CA2221676A1 - Coatings based on polyisocyanates and aliphatic aldimines that have improved mar and scratch resistance - Google Patents

Abstract

The present invention is directed to coatings that have good scratch and mar resistance and are prepared from coating compositions containing a) a polyisocyanate component containing i) 0 to 25% by weight of allophanate groups (calculated as HC2N2O3, MW 101) and/or ii) 0 to 25% by weight of uretdione groups (calculated as C2N202, MW 84), b) an aldimine corresponding to the formula X1-[N=CHCH(R1)(R2)]n wherein X1 represents the residue which is inert towards isocyanate groups at a temperature of 100°C or less and is obtained by removing the amino groups from an aliphatic polyamine having n amino groups and a molecular weight of less than 400 and R1 and R2 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100°C or less, or R1 and R 2 together with the .beta.-carbon atom form a cycloaliphatic or heterocyclic ring, n represents an integer with a value of at least 2, wherein components a) and b) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups to aldimine groups of 0.5:1 to 5:1.

Description

Mo4632 COATINGS BASED ON POLYISOCYANATES
AND ALIPHATIC ALDIMINES THAT HAVE
IMPROVED MAR AND SCRATCH RESISTANCE
BACKGROUND OF THE INVENTION
Field of the Invention The present invention is directed to coatings that possess improved mar and scratch resistance and are prepared from coating compositions based on aliphatic aldimines and polyisocyanates containing allophanate and/or uretdione groups.
10 Back~round of the Invention As automotive finishes have become glossier and more mirror-like, flaws in the coatings have become more visible. Two of the properties that must be possessed by these coatings to reduce the number of flaws are scratch and mar resistance and acid etch resistance, i.e., resistance 15 to acid rain, bird droppings, tree sap, etc. While melamine/acrylic based coating compositions possess good scratch and mar resistance, they do not possess good acid etch resistance.
Polyurethane coatings have been developed that overcome the problems of acid etch resistance associated with melamine/acrylic resins.
20 However, many in the industry believe that polyurethane coatings do not possess the level of scratch and mar resistance possessed by melamine/acrylic coatings. Accordingly, it is an object of the present invention to provide isocyanate-based coatings that possess good scratch and mar resistance.
This object can be achieved with the coatings according to the present invention, which are based on polyisocyanates containing allophanate and/or uretdione groups and aldimines prepared form aliphatic polyamines.

Mo4632 -2-Coating compositions based on polyisocyanates and aldimines are known and disclosed, e.g., in U.S. Patents 5,446,771, 5,516,873 and 5,523,376, and in copending application, U.S. Serial No. 08/171,550.
U.S. Patent 5,446,771 is directed to coating compositions based on 5 allophanate group-containing polyisocyanates and aldimines and U.S.
Patent 5,523,376 is directed to coating compositions containing uretdione group-containing polyisocyanates and aldimines. It disclosed that these polyisocyanates possess improved compatibility with aldimines when compared to other commercially available polyisocyanates.
U.S. Patent 5,516,873 is directed to coating compositions containing aspartates in addition to polyisocyanates and aldimines. The aspartates improve the compatibility between polyisocyanates and aldimines. Copending application, U.S. Serial No. 08/171,550, is directed coating compositions based on polyisocyanates and cycloaliphatic 15 aldimines. These coating compositions have long pot lives and may be rapidly cured under ambient conditions. Finally, U.S. Patents 3,420,800 and 3,567,692 disclose coating compositions containing polyisocyanates and either aldimines or ketimines, and U.S. Patent 5,214,086 discloses coating compositions containing polyisocyanates, aldimines, polyols and 20 optionally polyaspartates.
While all of the preceding patents disclose coating compositions containing various types of polyisocyanates and aldimines, none of these patents teach that coatings obtained from the particular polyisocyanates and aldimines required by the present invention would possess improved 25 scratch and mar resistance.

