SOLVENT-BASED COATING COMPOSITIONS, COATINGS FORMED THEREOF, AND METHODS FOR FORMING SUCH COATINGS

Abstract

A coating composition includes: (a) a polyol polymer with carboxylic acid functionality; (b) a melamine-formaldehyde crosslinker reactive with the polyol polymer with carboxylic acid functionality; (c) an acid catalyst; and (d) a non-aqueous liquid medium; the polyol polymer with carboxylic acid functionality has an acid number within the range of 30 to 120 mg KOH / g and a hydroxyl number within the range of 60 to 150 mg KOH / g; the melamine-formaldehyde crosslinker includes imino and methylol groups that together constitute 35 mol% or less of the total functionality of the melamine-formaldehyde crosslinker, and butyl and isobutyl groups that together constitute 5 mol% or more of the total functionality of the melamine-formaldehyde crosslinker; the coating composition cures at a temperature of 100°C or less.

Description

SOLVENT-BASED COATING COMPOSITIONS, COATINGS FORMED THEREOF, AND METHODS FOR FORMING SUCH COATINGS FIELD OF INVENTION The present invention relates to solvent-based coating compositions, coatings formed from them, and methods for forming such coatings. BACKGROUND OF THE INVENTION Coatings are applied to a wide variety of substrates to provide color and other visual effects, corrosion resistance, abrasion resistance, chemical resistance, and the like. Furthermore, various types of coatings, such as those applied to automotive substrates, including cars and motorcycles, can be formed from compositions that can be baked and formed at low curing temperatures. However, it is difficult to effectively cure solvent-based compositions at low temperatures. Accordingly, an objective of the present invention is to provide a solvent-based coating composition that can be cured at comparatively low temperatures. BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a coating composition comprising: (a) a polyol polymer with carboxylic acid functionality; (b) a melamine-formaldehyde crosslinker reactive with the polyol polymer with carboxylic acid functionality; (c) an acid catalyst; and (d) a non-aqueous liquid medium. The polyol polymer with carboxylic acid functionality has an acid number in the range of 30 to 120 mg KOH / g and a hydroxyl number in the range of 60 to 150 mg KOH / g. The melamine-formaldehyde crosslinker comprises imino and methylol groups that together comprise 35 mol% or less of the total functionality of the melamine-formaldehyde crosslinker, and butyl and isobutyl groups that together comprise 5 mol% or more of the total functionality of the melamine-formaldehyde crosslinker. The coating composition cures at a temperature of 100°C or less. The present invention also relates to substrates coated at least partially with the coating compositions described herein. The present invention further relates to a method for forming a coating on at least a portion of a substrate comprising applying a coating composition as described herein and curing the coating composition at a temperature of I 7ΟΠ / Ι 7Π7 / 3 / ΥΙΛΙ 100°C or less to form a coating on at least part of the substrate. DETAILED DESCRIPTION OF THE INVENTION For the purposes of the following detailed description, it should be understood that the invention can assume several alternative variations and sequences of steps, except where expressly stated otherwise. Furthermore, apart from any operational example, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims should be understood as modified in all cases by the term "approximately." Accordingly, unless otherwise stated, the numerical parameters stated in the following specification and appended claims are approximations that may vary depending on the desired properties obtained by the present invention.At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter must at least be interpreted in light of the number of significant digits reported and with the application of ordinary rounding techniques. Although the numerical ranges and parameters that define the broad scope of the invention are approximations, the numerical values ​​stated in the specific examples are reported as accurately as possible. However, any numerical value inherently contains certain errors that necessarily result from the standard variation found in their respective test measurements. Furthermore, it should be understood that any numerical interval mentioned here is intended to include all subintervals within it. For example, an interval from 1 to 10 is intended to include all subintervals between (and including) the minimum value of 1 and the maximum value of 10; that is, those with a minimum value greater than or equal to 1 and a maximum value less than or equal to 10. In this application, the singular includes the plural, and the plural includes the singular, unless specifically stated otherwise. Furthermore, in this application, the use of "or" means "and / or" unless specifically stated otherwise, although "and / or" may be explicitly used in certain cases. Additionally, in this application, the use of "a" means "at least one" unless specifically stated otherwise. For example, "a polymer," "a crosslinking agent," and the like refer to one or more of any of these elements. As described above, the present invention is directed to a coating composition comprising a polyol polymer with carboxylic acid functionality, a melamine-formaldehyde crosslinker reactive with the polyol polymer with carboxylic acid functionality, an acid catalyst, and a non-aqueous liquid medium. I zon / l 7P7 / 3 / YILI As used in this document, a polyol polymer refers to a polymer having two or more, such as three or more, hydroxyl groups. Furthermore, the term polymer refers to oligomers and homopolymers (e.g., prepared from a single monomer species), copolymers (e.g., prepared from at least two monomer species), terpolymers (e.g., prepared from at least three monomer species), and graft polymers. The term resin is used interchangeably with polymer. Therefore, a polyol polymer with carboxylic acid functionality refers to a polymer comprising both hydroxyl groups and carboxylic acid groups. It is observed that the polyol polymer with carboxylic acid functionality acts as a film-forming resin. As used herein, a film-forming resin refers to a continuous, self-supporting film on at least one horizontal surface of a substrate after the removal of any diluent or vehicle present in the composition or after curing. The terms curable, cured, and the like, as used in connection with a coating composition, mean that at least some of the components comprising the coating composition are polymerizable and / or crosslinkable.The curing, or degree of curing, can also be determined by dynamic mechanical thermal analysis (DMTA) using a Polymer Laboratories MK III DMTA analyzer performed under nitrogen where the degree of curing can be, for example, at least 10%, such as at least 30%, such as at least 50%, such as at least 70%, or at least 90% complete crosslinking as determined by DMTA. The coating composition of the present invention can be cured under ambient conditions, with heat, or by other means such as actinic radiation. The term actinic radiation refers to electromagnetic radiation that can initiate chemical reactions. Actinic radiation includes, but is not limited to, visible light, ultraviolet (UV) light, X-rays, and gamma radiation. Furthermore, ambient conditions refers to the conditions of the surrounding environment (e.g., the temperature, humidity, and pressure of the room or the external environment where the substrate is located, such as, for example, at a temperature of 23°C and a relative humidity of 35% to 75%). The polyol polymer with carboxylic acid functionality of the present invention can be obtained from reagents comprising (i) an ethylenically unsaturated compound comprising groups with hydroxyl functionality, (ii) an ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or an anhydride thereof, and (iii) an ethylenically unsaturated compound other than (i) and (iii). As used herein, ethylenically unsaturated refers to a group having at least one carbon-carbon double bond. Non-limiting examples of ethylenically unsaturated groups include, but are not limited to, [specific examples of ethylenically unsaturated groups]. I zon / l 7P7 / 3 / YILI are limited to (meth)acrylate groups, vinyl groups, other alkenes, and combinations thereof. As used herein, the term (meth)acrylate refers to both methacrylate and acrylate. An ethylenically unsaturated compound may comprise ethylenically unsaturated monomers and / or polymers. Ethylenically unsaturated compounds may also comprise monoethylenically unsaturated compounds, multiethylenically unsaturated compounds, or combinations thereof. A monoethylenically unsaturated compound refers to a compound comprising only one ethylenically unsaturated group, and a multiethylenically unsaturated compound refers to a compound comprising two or more ethylenically unsaturated groups. Ethylenically unsaturated compounds can be linear, branched, or cyclic. The term linear refers to a compound with a straight chain; the term branched refers to a compound with a chain in which one hydrogen atom is replaced by a substituent, such as an alkyl group, branching or extending from a linear chain; and the term cyclic refers to a closed ring structure. Furthermore, cyclic structures can include aromatic and / or aliphatic rings. As used herein, the term aromatic refers to a conjugated cyclic hydrocarbon structure with a stability (due to delocalization) that is significantly greater than that of a hypothetical localized structure. An aliphatic ring refers to a non-aromatic structure containing saturated carbon bonds. As indicated, the reagents that form the polyol polymer with carboxylic acid functionality may include an ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or the anhydride thereof. The compound may comprise one or multiple carboxylic acid groups or the anhydride thereof. Non-limiting examples of ethylenically unsaturated compounds comprising groups with carboxylic acid functionality, or the anhydride thereof, include (meth)acrylic acid, allylacetic acid, crotonic acid, vinylacetic acid, itaconic acid, maleic acid, fumaric acid, itaconic anhydride, maleic anhydride, isobutenylsuccinic anhydride, citraconic anhydride, tetrahydrophthalic anhydride, octenylsuccinic anhydride, and any combination thereof. When the compound comprises multiple carboxylic acid groups, or an anhydride, partial esters of the compound can be used. The ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or the anhydride thereof, may comprise at least 5% by weight, or at least 8% by weight, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality. The ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or