MXPA97004808A - Coating composition cura - Google Patents

Abstract

A curable coating composition is disclosed which comprises: (A) a carbamate functional component, which is the reaction product of: (1) a compound comprising a plurality of hydroxyl groups, at least one of which is the result of a ring opening reaction between an epoxy group and an organic acid group, and (2) cyanic acid or a compound comprising a carbamate group, and (B) a component comprising a plurality of groups that are reactive with the groups with carbamate functionality in the component (

Description

CURABLE COATING COMPOSITION Field of the Invention This invention relates to curable coating compositions, particularly curable compositions utilizing a carbamate functional compound as one of the components of the composition.

BACKGROUND OF THE INVENTION Curable coating compositions, such as thermoset coatings, are widely used in the coating trade. They are frequently used for final coatings in the automotive and industrial coatings industry. Color composite coatings plus clearcoat are particularly useful as topcoats where exceptional gloss quality, vividness of color, sharpness of the image or special metallic effects are desired. The automotive industry has extensively used these coatings for automotive body panels. However, color-plus-transparent composite coatings require an extremely high degree of clarity in the clear coat, to obtain the desired visual effect. High gloss coatings also require a low degree of visual aberration on the surface of the coating, in order to obtain the desired visual effect, such as high image sharpness (DOI). These coatings are particularly susceptible to a phenomenon known as environmental degradation. Environmental degradation manifests as spots or marks on, or on, the finish of the coating, which frequently can not be easily removed by rubbing. Frequently, it is also desirable to provide options of different types of materials with carbamate functionality, to provide coatings with a good combination of properties, such as durability, hardness, flexibility and resistance to scratching, wear, solvents and acids.

Curable coating compositions based on curable components having carbamate functionality have been described in the art to provide coatings resistant to degradation, for example, US Pat. UU 5,356,669 and WO 94/10211. The non-polymeric compounds with carbamate functionality, for coating compositions, have been described in 5,336,566 and EP 636,660, US Pat. In order to obtain smooth finishes which are often highly desirable in the coating industry, the coating compositions preferably tend to be fluid in nature, and exhibit good flow. Good flow is observed when the coating composition is sufficiently fluid at a certain point, after it is applied to the substrate, and before it is cured on a hard film, so that the surface of the coating acquires a smooth appearance. Some coating compositions exhibit good flow immediately upon application, and others present good flow when heated. One way of imparting fluid characteristics and a good flow to a coating composition is by incorporating volatile organic solvents into the compositions. These solvents can provide the desired fluidity and flow during the coating process, after which they evaporate, leaving only the coating components. However, the use of said solvents also increases the volatile organic content (VOC) of the coating composition. Due to the adverse impact that VOC has on the environment, many government regulations impose limitations on the amount of solvent that can be used. Therefore, it would be desirable to use components of coating compositions that provide good flowability and flow to the coating compositions, without the need for large amounts of solvent. Due to their other beneficial properties, it would also be desirable to provide compounds with carbamate functionality for use in coating compositions that do not require large amounts of solvent.

Summary of the Invention According to the present invention, a curable coating composition is provided comprising: (A) a carbamate functional component, which is the reaction product of: (1) a compound comprising a plurality of groups hydroxyl, at least one of which is the result of a ring opening reaction between an epoxy group and an organic acid group, and (2) cyanic acid or a compound comprising a carbamate group, and (B) a component comprising a plurality of groups that are reactive with the carbamate functional groups in component (A). The coating compositions of the present invention can reduce the need for organic solvents, and can also impart to the coating compositions the ability to be spray-applied at high viscosities, and still maintain the characteristics of good flow and appearance. The present invention provides coatings with a good combination of properties, such as durability, hardness and resistance to scratching, wear, solvents and acids. Coating compositions, according to the invention, can also provide low VOC levels, while maintaining other beneficial properties frequently found in coating compositions containing relatively high amounts of solvent, such as good sag resistance, leveling, low orange peel, brightness, image sharpness (DOI), substrate wetting, and pigment loading and dispersion, and uniform curing.

