,000-15,000 g / mol; The calculated glass transition temperature Tg of the oligomer backbone is 10-150°C, preferably 20-125°C, and more preferably 25-115°C; The at least one vinyl polymer PA and PB are characterized in that: The number-average molecular weight Mn is greater than 60,000 g / mol, preferably greater than 80,000 g / mol, and more preferably greater than 100,000 g / mol; The calculated glass transition temperature Tg of the polymer backbone is -70 to 50°C, preferably -45 to 45°C, and more preferably -25 to 40°C; The calculated glass transition temperatures (Tg) of PA and PB are at least 25°C, preferably at least 35°C, and more preferably at least 40°C lower than the glass transition temperatures of the main chains of the vinyl oligomers OLA and OLB.

3. The waterborne coating composition according to claim 1 or 2, wherein the first crosslinkable oligomer-stabilized vinyl polymer dispersion DA comprises 20-60 wt%, preferably 30-50 wt%, of a combination of PA and OLA based on the total weight of DA, and the combined PA and OLA comprises at least 35 wt%, preferably at least 40 wt%, more preferably at least 45 wt%, most preferably at least 50 wt%, and at most 75 wt%, preferably at most 70 wt%, more preferably at most 65 wt%, and most preferably at most 60 wt%, of OLA based on a combined weight of PA and OLA of 100 wt%.

4. The waterborne coating composition according to claim 1 or 2, wherein the second crosslinkable oligomer-stabilized vinyl polymer dispersion DB comprises 20-60 wt%, preferably 30-50 wt%, of a combination of PB and OLB based on the total weight of DB, wherein the combination of PB and OLB comprises at least 35 wt%, preferably at least 40 wt%, more preferably at least 45 wt%, most preferably at least 50 wt%, and at most 75 wt%, preferably at most 70 wt%, more preferably at most 65 wt%, and most preferably at most 60 wt%, of OLB based on a combined weight of PB and OLB of 100 wt%.

5. The waterborne coating composition according to any one of claims 1-4, comprising 25-50 wt% of a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA and 50-75 wt% of a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB based on a total weight of 100 wt% DA and DB.

6. The waterborne coating composition according to any one of claims 1-5, wherein the functional group of any one of the vinyl oligomers OLA and OLB and optionally any one of the vinyl polymers PA and PB that is reactive with the functional group of at least one crosslinking agent X is a chain-side functional group of the ketone, aldehyde or acetyl acetyl type.

7. The waterborne coating composition according to any one of claims 1-6, wherein the at least one crosslinking agent X having functional groups capable of reacting with functional groups of vinyl oligomers OLA and OLB and optionally at least one vinyl polymer PA and PB comprises functional groups selected from primary amines, secondary amines, hydrazides, acylhydrazides, hydrazones, and mixtures thereof.

8. The waterborne coating composition according to any one of claims 1-7, wherein the equivalent ratio of the functional groups of the vinyl oligomers OLA and OLB and optionally at least one vinyl polymer PA and PB to the functional groups of at least one crosslinking agent X is 0.5-10, preferably 0.75-5, more preferably 0.95-2.

5.

9. The waterborne coating composition according to any one of claims 1-8, wherein: The vinyl oligomer chains of OLA and OLB are polymerization products of the following substances: 1-45 wt% of at least one acid-functionalized olefinic unsaturated monomer M1 0.5-20 wt% of at least one olefinic unsaturated monomer M2 having a crosslinking functional group during film formation, preferably M2 is different from M1. At least one olefinic unsaturated monomer M3, comprising 50-98.5 wt%, wherein M3 is different from M1 and M2, and 0-8 wt% of at least one surfactant M5 containing an olefinic unsaturated group; The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 polymerized is at least partially converted to its salt, wherein the degree of neutralization is 0.2-0.8; and For the vinyl oligomer OLA, the carboxylic acid group of at least one acid-functional olefinic unsaturated monomer M1 polymerized is at least partially converted into an olefinic unsaturated side group by reacting with a bifunctional compound M6, wherein M6 comprises an olefinic unsaturated group and a group that can react with the carboxylic acid, wherein the degree of conversion is 0.2-0.

8.

10. The waterborne coating composition according to any one of claims 1-9, wherein: The vinyl polymer chains of PA and PB are polymerization products of the following substances: 0-5 wt% of at least one acid-functionalized olefinic unsaturated monomer M1 0-10 wt% of at least one olefinic unsaturated monomer M2 having a crosslinking functional group during film formation, preferably M2 is different from M1. At least one olefinic unsaturated monomer M3, 80-100 wt%, wherein M3 is different from M1 and M2, and 0.1-5 wt% of at least one polyfunctional olefinic unsaturated monomer M4 for imparting gel content; The acid group of at least one acid-functionalized olefinic unsaturated monomer M1 is at least partially converted to a salt during polymerization; and One or more vinyl polymers PA are different from one or more vinyl polymers PB.