the anhydride or ester thereof, may also comprise up to 20% by weight, up to 15% by weight, or up to 10% by weight, based on I zon / l 7P7 / 3 / YILI in the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality. The ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or the anhydride or ester thereof, may comprise an amount within a range such as 5% to 20% by weight, or 5% to 15% by weight, or 5% to 10% by weight, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality. The reagents that form the polyol polymer with carboxylic acid functionality may also include an ethylenically unsaturated compound comprising groups with hydroxyl functionality. The compound may comprise one or more hydroxyl groups. Non-limiting examples of ethylenically unsaturated compounds comprising groups with hydroxyl functionality include hydroxyalkyl esters of (meth)acrylic acid such as hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and combinations thereof. The ethylenically unsaturated compound comprising hydroxyl groups may comprise at least 8 wt%, at least 10 wt%, at least 12 wt%, or at least 15 wt%, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality. The ethylenically unsaturated compound comprising hydroxyl groups may also comprise up to 40 wt%, or up to 35 wt%, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality.The ethylenically unsaturated compound comprising groups with hydroxyl functionality may comprise an amount within a range such as 8 wt to 40 wt, or 10 wt to 40 wt, or 12 wt to 35 wt, or 15 wt to 35 wt, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality. As previously described, the reagents forming the polyol polymer with carboxylic acid functionality may further include an ethylenically unsaturated compound other than (i) and (i). That is, the ethylenically unsaturated compound other than (i) and (i) is selected from ethylenically unsaturated compounds that do not include carboxylic acid or groups with hydroxyl functionality. The ethylenically unsaturated compound other than (i) and (i) may include other functional groups, such as groups with epoxy functionality, for example. Alternatively, the ethylenically unsaturated compound other than (i) and (i) may comprise a non-functional ethylenically unsaturated compound. As used herein, a non-functional ethylenically unsaturated compound refers to a compound that contains only ethylenically unsaturated groups and is free of all other functional groups. I ZQn / l 7Π7 / 3 / ΥΙΛΙ reagents. The ethylenically unsaturated compound that is different from (i) and (ii) may comprise a multi-ethylenically unsaturated compound such as a non-functional multi-ethylenically unsaturated compound, a mono-ethylenically unsaturated compound having an extractable hydrogen, or a combination of these. As used in this document, an extractable hydrogen refers to a hydrogen atom in a compound that is removed from the compound by a radical. Non-limiting examples of extractable hydrogen atoms are hydrogen atoms bonded to tertiary carbon atoms, such as the hydrogen atoms bonded to the tertiary carbons in 2-ethylhexyl acrylate and isobornyl acrylate. Reagents forming the polyol polymer with carboxylic acid functionality may comprise one or more ionicly unsaturated ethyl compounds that have extractable hydrogens. For example, reagents forming the polyol polymer with carboxylic acid functionality may comprise a linear or branched monoethylenically unsaturated compound that has an extractable hydrogen and a cyclic monoethylenically unsaturated compound that has an extractable hydrogen. Non-limiting examples of suitable ionicly unsaturated compounds other than (i) and (ii) include styrene, σ-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, vinylnaphthalene, vinyltoluene, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-octadecene, 3-methyl-1-butene, 4-methyl-1-pentene, cyclopentene, 1,4-hexadiene, 1,5-hexadiene, and divinylbenzene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, acrylate of isobornyl, isobornyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, lauryl methacrylate, lauryl acrylate, octyl acrylate, octyl methacrylate, glycidyl methacrylate, vinyl methacrylate, acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetopropryl acrylate, di-nbutyl maleate,Dioctyl maleate, acrylonitrile, C3-C30 vinyl esters, C3-C30 vinyl ethers, and combinations thereof. The ethylenically unsaturated compound(s) other than (i) and (ii) may comprise at least 50% by weight, at least 55% by weight, or at least 60% by weight, based on the total weight of solids of the reactants used to form the polyol polymer with carboxylic acid functionality. The ethylenically unsaturated compound(s) other than (i) and (ii) may comprise up to 80% by weight, up to 75% by weight, or up to 70% by weight, based on the total weight of solids of the reactants used to form the polyol polymer with carboxylic acid functionality. The ethylenically unsaturated compound(s) other than (i) and (ii) may comprise an amount within a range such as 50 CJ I zon / l 7P7 / 3 / YILI at 80% by weight, or from 55 to 75% by weight, or from 60 to 70% by weight, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality. When ionicly unsaturated compounds other than (i) and (ii) comprise a multi-ethylenically unsaturated compound, such as a non-functional multi-ethylenically unsaturated compound, and a mono-ethylenically unsaturated compound having an extractable hydrogen, the mono-ethylenically unsaturated compound having an extractable hydrogen may be used in a greater amount, by weight, than the multi-ethylenically unsaturated compound. For example, the mono-ethylenically unsaturated compound(s) having an extractable hydrogen may comprise at least two times, at least three times, at least four times, at least five times, or at least six times the amount of multi-ethylenically unsaturated compound used to form the polyol polymer with carboxylic acid functionality. The polyol polymer with carboxylic acid functionality can also be formed with other types of reagents, such as other ethylenically unsaturated compounds, for example. Alternatively, the polyol polymer with carboxylic acid functionality can be formed with only the types of reagents described above. The polyol polymer with carboxylic acid functionality can be prepared by mixing and reacting all the desired reactants simultaneously. Alternatively, the reactants can be reacted in a stepwise manner by mixing and reacting only a portion of the reactants first to form a preliminary reaction product, and then mixing and reacting the remaining reactants with the preliminary reaction product. Various types of reaction aids, including but not limited to catalysts, can also be added to the reaction mixture. The reagents and other optional components can also be combined and reacted in a liquid medium, such as a non-aqueous liquid medium. As used herein, the term "non-aqueous" refers to a liquid medium comprising less than 50% by weight of water, based on the total weight of the liquid medium. According to the present invention, such non-aqueous liquid media may comprise less than 40% by weight of water, or less than 30% by weight of water, or less than 20% by weight of water, or less than 10% by weight of water, or less than 5% by weight of water, based on the total weight of the liquid medium. Solvents constituting more than 50% by weight of the liquid medium include organic solvents. Non-limiting examples of suitable organic solvents include polar organic solvents, for example, protic organic solvents (such as glycols, glycol ether alcohols, and alcohols); ketones, glycol diethers, esters, and diesters.Other non-limiting examples of organic solvents include aromatic and aliphatic hydrocarbons. r;1 ζοη / ι znz / 3 / γΐΛΐ It is noted that the carboxylic acid functional polyol polymer of the present invention may include an addition polymer comprising carboxylic acid and hydroxyl functional groups. As used herein, an addition polymer refers to a polymer derived at least partially from ethionically unsaturated monomers. For example, the carboxylic acid functional polyol polymer may comprise a (meth)acrylic polyol polymer with carboxylic acid functionality, wherein at least some of the polymer-forming reactants are (meth)acrylic compounds as previously described. The polymer may also comprise other functional groups such as keto functional groups (also called ketone functional groups), aldo functional groups (also called aldehyde functional groups), amine groups, epoxide groups, thiol groups, carbamate groups, amide groups, urea groups, and combinations thereof. Alternatively, the polymer of the present invention may be free of additional functional groups other than hydroxyl and carboxylic acid functional groups. The carboxylic acid functional polyol polymer may have a hydroxyl number within a range of 60 to 150 mg KOH / g, or 60 to 130 mg KOH / g, or 60 to 110 mg KOH / g, or 60 to 100 mg KOH / g, or 60 to 90 mg KOH / g, or 60 to 80 mg of KOH / g. The polyol polymer with carboxylic acid functionality may have an acid value of at least 30 mg KOH / g, at least 40 mg KOH / g, at least 50 mg KOH / g, at least 55 mg KOH / g, or at least 60 mg KOH / g. The polyol polymer with carboxylic acid functionality may have an acid value of up to 120 mg KOH / g, up to 110 mg KOH / g, up to 100 mg KOH / g, up to 95 mg KOH / g, or up to 90 mg KOH / g. The carboxylic acid functional polyol polymer may have an acid number within a range of 30 to 120 mg KOH / g, or 40 to 110 mg KOH / g, or 50 to 100 mg KOH / g, or 50 to 95 mg KOH / g, or 55 to 95 mg KOH / g. Acid and hydroxyl values ​​are determined using a Metrohm 798 MPT Titrino automatic titrator in accordance with ASTM D 4662-15 and ASTM E 1899-16 standards. The polyol polymer with carboxylic acid functionality can have a glass transition temperature (Tg) within a range of -20 to 50°C, or -10 to 40°C. The Tg is determined according to ASTM D6604-00 (2013) using differential heat flux scanning calorimetry (DSC) with the following parameters: sample trays: aluminum, reference: blank, calibration: indium and mercury, sample weight: 10 mg, heating rate: 20°C / min. The polyol polymer with carboxylic acid functionality may comprise a I 700 / 1 707 / 3 / YILI average molecular weight of at least 5,000 g / mol, at least 10,000 g / mol or at least 20,000 g / mol. The polyol polymer with carboxylic acid functionality may comprise an average molecular weight of up to 100,000 g / mol, up to 75,000 g / mol, up to 50,000 g / mol or up to 30,000 g / mol. The polyol polymer with carboxylic acid functionality may comprise a weight average molecular weight within a range of 5,000 g / mol to 100,000 g / mol, or 5,000 g / mol to 50,000 g / mol, or 10,000 g / mol to 50,000 g / mol, or 10,000 g / mol to 30,000 g / mol. The polyol polymer with carboxylic acid functionality may comprise a number-average molecular weight of at least 1,300 g / mol, or at least 1,500 g / mol. The polyol polymer with carboxylic acid functionality may comprise a number-average molecular weight of up to 4,000 g / mol, up to 3,500 g / mol, or up to 3,000 g / mol. The polyol polymer with carboxylic acid functionality may comprise a number-average molecular weight within a range of 1,300 g / mol to 4,000 g / mol, or from 1,300 g / mol to 3,500 g / mol, or from 1,500 g / mol to 3,000 g / mol. The weight average molecular weight and number average molecular weight are determined by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) is used as the eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns are used for the separation. The polyol polymer with carboxylic acid functionality may comprise at least 10% by weight, at least 30% by weight, or at least 35% by weight of the coating composition, based on the weight of resin solids in the coating composition. The polyol polymer with carboxylic acid functionality may comprise up to 85% by weight, up to 70% by weight, or up to 60% by weight of the coating composition, based on the weight of resin solids in the coating composition. The polyol polymer with carboxylic acid functionality may comprise from 10 to 85% by weight, from 30 to 70% by weight, or from 35 to 60% by weight of the coating composition, based on the weight of resin solids in the coating composition. As previously described, the coating composition comprises a melamine-formaldehyde crosslinker reactive with the polyol polymer having carboxylic acid functionality. As used herein, the term crosslinker refers to a molecule comprising two or more functional groups that are reactive with other functional groups and that is capable of linking two or more monomers or polymer molecules through chemical bonds, such as during a curing process. Therefore, the coating composition comprises a melamine-formaldehyde crosslinker that is reactive with at least some of the functional groups of the polyol polymer having carboxylic acid functionality. I zon / l 7P7 / 3 / YILI The melamine-formaldehyde crosslinker used in the present invention comprises 35 mol% or less of imino groups and methylol groups taken together, 30 mol% or less of imino groups and methylol groups taken together, 25 mol% or less of imino groups and methylol groups taken together, or 23 mol% or less of imino groups and methylol groups taken together, or 20 mol% or less of imino groups and methylol groups taken together, based on the total functionality of the melamine-formaldehyde crosslinker.The melamine-formaldehyde crosslinker used in the present invention may also comprise 5 mol% or more of imino groups and methylol groups taken together, or 8 mol% or more of imino groups and methylol groups taken together, or 10 mol% or more of imino groups and methylol groups taken together, or 12 mol% or more of imino groups and methylol groups taken together, based on the total functionality of the melamine-formaldehyde crosslinker, or 14 mol% or more of imino groups and methylol groups taken together, based on the total functionality of the melamine-formaldehyde crosslinker.The melamine-formaldehyde crosslinker used in the present invention may also comprise an amount within a range such as, for example, 5 mol% to 35 mol% of imino groups and methylol groups taken together, or 10 mol% to 35 mol% of imino groups and methylol groups taken together, or 12 mol% to 35 mol% of imino groups and methylol groups taken together, or 12 mol% to 30 mol% of imino groups and methylol groups taken together, or 12 mol% to 25 mol% of imino groups and methylol groups taken together, based on the overall functionality of the melamine-formaldehyde crosslinker. Furthermore, the melamine-formaldehyde crosslinker used in the present invention comprises 5 mol% or more of butyl and isobutyl groups taken together, or 10 mol% or more of butyl and isobutyl groups taken together, or 15 mol% or more of butyl and isobutyl groups taken together, or 18 mol% or more of butyl and isobutyl groups taken together, or 20 mol% or more of butyl and / or isobutyl groups, based on the total functionality of the melamine-formaldehyde crosslinker.The melamine-formaldehyde crosslinker used in the present invention may also comprise 70 mol% or less of butyl and isobutyl groups taken together, or 65 mol% or less of butyl and isobutyl groups taken together, or 60 mol% or less of butyl and isobutyl groups taken together, or 55 mol% or less of butyl and isobutyl groups taken together, or 50 mol% or less of butyl and isobutyl groups taken together, or 45 mol% or less of butyl and isobutyl groups taken together, or 40 mol% or less of butyl and isobutyl groups taken together, or 35 mol% or less of butyl and isobutyl groups taken together, or 30 mol% or less of butyl and isobutyl groups taken together, or 25 mol% or less of butyl groups and isobutyl groups taken together, based on the overall functionality of the melamine-formaldehyde crosslinker. The melamine-formaldehyde crosslinker used in the present invention. I 7OP / I 7P7 / 3 / YILI may also comprise an amount within a range such as, for example, from 5 mol% to 70 mol% of butyl groups and isobutyl groups taken together, or from 10 mol% to 65 mol% of butyl groups and isobutyl groups taken together, or from 15 mol% to 65 mol% of butyl groups and isobutyl groups taken together, or from 15 mol% to 35 mol% of butyl groups and isobutyl groups taken together, or from 15 mol% to 25 mol% of butyl groups and isobutyl groups taken together, based on the total functionality of the melamine-formaldehyde crosslinker. The mole percent of functional groups in the melamine resin was determined by quantitative 13C-NMR spectroscopy. Quantitative 13C-NMR data were acquired on a Bruker Avance II spectrometer operating at a carbon frequency of 75.48 MHz. Dimethyl sulfoxide-de (DMSO-de) was used as the NMR solvent. Cr(acac)3 was used as the relaxation agent for the quantitative 13C-NMR spectroscopy, which was recorded with a relaxation time of 3 s, a pulse angle of 90 degrees, and an acquisition time of 0.66 s. A possible structure of a melamine resin is shown below. Each triazine ring is substituted by six functional groups. In the structure shown below, the triazine is substituted with an imino group (-NH), a methylol group (-CH2OH), two methoxy groups (-CH2OMe), an n-butoxy group (CH2OBU), and an isobutoxy group (-CH2OISOBU).A fraction of the six functional groups on each triazine ring may be bridges with other triazine rings (often called crosslinks). These bridges must still be considered functional groups when calculating the percentage of functional groups in melamine that are imino or methylol. Specifically, as will be seen below, since the level of imino groups cannot be determined directly by 13C-NMR, it must be determined by the difference between the six theoretical functional groups per triazine ring and the level of other functional groups (which can be determined directly). Bridging groups, whose level can be determined by 13C-NMR, must be included when performing this calculation. I 700 / 1 707 / 3 / YILI H.CH2OH CH2Oiso-Bu CH2OBu Examples of characteristic 13C-NMR peaks for typical substituents are 55 ppm (-OMe), 28 ppm (so-Bu), 90 ppm (bridging or crosslinking), and 13 / 31.5 / 64 ppm (-nBu). The carbon peak for -NCH2OH occurs in the 66–70 ppm range, and the carbon peaks for NCH2OR occur in the 70–79 ppm range (where R includes an alkoxy group or a bridging group to another triazine ring). Furthermore, the -NCH2OH / -NCH2OR carbon peaks may overlap with substituent or solvent peaks. Therefore, these substituent or solvent peaks are considered to indicate the mole percent of the amino or methyl group. When using 13C-NMR data to calculate the percentage of melamine functional groups that are amino and / or methylol, the triazine ring carbons (166 ppm) are normalized to 3. For each triazine ring, there are theoretically 6 substituents. The molar percent of NH and methylol is calculated from the peak intensities after normalizing the triazine ring carbons to 3. The procedure described above is illustrated for two melamines, Resimene® HM 2608 (melamine formaldehyde resin, commercially available from INEOS) and Cymel® 202 (melamine formaldehyde resin, commercially available from Allnex), using the 13C-NMR obtained for these melamines. The mole percent of amino groups is calculated using the following equation 1: mole percent of amino = 100 x (6 - I-nch2or - I-nch2oh) / 6. In addition, the mole percent of methylol groups is calculated using equation 2: mole percent of methylol = 100 x (Inch2oh) / 6. With respect to equations 1 and 2, R is the alkyl group and I-nch2or is the maximum intensity of the -NCH2OR carbons, which can be obtained by I-nch2or = I(70-79ppm) - I-isobutanol (28ppm). Furthermore, I-nch2oh is the maximum intensity of the -NCH2OH carbons, which can be obtained by InCH2OH = I(66-70ppm) - I-nbutanol (31.5ppm) - I-isobutanol (30.5ppm). For Resimene® HM 2608, the calculation of the mole percent for imine using equation 1 is illustrated as follows: mole percent imine = 100 x (6 - I-nch2or - I-nch2oh) / 6 = 100 x [6 - (3.55-0.12) - (1.19-0.55)1 / 6 = 32.2%. For Resimene® HM 2608, the calculation of the mole percent for methylol using equation 2 is illustrated as follows: mole percent methylol = 100 x (I-NCH2OH) / 6 = 100 x (0.64) / 6 = 10.7%. For Cymel® 202, the calculation of the mole percent for imine using equation 1 is illustrated as follows: mole percent imine = 100 x (6 - I-nch2or - I-nch2oh) / 6 = 100 x [6 2.59 - (1.93-1.23)1 / 6 = 45.2%. For Cymel® 202, the calculation of the mole percent for methylol using equation 2 is illustrated as follows: mole percent methylol = 100 x (I-nch2oh) / 6 = 100 x (0.7) / 6 = 11.7%. The method described above for determining the mole percent of functional groups in melamine resin is referred to in this document as the mole percent method of the melamine functional group. It will be noted that the presence of other I 700 / 1 707 / 3 / YILI components or other types of substituents or solvents could generate additional peaks not previously described or interfere with the peak integrals, for example, NCH2OR carbons (70-79 ppm) in 13C-NMR, and their contribution would be considered for the calculation of imino and methylol functionalities, for example. It was found that a melamine-formaldehyde crosslinker comprising the previously described amounts of functional groups can react with the carboxylic acid functional polyol polymer of the present invention at low temperatures to form a coating with desirable properties. For example, the coating composition can be cured at a temperature of 100°C or less, 90°C or less, or 80°C or less. The coating