Acrylic epoxy hybrid based coatings for improved hardness

Abstract

The present invention relates to a two-component aqueous coating composition comprising a binder component and a curing component. The two-component aqueous coating composition comprises a coalescing agent package containing at least one coalescing agent and has a minimum film forming temperature of 0 DEG C to 25 DEG C. Methods of making the coatings and coated articles are also disclosed.

Description

BACKGROUND OF THE INVENTION

[0001] In the paint industry, particularly the industrial paint industry, coatings that simultaneously possess corrosion resistance and hardness are often required. Multilayer coatings have been developed to provide a first layer that provides adhesion and corrosion resistance to a substrate. Additional layers are then applied to provide weather resistance, chemical resistance, and / or a desired appearance. Epoxy resins are typically selected for the first layer, while polyurethane resins or acrylic resins are commonly used for the upper layers. Different resin chemistries are used because it is difficult to find a single resin chemistry that provides the necessary balance between corrosion resistance and weather resistance.

[0002] Acrylic epoxy hybrid (AEH) resins, such as those disclosed in U.S. Patent No. 8,658,742, have been developed to provide a better balance between corrosion resistance and weather resistance in a single chemical system. These AEH resin systems allow for a single-coat system that provides good corrosion resistance and weather resistance for many applications, such as directly applied to metal coatings.

[0003] However, for some applications, the hardness and / or weather resistance provided by existing AEH resin systems are insufficient.

[0004] There is a need for a low-cost and simple resin system that can provide improved hardness. It is also desirable to provide a coating with improved hardness that is compatible with existing coatings. SUMMARY OF THE INVENTION

[0005] In a first aspect, the present invention relates to a two-component aqueous coating composition comprising a binder component and a curing component, wherein the binder component comprises an aqueous dispersion of acrylic polymer particles absorbed with an epoxide, and wherein the coating composition comprises a coalescent package containing at least one coalescent and has a minimum film formation temperature (MFFT) of 0°C to 25°C.

[0006] In a second aspect, the present invention relates to a method for preparing a coating, the method comprising:

[0007] (i) providing a coating composition according to any one of the preceding claims;

[0008] (ii) applying the coating composition to a substrate to form a coating;

[0009] (iii) curing the coating at a temperature above room temperature for at least 10 minutes to form a coating on the substrate.

[0010] A third aspect of the present invention relates to an article comprising a coated substrate formed by the above method. DETAILED DESCRIPTION

[0011] In a first aspect, the present invention relates to a coating composition comprising a two-component aqueous coating composition having improved hardness.

[0012] The two-component aqueous coating composition comprises a binder component and a curing (i.e., crosslinking) component. The binder component comprises an aqueous dispersion of acrylic polymer particles that have absorbed an epoxide compound. As used herein, the term "acrylic" includes (meth)acrylic acid, (meth)acrylic alkyl esters, (meth)acrylamides, (meth)acrylonitriles, and modified forms thereof such as (meth)acrylic hydroxyalkyl esters. The fragment "(meth)acryloyl" refers to both "methacryloyl" and "acryloyl", such that for example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and (meth)methyl acrylate refers to both methyl methacrylate and methyl acrylate. As used herein, the term "has absorbed an epoxide compound" means that the epoxide compound is at least partially absorbed by the acrylic polymer particles, but does not react with the acrylic polymer particles and is not merely present on the surface of the acrylic polymer particles.

[0013] Preferably, the aqueous dispersion of acrylic polymer particles that have absorbed an epoxide compound comprises a stable aqueous dispersion of acrylic polymer particles that have absorbed a thermosetting compound having at least two epoxy groups. As used herein, the term "thermosetting compound" means a compound that will undergo a chemical reaction to form a thermoset compound that has different chemical and physical properties and does not undergo a reversible thermal transition upon exposure to heat.

[0014] The absorbed thermosetting compound preferably has a plurality of epoxy groups; more preferably, the thermosetting compound is a novolak resin, a di-, tri-, or tetra-glycidyl ether or a di-, tri-, or tetra-glycidyl ester.

