MXPA96004181A - Coatings containing hydrazine compounds, to have a better durabili - Google Patents

Abstract

A coating composition comprising: a) a polymer having at least one functional group that is reactive with a crosslinking agent, b) a crosslinking agent, c) a hydrazide group that is attached to polymer a), crosslinking agent b), or part of a compound other than a) or b). The base coat, the clear coat and the coatings of colored compounds plus clear coat comprising the composition described above provide a good resistance to surface degradation, caused by exposure to ultraviolet or visible light, or to severe exposure conditions. outdoor. In the same way, the coatings show a good retention of the sharpness of the image (DOI) and brightness, under an extended and severe exposure to the elements. When a hydrazide compound is used in a transparent layer of a coating of colored compound plus transparent layer, good inter-layer adhesion is obtained. One method for improving the resistance that a cured film has to environmental degradation comprises applying, to a substrate, a coating composition which is a base layer or a transparent layer comprising the coating composition described above.

Description

COATINGS CONTAINING HYDRAZIDE COMPOUNDS, TO HAVE A BETTER DURABILITY Field of the Invention The present invention relates to coating compositions that include hydrazide compounds. More specifically, the present invention relates to automotive coating compositions containing hydrazide compounds, for better durability on the outside, and methods for obtaining cured films having better durability.

BACKGROUND OF THE INVENTION Coatings for automotive applications frequently use a colored composite coating composition plus clear coat. The color layer composition comprises a composition of a pigmented base layer, which could include a crosslinking agent. The clearcoat composition is applied over the basecoating composition and may comprise a one component or two component coating composition. The coating composition of a component typically includes an aminoplast or an isocyanate crosslinking agent with blocking. Typically, the two component coating composition includes an isocyanate crosslinking agent without blocking. A color composite film plus transparent layer is formed when at least the first layer of a basecoat composition is applied to a substrate, and a clearcoat composition is applied over the basecoat. The layers can be cured simultaneously or sequentially to form a cured film, which is called a colored composite film plus transparent layer. When exposed to severe weathering conditions, colored composite films plus clearcoat, clearcoat or cured basecoat sometimes exhibit severe surface degradation and delamination problems. Although it is well known that ultraviolet radiation causes degradation of cured coating films, tests indicate that even visible light can stimulate rapid degradation of cured pigmented basecoat compositions. The current invention relates to coating compositions that result in cured films that demonstrate improved resistance to surface degradation and methods to minimize surface degradation of cured films, particularly color composite films plus clear coat .

Summary of the Invention The present invention is a coating composition comprising: a) a polymer having at least one functional group that is reactive with a crosslinking agent; b) a crosslinking agent; c) a hydrazide group that is linked to polymer a), crosslinking agent b), or part of a compound other than a) or b). Another embodiment of the invention relates to a method of preparing a coating in which the composition described above is applied to a substrate and baked to form a cured film. Yet another embodiment of the invention provides a method for improving the strength that a cured film has to degradation, comprising coating a substrate with a base layer or clear layer comprising the coating composition described above, or forming a composite film of more color. transparent layer, using a transparent layer or base layer comprising the coating composition described above. The base coat, the clear coat and the coatings of colored compounds plus clear coat comprising the composition described above provide a good resistance to surface degradation, caused by exposure to ultraviolet or visible light, or to severe exposure conditions. outdoor. The coatings show a good retention of image sharpness (DOI) and brightness, under extended and severe exposure to the weather. When a hydrazide compound is used in a transparent layer of a coating of colored compound plus transparent layer, good inter-layer adhesion is obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENT The coating composition of the present invention comprises a polymer having at least one functional group that is reactive with a crosslinking agent, an appropriate crosslinking agent and a hydrazide group that is attached to the polymer, the crosslinking agent, or a compound other than the polymer or crosslinking agent. Polymers useful for forming the coating composition include, for example, acrylic polymers, modified acrylic polymers, polyesters, polyepoxides, polycarbonates, polyurethanes, polyamides, polymers, polysiloxanes and carbamate polymers. When the acrylic polymers are used, said polymers can be prepared from monomers, such as acrylic acid and methacrylic acid, methacrylates and alkyl and cycloalkyl acrylates having from 1 to 18 carbon atoms, preferably