Acrylic-epoxy hybrid 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 includes a coalescent package containing at least one coalescent, and has a minimum film-forming temperature of 0° C. to 25° C. Methods for preparing the coating and coated articles are also disclosed.

Description

[Technical Field]

[0001] In the coatings industry, especially the industrial coatings industry, coatings that have both corrosion resistance and hardness are often desired. Multilayer coatings were developed to provide a first layer that provides adhesion and corrosion resistance to the substrate. Additional layers were then applied to provide weather resistance, chemical resistance, and / or the desired appearance. Epoxy resins were generally selected for the first layer, and polyurethane or acrylic resins were often used for the top layer. Because it was difficult to find a single resin chemistry that provided the necessary balance between corrosion resistance and weather resistance, different resin chemistries were used.

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

[0003] However, for some applications, the hardness and / or weatherability provided by existing AEH resin systems is not adequate.

[0004] Low cost, simple resin systems that can provide improved hardness are desired. It is further desirable to provide coatings with improved hardness that are 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 imbibed with an epoxy compound, and the coating composition comprises a coalescent package comprising at least one coalescent, and has a minimum film-forming temperature (MFFT) of 0°C to 25°C.

[0006] In a second aspect, the present invention relates to a method for preparing a coating 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 layer; (iii) curing the coating layer at a temperature above room temperature for at least 10 minutes to form a coating on the substrate.

[0007] A third aspect of the invention relates to an article comprising a coated substrate formed by the above method. DETAILED DESCRIPTION OF THE INVENTION

[0008] In a first aspect, the present invention relates to a coating composition comprising a two-component aqueous coating composition having improved hardness.

[0009] The two-component aqueous coating composition includes a binder component and a curing (i.e., crosslinking) component. The binder component includes an aqueous dispersion of acrylic polymer particles imbibed with an epoxy compound. As used herein, the term "acrylic" includes (meth)acrylic acid, (meth)alkyl acrylate, (meth)acrylamide, (meth)acrylonitrile, and modifications thereof, such as (meth)hydroxyalkyl acrylate. The fragment "(meth)acrylic" refers to both "methacrylic" and "acrylic," e.g., (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and methyl (meth)acrylate refers to both methyl methacrylate and methyl acrylate. As used herein, the term "imbibed with an epoxy compound" means that the epoxy compound is at least partially absorbed by the acrylic polymer particles, but does not react with the acrylic polymer particles and is not simply present on the surface of the acrylic polymer particles.

[0010] Preferably, the aqueous dispersion of acrylic polymer particles imbibed with an epoxy compound comprises a stable aqueous dispersion of acrylic polymer particles imbibed with a thermosetting compound having at least two oxirane groups. As used herein, the term "thermosetting compound" means a compound that undergoes a chemical reaction to form a thermosetting compound that has distinct chemical and physical properties and does not undergo a reversible thermal transition when exposed to heat.

[0011] The imbibed thermosetting compound preferably has multiple oxirane groups. More preferably, the thermosetting compound is a novolac resin, a di-, tri-, or tetraglycidyl ether, or a di-, tri-, or tetraglycidyl ester.

[0012] Examples of suitable thermosetting compounds include diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diglycidyl ester of phthalic acid, 1,4-cyclohexanedimethanol diglycidyl ether, 1,3-cyclohexanedimethanol diglycidyl ether, diglycidyl ester of hexahydrophthalic acid, and novolac resins, as well as combinations thereof. A commercially available thermosetting compound is DER 331 Liquid Epoxy Resin (available from Olin Corporation).

[0013] Aqueous dispersions of acrylic polymer particles (i.e., latexes) can be achieved by free radical emulsion or suspension addition polymerization, or by dispersing a preformed polymer in an aqueous medium under shear. Examples of suitable latexes include acrylic latexes and styrene acrylic latexes.

[0014] The acrylic polymer particles may further contain anti-agglomeration functional groups, which refer to hydrophilic groups that are sufficiently unreactive with oxirane groups (and ester groups, if present) so that the latex particles are heat aging stable for 10 days at 60° C. The term “heat aging stable for 10 days at 60° C” is used herein to mean that the particle size of a latex subjected to heat aging stability for 10 days at 60° C. does not increase by more than 30% above the particle size before such heat aging testing.