[0015] Examples of suitable thermosetting compounds include the diglycidyl ether of bisphenol A, the diglycidyl ether of bisphenol F, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, the diglycidyl ester of phthalic acid, 1,4-cyclohexanedimethanol diglycidyl ether, 1,3-cyclohexanedimethanol diglycidyl ether, the diglycidyl ether of hexahydrophthalic acid, and novolak resins, and combinations thereof. A commercially available thermosetting compound is D.E.R. 331 liquid epoxy resin (available from Olin Corporation).

[0016] The aqueous dispersion of acrylic polymer particles (i.e., latex) can be obtained by free radical emulsion or suspension addition polymerization reactions or by dispersing a preformed polymer into an aqueous medium under shear. Examples of suitable latexes include acrylic and styrene-acrylic based latexes.

[0017] The acrylic polymer particles may also contain an anti - coalescence functional group, which refers to a hydrophilic group that is sufficiently non - reactive with the epoxy - ethyl group (and the ester group, if present) such that the latex particles are stable for 10 days during thermal aging at 60 °C. The term "stable for 10 days during thermal aging at 60 °C" as used herein means that the particle size of the latex after 10 days of thermal aging at 60 °C increases by no more than 30% compared to the particle size before such thermal aging studies.

[0018] Anti - coalescence functional groups can be incorporated into the polymer particles using monomers containing anti - coalescence functional groups (anti - coalescence monomers), but such groups can also be incorporated by grafting. The anti - coalescence groups are considered effective because they are hydrophilic under thermal aging conditions and do not react with the epoxy - ethyl group. General classes of such groups include amide groups, acetoacetoxy groups, and strong protonic acids whose pH is adjusted to form their conjugate bases.

[0019] Specific examples of anti - coalescence monomers include acrylamide, ethyl phosphate methacrylate, sodium styrene sulfonate, ethyl acetoacetoxy methacrylate, and acrylamido - methyl - propane sulfonate. When present, the concentration of the anti - coalescence functional group in the polymer is preferably sufficient to stabilize the thermoplastic polymer under thermal aging conditions, preferably 0.5 wt%, and more preferably from 1 wt% to preferably 10 wt%, and more preferably up to 5 wt% based on the weight of the polymer.

[0020] Monomers suitable for preparing acrylic latexes include acrylates and methacrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate, 2 - ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2 - ethylhexyl methacrylate, and combinations thereof. In addition, acrylic latexes may also include structural units of other monomers such as styrene and acrylonitrile. As used herein, the term "structural unit" refers to the residue of the named monomer after polymerization.

[0021] It may also include structural units of one or more acid monomers, most notably acrylic acid, methacrylic acid, and itaconic acid. It may also include monomers capable of conferring co - curable functional groups, such as glycidyl acrylate and glycidyl methacrylate.

[0022] It may be advantageous to include a chain transfer agent in the latex preparation. Examples of chain transfer agents include, but are not limited to, dodecyl mercaptan, butyl mercaptopropionate, methyl mercaptopropionate, mercaptopropionic acid, etc.

[0023] In certain embodiments, it may be advantageous to incorporate copolymerized polyethylenically unsaturated monomer groups into the polymer. Polyethylenically unsaturated monomers include, for example, allyl (meth)acrylate, diallyl phthalate, 1,4-butanediol di(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and divinylbenzene. It can be particularly advantageous to incorporate such monomer groups non-uniformly into the polymer to form multiphase polymer particles, thereby producing core-shell, hemispherical, or occluded morphologies.