from 4 to 13 carbon atoms, in the alkyl or cycloalkyl portion, or mixtures of said monomers. Examples of these include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, and 2-methacrylate. ethylhexyl. The reactive functionality in the acrylic polymer can be incorporated by reacting functional monomers having carboxyl, hydroxyl, epoxy, amino and alkylamino functional groups. Among the carboxyls containing monomers are acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, 2-acryloxymethoxy-O-phthalic acid and 2-acryloxy-1-methylethoxy-0-hexahydrophthalic acid. Among the hydroxyl functional monomers are 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, allyl alcohol and metal alcohol. Among the epoxy-functional monomers is glycidyl methacrylate. Examples of methacrylates and alkylamino acrylates include methacrylates and acrylates of aminomethyl, aminoethyl, aminopropyl, aminobutyl and aminohexyl, dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate. Other suitable monomers include: N-alkoxymethylacrylamide monomers, such as N- (methoxymethyl) acrylamide, N- (propoxymethyl) acrylamide, N-isopropoxiraethylacrylamide and N- (butoxymethyl) acrylamide. Other ethylenically unsaturated monomers, such as vinyl, styrene, α-methylstyrene, vinyltoluene and t-butylstyrene could also be included to provide the desired physical characteristics. Modified acrylics such as acrylic polymer can also be used. Examples of these include acrylics modified with polyester or acrylics modified with polyurethane, which are well known in the trade. An example of a preferred acrylic modified with polyester is an acrylic polymer modified with α-caprolactone. Said polyester-modified acrylic is described in U.S. Pat. UU No. 4,546,046 issued to Etxell et al. Polyurethane-modified acrylics are well known in the trade. An example is set forth in U.S. Pat. UU No. 4,584,354, the disclosure of which is incorporated herein by reference. Polyesters having hydroxyl groups, acid groups or amino groups like the reactive groups, can also be used as the polymer in the composition, according to the invention. Said polyesters are well known in the trade, and can be prepared by the polyesterification of organic polycarboxylic acids (for example, phthalic acid, hexahydrophthalic acid, adipic acid, aleic acid) or their anhydrides with organic polyols containing primary or secondary hydroxyl groups . The polyurethanes useful as the polymer of the present invention can be prepared by reacting a polyisocyanate and a polyol with an equivalent ratio of OHtNCO greater than 1: 1., to obtain polyurethanes with terminal hydroxyl functionality. In this case, the isocyanate coating occurs simultaneously with the synthesis of the polyurethane resin. Alternatively, the polyurethane can be formed by reacting the polyisocyanate and the polyol with an OH: NCO ratio of less than 1: 1. In this case, where excess isocyanate is used, the polyurethane having unreacted isocyanate functionality is then reacted with a cover agent. Suitable reagents include amines or reactive alcohols. Examples of these are trimethylolpropane, ethanolamine, diethanolamine, Sol etal, diols, triols or a mixture of diols and triols. In order to form a cured coating, one or more of the polymers described above are crosslinked using a one component system or a two component system. In a one component system, the polymer is combined with a crosslinking agent to form a stable paint system at storage temperatures. In a two component system, the polymer and crosslinking agent are kept separate until just before application or at the time of application of the composition. The crosslinking agent should have at least two functional sites that are reactive with the polymer, and the crosslinking agent can be either monomeric or polymeric in nature. Examples of materials used as crosslinking agents include aminoplast crosslinking agents, polyepoxides, polyacids, polyols, polyisocyanates and any compatible mixture thereof. Aminoplast crosslinking agents are condensation products of aldehyde, melamine, glycoluril, urea, benzoguanamine or a similar compound. They can be soluble in aqueous or organic solvents. Generally, the aldehyde used is formaldehyde, although useful products can be prepared from other aldehydes, such as acetaldehyde, benzaldehyde and others. Melamine or urea condensation products are the most common and preferred, but products of other amines and amides in which at least one amine group may be present may also be used. These aldehyde condensation products contain methylol groups or similar alkylol groups, depending on the particular aldehyde used. If desired, these methylol groups can be etherified by reaction with an alcohol. Various alcohols are used for this purpose, including essentially a monohydric alcohol, although the preferred alcohols are methanol, butanol and similar lower alkanols having 8 carbon atoms or less. The aminoplast crosslinking agent may be monomeric or polymeric. A preferred crosslinking agent, which provides a high quality finish, is hexametoxymethylmelamine (obtainable as Cymel 303, sold by American Cyanamid, of Wayne, NJ), especially for high solids coating compositions. Preferably, a polymeric melamine is used as a crosslinking agent for compositions to be applied over water-based underlays. Another useful resin is a methoxy / butoxymethylmelamine (obtainable as Resimene 755 from Monsanto Chemical Co., of Springfield, MA). Suitable polyisocyanate