Description of the Preferred Embodiments According to the invention, the compound (A) (1) comprises a plurality of hydroxyl groups, at least one of which is the result of an opening reaction of a ring between an epoxy group and a organic acid group. This reaction frequently uses carboxylic acid groups, although other organic acids, such as phenolic compounds, can also be used. The acid / epoxy reaction is well known in the chemical guild, and could proceed spontaneously under ambient conditions, either in solvent or undiluted, and could advantageously be accelerated with heat. The compound (A) (1) can be prepared in a variety of ways, such as by reacting a monoepoxide with a hydroxy acid, reacting a monoepoxide with a polyacid, reacting a polyepoxide with a monoacid, reacting a polyepoxide with a hydroxy acid, or reacting a polyepoxide with a polyacid. Virtually any epoxide can be used in the practice of the present invention. Epoxides are well known in the guild, and could be characterized by the general formula: where R1, R2, R3 and R4 are each independently H (with the proviso that at least one of R-R4 is other than H), an organic radical, which could be polymeric or non-polymeric and which could contain heteroatoms and / or unsaturation, or one of R1 or R2 together with one of R3 or R4 could form a cyclic ring, which could contain heteroatoms and / or unsaturation. Useful epoxides can be prepared from alcohols, for example, butanol, trimethylolpropane, by reaction with an epihaiohydrin (for example, epichlorohydrin), or by reaction of an allyl group with peroxide. The epoxide can be monofunctional or polyfunctional, which can be controlled by selection of the starting material. For example, a monoepoxide can be prepared by reacting a monoalcohol or monoacid with an epihaiohydrin or a monounsaturated with peroxide, and a polyepoxide can be prepared by reacting a polyol (including diols, triols, and higher functionality polyols) with an epihaiohydrin or a compound polyunsaturated with peroxide. Polymeric or oligomeric polyepoxides, such as acrylic oligomers or polymers containing glycidyl methacrylate or polyglycidyl ethers terminated with epoxy, such as diglycidyl ether of bisphenol A (DGEBPA) can also be used. Polyester resins or epoxidized polyurethane resins can be prepared by reacting polyesters or polyurethanes containing OH groups, as they are known in the guild, with an epihaiohydrin. The epoxides can also be prepared by reacting with glycidol an isocyanate-terminated component, such as a polyisocyanate (including isocyanurates, for example, the isocyanurate of isophorone diisocyanate), or a polymer or an oligomer. Other known polyepoxides, for example epoxy-novolacs, can also be used. In a preferred embodiment, the epoxide is a monoepoxide, preferably an epoxy ester, also known as a glycidyl ester. The glycidyl esters can be prepared by reacting a monofunctional carboxylic acid (eg, octanoic acid, benzoic acid, benzyl acid, cyclohexanecarboxylic acid) with an epihaiohydrin (eg, epichlorohydrin) under conditions well known in the art. Glycidyl esters can be obtained commercially, for example, as Cardura® E from Shell Oil Company, Glydexx® N-10 from Exxon, or Araldite® PT910 from Ciba-Geigy. The glycidyl esters can be described by the formula where R is a hydrocarbon group, from 1 to 40 carbon atoms, preferably 1-20 carbon atoms, and more preferably 1-2 carbon atoms. This hydrocarbon group can be substituted, as is known in the guild. Polyglycidyl esters can also be used, and can be prepared by reacting a polyfunctional carboxylic acid (e.g. phthalic acid, thioglycolic acid, adipic acid) with an epihaiohydrin. The polyglycidyl esters can also be described by the formula indicated above, where "R is replaced by other glycidyl ester groups." Another useful class of mono-epoxides are the glycidyl ethers.The glycidyl ethers can be prepared by the reaction of monofunctional alcohols (e.g. n-butanol, propanol, 2-ethylhexanol, dodecanol, phenol, cresol, cyclohexanol, benzyl alcohol) with an epihaiohydrin (for example epichlorohydrin). Useful glycidyl ethers include the glycidyl ether of 2-ethanolhexanol, the glycidyl ether of dodecanol , the glycidyl ether of phenol, and the like These compounds can be obtained commercially under the family of Erisys ® products from CVC Specialties Polyglycidyl ethers can also be used, and can be prepared by reacting a polyfunctional alcohol (for example, bisphenol A, 1,6-hexanediol) with an epihaiohydrin Epoxides can also be prepared by reacting a since it contains one or more double bonds with peroxide or peracetic acid under conditions well known in the trade. Virtually any compound containing double bond can be used. A useful class of compounds containing double bond are the mono-unsaturated cycloaliphatic compounds, such as that can be sold as Union's Cyracure® products Carbide Among the other double-bonding compounds, which may be used in the practice of the invention, are ethylene, propylene, styrene, styrene oxide, cyclohexane, polybutadiene, and the like. The epoxide may also be an acrylic-containing oligomer or polymer, preferably