The invention relates to a coating composition, a method of applying the same, and a coated substrate.

Coatings used for painting motor vehicles and repairing the original paint are required to have good physical properties such as hardness, mechanical strength, and resistance to water, acids, and solvents. The coatings are also required to have good appearance properties, which means that films must be smooth and have a high gloss and high distinctness of image. It is also desirable that all properties are retained under prolonged outdoor weathering.

For environmental reasons, it is required to use a coating composition which can be applied easily using spray application at a low volatile organic content (VOC). Coatings with a lower organic solvent content emit lower levels of solvent when they are used and so the atmosphere becomes less polluted.

One way to achieve a lower solvent content is to use so-called high-solids compositions. Such compositions comprise a relatively high level of non- volatile materials such as film forming polymer, pigments, and filles, and a relatively low level of organic solvent. A problem when formulating high- solids coating compositions is that such compositions have an unacceptably high viscosity due to the high molecular weight of the conventional film forming polymer. The high viscosity gives rise to problems

in spray application with poor paint atomization and poor flow-out and, consequently, low gloss levels and poor appearance.

The use of low-molecular weight film forming polymers, which results in adequate application viscosities, has as a disadvantage that the resulting coating is soft and marks easily. The hardness build-up of the coating is therefore unacceptable.

Another way to reduce the amount of volatile organic compounds in coating compositions is the use of reactive diluents. Examples of reactive diluents include aldimines and ketimines. In EP-A-0 686 654 such compounds are discussed. Other reactive diluents, such as oxazolidines, are mentioned, but it is stated that they have limited utility as sole reaction partner with isocyanate, because of generally slow setting film properties.

US 5,506,328 refers to a two-component coating composition comprising a polyisocyanate having a structure selected from the group of biuret, isocyanurate, uretdione, urethane, and allophanate, and an isocyanate reactive compound selected from the group of monoahls, polyols, ketimines, aldimines, and oxazolidines. Exemplified is a coating prepared from an oxazolidine compound and the triisocyanurate of hexamethylene diisocyanate. It has not been recognized by this disclosure that the combination of oxazolidine and isocyanate compounds having an uretdione structure or allophanate structure shows improved and unexpected properties over the use of isocyanurate. The same can be said of the disclosures of EP-A-0 531 249 and US 5,412,056.

Surprisingly, it has now been found that coating compositions comprising an oxazolidine functional compound and an isocyanate functional compound comprising a uretdione and/or allophanate structure show far better properties than compared to coating composition of the prior art.

Especially, a lower VOC at the same viscosity and a higher pot life/drying balance is obtained when using coating compositions of the present invention while other paint properties remain on the same level.

Accordingly, the present invention provides a coating composition comprising a) at least one oxazolidine functional compound of formula I wherein x and y are independently selected from 0 to 10, with the proviso that x and y cannot both be 0; n is selected from the integers 2 or 3; m and p are independently selected from the integers 1 or 2; R"R2, R3, R4, Rs and R6 may be the same or different and are selected from the group of hydrogen, linear or branched (cyclo) alkyl, and linear or branched aryl, optionally substituted; R, and R2, R3 and R4, and R5 and R6 may be joined together to form a 5 or 6 carbon ring with the attached carbon atom of the ring in the

formula, i. e. R, and R2, R3 and R4, and R5 and R6 collectively represent a tetramethylene or a pentamethylene group; and R7 is a mono-or multivalent aliphatic, aromatic, arylaliphatic or cycloaliphatic moiety which may optionally contain oxygen, nitrogen, sulphur, and silica, and R7 may be H when x or y is zero; and b) at least one isocyanate functional compound comprising a uretdione and/or an allophanate structure wherein at least 20 wt% of compounds comprising NCO-reactive groups consists of the oxazolidine functional compound of formula 1.

Preferably, the oxazolidine functional compound is selected from one of the following formulae 11 and III

wherein n, m, p, R"R2, R3, R4, R5, R6, and R7 are as mentioned above, z is from 0 to 9, and R7 may be H when z is zero.