[0015] Anti-agglomeration functional groups can be incorporated into polymer particles using monomers containing anti-agglomeration functional groups (anti-agglomeration monomers), but such groups can also be incorporated by grafting. Anti-agglomeration groups are considered effective because they are hydrophilic and unreactive with oxirane groups under heat aging conditions. Common classes of such groups include amide groups, acetoacetoxy groups, and strong protonic acids, which are pH-adjusted to form their conjugate bases.

[0016] Specific examples of anti-agglomerating monomers include acrylamide, phosphoethyl methacrylate, sodium styrene sulfonate, acetoacetoxyethyl methacrylate, and acrylamido-methyl-propane sulfonate. If present, the concentration of anti-agglomerating functional groups in the polymer is preferably sufficient to stabilize the thermoplastic polymer under heat aging conditions, and is preferably from 0.5 wt. %, more preferably from 1 wt. %, preferably up to 10 wt. %, more preferably up to 5 wt. %, based on the weight of the polymer.

[0017] Suitable monomers for preparing acrylic latexes include acrylates and methacrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate, and combinations thereof. Additionally, acrylic latexes may contain structural units of other monomers such as styrene and acrylonitrile. As used herein, the term "structural unit" refers to the residue of a specified monomer after polymerization.

[0018] Structural units of one or more acid monomers may also be included, most notably acrylic acid, methacrylic acid, and itaconic acid. Monomers capable of imparting co-curable functionality, such as glycidyl acrylate and methacrylate, may also be included.

[0019] 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, and the like.

[0020] In certain embodiments, it may be advantageous to incorporate copolymerized multi-ethylenically unsaturated monomer groups into the polymer. Multi-ethylenically unsaturated monomers include, for example, allyl (meth)acrylate, diallyl phthalate, 1,4-butylene glycol di(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and divinylbenzene. It may also be advantageous to incorporate such monomer groups heterogeneously into the polymer to form multiphase polymer particles and create core-shell, hemispherical, or closed morphologies.

[0021] An aqueous dispersion of epoxy-imbibed acrylic polymer particles (i.e., an imbibed latex) is advantageously prepared separately from the thermosetting compound using conventional emulsion polymerization techniques and then mixed with the thermosetting compound, which may be neat or in the form of an aqueous emulsion, preferably as an aqueous emulsion, more preferably as a finely divided 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 ranging from about 0.5 to about 10% by weight. Nonionic surfactants are preferred, including APEO-free nonionic wetting agents such as polyalkylene oxide block copolymers, polyoxyethylene glycol alkyl ethers, glucoside alkyl ethers, fatty acid esters, glycerol alkyl esters, sorbitan alkyl esters, and polyoxyethylene glycol alkyl phenol ethers, as well as commercially available wetting agents such as TRITON™ X-405 octylphenol ethoxylate (a trademark of The Dow Chemical Company or its affiliates). If the thermosetting compound is mixed with the latex as a neat compound, absorption is facilitated by stirring at or above room temperature.

[0022] High solids absorption latex, ie, latex having a solids content of at least 40% by weight, especially in the range of 45 to 60% by weight, based on the total weight of the latex, can be used in the present invention.

[0023] The imbibed latex composition is useful as one component (i.e., the binder component) of a two-component formulation, the second component being a curing (i.e., cross-linking) component added prior to use to cure or solidify the thermosetting compound. Thus, the binder component of the present invention is substantially free of curing agents; i.e., it has an insufficient concentration of compounds that promote oxirane ring opening to destabilize the thermosetting compound. Preferably, the imbibed 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, based on the total weight of the imbibed latex composition.

[0024] Preferably, the imbibed latex in the binder component is cured with a water-compatible external curing agent containing a curing component. Preferably, the imbibed latex is cured with a carboxylic acid-based acrylic. Examples of carboxylic acid-based acrylics include, but are not limited to, acrylic polymer emulsions containing 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 and 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, t-butylaminoethyl methacrylate, stearyl methacrylate, glycidyl methacrylate, dicyclopentenyl methacrylate, phenyl methacrylate, and optionally styrene. For example, the acrylic polymer emulsion may include a styrene-acrylic polymer emulsion.