composition can be cured at the previously described temperatures in a time period of 1 hour or less, 30 minutes or less, or 20 minutes or less. The melamine-formaldehyde crosslinker may comprise at least 12% by weight, at least 15% by weight, or at least 20% by weight of the coating composition, based on the weight of the resin solids in the coating composition. The melamine-formaldehyde crosslinker may comprise up to 30% by weight, up to 28% by weight, or up to 26% by weight of the coating composition, based on the weight of the resin solids in the coating composition. The melamine-formaldehyde crosslinker may comprise from 12 to 30% by weight, from 15 to 28% by weight, or from 20 to 26% by weight of the coating composition, based on the weight of the resin solids in the coating composition. The coating composition of the present invention also includes an acid catalyst. That is, the coating composition utilizes an external acid catalyst to increase the reaction rate between the melamine-formaldehyde crosslinker and the polyol polymer with carboxylic acid functionality to cure the coating composition. Non-limiting examples of acid catalysts that may be used with the coating compositions of the present invention include sulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, citric acid, dodecylbenzenesulfonic acid, or any combination thereof. The acid catalyst may comprise 5% by weight or less, 4% by weight or less, or 3% by weight or less, based on the weight of resin solids of all hydroxyl-functional polymers used in the coating composition. The acid catalyst may comprise at least 0.5% by weight, or at least 1% by weight, or at least 2% by weight of the coating composition, based on the weight of resin solids of all hydroxyl-functional polymers used in the coating composition. The acid catalyst may comprise an amount within a range such as, for example, 0.5 to 5% by weight, or 1 to 3% by weight, of the coating composition, based on the weight of resin solids of I 700 / 1 707 / 3 / YILI all polymers with hydroxyl functionality used in the coating composition. The coating composition further comprises a non-aqueous liquid medium. The non-aqueous liquid medium comprises one or more organic solvents constituting more than 50% by weight of the liquid medium as previously defined. As such, the components forming the coating composition are combined and mixed in a non-aqueous liquid medium and are therefore solvent-based coating compositions. The coating composition may also include additional components. For example, the coating composition may also include additional film-forming resins. The additional resins may include any of a variety of thermoplastic and / or thermosetting resins known in the art. As used herein, the term thermosetting refers to resins that set irreversibly upon curing or crosslinking, in which the polymer chains are linked by covalent bonds. This property is usually associated with a crosslinking reaction, often induced, for example, by heat or radiation. Curing or crosslinking reactions may also occur under ambient conditions. Once cured, a thermosetting resin does not melt upon the application of heat and is insoluble in solvents. As noted, the additional resins may also include a thermoplastic resin.As used in this document, the term thermoplastic refers to resins that include polymeric components that are not held together by covalent bonds and can therefore experience liquid flow when heated. Additional film-forming resins can be selected from, for example, polyester polymers, polyurethanes, polyamide polymers, polyether polymers, polysiloxane polymers, epoxy resins, copolymers of these, and mixtures thereof. Thermosetting resins typically comprise reactive functional groups. Reactive functional groups may include, but are not limited to, hydroxyl groups, amine groups, epoxide groups, alkoxy groups, thiol groups, carbamate groups, amide groups, urea groups, and combinations thereof. Thermosetting resins are typically reacted with a crosslinking agent. Therefore, when additional film-forming resins are used in the coating composition, these additional film-forming resins may be reactive with additional crosslinking agents and / or the melamine-formaldehyde crosslinking agent. Non-limiting examples of such crosslinking agents include aziridines, epoxy resins, anhydrides, alkoxysilanes, carbodiimides, polyhydrazides, polyamines, polyamides, isocyanates, and blocked isocyanates, and any combination thereof. Thermosetting resins may also have self-reactive functional groups; in this way, such resins are self-crosslinking. The coating composition of the present invention may also be substantially free, essentially free, or completely free of any of the resins and / or I 700 / 1 707 / 3 / YILI additional crosslinkers such as, for example, being substantially free, essentially free, or completely free of isocyanates and blocked isocyanates. The terms substantially free of additional resins and / or crosslinkers mean that the coating composition contains less than 1000 parts per million (ppm) of additional resins and / or crosslinkers, essentially free of additional resins and / or crosslinkers means that the coating composition contains less than 100 ppm of additional resins and / or crosslinkers, and completely free of additional resins and / or crosslinkers means that the coating composition contains less than 20 parts per billion (ppb) of additional resins and / or crosslinkers. The weight is based on the total weight of the composition. A non-limiting example of an additional film-forming resin that can be used with the coating composition of the present invention and that can be used to further improve the final properties of the coating is a polyol polyester (i.e., a polyester comprising two or more hydroxyl groups). Such polymers can be prepared in a known manner by condensation of polyhydric alcohols and polycarboxylic acids. Suitable polyhydric alcohols include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, and dimethylolpropionic acid. Suitable polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and trimellitic acid.In addition to the polycarboxylic acids mentioned above, functional equivalents of polycarboxylic acids such as anhydrides, when available, or lower alkyl esters of polycarboxylic acids such as methyl esters may be used. When incorporated into the coating composition, polyester polyol may comprise 55% by weight or less, 40% by weight or less, or 35% by weight or less, based on the weight of resin solids in the coating composition. The polyol polymer with carboxylic acid functionality may also comprise an acid number selected within a certain range, which affects the amount of polyester polyol used in the coating composition. For example, when the polyol polymer with carboxylic acid functionality has an acid number within the range of 75 to 120 mg KOH / g, the polyester polyol comprises less than 15% by weight of the coating composition, based on the weight of the resin solids in the coating composition. Alternatively, when the polyol polymer with carboxylic acid functionality has an acid number within the range of 30 to less than 75 mg KOH / g, the polyester polyol comprises 30 to 55% by weight of the coating composition, based on the weight of the resin solids in the coating composition.It is observed that the polyester polyol can react with the melamine-formaldehyde resin or, if present, with an additional crosslinking agent. CJ I zon / l 7P7 / 3 / YILI Coating compositions may also include a colorant. As used herein, colorant refers to any substance that imparts color and / or other opacity and / or other visual effect to the composition. The colorant may be added to the coating in any suitable form, such as discrete particles, dispersions, solutions, and / or flakes. A single colorant or a mixture of two or more colorants may be used in the coatings of the present invention. Examples of colorants include pigments (organic or inorganic), dyes, and tints, such as those used in the paint industry and / or listed by the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. A colorant may include, for example, a finely divided solid powder that is insoluble but wettable under the conditions of use. A colorant may be organic or inorganic and may be agglomerated or non-agglomerated. Colorants can be incorporated into coatings by using a grinding vehicle, such as an acrylic grinding vehicle, the use of which will be familiar to someone skilled in the art. Examples of pigments and / or pigment compositions include, but are not limited to, crude carbazole pigment dioxazine, azo, monoazo, diazo, naphthol AS, benzimidazolone, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrole pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavantrone, pyrantrone, antantrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketopyrrole pyrrole red (DPPBO red), titanium dioxide, carbon black and mixtures thereof. Example dyes include, but are not limited to, solvent-based and / or aqueous dyes such as phthalo green or blue, iron oxide, bismuth vanadate, anthraquinone, perylene, and quinacridone. Example dyes include, but are not limited to, pigments dispersed in water-based vehicles or miscible in water such as commercially available AQUA-CHEM 896 from Degussa, Inc., and commercially available CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS from Accurate Dispersions Division of Eastman Chemical, Inc. Other non-limiting examples of components that can be used with the coating compositions of the present invention include plasticizers, abrasion-resistant particles, fillers including, among others, micas, talc, clays, inorganic minerals, antioxidants, hindered amine light stabilizers, ultraviolet light absorbers and stabilizers, surfactants, flow and surface control agents, thixotropic agents, reactive thinners, reaction inhibitors, corrosion inhibitors, and other common auxiliaries. After forming the coating composition of the present invention, the composition can be applied to a wide range of substrates known in the industry of Γ7 I ZQn / l 7Π7 / 3 / YILI coatings. For example, the coating composition of the present invention can be applied to automotive substrates (e.g., motor vehicles including, but not limited to, cars, buses, trucks, trailers, etc.), industrial substrates, aircraft and aircraft components, marine substrates and components such as ships, vessels, onshore and offshore installations, storage tanks, wind turbines, nuclear power plants, packaging substrates, wooden flooring and furniture, apparel, electronics including housings and circuit boards, glass and transparencies, sporting goods including golf balls, stadiums, buildings, bridges, and the like. These substrates can be, for example, metallic or non-metallic. Metallic substrates