Mo4632 -3-SUMMARY OF THE INVENTION
The present invention is directed to coatings that have good scratch and mar resistance and are prepared from coating compositions containing 5 a) a polyisocyanate component containing i) 0 to 25% by weight of allophanate groups (calculated as HC2N2O3, MW 101 ) and/or ii) 0 to 25% by weight of uretdione groups (c~lcul~ted as C2N2O2, MW 84), 10 provided that polyisocyanate component a) contains a total of at least 2%
by weight of allophanate groups and uretdione groups, b) an aldimine corresponding to the formula X1-[N=cHcH(R1)(R2)]n 1 5 and c) optionally a compound containing aspartate groups and corresponding to the formula X2 1~111 C--COOR3 ~) n 25 wherein X, represents the residue which is inert towards isocyanate groups at a temperature of 100~C or less and is obtained by removing the amino groups from an aliphatic polyamine having n amino groups and a molecular weight of less than 400 and Mo4632 -4-X2 represents an organic group which has a valency of n and is inert towards isocyanate groups at a temperature of 100~C or less, R, and R2 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100~C or less, or R1 and R2 together with the ,B-carbon atom form a cycloaliphatic or heterocyclic ring, R3 and R4 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100~C or less, R5 and Rô may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100~C or less and n represents an integer with a value of at least 2, 15 wherein components a), b) and c) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups to aldimine groups and aspartate groups of 0.5:1 to 5:1.
DETAILED DESCRIPTION OF THE INVENTION
When referring to isocyanate groups or isocyanate-reactive 20 groups, such as amino or hydroxy groups, the term "(cyclo)aliphatically bound" means that the groups are bound to aliphatic and/or cycloaliphatic carbon atoms. The term "aliphatically bound" means that the groups are bound to aliphatic carbon atoms.
In accordance with the present invention it has been discovered 25 that coatings, which are prepared from coating compositions based on polyisocyanates containing allophanate and/or uretdione groups and aldimines prepared from aliphatic polyamines, have excellent mar and scratch resistance. In addition to using the polyisocyanates containing allophanate and/or uretdione groups as the polyisocyanate component, 30 these polyisocyanates may also be blended with other monomeric Mo4632 -5-polyisocyanates, polyisocyanate adducts or NCO prepolymers, provided that the polyisocyanate component has the required amount of allophanate and/or uretdione groups.
The polyisocyanates containing allophanate groups may be 5 prepared by reacting mono-, di- or polyurethanes, which optionally contain isocyanate groups, with monomeric di- or polyisocyanates at elevated temperatures to form allophanate groups. The urethanes may be prepared in an initial step by either 1 ) reacting monomeric di- or polyisocyanates with monoalcohols or a mixture of mono and polyhydric 10 alcohols to form urethanes or 2) by reacting di- or polyhydric alcohols with monoisocyanates or a mixture of mono- and di- or polyisocyanates to form urethanes. If an excess of isocyanate groups is used, especially according to method 1), the resulting urethanes will contain terminal isocyanate groups. According to either method the urethane groups are 15 subsequently reacted with additional monomeric di- or polyisocyanates to form allophanate groups. Alternatively, the polyisocyanates containing allophanate groups may be prepared in situ by adding the alcohols to a sufficient excess of monomeric di- and polyisocyanates to form both the urethane and allophanate groups. Suitable processes for preparing 20 these products are described in U.S. Patents 4,160,080 and 3,769,318, the disclosures of which are herein incorporated by reference.
If the urethanes are l.re,uared by using the stoichiometric amount of isocyanate and hydroxy groups in accordance with either method 1 or 2, the resulting products will be substantially free of isocyanate groups.
25 The resulting urethanes can then be reacted with additional amounts of di- or polyisocyanates in accordance with the processes described in the previously mentioned U.S. patents.
Preferably the allophanate group-containing polyisocyanates are prepared from a mixture of diisocyanates and either monohydric alcohols 30 or a mixture of mono- and polyhydric alcohols.