by deriving its epoxy groups from the monomer of glycidyl methacrylate, glycidyl acrylate, ether-allyl glycidyl, cyclohexyl monoepoxymethacrylate, the epoxide of the cyclopentadiene methacrylate dimer or epoxidized butadiene, plus preferably glycidyl methacrylate. The epoxides described above are reacted with a compound containing an organic acid group to open the oxirane ring in the epoxide. Preferably, a monoepoxide must be reacted with a hydroxy acid or a polyacid in order to obtain a compound having a plurality of hydroxyl groups available for transesterification with the carbamate in the compound (A) (2). Alternatively, a compound having hydroxyl and epoxy groups (for example glycidol) can be reacted with a monoacid (or a polyacid) to result in a compound having a plurality of hydroxyl groups available for transesterification with the carbamate in the compound (A) (2) . Useful hydroxy acids include dimethylolpropionic acid, hydroxypivalic acid, malic acid, tartaric acid and citric acid. When hydroxy acids are used, the reaction is preferably carried out without catalyst, so that the undesired reaction of the hydroxyl groups with the epoxy groups is minimized. Useful polyacids include tricarballylic acid, adipic acid, azelaic acid, trimellitic anhydride, citric acid, malic acid, tartaric acid, bisphenol F and bisphenol A. A polyepoxide can also be reacted with a hydroxy acid or a polyacid, although in the case of the polyacid / polyepoxide reaction, the starting materials and the reaction conditions should be controlled in order to avoid any undesired branching or spreading of the chain, which could result in compounds with a high molecular weight, which could increase the volatile organic content (VOC) or cause gelation. Polyepoxides can also be reacted with monofunctional acids, such as benzoic acid, pivalic acid, octanoic acid, Versatic® acid, butyric acid, dodecanoic acid or benzophenol. The compound (A) (1) is reacted with a compound (A) (2) to form the compound (A) with carbamate functionality. In one embodiment, (A) (2) is cyanic acid, which can be formed by the well-known reaction of thermal decomposition of urea or by other methods, such as those described in US Patents 4,389,386 or 4,364,913. . In another embodiment, (A) (2) is a compound comprising a carbamate group. In this embodiment, it is believed that the reaction between (A) (1) and (A) (2) is a transesterification between the OH groups in (A) (1) and the carbamate ester in the compound (A) (2) . The carbamate in the compound (A) (2) can be any compound having a carbamate group capable of having a transesterification with the hydroxyl groups in the component (A) (1). These include, for example, methyl carbamate, butyl carbamate, propyl carbamate, 2-ethylhexyl carbamate, cyclohexyl carbamate, phenyl carbamate, hydroxypropyl carbamate, hydroxyethyl carbamate, and the like. Useful carbamate compounds can be characterized by the formula: R'-0- (C = 0) -NHR "where R 'is substituted or unsubstituted alkyl (preferably 1-8-carbon atoms), and RM is H, substituted or unsubstituted alkyl (preferably of 1-8 carbon atoms), substituted or unsubstituted cycloalkyl (preferably of 6-10 carbon atoms), or substituted or unsubstituted aryl (preferably of 6-10 carbon atoms). , R "is H. The transesterification reaction between the compounds (A) (1) and (A) (2) can be performed under typical transesterification conditions, for example, temperatures from room temperature to 150aC with transesterification catalysts, such as calcium octoate, metal hydroxides (e.g., KOH) , Group I and II metals (eg, Na, Li), metal carbonates (eg, K2C03) that could be improved by use in combination with crown ethers, metal oxides (eg, dibutyltin oxide), metal alkoxides ( for example, Na0CH3), A1 (0C3H7) 3), metal esters (eg, stannous octoate, calcium octoate) or protic acids (eg, H2S04), MgC03 or Ph4SbI. The reaction can also be carried out at room temperature, with a polymer-supported catalyst, such as Amberlyst-15® (Rohm &Haas), as described by R. Anand, Synthetic Communications, 24 (19), 2743-47 (1994), the revelation of which is incorporated herein by reference. The opening of the oxirane ring of an epoxide compound by a carboxylic acid results in a hydroxyester structure. Subsequent transesterification of the hydroxyl group in that structure, by the carbamate in the compound (A) (2) results in a component with carbamate functionality that can be represented by any of the structures: or a combination of these, where n is an integer of at least 1; Rx represents H, alkyl or cycloalkyl; R 2 represents alkyl, aryl or cycloalkyl; and X represents an organic radical that is a residue of the epoxide compound. As used herein, it is to be understood that these alkyl, aryl or cycloalkyl groups can be substituted. For example, when a monoepoxide is reacted with a polyacid, R 2 in the structures indicated above would represent the polyacid residue, and would be replaced by another carbamate group (s) resulting from the other acid groups in the polyacid reacting with the monoepoxide, followed by transesterification with the carbamate in the compound (A) (2).