crosslinking agents for use in a two component coating composition, according to the present invention, include, without limitation, toluene diisocyanate, toluene diisocyanate isocyanurates, 4,4'-diphenylmethane diisocyanate , isocyanurates of 4,4 * diphenylmethane diisocyanate, methylenebis-4,4'-isocyanatocyclohexane, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, isocyanurates of isophorone diisocyanate, 1,4-cyclohexane diisocyanate, diisocyanate -phenylene, 4,4 ', 4"-triphenylmethane triisocyanate, tetramethylxylene diisocyanate, metaxylene diisocyanate, dicyclohexylmethane, 1,3-bis (2-isocyanato-2-propyl) benzene diisocyanate (TMXDI). Another embodiment of the present invention is a one component coating composition, which uses an isocyanate crosslinking agent, reacted with one or more dialkyl malonates, acetoacetate or a mixture thereof. The crosslinking reaction using these isocyanate crosslinking agents occurs by reaction of the functional groups of the polymer with the diethyl malonate or acetoacetate in the crosslinking agent, rather than by reaction of the functional groups in the polymer with the isocyanate groups in the crosslinking agent. The acetoacetate or diethyl malonate group of the crosslinking agent goes through a transesterification reaction with the hydroxyl, carboxyl, epoxy, isocyanate, amino or other functionality in the polymer. For this embodiment of the invention optimum results are obtained when at least 50 percent, preferably at least 70 percent, of the isocyanate groups of the polyisocyanate or of the mixture of polyisocyanates are reacted with the malonates, acetoacetate or mixtures of these. The remaining isocyanate groups are reacted with compounds containing hydroxyl groups which are preferably cycloaliphatic or aliphatic polyols with low molecular weight, such as neopentyl glycol, dimethylolcyclohexane, ethylene glycol, diethylene glycol, propylene glycol, 2-methyl-2-propylpropane-3, diol, 2-ethyl-2-butylpropane-l, 3-diol, 2,2,4-trimethylpentane-1, 5-diol and 2,2,5-trimethylhexane-1,6-diol or synthetic resins containing groups of hydroxyl which can be used as polymer (a). Any polyisocyanate that is used for coatings can be used for the preparation of the isocyanate. However, it is preferred to use polyisocyanates whose isocyanate groups are attached to aliphatic or cycloaliphatic radicals. Examples of such polyisocyanates are hexamethylene diisocyanate, isophorone diisocyanate, trimethylhexaethylene diisocyanate, dicyclohexylmethane diisocyanate and 1,3-0bis (2-isocyanato-2-propyl) benzene (TMXDI) and adducts thereof, polyisocyanates. with polyols, in particular low molecular weight polyols, for example, trimethylolpropane and polyisocyanates which are derived from these polyisocyanates and contain isocyanurate groups and / or biuret groups. Particularly preferred isocyanates are hexamethylene diisocyanate and isophorone diisocyanate, polyisocyanates which are derived from these diisocyanates, contain isocyanurate or biuret groups, and preferably contain more than two isocyanate groups per molecule, and the reaction of hexamethylene diisocyanate and isophorone diisocyanate, or a mixture of hexamethylene diisocyanate and isophorone diisocyanate containing 0.3-0.5 equivalents of a low molecular weight polyol, having a molecular weight between 62 to 500, preferably between 104 to 204, particularly a triol, for example timethylolpropane. Among the examples of dialkyl malonates which can be used are dialkyl malonates having the β carbon atoms in each of the alkyl radicals, for example dimethyl malonate and diethyl malonate, and it is preferred to use the malonate of diethyl Among the preferred acetoacetates are alkyl acetoacetates having from 1 to 6 carbon atoms in the alkyl portion or a mixture of said alkyl acetoacetates. Another suitable coating composition, according to the present invention, includes a carbamate functional polymer, appropriate crosslinking agent and a hydrazide group that is attached to the polymer, the crosslinking agent or a compound other than the polymer or the crosslinking agent. cross-linking Suitable polymers with carbamate functionality can be prepared from an acrylic monomer having a carbamate functionality in the ester portion of the monomer. These monomers are well known in the guild and are described, for example, in U.S. Pat. 3,479,328, 3,674,838, 4,126,747, 4,279,833 and 4,340,497, the disclosures of which are incorporated herein by reference. A synthetic method includes the reaction of a hydroxy ester with urea to form the carbamyloxy carboxylate (for example, carbamate modified acrylate). Another synthetic method reacts an unsaturated acid ester a and β, with a carbamate hydroxy ester, to form the carbamyloxy carboxylate. Another additional technique includes the formation of hydroxyalkyl carbamate by reacting a primary or secondary diamine or amine with a cyclic carbonate, such as ethylene carbonate. The hydroxyl group in the hydroxyalkyl carbamate is then esterified by reacting with an acrylic or methacrylic acid to form the monomer. Other methods of preparing acrylic monomers modified with carbamate are described in the guild and can also be used. Then, the acrylic monomer can be polymerized together with the other ethylenically unsaturated monomers, if desired, by techniques well known in the art. An alternative method for preparing the polymer (a) used in the composition of the invention is to react an already formed polymer, such as an