include, but are not limited to, tin, steel (including electrogalvanized steel, cold-rolled steel, hot-dip galvanized steel, steel alloys, or polished / profiled steel), aluminum, aluminum alloys, aluminum-zinc alloys, zinc-aluminum alloy-coated steel, and aluminum-clad steel. As used herein, polished or profiled steel refers to steel that has undergone abrasive polishing, which involves mechanical cleaning by continuously impacting the steel substrate with abrasive particles at high speeds using compressed air or centrifugal impellers. The abrasives are typically recycled / reused materials, and the process can efficiently remove scale and rust. Standard cleaning grades for abrasive blasting are carried out in accordance with BS EN ISO 8501-1. In addition, non-metallic substrates include polymeric acid, plastic, polyester, polyolefin, polyamide, cellulosic, polystyrene, polyacrylic, poly(ethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic, other green polymer substrates, poly(ethylene terephthalate) (PET), polycarbonate, acrylobutadiene styrene polycarbonate (PC / ABS), polyamide, wood, veneer, wood composite, particleboard, medium-density fiberboard, cement, stone, glass, paper, cardboard, textiles, both synthetic and natural leather, and the like. The coating compositions of the present invention can be applied by any standard means in the art, such as electroplating, spraying, electrostatic spraying, dipping, lamination, brushing, and the like. The coatings formed from the coating compositions of the present invention can be applied to a dry film thickness of, for example, 20 to 100 micrometers, 30 to 70 micrometers, or 40 to 50 micrometers. The coating composition can be applied to a substrate to form a monolayer. As used herein, a monolayer refers to a single-layer coating system that is free of additional coating layers. Therefore, the coating composition comprising the corrosion inhibitor can be applied directly to a substrate without any intermediate coating layer and cure to form a CJ I 700 / 1 707 / 3 / YILI is a single-layer coating, i.e., a monolayer. The coating composition can also be applied directly onto a pretreated substrate as a monolayer. For example, the substrate can be pretreated with iron phosphate, zinc phosphate, zirconium, titanium, or silane. Alternatively, the coating composition can be applied to a substrate as a first coating layer along with additional coating layers, such as a second coating layer, to form a multi-layer coating system. It is appreciated that the multi-layer coating can comprise multiple coating layers, such as three or more, four or more, or five or more coating layers. For example, the coating composition described above comprising the present invention can be applied to a substrate as a primer and second and third coating layers, and optionally as additional coating layers, and can be applied over the primer layer as base coats and / or top coats.As used in this document, a primer refers to a coating composition from which an undercoat can be deposited onto a substrate to prepare the surface for the application of a protective or decorative coating system. A basecoat refers to a coating composition from which a coating is deposited over a primer and / or directly onto a substrate, optionally including components (such as pigments) that impact color and / or provide other visual impact, and which can be topcoated with a protective and decorative layer. Additional coating layers, such as a second and third coating layer, can be formed from a coating composition that includes a film-forming resin that is the same as or different from that of the first coating layer. These additional coating layers can be prepared using any of the film-forming resins, crosslinkers, colorants, and / or other components described above. Furthermore, each coating composition can be applied in a dry-on-dry process, where each coating composition dries or cures to form a coating layer before the application of another coating composition. Alternatively, all or certain combinations of each coating composition described herein can be applied in a wet-on-wet process and dried or cured together, as two or more, or three or more, compositions applied in a wet-on-wet process.Multi-layer coatings can also be prepared with a primer layer, a first base coat applied over at least a portion of the primer layer, a second base coat applied over at least a portion of the second base coat, and a top coat applied over at least a portion of the second base coat, wherein at least one of the layers, such as the first and / or second base coat or the top coat, is prepared from the coating composition of the present invention described. I ZQn / l 7Π7 / 3 / YΙΛΙ previously. The coating layer or layers prepared with the coating composition described above may be a colored layer (e.g., a base coat) or a transparent layer (e.g., a top coat). As used herein, a transparent coating layer refers to a coating layer that is at least substantially transparent or completely transparent. The term substantially transparent refers to a coating where a surface beyond the coating is at least partially visible to the naked eye when viewed through the coating. The term completely transparent refers to a coating where a surface beyond the coating is completely visible to the naked eye when viewed through the coating.It is understood that the transparent layer may contain colorants, such as pigments, provided that the colorants do not interfere with the desired transparency of the transparent top layer. Alternatively, the transparent layer may be free of colorants, such as pigments (i.e., unpigmented). The present invention also relates to a method for forming a coating on at least a portion of a substrate. The method includes applying the coating composition described above to at least a portion of a substrate and curing the coating composition to form a coating on at least a portion of the substrate. The coating composition can be cured at a temperature of 100°C or less, 90°C or less, or 80°C or less. The coating composition can be cured at the temperatures described above in a period of time of 1 hour or less, 30 minutes or less, or 20 minutes or less. It was found that the coating compositions of the present invention can be cured at comparatively low temperatures, such as those described above, to form a coating that has a high degree of cure with desirable film properties such as good film hardness. It was also found that the coating compositions of the present invention can provide a stable one-component (lk) composition that cures at the temperatures described above. As used in this document, a one-component composition refers to a composition where all coating components are kept in the same container after manufacturing, during storage, etc. In contrast, a multi-component composition, such as a two-component (2K) or higher composition, has at least two components that are kept in a different container after manufacturing, during storage, etc., prior to application and coating formation on a substrate. The present invention also relates to the following aspects. I 700 / 1 707 / 3 / YILI A first aspect is directed to a coating composition comprising: (a) a polyol polymer with carboxylic acid functionality comprising an acid number within the range of 30 to 120 mg KOH / g and a hydroxyl number within the range of 60 to 150 mg KOH / g; (b) a melamine-formaldehyde crosslinker reactive with the polyol polymer with carboxylic acid functionality, wherein the melamine-formaldehyde crosslinker comprises imino and methylol groups that together comprise 35 mol% or less of the total functionality of the melamine-formaldehyde crosslinker, and wherein the melamine-formaldehyde crosslinker comprises butyl and isobutyl groups that together comprise 5 mol% or more of the total functionality of the melamine-formaldehyde crosslinker; (c) an acid catalyst; and (d) a non-aqueous liquid medium, wherein the coating composition is cured at a temperature of 100°C or less. A second aspect is directed to the coating composition of the first aspect, wherein the polyol polymer with carboxylic acid functionality is obtained from reagents comprising: (i) an ethylenically unsaturated compound comprising groups with hydroxyl functionality; (ii) an ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or an anhydride thereof; and (iii) an ethylenically unsaturated compound that is different from (i) and (ii). A third aspect is directed to the coating composition of the first or second aspect, wherein the acid catalyst comprises 5% by weight or less of the coating composition, based on the weight of resin solids of all polymers with hydroxyl functionality in the coating composition. A fourth aspect is directed to the coating composition of any of the first to third aspects, wherein the melamine-formaldehyde crosslinker comprises 12 to 30% by weight of the coating composition, based on the weight of the resin solids of the coating composition. A fifth aspect is directed to the coating composition of any of the first to fourth aspects, wherein the polyol polymer with carboxylic acid functionality has an acidity index within a range of 50 to 95 mg KOH / g. A sixth aspect is directed to the coating composition of any of the first through fifth aspects, wherein the polyol polymer with carboxylic acid functionality has a hydroxyl index within a range of 60 to 100 mg KOH / g. A seventh aspect is directed to the coating composition of any of the first to sixth aspects, wherein the polyol polymer with carboxylic acid functionality has a glass transition temperature within a range of -20 to 50°C. An eighth aspect is directed at the coating composition of any of I zon / l 7P7 / 3 / YILI the first to seventh aspects, where the polyol polymer with carboxylic acid functionality has a weight average molecular weight greater than 5,000g / mol. A ninth aspect is directed to the coating composition of any of aspects two through eight, wherein the ethylenically unsaturated compound comprising groups with hydroxyl functionality comprises at least 10% by weight of the reagents, based on the total weight of the reagent solids used to form the polyol polymer with carboxylic acid functionality. A tenth aspect is directed to the coating composition of any of aspects two through nine, wherein the ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or the anhydride thereof, comprises at least 5% by weight of the reagents, based on the total weight of the reagent solids used to form the polyol polymer with carboxylic acid functionality. An eleventh aspect is directed to the coating composition of any of aspects two through ten, wherein the ethylenically unsaturated compound other than (i) and (ii) comprises a multi-ethylenically unsaturated compound, a