[0025] Preferably, the acrylic polymer emulsion contains 35 to 70 wt. % acrylic solids, more preferably 40 to 65 wt. % acrylic solids, based on the total weight of the acrylic polymer emulsion. Preferably, the acrylic particles have an average weight particle size in the range of 60 to 450 nm, an acid level of the acid monomer in the range of 0.1 to 15 wt. % based on the weight of the acrylic monomer, a weight average molecular weight in the range of 50,000 to 5,000,000 g / mol, and a glass transition temperature (Tg) in the range of 7 to 100°C, as measured by differential scanning calorimetry (DSC). The acrylic polymer dispersion preferably has a pH in the range of 6 to 10.

[0026] The amount of curing agent used generally varies with an epoxy to carboxylic acid stoichiometry of about 1:1 to 2.5:1, based on the moles of epoxide groups to the moles of 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 moles of epoxide groups and the moles of carboxylic acid 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 moles of epoxide groups and the moles of carboxylic acid in the coating composition.

[0027] 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 fuses polymer particles into a continuous film under ambient conditions.

[0028] 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™ 400 and TEXANOL™ Coalescent, both available from The Eastman Chemical Company.

[0029] Preferably, the at least one coalescent in the coalescent package is present in an amount ranging from 2 to 10 weight percent, preferably 3 to 9.5 weight percent, more preferably 4 to 9 weight percent, based on the total weight of solids in the binder and curing components of the coating composition, where the total solids amount does not include additional components (e.g., pigments present in the coating composition).

[0030] The coating composition has a minimum film formation temperature (MFFT) of 0°C to 25°C, preferably 5°C to 15°C. MFFT is the lowest temperature at which polymer particles in an aqueous dispersion coalesce with each other and form a continuous film as the volatile components (e.g., water) evaporate. MFFT can be measured according to GB / T 9267-2008.

[0031] The coating compositions 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, clay, etc.; polymer-encapsulated pigments, such as polymer-encapsulated or partially encapsulated titanium dioxide, zinc oxide, or lithopone; polymers or polymer emulsions that adsorb or bond to the surface of pigments such as titanium dioxide; hollow pigments, including pigments with one or more voids; dispersants, such as amino alcohols and polycarboxylates; surfactants; defoamers; preservatives such as biocides, fungicides, bactericides, algicides, and combinations thereof; flow agents; leveling agents; and additional neutralizing agents, such as hydroxides, amines, ammonia, carbonates.

[0032] The volatile organic compound (VOC) content of the coating composition can range from 0.2 to 1 lb / gal, preferably from 0.25 to 0.85 lb / gal, and more preferably from 0.25 to 0.75 lb / gal.

[0033] The pigment volume concentration (PVC) of the coating composition can be calculated by the following formula:

[0034]

number

[0035] For example, the PVC of the coating composition may range from 7.5 to 12.5%.

[0036] A second aspect of the present invention relates to a method for preparing a coating, the method comprising the coating composition as described above.

[0037] The coating composition is applied to a substrate to form a coating layer. The coating layer is then cured at a temperature higher than 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 layer can be flashed at room temperature before curing to evaporate volatile components.

[0038] Preferably, the substrate is a metal substrate, which can be either a bare metal (e.g., the coating is a direct-to-metal coating) or a primed metal substrate (e.g., a metal substrate primed with a zinc-rich primer).

[0039] In a preferred embodiment, a coating layer is formed on a substrate including a cured basecoat layer such that the coating layer forms a topcoat on the basecoat. Preferably, the basecoat layer is formed from a two-component aqueous basecoat coating composition including a basecoat binder component and a basecoat curing component. The basecoat binder component may be the same as or different from the binder component of the topcoat coating composition. Similarly, the basecoat curing component may be the same as or different from the curing component of the topcoat coating composition. Preferably, the basecoat binder component is the same as the binder component of the topcoat coating composition, and the basecoat curing component is the same as the curing component of the topcoat coating composition, i.e., the basecoat coating composition and the topcoat coating composition are based on a single chemical resin system.