acrylic polymer, with another component, to form a group with carbamate functionality attached to the polymer structure, according to is described in U.S. Pat. 4,758,632, the disclosure of which is incorporated herein by reference. A technique for preparing polymers useful as component (a) includes the thermal decomposition of urea (to release ammonia and HNCO) in the presence of a hydroxyl-functional acrylic polymer, to form an acrylic polymer with carbamate functionality. Another technique includes reacting the hydroxyalkyl carbonate hydroxyalkyl group with the isocyanate group of an isocyanate-functional vinyl or acrylic monomer to form the carbamate-functional acrylic. Acrylics with isocyanate functionality are known in the trade and are described, for example, in U.S. Pat. 4,301,257, the disclosure of which is incorporated herein by reference. Vinyl-substituted isocyanate monomers are well known in the trade and include isopropenyl-a, o-dimethylbenzyl isocyanate (which American Cyanamid sells as TMI®). Another additional technique is to react with ammonia the cyclic carbonate group of an acrylic with cyclic carbonate functionality, in order to form the acrylic with carbamate functionality. Acrylic polymers with cyclic carbonate functionality are known in the trade and are described, for example, in U.S. Pat. 2,979,514, the disclosure of which is incorporated herein by reference. A more difficult, but feasible, way to prepare the polymer would be to transesterify an acrylate polymer with a hydroxyalkyl carbamate. The polymer (a) will generally have a molecular weight of 2000-20,000, and preferably of 4000-6000. The molecular weight can be determined by the gas phase chromatography method, using a polystyrene standard. The carbamate content of the polymer, at a molecular weight per equivalent of carbamate functionality, will generally be between 200 and 1500, and preferably between 300 and 500. The vitreous transition temperature, Tg, of component (a) can be adjusted to obtain a cured coating having the Tg for the particular application in question. The average Tg of the unreacted component (a) must be between 10aC and 80ßC, and the individual Tg's are adjusted to obtain the optimum performance. The component (a) of the polymer can be represented by the units repeated at random, according to the following formula: In the formula indicated above, R: represents H or CH3. represents H, alkyl, preferably of 1 to 6 carbon atoms, or cycloalkyl, preferably of up to 6 carbon atoms in the ring. It is to be understood that the terms alkyl and cycloalkyl include substituted alkyl and cycloalkyl, such as cycloalkyl or alkyl substituted by halogen. However, substituents that will have an adverse impact on the properties of the cured material should be avoided. For example, it is thought that ether bonds are susceptible to hydrolysis, and should be avoided at sites that would place the ether link in the crosslinking matrix. The values x and y represent percentages of weight, where x is from 10 to 90% and preferably from 40 to 60%, and y is from 90 to 10% and preferably from 60 to 40%. In the formula, A represents repeated units derived from one or more monomers with unsaturated ethylene. Such monomers are known in the trade for copolymerization with acrylic monomers. These include alkyl esters of acrylic or methacrylic acid, for example, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, isodecyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and the like; and vinyl monomers such as meta-isopropenyl-a, a-dimethylbenzyl isocyanate (which American Cyanamid sells as TMI®), styrene, vinyltoluene and the like. L represents a divalent linking group, preferably an aliphatic of 1 to 8 carbon atoms, cycloaliphatic or aromatic linking group of 6 to 10 carbon atoms. Examples of L include: - (CH2) -, - (CH2) 2-, - (CH2) - and the like. In a preferred embodiment, -L- is represented by -COO-L1-, where L 'is a divalent linking group. Therefore, in a preferred embodiment of the invention, the polymer component (a) is represented by repeating units at random, according to the following formula: In this formula, RL, R2, A, x and y are as defined above. L1 can be a divalent aliphatic linking group, preferably 1 to 8 carbon atoms, for example, - (CH2) -, - (CH2) 2-, - (CH2) 4- and the like, or a cycloaliphatic linking group divalent, preferably up to 8 carbon atoms, for example, cyclohexyl and the like. However, other divalent linking groups can be used, depending on the technique used to prepare the polymer. For example, if a hydroxyaluyl carbamate adduct is formed on an acrylic polymer with isocyanate functionality, then the linking group L 'would include a urethane linkage -NHCOO- as a residue of the isocyanate group. The composition of the invention is cured by a reaction of the polymer (a), with carbamate functionality, with a crosslinking agent (b) which is a compound having a plurality of functional groups that are reactive with the carbamate groups of the component (to) . Among said reactive groups are active groups of methylalkoxy or methylol in aminoplast crosslinking agents or in other components, such as phenol / formaldehyde adducts, isocyanate groups, siloxane groups, cyclic carbonate 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 ureafor aldehyde resin, alkoxyureas, such as butylated urea-formaldehyde resin), polyanhydrides (for example polysuccinic anhydride), and polysiloxanes (for example, tri-ethoxysiloxane).