[0024] Advantageously, an aqueous dispersion of acrylic polymer particles absorbed with an epoxide (i.e., absorbed latex) is separately prepared using conventional emulsion polymerization techniques and then combined with a thermosetting compound, which can be pure or in the form of an aqueous emulsion, preferably in the form of an aqueous emulsion, more preferably in the form of a micronized aqueous emulsion. When the thermosetting compound is added as an aqueous emulsion, the emulsion is stabilized with a stabilizing amount of surfactant, preferably at a concentration in the range of about 0.5 to about 10 wt%. Nonionic surfactants are preferred and include APEO-free nonionic wetting agents such as polyalkylene oxide block copolymers, polyoxyethylene alkyl ethers, glucoside alkyl ethers, fatty acid esters, glycerol alkyl esters, sorbitan alkyl esters, and polyoxyethylene alkylphenol ethers, including commercially available wetting agents such as TRITON TM X-405 octylphenol ethoxylate (a trademark of Dow Chemical Company or its affiliates). When the thermosetting compound is combined with the latex as a pure compound, absorption is facilitated by stirring at room temperature or above room temperature.

[0025] Based on the total weight of the latex, a high solids content absorbed latex, i.e., a latex having a solids content of at least 40 wt% and especially 45 wt% to 60 wt%, can be used in the present invention.

[0026] The absorbed latex composition can be used as part of a two-component formulation (i.e., the binder component), and the second component is a curing (i.e., crosslinking) component added prior to use, which cures or solidifies the thermosetting compound. Thus, the binder component of the present invention is substantially free of a curing agent; that is, the concentration of the compound that promotes the ring opening of ethylene oxide is not sufficient to destabilize the thermosetting compound. Preferably, based on the total weight of the absorbed latex composition, the absorbed latex composition contains no more than 0.05 wt%, more preferably no more than 0.005 wt%, and most preferably 0 wt% of a curing agent.

[0027] Preferably, the absorbed latex in the binder component is cured with a water-compatible external curing agent comprising a curing component. Preferably, the absorbed latex is cured with a carboxylic acid-based acrylic. Examples of carboxylic acid-based acrylics include, for example, acrylic polymer emulsions, which include but are not limited to structural units derived from carboxylic acids such as, for example, methacrylic acid, itaconic acid, and acrylic acid, and acrylic monomers, including methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isooctyl acrylate, n-decyl acrylate, isodecyl acrylate, tert-butyl acrylate, methyl methacrylate, butyl methacrylate, hexyl methacrylate, isobutyl methacrylate, isopropyl methacrylate, 2-hydroxyethyl acrylate, acrylamide, acrylonitrile, methacrylonitrile, isobornyl acrylate, n-propyl methacrylate, sec-butyl methacrylate, cyclohexyl methacrylate, tert-butylaminoethyl methacrylate, stearyl methacrylate, glycidyl methacrylate, dicyclopentenyl methacrylate, and phenyl methacrylate, and optionally structural units derived from styrene. For example, the acrylic polymer emulsion may comprise a styrene-acrylic polymer emulsion.

[0028] Preferably, the acrylic polymer emulsion comprises from 35 wt% to 70 wt%, and more preferably from 40 wt% to 65 wt%, of acrylic solids based on the total weight of the acrylic polymer emulsion. Preferably, the acrylic particles have a weight-average particle size in the range of 60 nm to 450 nm, an acid content in the range of 0.1 wt% to 15 wt% of acid monomers based on the weight of the acrylic monomers, a weight-average molecular weight in the range of 50,000 g / mol to 5,000,000 g / mol, and a glass transition temperature (Tg) in the range of 7 °C to 100 °C, as measured by differential scanning calorimetry (DSC). The pH of the acrylic polymer dispersion is in the range of 6 to 10.

[0029] Based on the molar ratio of epoxy groups to carboxylic acid groups, the amount of curing agent used typically varies from about 1:1 to 2.5:1 in terms of the stoichiometry of epoxy resin to carboxylic acid. Preferably, the curing component is present in the coating composition in an amount such that the stoichiometry between epoxy groups and acid groups is in the range of 1:1 to 1.5:1 based on the molar ratio of epoxy groups to carboxylic acid groups in the coating composition. More preferably, the curing component is present in the coating composition in an amount such that the stoichiometry between epoxy groups and acid groups is in the range of 1:2 to 1.4:1 based on the molar ratio of epoxy groups to carboxylic acid groups in the coating composition.