[0040] The basecoat coating composition further comprises a basecoat coalescent package comprising at least one coalescent, which may be the same as or different from the at least one coalescent of the topcoat coating composition. The at least one coalescent in the basecoat coalescent package may be present in an amount of 10 to 30 wt. %, preferably 15 to 25 wt. %, based on the total weight of solids in the basecoat binder component and the basecoat curing component of the basecoat coating composition, where the total solids amount does not include any additional components (e.g., pigments present in the basecoat coating composition).

[0041] The basecoat coating composition preferably has a MFFT of less than 5°C, preferably between -10°C and 5°C.

[0042] The basecoat curing component may be present in the basecoat coating composition in an amount of from 1.75:1 to 2.5:1 epoxy to carboxylic acid stoichiometry, preferably from 2.0:1 to 2.5:1, based on the number of moles of epoxide groups to the number of moles of carboxylic acid in the basecoat coating composition.

[0043] The basecoat coating composition may have a VOC content ranging from 0.75 to 1.25 lb / gal and a PVC ranging from 15 to 20%.

[0044] A third aspect of the present invention relates to an article having a coating layer formed from the coating composition.

[0045] The coating layer preferably has a Persoz hardness of at least 50 seconds, more preferably at least 60 seconds, and even more preferably at least 70 seconds, when measured according to the method described below.

[0046] EXAMPLES: The following examples are included for illustrative purposes only and are not intended to limit the scope of the invention. The following materials are used in the examples. AEH-1 is an AEH dispersion having a solids content of 53.9%, an epoxy equivalent weight of 312 g / eq based on solids weight, and a pH of 7. AEH-2 is an AEH dispersion having a solids content of 52.2%, an epoxy equivalent weight of 468 g / eq based on solids weight, and a pH of 7. SAP is a carboxylic acid functional styrene acrylic polymer dispersion with 49.5% solids and an acid equivalent weight of 2457 g / eq on polymer solids, used as a curing agent. DOWANOL™ DPnB is dipropylene glycol mono n-butyl ether available from The Dow Chemical Company and is used as a coalescent. OPTIFILM 400 is a coalescing agent available from Eastman Chemical Company. OROTAN™ 681 is a polymethacrylic acid with a hydrophobic comonomer available from The Dow Chemical Company and is used as a dispersing agent. ACRYSOL™ RM-12W is a nonionic urethane rheology modifier available from The Dow Chemical Company. TEGO Airex 902W is a polyether siloxane copolymer emulsion available from Evonik Corporation and is used as a defoamer. Ti-PURE R-706 is a titanium dioxide pigment available from The Chemours Company. TAMOL™ 681 is a hydrophobic copolymer dispersant available from The Dow Chemical Company. TRITON™ HW-1000 is a nonionic surfactant available from The Dow Chemical Company. ANCAMINE K-54 is a tris-(dimethylaminomethyl)phenol curing agent available from Evonik Corporation. XIAMETER™ OFS-6020 is an aminoethylaminopropyltrimethoxysilane coupling agent available from The Dow Chemical Company.

[0047] Preparation of the Coating Composition Base 1, Base 2, and pigment grinds for the coating compositions of the present invention were prepared according to Table 1 below. The following ingredients were added to a 1-liter stainless steel container and mixed at low shear (1000 rpm) in a disperser with a 2-inch cowl blade until uniform (approximately 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 approximately 5 minutes, 1123.15 g TiPure R706 was slowly added under shear. The mixing speed was gradually increased to achieve a good vortex. After all the TiO2 was added, the disperser was stopped so that the blade, shaft, and sides of the container could be scraped with a metal spatula. The disperser was then started and the speed increased to approximately 2000 rpm. Mixing was complete after approximately 15 minutes when the Hegman gauge indicated 7-8 units. The pigment grind was then ready to be added to the formulation in Table 2, as listed below.