Aminoplast resins, such as melamine formaldehyde resin or ureaformaldehyde resin, are especially preferred. Even more preferred are aminoplast resins, where one or more of the amino nitrogens is substituted with a carbamate group for use in a process with a curing temperature of less than 150BC, as described in U.S. Pat. UU No. 5,300,328. The coating composition of the present invention also includes a hydrazide group. The hydrazide group can be attached to either the polymer (a), the polyisocyanate (b) or can be part of a compound other than (a) or (b). In a preferred embodiment of the invention, the hydrazide group has the formula: where Ri and R2 each independently represents H or substituted or unsubstituted alkyl. Compounds containing one or more hydrazide groups are well known in the art. They are described, for example, in C. Clark, Hydrazine. Matheson Chemical Corp., Baltimore, 1953, the disclosure of which is incorporated herein by reference. In one embodiment, the compound containing the hydrazide group also comprises an obstructed amine group, as is frequently found in compounds known as light stabilizer compounds of the clogged amine (HALS). An example of said compound has the formula: In another embodiment, the compound containing the hydrazide group has the formula: wherein R3 and R4 each independently represents H or substituted or unsubstituted alkyl, and R5 represents substituted or unsubstituted alkyl, substituted or unsubstituted aryl, or , where L represents a divalent linking group, -NH or -0-. The linking group is preferably aliphatic, but could also be aromatic, cycloaliphatic or heterocyclic. Preferably, at least one of R3 and R4, and at least one of R6 and R represents hydrogen. In another preferred embodiment, all R3r R4, R5 and R6 represent hydrogen. The compounds containing the hydrazide group can be prepared from aliphatic organic acids, such as acetic acid, propionic acid, n-octanoic acid, adipic acid, oxalic acid, sebacic acid and the like. The acid groups are typically reacted with hydrazide, as known in the art, to produce the acid hydrazide derivative. For purposes of the present invention, a preferred compound containing a hydrazide group is adipic dihydrazide. Examples of useful compounds other than (a) or (b) comprising hydrazide groups include: Compounds Formula Hydrazides R (-C0-NH-NH2) n Bis-hydrazides NH2-NH-C0-NH-NH2 Semicarbazides R-NH-CO-NH-NH2 Thiohydrazides R (-CS-NH-NH2) n Thiosemicarbazides R-NH -CS-NH-NH2 According to the formulas indicated above for the compounds containing a hydrazide group, n is a positive integer of at least 1. In a preferred embodiment, n = 2. R can be hydrogen (except for hydrazides or thiohydrazides, where n is 1) or an organic radical. Useful organic radicals include aliphatic, cycloaliphatic, aromatic or heterocyclic groups, preferably from 1 to 20 carbon atoms. The R groups should be free of substituents that are reactive with the hydrazide groups. The polyhydrazides (for example, hydrazides or thiohydrazides, as shown above, where n = 2) can be used to incorporate hydrazide groups into the polymer (a) or the crosslinking agent (b). This can be done by reacting one of the hydrazide groups with a hydrazide reactive group in the polymer or with the polyisocyanate crosslinking agent. The hydrazide functionality can also be introduced by reacting hydrazide with a polyisocyanate crosslinking agent. The polyhydrazide can be reacted in the polymer (a), by reacting a polyhydrazide with a polyester or acrylic polymer having anhydride or epoxy. Alternatively, the hydrazide can be reacted with acid groups in an acrylic polymer to form a hydrazide-functional polymer. The polyhydrazide can be reacted in the crosslinking agent (b), where the crosslinking agent contains groups reactive with the hydrazide. The incorporation of the hydrazide group into the isocyanate crosslinking agent can be effected by first reacting the polyisocyanate with an amount of polyhydrazide which will leave unreacted isocyanate groups, and then covering the remaining unreacted isocyanate groups. This reaction is preferably carried out under conditions in which no significant amount of chain extension of the polyisocyanate occurs., for example, by blocking one or more of the hydrazide groups. Alternatively, this can be done by partially covering the polyisocyanate first, and then reacting all or part of the isocyanate groups that are still active with a polyhydrazide, and then covering any remaining isocyanate active group. In a preferred embodiment, the hydrazide dispersion is made as a separate component and introduced into the coating composition. The hydrazide dispersion is formed of a mixture of acrylic resin, solvent and hydrazide. The hydrazide composition is present in an amount between 0.25 and 5.0%, by weight, preferably between 0.5 and 2.0%, by weight, based on the total weight of the fixed vehicle of the coating composition. Total weight of the fixed vehicle means the total solids content of the coating composition. The coating compositions of the current invention could be base coat or clear coat compositions. The composition could be in the form of a substantially solid powder, a dispersion or in a substantially liquid state. The liquid coatings could be solvent based or water based. The coatings may also include solvents, pigments, catalysts, light stabilizers of the clogged amine, ultraviolet light absorbers, rheology control additives and other additives known to those skilled in the trade. 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. After an article is coated with the layers described above, the composition is subjected to conditions to cure the coating layers. Although various coating methods can be used, thermal curing is preferred. Generally, thermal curing is carried out by exposing the coated article to high temperatures, provided mainly by sources of heat by radiation. Curing temperatures will vary, depending on the particular blocking groups used in the crosslinking agents, but are generally within a range of 93 ° C and 177 ° C, and are preferably between 121 ° C and 141 ° C. 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 vary between 15 to 60 minutes. The current invention is illustrated by the following non-limiting examples. All the quantities indicated in the following tables are expressed as a percentage by weight, based on the total weight of the coating composition.