11. The waterborne coating composition according to claim 9 or 10, wherein the acid-functionalized olefinic unsaturated monomer M1 is selected from acrylic acid, methacrylic acid, itaconic acid, and mixtures thereof.

12. The waterborne coating composition according to any one of claims 9-11, wherein the olefinic unsaturated monomer M2 having crosslinking functional groups upon film formation is selected from acetyl acetoxyethyl methacrylate, diacetone acrylamide, and mixtures thereof.

13. The waterborne coating composition according to any one of claims 9-12, wherein the monomer M3, which is different from M1 and M2, is selected from vinyl monomers; (meth)acrylates of the formula CH=CR1-C(O)OR2, wherein R1 is H or methyl, and R2 is optionally substituted C1-C20 alkyl, cycloalkyl, aryl or (alkyl)aryl; and mixtures thereof.

14. The waterborne coating composition according to any one of claims 9-13, wherein the polyfunctional olefinic unsaturated monomer M4 is selected from 1,3-butadiene, isoprene, divinylbenzene, triallyl cyanurate, vinyl (meth)acrylate or allyl acrylate, diol di(meth)acrylate, methylene bis(meth)acrylamide, and mixtures thereof.

15. The waterborne coating composition according to any one of claims 9-14, wherein the bifunctional compound M6 comprising an olefinically unsaturated group and a group reactive to a carboxylic acid is an olefinically unsaturated monoepoxide.

16. The waterborne coating composition according to any one of claims 1-15, comprising 0.1-2.0 wt%, preferably 0.3-1.7 wt%, more preferably 0.5-1.5 wt% of one or more photoinitiators, preferably sunlight initiators.

17. The waterborne coating composition according to any one of claims 1-16, comprising one or more additives and auxiliaries selected from the following: pigments, dyes, emulsifiers, surfactants, plasticizers, thickeners, heat stabilizers, leveling agents, anti-cratering agents, fillers, sedimentation inhibitors, UV absorbers, antioxidants, desiccant salts, organic cosolvents, wetting agents, and mixtures thereof.

18. A method for preparing a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB as defined in any one of claims 1-17, comprising the following steps: a. Preparing an aqueous emulsion or solution of a vinyl oligomer OLB comprising a carboxylic acid-functionalized monomer, wherein the amount of the carboxylic acid-functionalized monomer is sufficient to impart water solubility or water dispersibility to the vinyl oligomer OLB. b. Neutralize the vinyl oligomer OLB at least partially with an alkali. c. Add a monomer mixture to the at least partially neutralized vinyl oligomer OLB formed in the preceding steps, and emulsion polymerize the monomer mixture to form a vinyl polymer PB dispersion with lower hydrophilicity than the vinyl oligomer OLB, thereby forming a mixture of vinyl polymer PB and vinyl oligomer OLB.

19. A method for preparing a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA as defined in any one of claims 1-17, comprising the following steps: a. Preparing an aqueous emulsion or solution of a vinyl oligomer OLA precursor comprising a carboxylic acid-functionalized monomer, wherein the amount of the carboxylic acid-functionalized monomer is sufficient to impart water solubility or water dispersibility to the vinyl oligomer OLA precursor. b. Neutralize the vinyl oligomer OLA precursor at least partially with a base. c. Add a monomer mixture to the at least partially neutralized vinyl oligomer OLA precursor formed in the previous step, and emulsion polymerize the monomer mixture to form a vinyl polymer PA dispersion with lower hydrophilicity than the vinyl oligomer OLA precursor. d. Reacting the carboxylic acid groups (formed) in a vinyl oligomer OLA precursor with a bifunctional compound comprising an olefinically unsaturated group and a group capable of reacting with the carboxylic acid groups (formed) in the vinyl oligomer OLA precursor, thereby at least partially converting the carboxylic acid groups of the vinyl oligomer OLA precursor into olefinically unsaturated groups, thereby forming a mixture of vinyl polymer PA and vinyl oligomer OLA.

20. The waterborne coating composition according to claim 17, prepared by blending a first crosslinkable oligomer-stabilized vinyl polymer dispersion DA, a second crosslinkable oligomer-stabilized vinyl polymer dispersion DB, at least one crosslinking agent X, one or more photoinitiators, and one or more additives and auxiliaries, wherein the photoinitiator is preferably a sunlight initiator.

21. Use of the coating composition of claim 20 for coating a wood or wood-based substrate, wherein the substrate is selected from medium-density fiberboard (MDF), high-density fiberboard (HDF), particleboard, oriented strand board (OSB), solid wood, and composite materials.

22. A coated article comprising a wood or wood-based substrate at least partially coated with the waterborne coating composition of claim 17 or the waterborne coating composition prepared according to claim 20.

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