Mo4632 -6-Suitable monomeric di- and polyisocyanates that may be used to prepare the allophanate group-containing polyisocyanates include the known polyisocyanates, preferably diisocyanates, containing aliphatically-, cycloaliphatically-, araliphatically- and/or aromatically bound isocyanate groups that are described in U.S. Patents 5,466,771 and 5,523,376, the disclosures of which are herein incorporated by reference.
Examples include of suitable organic diisocyanates include 1,4-tetramethyiene diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-10 3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis-(4-iso-cyanatocyclohexyl)-methane, 2,4'-dicyclohexyl-methane diisocyanate, 1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-methyl-cyclohexyl)-methane, a,a,a',a'-tetramethyl-1,3- and/or -1,4-xylylene diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl 15 cyclohexane, 2,4- and/or 2,6-hexahydrotoluylene diisocyanate, 1,3-and/or 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, and 2,4- and/or 4,4'-diphenylmethane diisocyanate.
Polyisocyanates containing 3 or more isocyanate groups such as 4-isocyanatomethyl-1,8-octamethylene diisocyanate and aromatic 20 polyisocyanates such as 4,4',4"-triphenylmethane triisocyanate and polyphenyl polymethylene polyisocyanates obtained by phosgenating aniline/formaldehyde condensates may also be used.
P~eferled diisocyanates are 1,6-hexamethylene diisocyanate, isophorone diisocyanate and bis-(4-isocyanato-cyclohexyl)-methane. 1,6-25 hexamethylene diisocyanate (HDI) is especially preferred.
Suitable mono- and polyhydric alcohols that may be used to prepare the polyisocyanates containing allophanate groups include saturated or unsaturated, preferably saturated, alcohols containing aliphatically-, cycloaliphatically-, araliphatically- and/or aromatically-bound 30 hydroxy groups, such as the monoalcohols disclosed in U.S. Patents Mo4632 -7-5,466,771 and 5,523,376, the disclosures of which are herein incorporated by reference. The alcohols may be linear, branched or cyclic, contain at least one carbon atom and have a molecular weight of up to 2500. The alcohols may optionally contain other hetero atoms in 5 the form of, e.g., ether groups, ester groups, etc. Preferred monoalcohols are hydrocarbon monoalcohols and monoalcohols containing ether groups, more preferably the hydrocarbon monoalcohols.
The hydrocarbon monoalcohols preferably contain 1 to 36, more preferably 1 to 20 and most preferably 1 to 8 carbon atoms. Examples 10 of suitable monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert. butanol, neopentyl alcohol, n-hexanol, n-octanol, 2-ethyl hexanol, cyclohexanol, benzyl alcohol, phenol, decanol, dodecanol, tetradecanol, hexadecanol and octadecanol. It is also possible in accordance with the present invention to use mixtures of 15 the previously described monoalcohols or other alcohols.
Preferred polyhydric alcohols for preparing the allophanate group-containing polyisocyanates are those having a molecular weight of less than 400, such as ethylene glycol, propylene glycol, butanediol-1,4, hexanediol-1,6, neopentyl glycol, 2-methylpropanediol-1,3, 2,2,4-20 trimethylpentanediol-1,3, dimeric fatty alcohols, trimeric fatty alcohols, glycerol, trimethylolpropane, trimethylolethane, the isomeric hexanetriols, pentaerythritol and sorbitol. Also suitable are unsaturated alcohols such as allyl alcohol, trimethylolpropane diallyl ether, butenediol and monofunctional alcohols that are derived from corresponding acids or 25 acidic mixtures of unsaturated synthetic and naturally-occurring fatty acids. Also suitable are alkoxylation products containing ether groups of these polyhydric alcohols.
The polyisocyanates containing uretdione groups may be prepared from any of the previously disclosed monomeric diisocyanates by any of 30 the known prior art methods, e.g., by catalytic dimerization in the - Mo4632 -8-presence of phosphine catalysts. These polyisocyanates may also be prepared in accordance with U.S. Patent 4,929,724 (the disclosure of which is herein incorporated by reference) by dimerizing a portion of the isocyanate groups of an organic diisocyanate in the presence of a 5 dimerization catalyst containing phosphorus-nitrogen bonds and a co-catalyst containing an isocyanate-reactive group and having a pKa-value of at least 6. Another method for preparing these polyisocyanates is through the use of dimerization catalysts which are covalently bound to an insoluble inorganic matrix substrate as disclosed in U.S. Patent 10 5,315,004 (the disclosure of which is herein incorporated by reference).
The polyisocyanates containing allophanate and/or uretdione groups may be blended with the previously described monomeric diisocyanates, with other polyisocyanate adducts or with NCO
prepolymers, provided that the polyisocyanate component contains the 15 required amounts of allophanate groups and/or uretdione groups. The other polyisocyanate adducts include those containing isocyanurate, biuret, urethane, allophanate, carbodiimide and/or oxadiazinetrione groups. The polyisocyanates adducts have an average functionality of 2 to 6 and an NCO content of 5 to 30% by weight. These polyisocyanate 20 adducts and methods for their preparation are described in U.S. Patents 5,466,771 and 5,523,376, the disclosures of which are herein incorporated by reference.
Preferred polyisocyanate adducts are the polyisocyanates containing isocyanurate groups, biuret groups or urethane groups, 25 especially isocyanurate groups.
Instead of using mixtures of polyisocyanates containing allophanate groups and polyisocyanate adducts which have been separately prepared, in certain cases it is possible to prepare these mixtures in one step. For example, mixtures of polyisocyanates 30 containing allophanate and isocyanurate groups may be prepared by Mo4632 -9-trimerizing the isocyanate starting material in the presence of trimerization catalysts and monoalcohols, or by allophanatizing urethane group-containing starting materials in the presence of a trimerization catalyst. Suitable catalysts and methods of the production of these polyisocyanate mixtures are disclosed, e.g., in U.S. Patents 5,124,427, 5,208,334, 5,235,018 and 5,444,146, the disclosures of which are herein incorporated by reference. Similarly, it is possible to prepare mixtures of polyisocyanates containing uretdione groups and isocyanurate groups in one step by trimerizing the isocyanate starting material in the presence of 10 dimerization/trimerization catalysts such as tertiary phosphines or peralkylated phosphorus acid triamides. Suitable catalysts and methods of the production of these polyisocyanate mixtures are disclosed, e.g., in U.S. Patents 4,614,785 and 4,994,541, the disclosures of which are herein incorporated by reference.
Preferred mixtures of polyisocyanates are those containing allophanate and isocyanurate groups or uretdione and isocyanurate groups. The polyisocyanates according to the invention generally contain a total of less than 2, preferably less than 1% of free (unreacted) monomeric diisocyanates.
In addition to monomeric polyisocyanates and polyisocyanates adducts, the polyisocyanates containing allophanate and/or uretdione groups may also be blended with NCO prepolymers to improve their compatibility with aldimines. Suitable NCO prepolymers are disclosed in U.S. Patents 5,466,771 and 5,523,376, the disclosures of which are 25 herein incorporated by reference.
In accordance with the present invention the polyisocyanate component may have an allophanate group content (c~lc~ ted as HC2N2O3, MW 101 ) of at least 2%, preferably at least 4% by weight and/or a uretdione group content (calculated as C2N2Oz, MW 84) of at 30 least 2%, preferably at least 4% by weight, in which the preceding Mo4632 -1 0-percentages are based on the weight of polyisocyanate solids.
Polyisocyanate component a) should have a minimum total content of allophanate groups and uretdione groups of 2%, preferably 4% by weight, and a maximum total content of allophanate groups and uretdione groups of 25%, preferably 20%, more preferably 15% by weight, in which the preceding percentages are based on the weight of polyisocyanate solids.
Suitable aldimines for as component b) include those prepared from an aldehyde and polyamines corresponding to the formula X1 (NH2)n wherein X, represents the residue which is inert towards isocyanate groups at a temperature of 100~C or less and is obtained by removing the amino groups from an aliphatic polyamine having n amino groups and a molecular weight of less than 400, preferably a divalent hydrocarbon group, and n represents an integer with a value of at least 2, preferably 2 to 6, more prererably 2 to 4 and most preferably 2.
Suitable low molecular aliphatic polyamine starting compounds include tetramethylene diamine, ethylene diamine, 1,2- and 1,3-propane diamine, 2-methyl-1,2-propane diamine, 2,2-dimethyl-1,3-propane diamine, 1,3- and 1,4-butane diamine, 1,3- and 1,5-pentane diamine, 2-methyl-1,5-pentane diamine, 1,6-hexane diamine, 1,7-heptane diamine, 1,8-octane diamine, 1,9-nonane diamine, 1,10-decane diamine, 1,11-undecane diamine, 1,12-dodecane diamine, 4-aminomethyl-1,8-octamethylene diamine, hydrazine, N,N,N-tris-(2-aminoethyl)-amine, N-(2-aminoethyl)-1,3-propane diamine, and mixtures thereof.