[0030] The two-component aqueous coating composition further comprises a coalescent package. The coalescent package comprises at least one coalescent. As used herein, the term "coalescent" refers to a non-volatile or slow-evaporating solvent that causes polymer particles to fuse into a continuous film under ambient conditions.

[0031] Examples of suitable coalescents include 2-n-butoxyethanol, dipropylene glycol n-butyl ether, propylene glycol n-butyl ether, dipropylene glycol methyl ether, propylene glycol methyl ether, propylene glycol n-propyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, triethylene glycol monobutyl ether, dipropylene glycol n-propyl ether, n-butyl ether, or mixtures thereof. Preferred coalescents include dipropylene glycol n-butyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, n-butyl ether, or mixtures thereof. Commercially available coalescents include, for example, OPTIFILM TM 400 and TEXANOL TM coalescents, both of which are available from Eastman Chemical Company.

[0032] Preferably, at least one coalescent in the coalescent package is present in an amount in the range of 2 wt% to 10 wt%, preferably 3 wt% to 9.5 wt%, and more preferably 4 wt% to 9 wt% based on the total weight of solids in the binder component and the curing component of the coating composition, where the total solids amount does not include any additional components (e.g., pigments present in the coating composition).

[0033] The minimum film-forming temperature (MFFT) of the coating composition is 0 °C to 25 °C, preferably 5 °C to 15 °C. The MFFT is the lowest temperature at which polymer particles on an aqueous dispersion will coalesce with each other and form a continuous film when volatile components (e.g., water) evaporate. The MFFT can be measured according to GB / T 9267-2008.

[0034] The coating composition according to the present invention may further comprise one or more of the following additives: solvents; fillers; pigments such as titanium dioxide, mica, calcium carbonate, silica, zinc oxide, ground glass, aluminum trihydrate, talc, antimony trioxide, fly ash, and clay; polymer-encapsulated pigments such as polymer-encapsulated or partially encapsulated titanium dioxide, zinc oxide, or lithopone; polymers or polymer emulsions adsorbed or bound to the surface of pigments such as titanium dioxide; hollow pigments, including pigments having one or more voids; dispersants such as amino alcohols and polycarboxylates; surfactants; defoamers; preservatives such as biocides, mildew inhibitors, fungicides, algaecides, and combinations thereof; flow agents; leveling agents; and additional neutralizing agents such as hydroxides, amines, ammonia, and carbonates.

[0035] The volatile organic compound (VOC) content of the coating composition can range from 0.2 lb / gal to 1 lb / gal, preferably from 0.25 lb / gal to 0.85 lb / gal, and more preferably from 0.25 lb / gal to 0.75 lb / gal.

[0036] The pigment volume concentration (PVC) of the coating composition can be calculated by the following equation:

[0037]

[0038] For example, the PVC of the coating composition can range from 7.5% to 12.5%.

[0039] The second aspect of the present invention relates to a method for preparing a coating. The method includes the coating composition as described above.

[0040] A coating is formed by applying the coating composition to a substrate. Then the coating is cured at a temperature above room temperature for at least 10 minutes. Preferably, the curing temperature is at least 50 °C, more preferably at least 60 °C, and the curing time is preferably at least 15 minutes. The coating can be flash evaporated at room temperature before curing to allow the evaporation of volatile components.

[0041] Preferably, the substrate is a metal substrate. The metal substrate can be bare metal (e.g., the coating is a direct-to-metal coating) or a primed metal substrate (e.g., a metal substrate coated with a zinc-rich primer).