[0048] [Table 1]

[0049] Two basecoat coating compositions, Base 1 and Base 2, and coatings according to the present invention, were prepared using two different acrylic-epoxy hybrids, AEH-1 and AEH-2, respectively. The Part B side mixture was prepared in a plastic container of appropriate size (8 oz. to 32 oz.) for the contents using a metal paddle blade (1-inch diameter) on a laboratory mixer set at an appropriate speed (500-1000 rpm) to maintain a good vortex. The first component was added with a laboratory balance, and additional components were added while mixing to ensure good incorporation. After the last component was added, the mixture was mixed for an additional 15 minutes at approximately 1100 rpm. The Part B side was allowed to equilibrate overnight before being mixed with a tongue depressor to create the coating.

[0050] [Table 2]

[0051] The properties of Base 1, Base 2, and the coating composition of the present invention are shown in Table 3.

[0052] [Table 3]

[0053] Double coated metal sample Samples were prepared by coating iron phosphate (BONDERITE 1000) cold-rolled steel substrates with two-layer coatings. In Example 1, a first coating of Base 1 was applied, followed by a coating of the coating composition of the present invention. Example 2 was prepared by coating the substrate with a first layer of Base 2 and a second layer of the coating composition of the present invention. Comparative Example 1 was prepared by coating the substrate with a first layer of Base 2 and a second layer of Base 1. To prepare Example 3, two layers of the coating composition of the present invention were applied. For each of the two-layer coated samples, the first layer was applied, flashed off at room temperature for 30 minutes, and then cured at 80°C for 20 minutes. The samples were then allowed to cool to room temperature for 1-2 hours before applying the second layer. The second coating was flashed off 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.

[0054] A Persoz pendulum was used to test the hardness of each of the coated metal samples in accordance with ASTM-D4366. The results of the Persoz hardness tests are shown in Table 4 below and further demonstrate that each sample had relatively similar thickness and gloss when tested with a micro-TRI-gloss machine (BYK Company). The hardness of Examples 1, 2, and 3 was significantly improved compared to the two-layer coating of Comparative Example 1, which lacked the layer containing the coating composition of the present invention.

[0055] [Table 4]

[0056] Single-layer coated metal sample Single-layer coated metal samples were prepared on iron phosphate (BONDERITE 1000) coated cold-rolled steel substrates. Comparative Example 2 was prepared by coating Base 2 onto a metal substrate. Comparative Example 3 was prepared by mixing Base 2 and the inventive coating composition 1:1 to form a single layer on the substrate. Example 4 was prepared by coating a metal substrate with a single layer of the inventive coating composition. Each sample was prepared by coating a single layer onto the substrate, flashing off at room temperature for 30 minutes, curing at 80°C for 20 minutes, and then curing at room temperature for 7 days before testing.

[0057] The results of the hardness test are shown in Figure 5.

[0058] [Table 5]

[0059] Although Comparative Example 3 exhibited slightly better hardness than Comparative Example 2, the hardness of Comparative Example 3 was significantly lower than the two-layer coated metal sample of Example 2. Example 4 had significantly higher hardness compared to Comparative Examples 2 and 3.

[0060] A direct comparison of Example 2 and Comparative Example 3 clearly demonstrates that by using different formulations for two separate layers, with at least partial curing between each layer, the hardness of the resulting coating can be significantly improved.

Claims

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

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

3. 3. The coating composition of claim 1, 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. 4. The coating composition of claim 1, wherein the coalescent package is present in an amount comprising 2 to 10 wt. %, based on the total weight of solids in the binder component and the curing component of the two-component coating composition.

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

6. The coating composition of any one of claims 1 to 5, wherein the coating composition has a MFFT of 0°C to 15°C.

7. The coating composition of any one of claims 1 to 6, wherein the VOC content of the coating composition ranges from 0.2 to 1 lb / gal.

8. The coating composition of any one of claims 1 to 7, wherein the coating composition has a PVC of 7.5 to 12.5%.

9. 1. A method for preparing a coating, comprising: (i) providing a coating composition according to any one of claims 1 to 8; (ii) applying the coating composition to a substrate to form a coating layer; (iii) curing the coating layer at a temperature above room temperature for at least 10 minutes to form a coating on the substrate.

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

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

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

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

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

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

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