Mo4632 -1 1-Preferred polyamines are 1,6-diaminohexane, 2-methyl-1,5-pentane diamine, 4-aminomethyl-1,8-octamethylene diamine and ethylene diamine.
Suitable aldehydes are those corresponding to the formula O=CHCH(R,)(R2) wherein R, and R2 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100~C or less, preferably containing 1 to 10, more preferably 1 to 6, carbon atoms, or R, and R2 together with the ~-carbon atom form a cycloaliphatic or heterocyclic ring.
Examples of suitable aldehydes include isobutyraldehyde, 2-ethyl hexanal, 2-methyl butyraldehyde, 2-ethyl butyraldehyde, 2-methyl valeraldehyde, 2,3-dimethyl valeraldehyde, 2-methyl undecanal and 15 cyclohexane carboxaldehyde.
The aldimines may be prepared in known manner by reacting the polyamines with the aldehydes either in stoichiometric amounts or with an excess of aldehyde. The excess aldehyde and the water which is produced can be removed by distillation. The reactions may also be 20 carried out in solvents, other than ketones. The solvents may also be removed by distillation after completion of the reaction.
Component c) is selected from compounds having at least two aspartate groups and corresponding to the formula:

Rs Xz r~l I C--COOR3 (1) n Mo4632 -1 2-wherein X2 represents an organic group which has a valency of n and is inert towards isocyanate groups at a temperature of 100~C or less, preferably a hydrocarbon group obtained by removing the amino groups from an aliphatic, araliphatic, cycloaliphatic or aromatic polyamine, more preferably a diamine, R3 and R4 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 1 00~C or less, preferably methyl or ethyl groups, 10 R5 and R6 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100~C or less, preferably hydrogen and n represents an integer with a value of at least 2, preferably 2 to 6, more preferably 2 to 4 and most preferably 2.
These compounds are prepared in known manner by reacting the corresponding primary polyamines corresponding to the formula X2 (NH2)n with optionally substituted maleic or fumaric acid esters corresponding to the formula R3OOC-CR5=CR6-COOR4 (Ill) Suitable polyamines include high molecular weight amines having molecular weights of 400 to about 10,000, preferably 800 to about 6,000, 30 and low molecular weight amines having molecular weights below 400.