mono-ethylenically unsaturated compound having an extractable hydrogen, or a combination thereof. A twelfth aspect is directed to the coating composition of the eleventh aspect, wherein the ethylenically unsaturated compound that is different from (i) and (ii) comprises at least two different monoethylenically unsaturated compounds having an extractable hydrogen. A thirteenth aspect is directed to the coating composition of any of the second to twelfth aspects, wherein the ethylenically unsaturated compound other than (i) and (ii) comprises at least 50% by weight of the reagents, based on the total weight of the reagent solids used to form the polyol polymer with carboxylic acid functionality. A fourteenth aspect is directed to the coating composition of any of the first to thirteenth aspects, which further comprises a polyester polyol. A fifteenth aspect is directed to the coating composition of the fourteenth aspect, wherein the polyester polyol comprises less than 15% by weight of the coating composition, based on the weight of resin solids of the coating composition. A sixteenth aspect is directed to the coating composition of the fourteenth aspect, wherein the polyester polyol comprises 30 to 55% by weight of the coating composition, based on the weight of resin solids of the coating composition. I zon / l 7P7 / 3 / YILI A seventeenth aspect is directed to a substrate at least partially coated with a coating formed from the coating composition of any of the first through sixteenth aspects. An eighteenth aspect is directed to the substrate of the seventeenth aspect, wherein the coating composition is applied directly onto at least a portion of the substrate. A nineteenth aspect is directed to the substrate of the seventeenth aspect, wherein the coating composition is applied over at least a portion of a first coating layer formed over at least a portion of the substrate. A twentieth aspect relates to a method for forming a coating on at least a portion of a substrate comprising: applying a coating composition onto at least a portion of a substrate, wherein the coating composition comprises: (a) a polyol polymer with carboxylic acid functionality comprising an acidity index in the range of 30 to 120 mg KOH / g and a hydroxyl index in the range of 60 to 150 mg KOH / g; (b) a melamine-formaldehyde crosslinker reactive with the polyol polymer having carboxylic acid functionality, wherein the melamine-formaldehyde crosslinker comprises imino and methylol groups that together comprise 35 mol% or less of the total functionality of the melamine-formaldehyde crosslinker, and wherein the melamine-formaldehyde crosslinker comprises butyl groups and isobutyl groups that together comprise 5 mol% or more of the total functionality of the melamine-formaldehyde crosslinker;(c) an acid catalyst; and (d) a non-aqueous liquid medium, and cure the coating composition at a temperature of 100°C or less to form a coating on at least a portion of the substrate. A twenty-first aspect is directed to the twentieth aspect method, wherein the coating composition is cured at a temperature of 90°C or less to form a coating over at least a portion of the substrate. A twenty-second aspect is directed to the method of the twentieth or twenty-first aspect, further comprising applying one or more additional coating compositions as a wet-on-wet process before or after applying the coating composition comprising components (a) - (d) and curing the coating compositions simultaneously. A twenty-third aspect is directed to the method of any of the twentieth to twenty-second aspects, wherein the coating composition is the coating composition defined in any of the first to sixteenth aspects. The following examples are presented to demonstrate the general principles of the invention. The invention should not be considered limited to the specific examples presented. All parts and percentages in the examples are by weight unless otherwise stated. r;1 ζοη / ι ζηζ / 3 / γΐΛΐ EXAMPLE 1 Preparation of polyol polymers. The AG polyol polymers were prepared as follows: Polymer A: First, 247 g of SOLVESSO™ 100 (an aromatic hydrocarbon fluid, commercially available from ExxonMobil Chemical) was loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser and covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, an initiator mixture of 80 g of SOLVESSO™ 100 and 26.8 g of tert-butyl peroxyacetate was loaded into the flask for 5 hours and 15 minutes. Simultaneously, a monomer mixture of 287.5 g isobornyl acrylate, 287.5 g 2-ethylhexyl acrylate, 115 g hydroxyethyl methacrylate, 76.7 g hexanediol diacrylate, and 103 g SOLVESSO™ 100 was loaded into the flask for 5 hours. After loading the initiator mixture, the reaction was maintained at 155°C for an additional 1 hour. The polymer was then cooled and drained. The final measured solids content by weight of the resulting polymer was 62%.9%, with a weight mean molecular weight of 9696 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for separation. Polymer B: First, 250 g of butyl acetate were loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser, and covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, an initiator mixture of 80 g of butyl acetate and 26.8 g of t-butyl peroxyacetate was loaded into the flask and heated for 5 hours and 15 minutes. Simultaneously, a monomer mixture of 265 g of isobornyl acrylate, 265 g of 2-ethylhexyl acrylate, 115 g of hydroxyethyl methacrylate, 88 g of acrylic acid, and 103 g of butyl acetate was loaded into the flask and heated for 5 hours. Once the initiator mixture was loaded, the reaction was maintained at 155°C for an additional hour. After that, the polymer was cooled and discharged. The final measured solids content by weight of the resulting polymer was 61%.6%, with a weight mean molecular weight of 7585 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for separation. Polymer C: First, 246.7 g of SOLVESSO™ 100 were loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser and The mixture was covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, an initiator mixture of 80 g of SOLVESSO™ 100 and 26.8 g of t-butyl peroxyacetate was charged into the flask for 5 hours and 15 minutes. Simultaneously, a monomer mixture of 552 g of isobornyl acrylate, 115 g of hydroxyethyl methacrylate, 22 g of acrylic acid, 76.7 g of hexanediol diacrylate, and 103 g of SOLVESSO™ 100 was charged into the flask for 5 hours. Once the initiator mixture was charged, the reaction was held at 155°C for an additional 1 hour. After that, the polymer was cooled and discharged. The final measured solids content by weight of the resulting polymer was 64%.7%, with a weight mean molecular weight of 8274 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for separation. Polymer D: First, 642 g of SOLVESSO™ 100 was loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser and covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, a starter mixture of 208 g of SOLVESSO™ 100 and 69.8 g of t-butyl peroxyacetate was loaded into the flask for 5 hours and 15 minutes. Simultaneously, a mixture of monomers consisting of 667 g isobornyl acrylate, 667 g 2-ethylhexyl acrylate, 299 g hydroxyethyl methacrylate, 159 g acrylic acid, 199 g hexanediol diacrylate, and 268 g SOLVESSO™ 100 was loaded into the flask for 5 hours. Once the initiator mixture was loaded, the reaction was maintained at 155°C for an additional 1 hour. After this, the polymer was cooled and drained. The final measured solids content by weight of the resulting polymer was 64.3%, with a weight average molecular weight of 36589 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for separation. Polymer E: First, 642 g of ethyl 3-ethoxypropionate (EEP) was loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser and covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, an initiator mixture of 208 g of EEP and 69.8 g of tert-butyl peroxyacetate was loaded into the flask for 5 hours and 15 minutes. Simultaneously, a monomer mixture of 908 g of isobornyl acrylate, 379 g of 2-ethylhexyl acrylate, 284 g of hydroxyethyl methacrylate, 196 g of acrylic acid, 196 g of hexanediol diacrylate, and 255 g of EEP was loaded into the flask for 5 hours. Once the initiator mixture was loaded, the reaction was maintained at 155°C for another hour. After that, the polymer was cooled and discharged. The contents of The final measured solids by weight of the resulting polymer was 64.6%, with a mean molecular weight of 22576 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for the separation. Polymer F: First, 642 g of ethyl 3-ethoxypropionate (EEP) was loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser and covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, an initiator mixture of 198 g of EEP and 66.3 g of tert-butyl peroxyacetate was loaded into the flask for 5 hours and 15 minutes. Simultaneously, a mixture of monomers consisting of 927 g isobornyl acrylate, 379 g 2-ethylhexyl acrylate, 284 g hydroxyethyl methacrylate, 235 g acrylic acid, 137 g hexanediol diacrylate, and 255 g EEP was loaded into the flask for 5 hours. Once the initiator mixture was loaded, the reaction was maintained at 155°C for an additional hour. After this, the polymer was cooled and drained. The final measured solids content by weight of the resulting polymer was 65%.1%, with a weight average molecular weight of 14154 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for separation. Polymer G: First, 650 g of ethyl 3-ethoxypropionate (EEP) was loaded into a four-necked round-bottom flask equipped with a thermocouple, mechanical stirrer, and condenser, and covered with N2. The mixture was heated to 155°C and held for 10 minutes. After that, an initiator mixture of 208 g of EEP and 69.8 g of tert-butyl peroxyacetate was loaded into the flask for 5 hours and 15 minutes. Simultaneously, a monomer mixture of 689 g of isobornyl acrylate, 689 g of 2-ethylhexyl acrylate, 299 g of hydroxyethyl methacrylate, 229 g of acrylic acid, and 268 g of EEP was loaded into the flask for 5 hours. Once the initiator mixture was loaded, the reaction was maintained at 155°C for an additional hour. After that, the polymer was cooled and discharged. The final measured solids content by weight of the resulting polymer was 62%.2%, with a weight mean molecular weight of 9409 g / mol measured by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for separation. The percentage composition of the components used to form the AG polymers and the properties of the resulting polymers are shown in Table 1. I 700 / 1 707 / 3 / YILI I 7ΟΠ / Ι 7Π7 / 3 / ΥΙΛΙ TABLE 1 Component or Property Polymer A Polymer B Polymer C Polymer D Polymer E Polymer F Polymer G Isobornyl acrylate 37.5 36 70 33.5 49 49 36 2-ethylhexyl acrylate 37.5 36 0 33.5 19 19 36 Hydroxyethyl methacrylate 15 16 15 15 15 15 16 Acrylic acid 0 12 3 8 10 12 12 Hexanediol diacrylate 10 0 10 10 10 7 0 Mw1 9696 7585 8274 36589 22576 14154 9409 Mn1 1811 2717 1678 2176 2530 2332 2922 Hydroxyl value (in solids)2 64.5 69.0 64.5 64.5 64.5 64.5 69.0 Acid value (in solids)2 2.1 93.2 21.1 54.5 71.4 84.2 91.4 Gardner-Holdt viscosity 3 O- Z+ Z1 + Z6 Z2- Z2- Z1 + Tq (°C)4 -6 -3 82 -2 29 29 -3 1The weight average molecular weight (M„) and number average molecular weight (Mn) were determined by gel permeation chromatography using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector) and polystyrene standards in which tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 ml / min and two PL Gel Mixed C columns were used for the separation. 