Also mixtures of oxazolidine functional compounds may be present in the coating composition of the present invention, preferably a mixture comprising an oxazolidine functional compound of the formula 11 and an oxazolidine functional compound of the formula 111. The ratio of bicyclic oxazolidine (III) to monocyclic oxazolidine (II) is preferably in the range of 5: 1 to 1: 2; more preferably 3: 1 to 1: 1, and most preferably 2: 1.

Preferably, n is 2 and m and p are 1. Preferably, z is from 0 to 3.

Preferably, R,, R2, R3, R4, R5, and R6 are selected from the group of hydrogen, phenyl, benzyl or a linear or branched C,, 2 alkyl group. More preferably, R"R2, R3, R4, Rs, and R6 are selected from the group of hydrogen and isopropyl.

Preferably, in formula II R7 is multivalent. R7 is preferably an aliphatic, arylaliphatic or cycloaliphatic moiety comprising 2 to 15 carbon atoms and, optionally, ester, carbonate, and urethane groups.

Compounds of the formula 11 having a R7 group comprising ester groups may be based on acrylate polymers such as described in GB-B-992,721.

More preferably, z is 1 and R7 is a divalent moiety comprising either a carbonate group or at least two urethane groups.

Compounds of the formula II having a R7 group comprising carbonate groups are described in EP-A-0 499 188. R7 may be for example

When R7 comprises at least two urethane groups R7 may be selected from the group of the following multivalent moieties

Preferably, in formula 11 z is 1, n is 2, R, is hydrogen, R2 is isopropyl, and R7 is as mentioned above.

Preferably, in formula III z is 0 and R7 is an alkyl group comprising 1 to 10 carbon atoms, more preferably methyl, ethyl, and propyl. Examples include 1-aza-3,7-dioxo-2,8-diisopropyl-5-ethyl bicyclo (3,3,0) octane, i. e. Zoldines RD-20 ex Angus Chemical Company:

Examples of suitable polyisocyanates to be used as starting materials for preparing the isocyanate functional compound comprising a uretdione structure include organic polyisocyanates represented by the formula R(NCO) k wherein k is 2 or higher and R represents an organic group obtained by removing the isocyanate groups from an organic polyisocyanate having aromatically or (cyclo) aliphatically bound isocyanate groups. Preferred are diisocyanates represented by the above formula wherein k is 2 and R represents a divalent aliphatic hydrocarbon group having 2 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon group having 5 to 15 carbon atoms, a divalent araliphatic hydrocarbon group having 7 to 15 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms. Examples of the organic diisocyanates which are particularly suitable for the process include ethylene diisocyanate, 1,3-propylene diisocyanate 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1, 6-hexamethylene diisocyanate, 2-methyl- 1,5-diisocyanate pentane, 2-ethyl-1,4-diisocyanate butane, 1,12- dodecamethylene diisocyanate, cyclohexane-1,3- and-1,4-diisocyanate, 1-

isocyanato-2-isocyanatomethyl cyclopentane, isophorone diisocyanate, bis- (4-isocyanatocyclohexyl)-methane, 2,4'-d icyclohexyl methane diisocyanate, 1,3- and 1,4-bis (isocyanatomethyl)-cyclohexane, bis- (4-isocyanato-3- methyl-cyclohexyl)-methane, 1-methyl-2,4-diisocyanato cyclohexane, 1- isocyanato-1-methyl-4 (3)-isocyanatomethyl cyclohexane, xylene diisocyanate, 1-methyl-2,4-diisocyanato benzene, a, a, a', a'-tetramethyl-1,3- and-1,4-xylylene diisocyanate, 2,4- and 2,6-hexahydrotoluylene diisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-toluylene diisocyanate, 2,4- and 4,4'-diphenylmethane diisocyanate, 1,5-diisocyanato naphthalene and mixtures thereof. Aliphatic polyisocyanates containing 3 or more isocyanate groups such as 4-isocyanatomethyl-1,8-octane diisocyanate and aromatic polyisocyanate containing 3 or more isocyanate groups such as 4,4', 4"-triphenylmethane triisocyanate, 1,3,5-triisocyanate benzene, polyphenyl polymethylene polyisocyanates obtained by phosgenating aniline/formaldehyde condensates, the adduct of trimethylolpropane and m-tetramethylxylylene diisocyanate, and mixtures thereof may also be used. Preferred diisocyanates are 1,6-hexamethylene diisocyanate and isophorone diisocyanate.