Mo4632 -1 3-The molecuiar weights are number average molecular weights (Mn) and are determined by end group analysis (NH number).
Suitable low molecular weight polyamines include those previously set forth for preparing aldimines b) and also 1-amino-3-aminomethyl-5 3,5,5-trimethyl cyclohexane (isophorone diamine or IPDA), 2,4- and/or 2,6-hexahydro-toluylene diamine, 2,4'- and/or 4,4'-diamino-dicyclohexyl-methane, 3,3'-dialkyl-4,4'-diamino-dicyclohexyl methanes (such as 3,3'-dimethyl-4,4'-diamino-dicyclohexyl methane and 3,3'-diethyl4,4'-diamino-dicyclohexyl methane), 1,3- and/or 1,4-cyclohexane diamine, 1,3-10 bis(methylamino)-cyclohexane, 1,8-p-menthane diamine, phenylene diamine, 2,4- and 2,6-toluylene diamine, 2,3- and 3,4-toluylene diamine, 2,4'- and/or 4,4'-diaminodiphenyl methane, higher functional polypheny-lene polymethylene polyamines obtained by the aniline/formaldehyde condensation reaction, guanidine, melamine, 3,3'-diamino-benzidine, 2,4-15 bis-(4'-aminobenzyl)-aniline, polyoxypropylene amines, polyoxyethylene amines and mixtures thereof.
Preferred polyamines are 1,4-diaminobutane, 1,6-diaminohexane, 2,2,4- and 2,4,4-trimethyl-1,6-diamino-hexane, 1,3- and/or 1,4-cyclo-hexane diamine, 1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane, 20 2,4- and/or 2,6-hexahydrotoluylene diamine, 4,4'-diamino-dicyclohexyl methane, 3,3-dimethyl-4,4'-diamino-dicyclohexyl methane and 3,3-diethyl-4,4'-diamino-dicyclohexyl methane.
Suitable high molecular weight aliphatic polyamines correspond to the polyhydroxyl compounds used to prepare the NC0 prepolymers with 25 the exception that the terminal hydroxy groups are converted to amino groups, either by amination or by reacting the hydroxy groups with a diisocyanate and subsequently hydrolyzing the terminal isocyanate group to an amino group. Preferred high molecular weight polyamines are amine-terminated polyethers such as the Jeffamine resins available from 30 Texaco.

Mo4632 -1 4-Examples of optionally substituted maleic or fumaric acid esters suitable for use in the preparation of the compounds corresponding to formula I include dimethyl, diethyl and di-n-butyl esters of maleic acid and fumaric acid and the corresponding maleic or fumaric acid esters 5 substituted by methyl in the 2- and/or 3-position.
The preparation of the "polyaspartic acid derivatives"
corresponding to formula I from the above mentioned starting materials may be carried out, for example, at a temperature of 0 to 100~C using the starting materials in such proportions that at least 1, preferably 1, 10 olefinic double bond is present for each primary amino group. Excess starting materials may be removed by distillation after the reaction. The reaction may be carried out solvent-free or in the presence of suitable solvents such as methanol, ethanol, propanol, dioxane and mixtures of such solvents.
The binders present in the coating compositions according to the invention contain polyisocyanate component a), aldimine component b) and optionally aspartate component c). The coating compositions may contain other isocyanate-reactive compounds, such as polyols; however, this is not preferred since their presence may reduce the overall properties of the coating compositions and the resulting coatings.
Components a), b) and c) are used in amounts sufficient to provide an equivalent ratio of isocyanate groups to aldimine groups and aspartate groups of 0.5:1 to 5:1, preferably 0.8:1 to 3:1 and more preferably 1:1 to 2:1 .
When component c) is present, it is present in an amount of at least 5%, preferably at least 10% by weight, up to an amount of 75%, preferably up to 60% by weight, wherein these percentages are based on the weight of components b) and c), to improve the compatibility between polyisocyanates and aldimines so that the clarity, gloss and DOI of the Mo4632 -1 5-resulting coatings is also improved, and to improve the weatherability or durability of the resulting coatings.
The binders to be used according to the invention are prepared by mixing all of the individual components together or by premixing two of the components before adding the third component. For example, aspartate c) may be initially blended with the component a) or component b), preferably component b) before the addition of the other component.
Preparation of the binders is carried out solvent-free or in the presence of the solvents conventionally used in polyurethane or polyurea 10 coatings. It is an advantage of the process according to the invention that the quantity of solvent used may be greatly reduced when compared with that required in conventional two-component systems based on polyisocyanates and polyols.
Examples of suitable solvents include xylene, butyl acetate, methyl 15 isobutyl ketone, methoxypropyl acetate, N-methyl pyrrolidone, Solvesso solvent, petroleum hydrocarbons and mixtures of such solvents.
In the coating compositions to be used for the process according to the invention, the ratio by weight of the total quantity of binder components a), b) and c) to the quantity of solvent is about 40:60 to 20 100:0, preferably about 60:40 to 100:0.
In addition to binder components a), b) and c), the coating compositions may also contain the known additives from coatings technology, such as fillers, pigments, softeners, high-boiling liquids, catalysts, UV stabilizers, anti-oxidants, microbiocides, algicides, 25 dehydrators, thixotropic agents, wetting agents, flow enhancers, matting agents, anti-slip agents, aerators and extenders. The additives are chosen based on the requirements of the particular application and their compatibility with components a) and b). The coating compositions may be applied to the substrate to be coated by conventional methods such 30 as painting, rolling, pouring or spraying.