EXAMPLES EXAMPLES 1-4 TRANSPARENT ACRYLIC LAYER CURED WITH MELAMINE SAMPLE 1 * 2 INGREDIENT (The quantities are indicated in% by weight) ACRYLIC RESIN WITH FUNCTIONALITY 55.0 53.8 54.3 54.7 OF OH OHETHYL OXIDE "CELLOSOLVE" 0.9 0.9 0.9 0.9 N-BUTANOL 3.8 3.7 3.7 3.8 MELAMINE RESIN 15.1 14.7 14.9 15.0 SMOKE SILICA 15.7 15.3 15.5 15.6 DISPERSION OF SMOKE SILICA 4.1 4.0 4.1 4.1 ACID CATALYST 1.2 1.2 1.2 1.2 STABILIZER OF LIGHT OF THE AMINA OBSTRUCED (HALS) 0.0 0.0 0.0 0.0 FLOW ADDITIVE 0.5 0.4 0.4 0.5 LIGHT ABSORBENT ULTRAVIOLET (UVA) 0.0 0.0 0.0 0.0 POLYACRYLATE RESIN 0.8 0.7 0.7 0.7"CELLOSOLVE" BUTYL ACETATE 2.9 2.8 2.7 2.9 HIDRAZIDE DISPERSION1 2.5 1.6 0.6 TOTAL 00.0 100.0 100.0 100.0 * Comparative Example 1 The hydrazide dispersion used in Examples 2- 4, 6-8 and 11-13 has the following composition. Formulation of Hydrazide Dispersion: TABLE 1 RESULTS OF DEGRADATION, EJ. 1-4 EXAMPLES 5-8 COMPOSITIONS OF TRANSPARENT ACRYLIC LAYER WITH AGENT OF ENTRANCING OF ISOCYANATE EXAMPLE 5 * 6 7 INGREDIENT (The quantities are indicated in% by weight) ACRYLIC RESIN 47.5 46.3 46.8 47.2 POLYISOCIANATE 24.6 24.0 24.2 24.5 MELAMINE RESIN 8.2 8.0 8.0 8.1 ISOBUTANOL 4.2 4.1 4.2 4.2 PROPYLPROPASOL 3.6 3.5 3.5 3.6 OXOHEXILACETATE 7.2 7.1 7.1 7.2 ULTRAVIOLET LIGHT ABSORBENT 0.0 0.0 0.0 0.0 FLOW ADDITIVE 0.1 0.1 0.1 0.1 ACRYLIC ADDITIVE 1.2 1.1 1.1 1.1 AMINA LIGHT STABILIZER OBSTRUCED (HALS) 0.0 0.0 0.0 0.0 ISOBUTANOL 2.2 2.1 2.2 2.2 HEXAHEXILO ACETATE 1.2 1.2 1.2 1.2 HIDRAZIDE DISPERSION 2.5 1.6 0.6 TOTAL 100.0 100.0 100.0 100.0 * Comparative Example TABLE 2 DEGRADATION RESULTS, EXAMPLES 5-8 EXAMPLES 9-13 COMPOSITIONS OF TRANSPARENT ACRYLIC LAYER WITH AGENT OF ENTRECRUZAMIENTO DE ISOCI NATO EXAMPLE 9 * 10 * 11 12 13 INGREDIENT (The quantities are indicated in% by weight) ACRYLIC RESIN 48.9 47.1 47.4 47.5 48.1 BUTYL ACETATE "CELLOSOLVE" 5.1 4.9 4.9 5.0 5.0 DIISOBUTILCETONA 2.8 2.7 2.7 2.8 2.8 FLOW ADDITIVE 2.2 2.1 2.1 2.1 2.1 ABSORBENT OF LIGHT ULTRAVIOLET 1.7 OBSTRUCED AMINE LIGHT STABILIZER (HALS) 0.8 --- --- --- N-BUTYL ACETATE 2.1 2.0 2.0 2.0 2.0 BUFFET ACETATE "CARBITOL" 5.5 5.3 5.3 5.4 5.4 POLYNOCYANATE 28.7 28.7 28.6 28.9 29.2 DIISOBUTILCETONA 4.7 4.7 4.5 4.7 4.8 DISPERSION OF DIHIDRAZIDA 2.5 1.6 0.6 TOTAL 100.0 00.0 100.0 100.0 100.0 * Comparative Example TABLE 3 RESULTS OF DEGRADATION, EJ. 9-13 EXAMPLE 14 COMPOSITION OF THE BASE LAYER EXAMPLE 14A 14B 14C 14D INGREDIENT (Quantities are indicated in% by weight) MICROGEL CONCENTRATE 19.5 19.3 19.1 18.9 N-BUTYLE ACETATE 2.0 2.0 2.0 2.0 ABSORBENT DISSOLUTION 2.8 2.7 2.7 2.6 ULTRAVIOLET LIGHT MELAMINE RESIN 15.1 15.0 14.9 14.8 ACRYLATE RESIN 12.6 12.5 12.4 12.3 METANOL 2.2 2.2 2.2 2.2 CELLULOSE ADDITIVE 5.4 5.4 5.3 5.2 DISPERSION OF BLACK PIGMENT 14.5 14.4 14.2 14.1 CHARCOAL PIGMENTO AZUL 0.8 0.8 0.8 0.8 WHITE PIGMENT 0.2 0.2 0.2 0.2 DISPERSION OF PIGMENT 2.5 2.4 2.4 2.4 SMOKE SILICA 5.7 5.6 5.5 5.4 ULTRAVIOLET LIGHT ABSORBENT 3.7 3.7 3.7 3.7 ACRYLIC RESIN 2.6 2.5 2.5 2.5 PIGMENT ADDITIVE 3.8 3.7 3.7 3.7 ACID CATALYST 1.3 1.3 1.3 1.3 METANOL 0.4 0.4 0.4 0.4 N-BUTYL ACETATE 4.9 5.3 5.1 5.0 HIDRAZIDE DISPERSION 0.0 0.6 1.6 2.5 TOTAL 100.0 100.0 100.0 100.0 * No degradation results available.

EXAMPLES 15-17 CARBAMATE TRANSPARENT LAYER COMPOSITIONS EXAMPLE 15 16 17 18 INGREDIENT (The quantities are given in% by weight) ACRYLIC RESIN WITH FUNCTIONALITY 53.9 55.8 55.1 54.4 OF CARBAMATE CARBAMATE ADDITIVE 7.9 8.1 8.0 8.0 MELAMINE 7.9 8.1 8.0 8.0 ULTRAVIOLET LIGHT ABSORBENT 1.7 0.0 0.0 0.0 AMINO LIGHT STABILIZER 0.8 0.0 0.0 0.0 OBSTRUCTED ACID CATALYST 2.2 2.2 2.2 2.1 AGENT FOR RHEOLOGY CONTROL 8.4 8.2 8.2 8.1 FLOW ADDITIVE 0.1 0.1 0.1 0.1 ADHESION PROMOTER 0.6 0.6 0.6 0.6 ISOBUTANOL 2.2 2.2 2.2 2.2 OXIDECIL ACETATE 3.3 3.3 3.2 3.2 METIL ISOAMIL CETONA 5.5 5.4 5.4 5.4 OXIOCYTUM ACETATE 5.5 5.4 5.4 5.4 HIDRAZIDE DISPERSION 0 0.6 1.6 2.5 TOTAL 00.0 100.0 0.0 100.0 TABLE 4 DEGRADATION RESULTS, EXAMPLES 15-18

Claims (24)

Claims;
1. l. A coating composition comprising: a) a polymer selected from the group consisting of acrylic, modified acrylic, polyurethane, polyester, polycarbonate, polyamide, polyimide, polysiloxane, epoxy and carbamate polymers, and mixtures thereof, having a reactive functionality towards a crosslinking agent, b) a crosslinking agent selected from the group consisting of polyisocyanates, aminoplasts, carbamates and mixtures thereof, c) a hydrazide in a), b) or part of a compound other than a) or b), present in an amount between 0.25 and 5.0%, by weight, based on the total weight of the fixed vehicle.