The composition of the invention is cured by a reaction of the compound (A) with carbamate functionality with a component (B) which is a compound having a plurality of functional groups that are reactive with the carbamate groups in the component (A) . Among said reactive groups are active methylol or methylalkoxyl groups in aminoplast crosslinking agents or in other compounds, such as phenol / formaldehyde adducts, siloxane or silane groups and anhydride groups. Examples of compounds (B) include melamine formaldehyde resin (including monomeric or polymeric melamine resin and partially or fully alkylated melamine resin), urea resins (eg, methylolureas, such as ureaformaldehyde resin, alkoxyurea, as butylated urea-formaldehyde resin), N-methylolacrylamide emulsions, isobutoxymethylacrylamide emulsions, polyanhydrides (e.g., polysuccinic anhydride) and siloxanes or silanes (e.g., dimethyldimethoxysilane). Aminoplast resins, such as melamine formaldehyde resin or ureaformaldehyde resin are particularly preferred. Also useful are aminoplast resins, where one or more of the amine nitrogens is substituted with a carbamate group for use in a process with a curing temperature of less than 150 ° C, as described in U.S. Patent 5,300,328. UU A solvent could optionally be used in the coating composition used in the practice of the current invention. The coating composition, according to the present invention, can be applied without solvent, especially if the degree of chain extension of the component (A) is limited. However, in many cases, it is desirable to also use a solvent in the coating composition. This solvent must act as a solvent, both in relation to the compound (A) with carbamate functionality, and with the component (B). In general, depending on the solubility characteristics of the components (A) and (B), the solvent can be any organic solvent and / or water. In a preferred embodiment, the solvent is a polar organic solvent. More preferably, the solvent may be polar aliphatic solvents or polar aromatic solvents. Still more preferably, the solvent is a ketone, ester, acetate, aprotic amide, aprotic sulfoxide or aprotic amine. Examples of useful solvents include ethyl ethyl ketone, methyl isobutyl ketone, amyl acetate, ethylene glycol butyl ether acetate, propylene glycol monomethyl ether acetate, xylene, N-methylpyrrolidone or mixtures of aromatic hydrocarbons. In another embodiment, the solvent may be water or a mixture of water with cosolvents. The coating composition used in the practice of the invention could include a catalyst for increasing or accelerating the curing reaction. For example, when the compounds to non-plastics, particularly the monomeric melamines, are used as component (B), then a strong acid catalyst can be used to increase or accelerate the curing reaction. Such catalysts are well known in the art and include, for example, toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, dodecylbenzenesulfonic acid, phenyl acid phosphate, monobutyl maleate, butyl phosphate and hydroxyphosphate ester. Other catalysts that could be useful in the composition of the invention are Lewis acids, zinc salts and tin salts. Although a solvent may be present in the coating composition, in an amount of between about 0.01 percent, by weight, to about 99 percent, by weight, it is preferably present in an amount of less than 30%, more preferably less. of 20%, and most preferably less than 10%. The coating composition preferably has a VOC (VOC is defined herein as the VOC according to ASTM D3960) of less than 3.8 pounds / gallon (455 kg / m3), more preferably less than 3.0 pounds / gallon (359 kg / m3) ), still more preferably less than 2.0 pounds / gallon (240 kg / m3) and most preferably less than 1.0 pounds / gallon (120 kg / m3). The coating compositions can be coated on the article by any of a number of techniques well known in the art. These include, for example, spray coating, dip coating, roller coating, curtain coating and the like. For car body panels, spray coating is preferred. An advantage that can be obtained with the coating compositions, according to the invention, is that coatings with a high degree of flexibility can be prepared. Therefore, in a preferred embodiment, the substrate on which the coating is applied is flexible, such as plastic, leather or fabric substrates. Any additional agent used, for example, surfactants, fillers, stabilizers, wetting agents, dispersing agents, adhesion promoters, ultraviolet light absorbers, light stabilizers of the clogged amine, etc., could be incorporated into the coating composition. Although the agents are well known in the art, the amount used must be controlled to avoid adversely affecting the characteristics of the coating. In a preferred