Mo4632 -1 6-The coatings according to the invention have high hardness, elasticity, very good resistance to chemicals, high gloss, good weather resistance, good environmental etch resistance and good pigmenting qualities. Most importantly, the coatings possess good mar and scratch resistance.
The invention is further illustrated, but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.
EXAMPLES
10 Polyisocyanate 1 An polyisocyanate which contains allophanate groups and isocyanurate groups, is prepared from 1,6-hexamethylene diisocyanate and has an isocyanate content of 19%, a monoallophanate group content of 11%, a content of monomeric diisocyanate of <0.2% and a viscosity at 15 25~C of about 270 mPa s (available from Bayer Corporation as Desmodur XP-7040).
Polyisocyanate 2 An polyisocyanate which contains allophanate groups and isocyanurate groups, is prepared from 1,6-hexamethylene diisocyanate 20 and has an isocyanate content of 20.3%, a monoallophanate group content of 4.4%, a content of monomeric diisocyanate of <0.2% and a viscosity at 25~C of about 1100 mPa s (available from Bayer Corporation as DesmodurXP-7100).
PolyisocYanate 3 A mixture containing 70 parts by weight of a uretdione group-containing polyisocyanate, i.e., dimerized 1,6-hexamethylene diisocyanate and 30 parts by weight of N,N',N"-tris-(6-isocyanatohexyl)-isocyanurate together with minor quantities of higher homologs of both products. In its 100% solvent free form, the polyisocyanate had an - Mo4632 -17-average viscosity of 150 mPa s at 23~C and an average NCO content of 22.5% (available from Bayer Corporation as Desmodur N 3400).
Polyisocyanate 4 An isocyanurate group-containing polyisocyanate prepared from 5 1,6-hexamethylene diisocyanate and having an isocyanate content of 21.6%, a content of monomeric diisocyanate of <0.2% and a viscosity at 20~C of 3000 mPa s (available from Bayer Corporation as Desmodur N 3300).
Preparation of Aldimines The following aldimines were prepared by initially charging 21 equivalents of isobutraldehyde and then slowly charging 20 equivalents of the polyamine over a period of thirty minutes to avoid an exotherm.
After the addition of the polyamine the reaction mixture was stirred for one hour. At this time stirring was stopped and water was allowed to 15 settle to the bottom of the reactor. As much water as possible was drained from the bottom of the reactor. The reaction mixture was then heated to 100~C to remove excess isobutraldehyde. While maintaining a temperature of 100~C, a vacuum of approximately 20 mm Hg was applied to remove any final traces of aldehyde. Thereafter the vacuum 20 was increased to 1 mm Hg to remove water until the water content was less than 0.05% (approximately 1 to 3 hours.) Aldimine 1 The aldimine of 2-methyl pentamethylene diamine and isobutyraldehyde was prepared using the procedure described for 25 aldimine 1. The resulting aldimine had an equivalent weight of 112 and a viscosity of 10 mPa s at 25~C.
Aldimine 2 The aldimine of hexamethylene diamine and isobutyraldehyde.
The resulting aldimine had an equivalent weight of 112 and a viscosity of 30 10 mPa s at 25~C.

- Mo4632 -18-Aldimine 3 The aldimine of 4-aminomethyl-1,8-octamethylene diamine and isobutyraldehyde. The resulting aldimine had an equivalent weight of 112 and a viscosity of 12-15 mPa s at 25~C.
5 Aldim ine 4 The aldimine of bis-(4-aminocyclohexyl)-methane and isobutraldehyde. The resulting aldimine had an equivalent weight of 159 and a viscosity of 70 mPa s at 25~C.
Aldimine 5 The aldimine of isophorone diamine and isobutraldehyde. The resulting aldimine had an equivalent weight of 140 and a viscosity of 30 mPa s at 25~C.
Preparation of Aspartates 1 mole of the diamine was added dropwise with stirring to 2 moles 15 of maleic acid diethylester that were previously charged at ambient temperature to a 1 L three necked flask equipped with a stirrer, thermometer and an addition funnel. The amine was added at a rate such that the exotherm did not increase the temperature of the reaction mixture above 50~C. Upon complete addition the contents of the reaction 20 flask were maintained at 50~C for a period of 12 hours. The resulting product was a clear, colorless liquid.
Polyaspartate 1 The aspartate of 4,4'-diamino-dicyclohexylmethane, which has a viscosity of about 1400 mPa s (25~C) and an equivalent weight of about 25 276 g/eq.
Polyaspartic Acid Ester 2 The aspartate of bis-(4-amino-3-methyl-cyclohexyl)-methane, which has a viscosity of about 1500 mPa s (25~C) and an equivalent weight of about 291 g/eq.