[0042] In a preferred embodiment, a coating is formed on a substrate comprising a cured primer layer such that the coating forms a topcoat over the primer. Preferably, the primer layer is formed from a two-component aqueous primer coating composition comprising a primer binder component and a primer curing component. The primer binder component can be the same as or different from the binder component of the topcoat coating composition. Similarly, the primer curing component can be the same as or different from the curing component of the topcoat coating composition. Preferably, the primer binder component is the same as the binder component of the topcoat coating composition, and the primer curing component is the same as the curing component of the topcoat coating composition, i.e., the primer coating composition and the topcoat coating composition are based on a single chemical resin system.

[0043] The primer coating composition further comprises a primer coalescent package, the primer coalescent package comprising at least one coalescent, the at least one coalescent can be the same as or different from the at least one coalescent of the topcoat coating composition. The at least one coalescent in the primer coalescent package can be present in an amount ranging from 10 wt% to 30 wt%, preferably from 15 wt% to 25 wt%, based on the total weight of solids in the primer binder component and the primer curing component of the primer coating composition, wherein the total solids amount does not include any additional components (e.g., pigments present in the primer coating composition).

[0044] The primer coating composition preferably has a MFFT of less than 5 °C, preferably -10 °C to 5 °C.

[0045] The primer curing component may be present in the primer coating composition in an epoxy resin to carboxylic acid stoichiometric amount of 1.75:1 to 2.5:1, preferably 2.0:1 to 2.5:1, based on the number of moles of epoxy groups and the number of moles of carboxylic acid in the primer coating composition.

[0046] The primer coating composition may have a VOC content in the range of 0.75 lb / gal to 1.25 lb / gal and a PVC in the range of 15% to 20%.

[0047] A third aspect of the present invention relates to an article comprising a coating formed from a coating composition.

[0048] Preferably, the coating has a Persoz hardness of at least 50 seconds, more preferably at least 60 seconds, and even more preferably at least 70 seconds, as measured according to the following method.

[0049] Examples - The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. The following materials were used in the examples:

[0050] AEH-1 is an AEH dispersion with a solids content of 53.9%, an epoxy equivalent weight of 312 g / eq based on solid weight, and a pH of 7.

[0051] AEH-2 is an AEH dispersion with a solids content of 52.2%, an epoxy equivalent weight of 468 g / eq based on solid weight, and a pH of 7.

[0052] SAP is a carboxylic acid-functional styrene-acrylic polymer dispersion with a solids content of 49.5% and an acid equivalent weight of 2457 g / eq based on polymer solids, and is used as a curing agent.

[0053] DOWANOL TM DPnB is dipropylene glycol monobutyl ether available from The Dow Chemical Company and is used as a coalescent.

[0054] OPTIFILM 400 is a coalescent available from Eastman Chemical Company.

[0055] OROTAN TM 681 is polymethacrylic acid with a hydrophobic comonomer available from The Dow Chemical Company and is used as a dispersant.

[0056] ACRYSOL TMRM-12W is a nonionic polyurethane rheology modifier available from The Dow Chemical Company.

[0057] TEGO Airex 902W is a polyether silicone copolymer emulsion available from Evonik Corporation and is used as an antifoaming agent.

[0058] Ti-PURE R-706 is a titanium dioxide pigment available from Chemour Company.

[0059] TAMOL TM 681 is a hydrophobic copolymer dispersant available from The Dow Chemical Company.

[0060] TRITON TM HW-1000 is a nonionic surfactant available from The Dow Chemical Company.

[0061] ANCAMINE K-54 is a tris-(dimethylaminomethyl)phenol curing agent available from Evonik Corporation.

[0062] XIAMETER TM OFS-6020 is an aminoethylaminopropyltrimethoxysilane coupling agent available from The Dow Chemical Company.