embodiment, the coating composition, according to the invention, is preferably used in a high gloss coating and / or as the clear coat of a colored composite coating plus clear coat. High gloss coatings, as used herein, are coatings with a gloss of 20B (ASTM D523-89) or an image sharpness (DOI) (ASTM E430-91) of at least 80. In other preferred embodiments, you can use the coating composition to prepare enamel or low gloss or high gloss coatings. When the coating composition of the invention is used as a pigmented paint coating with high gloss, the pigment can be any organic or inorganic compound, or fillings or colored materials, metallic materials or other materials with inorganic flakes, such as mica or aluminum flakes, and other materials of the type that the guild normally calls pigments. The pigments are generally used in the composition in an amount of 2% to 350%, based on the total weight (not including the solvent) of components A and B (for example, a P: B ratio of 0.02 to 3.5) . When the coating composition, according to the invention, is used as the transparent layer of a colored composite coating plus transparent layer, the composition of the pigmented base layer could be any of a number of well-known types in the trade, and it does not require that it be explained in detail here. The polymers known in the art to be useful in basecoat compositions include acrylics, vinyls, polyurethanes, polycarbonates, polyesters, alkyd compounds and siloxanes. Among the preferred polymers are acrylics and polyurethanes. In a preferred embodiment of the invention, the composition of the base layer also uses an acrylic polymer with carbamate functionality. The base layer polymers preferably have crosslinking capability and, therefore, include one or more types of crosslinkable functional groups. Such groups include, for example, hydroxyl, isocyanate, amine, epoxy, acrylate, vinyl, silane and acetoacetate groups. These groups could be hidden or blocked in such a way that they are unblocked and available for the crosslinking reaction under the desired curing conditions, generally at elevated temperatures. Among the useful functional groups with cross-linking ability are the hydroxyl, epoxy, acid, anhydride, silane and acetoacetate groups. Among the preferred functional groups with crosslinking capability are the hydroxyl functional groups and the amine functional groups. The polymers of the base layer could have self-crosslinking capability, or they could require a separate crosslinking agent that is reactive with the functional groups of the polymer. When the polymer includes hydroxyl functional groups, for example, the crosslinking agent could be an aminoplast resin, isocyanates and isocyanates with blocking (including isocyanurates), and crosslinking agents with acid functionality or anhydride functionality. The coating compositions described herein are preferably subjected to conditions for the coating layers to cure. Although various curing methods may be used, heat curing is preferred. Generally, heat curing is effected by exposing the coated article to elevated temperatures provided primarily by sources of radioactive heat. Curing temperatures will vary, depending on the particular blocking groups used in the crosslinking agents; however, they are generally in a range between 93 BC and 177 BC. The coating composition, according to the present invention, is curable even at relatively low curing temperatures. Therefore, in a preferred embodiment, the curing temperature is preferably between 115BC and 150BC, and more preferably at temperatures between 115BC and 138BC for a blocked acid catalyzed system. For an acid catalyzed system without blocking, the curing temperature is preferably between 82 BC and 99 BC. The curing time will vary, depending on the particular components used and the physical parameters, such as the thickness of the layers; however, typical curing times have a range of 15 to 60 minutes and preferably 15-25 minutes for acid catalyzed systems with blocking and 10-20 minutes for systems catalyzed with acid without blocking. In various embodiments in the current invention, the curable coating composition, when cured, can result in coatings having a surprising combination of high crosslinking density without being brittle. As used herein, the crosslink density is determined, as described in "Paint and Coatings Testing Manual," Gardner-Sward Handbook, Gardner-Sward Manual, 14th ed. , chapter 46, p. 534, ASTM, 1995. Therefore, an embodiment of the invention is directed toward a cured coating derived from the curable coating compositions described above, with a crosslinking density of at least 3, and preferably, at least 10. The invention is further described in the following examples.