2The acid and hydroxyl values ​​were determined using a Metrohm 798 MPT Titrino automatic titrator in accordance with ASTM D 4662-15 and ASTM E 1899-16 standards. 3The Gardner-Holdt viscosity was determined by pouring the polymer into a tube with an inner diameter of 10.65 ± 0.025 mm and an outer length of 114 ± 1 mm. The polymer was added until the 100 mm mark of the tube was reached. After inserting a cork, the tube was placed on an inversion grid and immersed in a water bath at 25 ± 1°C. The polymer-filled tube was left to stand in the water bath for a minimum of 20 minutes. The inversion grid was then removed from the water bath and quickly rotated 180°. The speed at which an air bubble traveled through the polymer between the 27 mm and 100 mm marks of the tube was recorded and associated with a corresponding Gardner-Holdt viscosity. 4The glass transition value (Tg) was determined according to ASTM D6604-00 (2013) using differential heat flux scanning calorimetry (DSC) with the following parameters: sample trays: aluminum, reference: blank, calibration: indium and mercury, sample weight: 10 mg, heating rate: 20°C / min. EXAMPLES 2-8 Preparation of coating compositions Several coating compositions were prepared with the components shown in Table 2. I ZQn / l 7Π7 / 3 / YILI TABLE 2 Component Ex· 2 Comp. Ex. 3 Comp. Ex.4 Comp. Ex. 5 Comp. Ex. 6 Comp. Ex· 7 Ex.8 SOLVESSO™ 100 4.49 6.93 6.73 2.95 4.17 1.92 7.05 Polymer A 0 0 0 0 10 10 0 Polymer B 0 0 0 0 0 0 16.2 Polymer C 0 15.7 0 10 0 0 0 Polymer D 10.0 0 15.7 0 0 0 0 Cymel ® 11615 2.14 2.57 0 2.14 2.10 2.14 3.45 Resimene ® HM 26086 0 0 2.84 0 0 0 0 Dodecyl benzenesulfonic acid 0.18 0.25 0.25 0.71 0.17 1.06 0.27 5 Highly monomeric methylated / isobutylated melamine crosslinker, commercially available from Allnex. 6Highly reactive methylated melamine-formaldehyde resin of the imino type, commercially available from Ineos. Examples 2-8 were prepared by mixing the ingredients described in Table 2. All compositions were adjusted to 50% resin solids by weight with the defined amount of SOLVESSO™ 100. EXAMPLE 9 Coating preparation and evaluation The coating compositions of Examples 2-8 were applied using a 5-mil spacing stretcher bar available through BYK onto steel panels pre-coated with ED7400 electrodeposition primer (available from PPG Industries, Inc.). After drying at room temperature for 10 minutes, the panels were baked at 80°C for 30 minutes. After removal from the oven, the panels were stored for 24 hours under ambient conditions and then tested for solvent resistance using double methyl ethyl ketone (MEK) rubs, in accordance with ASTM D5042-15. The test results are shown in Table 3. TABLE 3 Composition used to form the coating. Double rub with MEK to remove the coating. Example 2 >200. Comparative Example 3 80. Comparative Example 4 60. Comparative Example 5 140. Comparative Example 6 120. Comparative Example 7 130. Example 8 >200 Regarding the comparative examples and in comparison with the present invention: comparative example 3 was formed with a polyol polymer having an acid value of 21.1; comparative example 4 was formed with a highly functional melamine-formaldehyde resin crosslinker of the inmino type; comparative example 5 was formed with a polyol polymer having an acid value of 21.1 and a large amount of external catalyst; comparative example 6 was formed with a polyol polymer prepared without a component having carboxylic acid functionality and having an acid value of 2.1; and comparative example 7 was formed with a large amount of external catalyst and a polyol polymer prepared without a component having carboxylic acid functionality and having an acid value of 2.1. As shown in Table 3, Examples 2 and 8 of the present invention exhibited significantly better solvent resistance than Comparative Examples 3-7, showing that coatings formed from the coating compositions of the present invention provided a better and greater degree of curing. COMPARATIVE EXAMPLE 10 A coating composition was prepared using a commercial melamine 1C clearcoat (TMAC9000 solvent-based clearcoat, available from PPG Industries, Inc.), which did not contain any external catalyst. The coating composition was applied to the electro-coated steel panel according to Example 9. The resulting coating did not exhibit any significant crosslinking. To provide sufficient crosslinking, the coating composition required a high baking temperature of 140°C for 30 minutes. EXAMPLES 11-13 Preparation of coating compositions Several coating compositions were prepared with the components shown in Table 4. I zon / l 7P7 / 3 / YILI I 7ΟΠ / Ι 7Π7 / 3 / ΥΙΛΙ TABLE 4 Component Ex. 11 Ex. 12 Ex. 13 Methylamylketone 22.10 22.10 20.40 Ethyl 3-Ethoxypropionate 51.3 46.3 31.2 Polymer E 146.8 0 0 Polymer F 0 145.8 0 Polymer G 0 0 144.8 CYMEL® 11615 31.63 31.63 30.0 Polysiloxane borate7 2.03 2.03 0 DISPARLON OX-608 0.47 0.47 0 Dodecylbenzenesulfonic acid 2.53 2.53 2.40 7Prepared as described in Example D of U.S. Patent No. 8,871,848, which is incorporated herein by reference. 8Surface control agent, commercially available from Kusumoto Chemicals. Examples 11-13 were prepared by mixing the ingredients described in Table 4. Example 11 contained 51.7 wt% resin solids and had a No. 4 Ford cup viscosity of 35.5 seconds at room temperature. Example 12 contained 53.0 wt% resin solids and had a No. 4 Ford cup viscosity of 35.4 seconds at room temperature. Example 13 contained 53.4 wt% resin solids and had a No. 4 Ford cup viscosity of 30.4 seconds at room temperature. EXAMPLE 14 Coating preparation and evaluation The coating compositions for Examples 11–13 were applied using a siphon-fed spray gun attached to a Spraymation automatic sprayer onto steel panels pre-coated with ED7400 electrodeposition primer (available from PPG Industries, Inc.) in two coats. All coated panels were then dried at room temperature for 8 minutes and transferred to the oven. Examples 11 and 12 were oven-baked at 90°C for 30 minutes, and Example 13 was oven-baked at 80°C for 30 minutes. After removal from the oven, the panels were stored for 24 hours at room temperature. The panels were tested for solvent resistance using double methyl ethyl ketone (MEK) rubs, in accordance with ASTM D5042-15, and Fisher microhardness using a Fischer Technologies H100C microhardness measuring system in accordance with ISO 14577-4: 2016.The test results are shown in Table 5. I 7ΟΠ / Ι 7Π7 / 3 / ΥΙΛΙ TABLE 5 Composition used to form the coating. Double rubs with MEK to remove the coating. Fisher microhardness. Example 11 >200 130.7. Example 12 >200 122.6. Example 13 >200 133.3 As shown in Table 5, Examples 11-13, which were applied using a spraying method, provided good solvent resistance (i.e., a high degree of curing) and good film hardness. EXAMPLE 15 Coating preparation and evaluation Several coatings were prepared from the components of the coating composition of Example 2 listed in Table 2, except that different melamine resins were used instead to form the composition and that they had a certain molar percentage of methylol and imino functionality, as well as a certain mole percentage of butyl and isobutyl functionality, as described in Table 6. Furthermore, polymer D, which was used to form the compositions, was blended with each of the different melamines, respectively, in an 80:20 ratio based on resin solids. The coating compositions were applied using a 5-mil stretch bar available through BYK onto steel panels pre-coated with the ED7400 electrodeposition primer (available from PPG Industries, Inc.). After drying at room temperature for 10 minutes, the panels were baked at 90°C for 30 minutes. Next, the solvent resistance (double rubs with MEK) and Fisher microhardness of the coatings were evaluated according to the methods described above. The results are shown in Table 6. TABLE 6 Coating sample Melamine resin sample 9% NH + %CH2OH of total melamine functionality (mol %) 9% O-Bu + %IsoOBu of total melamine functionality (mol %) 9 Solvent resistance Fisher microhardness 1 A 13.9 23.7 >200 111 2 B 23.1 18.7 >200 149 3 C 33.3 61.9 >200 98 4 D 41.5 2.0 110 91 5 E 19.7 0 43 48 9The AE melamine resin samples contained different molar % levels of imino, methylol, butyl, and isobutyl functional groups and are shown in Table 6. The molar % of imino (% NH) and methylol (% CH2OH) functional groups, taken together, and the butyl (% O-Bu) and isobutyl (% Iso-OBu) functional groups, taken together, were determined based on the melamine functional group mol % method described earlier in this document. Γ7 I 7ΟΠ / Ι 7Π7 / 3 / ΥΙΛΙ As shown in Table 6, coating samples 1-3 exhibited good solvent resistance and coating hardness and were prepared with a melamine resin having: (i) mino and methylol functional groups that together comprise 13.9 mol%, 23.1 mol% and 33.3 mol%, respectively, of the total functionality of the melamine resin; and (ii) butyl and isobutyl functional groups that together comprise 23.7 mol%, 18.7 mol% and 61.9 mol%, respectively, of the total functionality of the melamine resin. Furthermore, comparative coating sample 4, which was prepared with a melamine resin having imino and methylol functional groups that together comprise 41.5 mol% of the total functionality of the melamine resin, and butyl and isobutyl functional groups that together comprise 2.0 mol% of the total functionality of the melamine resin, exhibited worse solvent resistance and coating hardness than samples 1-3. In addition, comparative coating sample 5, which was prepared with a melamine resin having imino and methylol functional groups that together comprise 19.7 mol% of the total functionality of the melamine resin, and 0 mol% of the butyl and isobutyl functional groups, also exhibited worse solvent resistance and coating hardness than samples 1-3. Although particular embodiments of this invention have been described above for illustrative purposes, it will be evident to those skilled in the art that numerous variations of the details of the present invention can be made without departing from the invention as defined in the appended claims.