[0063] Preparation of the coating composition

[0064] Prepare the pigment grind for Base 1, Base 2, and the coating compositions of the present invention according to Table 1 below. Add the following ingredients to a 1 L stainless steel container and mix on a disperser with a 2" cowles blade at low shear (1000 rpm) until homogeneous (about 5 minutes): 299.56 g deionized water, 11.68 g ammonia (28%), 7.49 g Foamex 1488, 48.13 g Tamol 681, and 9.99 g Triton HW1000. After about 5 minutes, slowly add 1123.15 g TiPure R706 under shear. Gradually increase the mixing speed to achieve good vortexing. After adding all of the TiO2, stop the disperser so that the blades, shaft, and sides of the container can be scraped with a metal spatula. Then turn on the disperser and increase the speed to about 2000 rpm. After about 15 minutes, when the Hegman gauge reads 7 - 8 units, mixing is complete. Then the pigment grind is ready to be added to the formulations in Table 2 listed below.

[0065] Table 1

[0066] Component Weight (g) Deionized water 499.27 Ammonia (28%) 19.47 TEGO Foamex 1488 12.48 <![CDATA[TAMOL TM 681]]> 80.22 <![CDATA[TRITON TM HW1000]]> 16.64 Ti-Pure R-706 TiO2 1871.91 Total 2500

[0067] Two different acrylic epoxy hybrids, AEH-1 and AEH-2, were used to prepare two primer coating compositions, Basecoat 1 and Basecoat 2, and the coatings according to the present invention. The Part B side mixtures were prepared in plastic containers with appropriate content sizes (8 oz. to 32 oz.) using a metal blade (1" diameter) on a laboratory mixer set at an appropriate speed (500 rpm - 1000 rpm) to maintain a good vortex. The first component was added on a laboratory balance, and additional components were added during mixing to achieve good incorporation. After adding the last component, the mixture was remixed at about 1100 rpm for 15 minutes. The Part B side was allowed to equilibrate overnight, then mixed with a tongue depressor and the coatings were prepared.

[0068] Table 2

[0069]

[0070] The properties of Basecoat 1, Basecoat 2, and the coating compositions of the present invention are shown in Table 3.

[0071] Table 3

[0072] <![CDATA Binder 1 > <![CDATA Binder 2 > <![CDATA Coating composition of the present invention > Characteristic Value Value Value Molar ratio (epoxy / acid) 2.3 / 1 2.3 / 1 1.3 / 1 % PVC 17.0 17.0 10.0 VOC (lb / gal) 0.91 0.91 0.33 % Weight solids 52.8 52.9 49.2 % Volume solids 40.9 40.9 40.8 % Coalescing agent 19.7 19.6 6.0

[0073] Two-layer coated metal sample

[0074] Samples were prepared by coating cold-rolled steel substrates of iron phosphate (BONDERITE 1000) with two layers of coating. In Example 1, the first coating of Basecoat 1 was applied, and then the coating of the coating composition of the present invention was applied. Example 2 was prepared by coating the substrate with the first layer of Basecoat 2 and the second layer of the coating composition of the present invention. Comparative Example 1 was prepared by coating the substrate with the first layer of Basecoat 2 and the second layer of Basecoat 1. To prepare Example 3, two layers of the coating composition of the present invention were applied. In each of the 2-layer coating samples, the first layer was applied and flash-evaporated at room temperature for 30 minutes, and then cured at 80 °C for 20 minutes. Then, before applying the second layer, the sample was cooled for 1 to 2 hours until it reached room temperature. The second coating was flash-evaporated at room temperature for 30 minutes, and then cured at 80 °C for 20 minutes. After curing, the coated metal samples were kept at room temperature for 7 days before testing.

[0075] In accordance with ASTM-D4366, the hardness of each of the coated metal samples was tested using a Persoz pendulum. The results of the Persoz hardness tests are shown in Table 4 below, which also shows that each sample had relatively similar thickness and glossiness, as tested by a micro-TRI-gloss machine (BYK Company). Compared with the two-layer coating of Comparative Example 1 that lacked the layer containing the coating composition of the present invention, the hardness of Examples 1, 2, and 3 was significantly improved.