Preparation 1 In the first step, 120 parts of dimethylolpropionic acid (DMPA), an aliquot of 25% of the stoichiometric ratio, was charged with 943 parts of glycidyl neodecanoate Glydexx® N-10 to a reaction vessel. The mixture was heated to a temperature of 128BC. After a slight exothermic reaction, three more 25% increments of 120 parts of DMPA were added, spaced over a period of 4 hours, and the temperature was maintained at 130 ° C. The reaction was monitored by means of the acid number, at a value of < 3 and did not contain any residual epoxy group. In step two, 1211 parts of methyl carbamate, an excess of 50%, were added together with 10 parts of dibutyltin oxide catalyst and 950 parts of toluene. A reflux temperature of 109-117BC was maintained for 32 hours as the methanol was removed. The progress of the reaction was monitored by the hydroxyl number to at least 95% of the termination. Excess methyl carbamate and solvent were removed and 450 parts of amyl acetate was added to reduce to a non-volatile content of 80%. Preparation 2 In the first step, 89 parts of citric acid, an aliquot of 25% of the stoichiometric ratio, was charged with 1470 parts of glycidyl neodecanoate Glydexx® N-10 to a reaction vessel. The mixture was heated to a temperature of 128 BC.

After a slight exothermic reaction, three more than 25% increments of 89 parts of citric acid were added, spaced over a period of 4 hours, and the temperature was maintained at 130BC. The reaction was monitored by means of the acid number, at a value of < 3 and did not contain any residual epoxy group. In step two, 840 parts of methyl carbamate, an excess of 50%, were added together with 12.8 parts of dibutyltin oxide catalyst and 1200 parts of toluene. A reflux temperature of 109-117 aC was maintained for 32 hours as the methanol was removed. The progress of the reaction was monitored by the hydroxyl number to at least 95% of the termination. Excess methyl carbamate and solvent were removed and 425 parts of amyl acetate were added to reduce to a non-volatile content of 80%. Example 1 A coating composition was prepared, by mixing 84 parts of the product of Preparation 1, with 27 parts of a commercial liquid hexamethoxymethylmelamine resin. In addition, 4 parts of blocking dodecylbenzenesulfonic acid catalyst were added, together with 22 parts of amyl acetate, to yield a coating composition with a non-volatile content of 61%, by weight. The coating composition was sprayed on a panel, on a conventional high-solids basecoat, containing a hydroxyl-functional acrylic polymer and a melamine resin curing agent, and cured for 20 minutes, at a temperature of 132BC metal. The resulting coating exhibited good film properties as measured by moisture resistance, solvent resistance, hardness, resistance to degradation, gravametry and weathering resistance. Example 2 A coating composition was prepared, by mixing 97 parts of the product of Preparation 2, with 19 parts of a commercial liquid hexamethoxymethylmelamine resin. In addition, 4 parts of blocked dodecylbenzenesulfonic acid catalyst were added, along with 20 parts of amyl acetate, to yield a coating composition with a non-volatile content of 64%, by weight. The coating composition was sprayed on a panel, on a conventional high-solids basecoat, containing a hydroxyl-functional acrylic polymer and a melamine resin curing agent, and cured for 20 minutes, at a temperature of metal of 132 BC. The resulting coating exhibited good film properties as measured by moisture resistance, solvent resistance, hardness, resistance to degradation, gravametry and weathering resistance. The invention has been described in detail in relation to preferred embodiments thereof. However, it should be understood that variations and modifications may be made within the spirit and scope of the invention.