Mo4632 -1 9-ExamPles 1-8 and Comparison Examples 1-8 A commercial black waterborne OEM basecoat was spray applied to pretreated steel panels at a dry film thickness of 0.7 to 0.8 mils. The basecoats were flashed for 5 min. at ambient temperature and then force 5 dried for 10-15 min. at 83~C. They were cooled to ambient temperature before the clearcoat was spray applied at a dry film thickness of 1.5 to 1.8 mils. The basecoaVclearcoat panels were then baked for 30 min. at 120~C.
The compositions of the binders for the clearcoats are set forth in 10 the following table. In addition to these binder components, the coating compositions also contained 0.65% of an acrylate copolymer (available as Byk 358 from Byk Chemie), 0.85% of a hindered amine light stabilizer (available as Tinuvin 292 from Ciba-Geigy), 1.7% of a benzotriazole light stabilizer (available as Tinuvin 1130 from Ciba-Geigy), 0.25% of octanoic 15 acid and 11.7% of butyl acetate, in which all percentages are based on the total weight of the coating compositions. The binder components were formulated an NCO:NH equivalent ratio of 1.1 :1Ø
Test Method to Assess Mar and Scratch Resistance of Coatings An Atlas MTCC Crockmeter, Model CM-5 (Atlas Electric Devices 20 Company, Chicago, IL) wàs used to measure mar resistance.
BasecoaVclearcoat panels measuring 3"x 6" were prepared. A foam pad about 4.4 cm wide by 1.9 cm deep was applied to the acrylic finger on the Crockmeter. For east test, a fresh piece of linen cloth the size of the pad was applied to the bottom of the foam pad. Bon Ami Cleanser was 25 applied to the coated panel and the excess tapped off, leaving a thin film of cleanser on the panel. The panel was situated on the Crockmeter, and the meter was set for 10 back and forth rubs. After testing, the panel was washed with water to remove the cleanser, and carefully dried.
Mar resistance was determined by 20~ gloss loss, i.e., the gloss reading 30 after abrading the panel was subtracted from the reading before the test.

Mo4632 -20-The reported gloss loss is the average of 3 readings from each of the duplicate panels.

Table Examples according 1 2 3 4 5 6 7 8 ~
to the invention Aldimine/Amount 1/287.2 2122.2 3124.6 3124.2 3/15.4 1/15.3 2/15.4 3/14.5 Aspartate/Amount -- -- -- -- 1/15.4 1/15.3 2/15.4 2/14.5 Isocyanate/Amount 2/316.6 1/48.4 3145.9 2147.3 2142.3 2/42.1 2/41.7 1/43.8 Gloss Loss 0.5 0 0.1 0 0.9 1.6 0 1.6 D

Comparison 1 2 3 4 5 6 7 8 Examples Aldimine/Amount 5/329.8 5/308.0 4/30.7 -- 4/17.6 5/16.7 5/16.9 4/16.7 Aspartate/Amount -- -- -- 1/42.4 1/17.6 1/16.7 2/16.9 2/16.7 Isocyanate/Amount 2/519.4 1/541.1 3/40.3 2133.5 2138.2 2139.6 2139.3 1/39.7 Gloss Loss 13.1 23.3 19.6 17.1 28.1 7.3 6.5 11.2 - Mo4632 -22-In the preceding examples, the examples according to the invention are identical to the corresponding comparison examples (i.e., Example 1 is identical to comparison example 1, etc.) except for the fact that aliphatic aldimines are used in the examples according to the invention and cycloaliphatic or mixed aliphatic/cycloaliphatic aldimines are used in the comparison examples.
The preceding examples demonstrate that coatings prepared from aliphatic aldimines have much better gloss retention than coatings prepared from cycloaliphatic aldimines or mixed aliphatic/cycloaliphatic aldimines. The improved gloss retention is indicative of improved mar and scratch resistance.
Example 9 and ComParison Examples 9 and 10 A commercial solvent-borne black refinish basecoat was spray applied to aluminum panels at a dry film thickness of 0.7 to 0.8 mils.
The basecoats were then flashed for 30 min. at ambient temperature.
The clearcoat was spray applied over the basecoat at a dry film thickness of 1.5 to 1.8 mils and the basecoaVclearcoat panels were then baked for 30 min. at 120~C. The binder components for the clearcoats were formulated an NCO:NH equivalent ratio of 1.1:1.0 and had the following compositions:
Example 9 - According to the invention 20.4 parts aldimine 2 0.3 parts acrylate copolymer (available as Byk 358 from Byk Chemie) 19.8 parts butyl acetate 30 41.0 parts polyisocyanate 2 Comparison Example 9 A commercial OEM clearcoat based on acrylic/melamine chemistry.