2. 2. A coating composition, as defined in claim 1, wherein the reactive functionality of a) is selected from the group consisting of hydroxyl, epoxy, carboxy, carbamate, amino, hydrazide and thiol functionalities.
3. 3. A coating composition, as defined in claim 1, wherein the composition is a basecoat composition.
4. 4. A coating composition, as defined in claim 1, wherein the composition is a clear coat composition.
5. 5. A coating composition, as defined in claim 3, wherein the reactive functionality in polymer a) is selected from the group consisting of hydroxyl and amino functionalities, and the crosslinking agent b) is melamine.
6. 6. A coating composition, as defined in claim 4, wherein the reactive functionality in polymer a) is hydroxyl functionality and the crosslinking agent b) is melamine.
7. 7. A coating composition, as defined in claim 3, wherein the reactive functionality in polymer a) is hydroxyl functionality and the crosslinking agent b) is a polyisocyanate.
8. 8. A coating composition, as defined in claim 4, wherein the reactive functionality in polymer a) is hydroxyl functionality and the crosslinking agent b) is a polyisocyanate.
9. 9. A coating composition, as defined in claim 3, wherein the polymer a) has hydroxyl functionality and the crosslinking agent b) is a polyisocyanate reacted with a compound selected from the group consisting of dialkyl malonates, acetoacetates and mixtures thereof .
10. 10. A coating composition, as defined in claim 4, wherein the polymer a) has hydroxyl functionality and the crosslinking agent b) is a polyisocyanate reacted with a compound selected from the group consisting of dialkyl malonates, acetoacetates and mixtures thereof .
11. 11. A coating composition, as defined in claim 3, wherein the polymer a) is a polymer with carbamate functionality and the crosslinking agent b) is an aminoplast crosslinking agent.
12. 12. A coating composition, as defined in claim 3, wherein the polymer a) is a polymer with carbamate functionality and the crosslinking agent b) is an aminoplast crosslinking agent.
13. 13. A coating of color composite plus transparent layer comprising a basecoat composition, with an overcoat of a clearcoat composition, wherein the composition of the clearcoat is as defined in claim 1.
14. 14. A coating of color composite plus transparent layer comprising a basecoat composition, with an overcoat of a clearcoat composition, wherein the composition of the basecoat is as defined in claim 1.
15. 15. A coating composition, as defined in claim 1, wherein the hydrazide has the formula , where Ri and R2 each represent individually H, or substituted or unsubstituted alkyl groups.
16. 16. A coating composition, as defined in claim 1, wherein at least one of Rx and R2 is H.
17. 17. A coating composition, as defined in claim 1, wherein both, Rx and R2 are hydrogen.
18. 18. A coating composition, as defined in claim 1, wherein the hydrazide component is a functionality in polymer a).
19. 19. A coating composition, as defined in claim 1, wherein the hydrazide component is a functionality in the crosslinking agent b).
20. 20. A coating composition, as defined in claim 1, wherein the hydrazide component is part of a compound other than a) or b).
21. 21. A coating composition, as defined in claim 1, wherein the hydrazide is a hydrazide compound of aliphatic acid.
22. 22. A coating composition, as defined in claim 1, wherein the hydrazide has the formula where R3 and R4 each independently represent groups selected from the group consisting of H, substituted alkyl groups and unsubstituted alkyl, R5 represents a substituted or unsubstituted alkyl group.
23. 23. A coating composition, as defined in claim 1, wherein the hydrazide has the formula , where L is a divalent linking group, -NH or -O-, and at least one of R6 and R7 represents H, where the other is substituted with a functionality selected from the group consisting of H, substituted alkyl groups and unsubstituted alkyl , and substituted and unsubstituted aryl groups.
24. 24. A method for improving the resistance that a cured coating has to environmental degradation, comprising the steps of applying a basecoating composition to a substrate, to form a basecoat, and subsequently applying a clearcoat composition including a) a polymer selected from the group consisting of acrylic polymers, modified acrylics, polyurethanes, polyesters, polycarbonates, polyamides, polyimides, polysiloxanes, epoxy and carbamate, and mixtures thereof, having a reactive functionality towards a crosslinking agent, b) an agent of crosslinking selected from the group consisting of polyisocyanates, aminoplasts, carbamates and mixtures thereof, c) a hydrazide in a), b) or part of a compound other than a) or b), present in an amount between 0.25 and 5.0%, by weight, based on the total weight of the fixed vehicle, to form a transparent layer and cure the layers, either sequentially or simultaneously, to form a cured film.