Claims (15)

1. CLAIMS: . A curable coating composition comprising: (A) a carbamate functional component, which is the reaction product of: (1) a compound comprising a plurality of hydroxyl groups, at least one of which is the result of a ring opening reaction between an epoxy group and an organic acid group, and (2) cyanic acid or a compound comprising a carbamate group, and (B) a component comprising a plurality of groups that are reactive with the groups with carbamate functionality in component (A).
2. 2. A curable coating composition according to claim 1, wherein said compound (A) (1) (a) comprises a plurality of hydroxyl groups which are the result of the ring opening reaction between an epoxy group and a carboxyl group.
3. 3. A curable coating composition, according to claim 1, wherein said compound with carbamate functionality is represented by any of the structures: or a combination of these, where n is an integer of at least 1; Rx represents H, alkyl or cycloalkyl; R 2 represents alkyl, aryl or cycloalkyl; and X represents an organic radical.
4. 4. A curable coating composition according to claim 3, wherein n is a positive integer of at least 2. A curable coating composition according to claim 3, wherein n is a positive integer of 2 to 6. 6. A curable coating composition according to claim 1, wherein at least two of said hydroxyl groups are the result of a ring opening reaction between an epoxy group and a carboxyl group. 7. A curable coating composition, according to claim 1, having a volatile organic content (VOC) of less than 3.8 lbs / ft3 (455 kg / m3). 8. A curable coating composition, according to claim 7, having a volatile organic content (VOC) of less than 3.0 pounds / ft3 (359 kg / m3). 9. A curable coating composition, according to claim 8, having a volatile organic content (VOC) of less than 2.0 pounds / ft3 (240 kg / m3). 10. A curable coating composition, according to claim 9, having a volatile organic content (VOC) of less than 1.0 pounds / ft3 (120 kg / m3). 11. A curable coating composition, according to claim 1, wherein the component (B) is an aminoplast resin. 12. A curable coating composition, according to claim 11, wherein said aminoplast resin is a melamine resin. 13. A curable coating composition, according to claim 1, wherein said organic acid group is a carboxyl group. 14. A curable coating composition, according to claim 1, wherein said compound (A) (2) is cyanic acid. 15. A curable coating composition, according to claim 1, wherein said compound (A) (1) is a compound comprising a carbamate group. A cured coating composition, comprising the reaction product of a coating composition according to claim 1. A cured coating, according to claim 16, having a crosslinking density of at least 3. A cured coating, according to claim 17, with a crosslink density of at least 10. A coating, according to claim 16, with a gloss of 20B, as defined by ASTM D523-89, of at least 80. A coating , according to claim 16, with an image sharpness (DOI), as defined by ASTM E430-91, of at least 80. A colored composite coating plus transparent layer, wherein the transparent layer is derived from a composition of coating according to claim 1.