[0076] Table 4

[0077]

[0078] Single-layer coated metal sample

[0079] Single-layer coated metal samples were prepared on a phosphated (BONDERITE 1000) cold-rolled steel substrate. Comparative Example 2 was prepared by coating the basecoat 2 on the metal substrate. Comparative Example 3 was prepared by blending the basecoat 2 and the coating composition of the present invention at a ratio of 1:1, and the coating was formed as a single layer on the substrate. Example 4 was prepared by coating the metal substrate with a single layer of the coating composition of the present invention. Each sample was prepared by coating a single layer on the substrate, flash-evaporating at room temperature for 30 minutes, curing at 80 °C for 20 minutes, and then curing at room temperature for 7 days before testing.

[0080] The results of the hardness tests are shown in Table 5 below.

[0081] Table 5

[0082]

[0083] Although Comparative Example 3 showed slightly better hardness than Comparative Example 2, the hardness of Example 3 was significantly lower than that of the two-layer coated metal sample of Example 2. Example 4 had significantly higher hardness compared to Comparative Examples 2 and 3.

[0084] A direct comparison between Example 2 and Comparative Example 3 clearly shows that using different formulations in two separate layers (with at least partial curing between each layer) can significantly improve the hardness of the resulting coating.

Claims

1. A two-component coating composition, the two-component coating composition comprising a binder component and a curing component, wherein the binder component comprises an aqueous dispersion of acrylic polymer particles absorbed with an epoxide compound, and wherein the two-component aqueous coating composition comprises a coalescent package containing at least one coalescent and has a minimum film formation temperature (MFFT) of 0 °C to 25 °C.

2. The coating composition according to claim 1, wherein the curing component is selected from carboxylic acid-based acrylic curing agents.

3. The coating composition according to claim 1 or 2, wherein the curing component is present in an amount such that the molar ratio of epoxy groups to carboxylic acid groups in the coating composition is in the range of 1:1 to 2.5:

1.

4. The coating composition according to any one of the preceding claims, wherein the coalescent package is present in an amount of 2 wt% to 10 wt% based on the total weight of the solids in the binder component and the curing component of the two-component coating composition.

5. The coating composition according to claim 4, wherein the coalescent package is present in an amount of 3 wt% to 9.5 wt% based on the total weight of the solids in the binder component and the curing component of the coating composition.

6. The coating composition according to any one of the preceding claims, wherein the coating composition has an MFFT of 0 °C to 15 °C.

7. The coating composition according to any one of the preceding claims, wherein the coating composition has a VOC content in the range of 0.2 lb / gal to 1 lb / gal.

8. The coating composition according to any one of the preceding claims, wherein the coating composition has a PVC of 7.5% to 12.5%.

9. A method of preparing a coating, the method comprising: (i) providing a coating composition according to any one of the preceding claims; (ii) applying the coating composition to a substrate to form a coating; (iii) curing the coating at a temperature above room temperature for at least 10 minutes to form a coating on the substrate.

10. The method according to claim 9, wherein the substrate comprises a metal substrate.

11. The method according to claim 9 or 10, wherein the substrate comprises at least one primer layer formed thereon prior to step (ii) of applying the coating composition.

12. The method according to claim 11, wherein the primer layer is formed from a two-component primer coating composition comprising a primer binder component and a primer curing component, wherein the primer binder component and the primer curing component are independently the same as or different from the binder component and the curing component of the coating composition, wherein the primer binder component comprises an aqueous dispersion of acrylic polymer particles absorbed with an epoxide compound, and wherein the two-component primer coating composition comprises a primer coalescent package containing at least one coalescent and has an MFFT of less than 5 °C.

13. The method according to claim 12, wherein the primer binder component and the primer curing component are the same as the binder component and the curing component of the coating composition.

14. The method according to any one of claims 9 to 13, wherein the step (iii) of curing the second coating comprises curing the second coating at a temperature of at least 50 °C for at least 15 minutes.

15. An article comprising a coated substrate formed by the method according to any one of claims 9 to 14.

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