Mo4632 -23-Comparison Example 10 45.9 parts acrylic/polyester blend polyol (Desmophen A-565, available from Bayer Corp, OH equivalent weight, 654) 0.4 parts acrylate copolymer (available as Byk 358 from Byk Chemie) 19.8 parts solvent (a 3:2:1:1 blend of butyl acetate/methylisobutyl acetate/Solvesso 100 solvenVmethylamyl ketone) 15.6 parts polyisocyanate 4 Results - 20~ Gloss Loss Example # 20~ Gloss Loss Example 9 0 Comparison Example 9 9 Comparison Example 10 4 These examples demonstrate that even when compared to standard commercials coatings, such as acrylic melamines (Comparison Example 9) or polyurethanes (Comparison Example 10), the coatings according to the invention possess improved scratch and mar resistance 20 as evidenced by the increase in gloss retention.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of 25 the invention except as it may be limited by the claims.

Claims (20)

1. A coating that has good scratch and mar resistance and is prepared from a coating composition comprising a) a polyisocyanate component comprising i) 0 to 25% by weight of allophanate groups (calculated as HC2N203, MW 101) and/or ii) 0 to 25% by weight of uretdione groups (calculated as C2N2O2, MW 84), provided that polyisocyanate component a) contains a total of at least 2%
by weight of allophanate groups and uretdione groups, b) an aldimine corresponding to the formula X,-[N=CHCH(R1)(R2)]n and c) optionally a compound containing aspartate groups and corresponding to the formula (i) wherein X1 represents the residue which is inert towards isocyanate groups at a temperature of 100°C or less and is obtained by removing the amino groups from an aliphatic polyamine having n amino groups and a molecular weight of less than 400 and X2 represents an organic group which has a valency of n and is inert towards isocyanate groups at a temperature of 100°C or less, R1 and R2 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100°C or less, or R1, and R2 together with the .beta.-carbon atom form a cycloaliphatic or heterocyclic ring, R3 and R4 may be identical or different and represent organic groups which are inert towards isocyanate groups at a temperature of 100°C or less, R5 and R6 may be identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100°C or less and n represents an integer with a value of at least 2, wherein components a), b) and c) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups to aldimine groups and aspartate groups of 0.5:1 to 5:1.

2. The coating of Claim 1 wherein polyisocyanate component a) contains allophanate groups.

3. The coating of Claim 1 wherein polyisocyanate component a) contains uretdione groups.

4. The coating of Claim 2 wherein polyisocyanate component a) is based on 1,6-hexamethylene diisocyanate.

5. The coating of Claim 3 wherein polyisocyanate component a) is based on 1,6-hexamethylene diisocyanate.

6. The coating composition of Claim 1 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

7. The coating composition of Claim 2 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

8. The coating composition of Claim 3 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

9. The coating composition of Claim 4 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

10. The coating composition of Claim 5 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

11. A coating that has good scratch and mar resistance and is prepared from a coating composition comprising a) a polyisocyanate component comprising i) 0 to 25% by weight of allophanate groups (calculated as HC2N2O3, MW 101) and/or ii) 0 to 25% by weight of uretdione groups (calculated as C2N2O2, MW 84), provided that polyisocyanate component a) contains a total of at least 2%
by weight of allophanate groups and uretdione groups, b) an aldimine corresponding to the formula X1-[N=CHCH(R1)(R2)]n and c) optionally a compound containing aspartate groups and corresponding to the formula wherein X1 represents the residue which is inert towards isocyanate groups at a temperature of 100°C or less and is obtained by removing the amino groups from an aliphatic polyamine having n amino groups and a molecular weight of less than 400 and X2 represents an organic group which has a valency of n and is inert towards isocyanate groups at a temperature of 100°C or less, R1 and R2 may be identical or different and represent hydrocarbon radicals containing 1 to 6 carbon atoms, R3 and R4 may be identical or different and represent methyl or ethyl groups, R5 and R6 represent hydrogen and n represents an integer with a value of at least 2, wherein components a), b) and c) are present in an amount sufficient to provide an equivalent ratio of isocyanate groups to aldimine groups and aspartate groups of 0.5:1 to 5:1.

12. The coating of Claim 11 wherein polyisocyanate component a) contains allophanate groups.

13. The coating of Claim 11 wherein polyisocyanate component a) contains uretdione groups.

14. The coating of Claim 12 wherein polyisocyanate component a) is based on 1,6-hexamethylene diisocyanate.

15. The coating of Claim 13 wherein polyisocyanate component a) is based on 1,6-hexamethylene diisocyanate.

16. The coating composition of Claim 11 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

17. The coating composition of Claim 12 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

18. The coating composition of Claim 13 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

19. The coating composition of Claim 14 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).

20. The coating composition of Claim 15 wherein component c) is present in an amount of at least 5% by weight, based on the weight of components b) and c).