Claims

1. A coating composition comprising: (a) a polyol polymer with carboxylic acid functionality comprising an acid number within the range of 30 to 120 mg KOH / g and a hydroxyl number within the range of 60 to 150 mg KOH / g; (b) a melamine-formaldehyde crosslinker reactive with the polyol polymer with carboxylic acid functionality, wherein the melamine-formaldehyde crosslinker comprises imino and methylol groups that together comprise 35 mol% or less of the total functionality of the melamine-formaldehyde crosslinker, and wherein the melamine-formaldehyde crosslinker comprises butyl and isobutyl groups that together comprise 5 mol% or more of the total functionality of the melamine-formaldehyde crosslinker; (c) an acid catalyst; and (d) a non-aqueous liquid medium, wherein the coating composition cures at a temperature of 100°C or less.

2. The coating composition according to claim 1, wherein the polyol polymer with carboxylic acid functionality is obtained from reagents comprising: (i) an ethylenically unsaturated compound comprising groups with hydroxyl functionality; (ii) an ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or an anhydride thereof; and (iii) an ethylenically unsaturated compound other than (i) and (ii).

3. The coating composition according to claim 1, wherein the acid catalyst comprises 5% by weight or less of the coating composition, based on the total weight of solids of all polymers with hydroxyl functionality in the coating composition.

4. The coating composition according to claim 1, wherein the melamine-formaldehyde crosslinker comprises 12 to 30% by weight of the coating composition, based on the weight of resin solids of the coating composition.

5. The coating composition according to claim 1, wherein the polyol polymer with carboxylic acid functionality has an acid value within a range of 50 to 95 mg KOH / g.

6. The coating composition according to claim 1, wherein the polyol polymer with carboxylic acid functionality has a hydroxyl index within a range of 60 to 100 mg KOH / g.

7. The coating composition according to claim 1, wherein the polyol polymer with carboxylic acid functionality has a glass transition temperature within a range of -20 to 50°C.

8. The coating composition according to claim 1, wherein the polyol polymer with carboxylic acid functionality has a weight average molecular weight greater than 5,000 g / mol.

9. The coating composition according to claim 2, wherein the ethylenically unsaturated compound comprising groups with hydroxyl functionality comprises at least 10% by weight of the reagents, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality.

10. The coating composition according to claim 2, wherein the ethylenically unsaturated compound comprising groups with carboxylic acid functionality, or the anhydride, comprises at least 5% by weight of the reagents, based on the total weight of solids of the reagents used to form the polyol polymer with carboxylic acid functionality.

11. The coating composition according to claim 2, wherein the ethylenically unsaturated compound that is different from (i) and (ii) comprises a multi-ethylenically unsaturated compound, a mono-ethylenically unsaturated compound having an extractable hydrogen, or a combination thereof.

12. The coating composition according to claim 11, wherein the ethylenically unsaturated compound that is different from (i) and (ii) comprises at least two different monoethylenically unsaturated compounds having an extractable hydrogen.

13. The coating composition according to claim 2, wherein the ethylenically unsaturated compound other than (i) and (ii) comprises at least 50% by weight of the reactants, based on the total weight of solids of the reactants used to form the polyol polymer with carboxylic acid functionality.

14. The coating composition according to claim 1, further comprising a polyester polyol.

15. The coating composition according to claim 14, wherein the polyester polyol comprises less than 15% by weight of the coating composition, based on the weight of resin solids of the coating composition.

16. The coating composition according to claim 14, wherein the polyester polyol comprises 30 to 55% by weight of the coating composition, based on the weight of resin solids of the coating composition.

17. A substrate coated at least partially with a coating formed from the coating composition according to claim 1.

18. The substrate according to claim 17, wherein the coating composition I 700 / 1 707 / 3 / YILI is applied directly onto at least a portion of the substrate.

19. The substrate according to claim 17, wherein the coating composition is applied over at least a portion of a first coating layer formed over at least a portion of the substrate.

20. A method for forming a coating on at least a portion of a substrate comprising: applying a coating composition on at least a portion of a substrate, wherein the coating composition comprises: (a) a polyol polymer with carboxylic acid functionality comprising an acid number within a range of 30 to 120 mg KOH / g and a hydroxyl number within a range of 60 to 150 mg KOH / g; (b) a melamine-formaldehyde crosslinker reactive with the polyol polymer having carboxylic acid functionality of (a), wherein the melamine-formaldehyde crosslinker comprises μmino and methylol groups together comprising 35 mol% or less of the total functionality of the melamine-formaldehyde crosslinker and wherein the melamine-formaldehyde crosslinker comprises butyl groups and μsobutyl groups together comprising 5 mol% or more of the total functionality of the melamine-formaldehyde crosslinker;(c) an acid catalyst; and (d) a non-aqueous liquid medium; and curing the coating composition at a temperature of 100°C or less to form a coating on at least a portion of the substrate.

21. The method according to claim 20, wherein the coating composition is cured at a temperature of 90°C or less to form a coating over at least a portion of the substrate.

22. The method according to claim 20, further comprising applying one or more additional coating compositions as a wet-on-wet process before or after applying the coating composition comprising components (a) - (d) and curing the coating compositions simultaneously.