Examples of suitable polyisocyanates to be used as starting materials for preparing the isocyanate functional compound comprising an allophanate structure include the above-mentioned organic polyisocyanates reacted with a mono-or polyalcohol.

Suitable mono-or polyalcohols which may be used to prepare the polyisocyanates containing allophanate groups include aliphatic, cycloaliphatic, araliphatic or aromatic mono-or polyalcohols. The mono-or polyalcohols may be linear, branched or cyclic, contain at least one carbon

atom and have a molecular weight of up to 2500. The mono-or polyalcohols may optionally contain other hetero atoms in the form of, e. g., ether groups, ester groups, etc. However, the mono-or polyalcohols preferably do not contain hetero atoms other than the hydroxyl group (s).

The molar ratio of mono-or polyalcohol to polyisocyanate is about 0.01 to 0.5, preferably about 0.04 to 0.2. Preferred mono-or polyalcohols are hydrocarbon mono-or polyalcohols and mono-or polyalcohols containing ether groups. The hydrocarbon mono-or polyalcohols preferably contain 1 to 36, more preferably 1 to 20 and most preferably 1 to 8 carbon atoms.

Examples of suitable monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, n-pentanol, 2-hydroxy pentane, 3-hydroxy pentane, the isomeric methyl butyl alcohols, the isomeric dimethyl propyl alcohols, neopentyl alcohol, n-hexanol, n- heptanol, n-octanol, n-nonanol, 2-ethyl hexanol, trimethyl hexanol, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol, 2,6,8- trimethylnonanol, 2-t-butyl-cyclohexanol, 4-cyclohexyl-1-butanol, cyclohexanol, benzyl alcohol, phenol, the cresols, the xylenols, the trimethylphenols, 2,4,6-trimethyl benzyl alcohol, branched chain primary alcools and mixtures thereof (which are available from Henkel (Minneapolis, MN) under the"STANDAMULO"trademark) and mixtures of linear primary alcools (which are available from Shell (Houston, TX) under the"NEODOLO"trademark).

Preferred ether-containing monoalcohols include ethoxy methanol, methoxy ethanol, ethoxy ethanol. the isomeric methoxy or ethoxy propanols, the isomeric propoxy methanols and ethanols, the isomeric methoxy butanols, the isomeric butoxy methanols, furfuralcohol and other

monoalcohols which have a molecular weight of up to 2500 and are based on ethylene oxide, propylene oxide and/or butylene oxide. It is also possible in accordance with the present invention to use mixtures of the previously described monoalcohols.

Examples of suitable polyalcohols having two or more hydroxyl groups include ethane diol, 1,3-propanediol, 1,2-propanediol, 2-methyl-1,3- propanediol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, neopentylglycol, glycerol, pentaerythritol, trimethylol propane, ditrimethylol propane, 1,4-cyclohexane dimethanol, the monoester of neopentylglycol and hydroxy pivalic acid, 2,2,4-trimethyl pentanediol, and dimethylol propionic acid, and mixtures thereof. Other preferred polyalcohols for the production of suitable polyurethanes include polyester and polyether diols having a number average molecular weight of less than 1000, for example the polyester diol prepared form 1 mole of phthalic anhydride and 2 moles of neopentyl glycol. It is also possible in accordance with the present invention to use mixtures of the polyalcohols and mixtures of a polyalcohol and the previously described monoalcohols.

Preferably, isocyanate functional compound comprising an allophanate structure are prepared from 1,6-hexamethylene diisocyanate and/or isophorone diisocyanate reacted with an alcohol, preferably butanol.

The isocyanate functional compounds comprising a uretdione or an allophanate structure may be blended together, with the previously described monomeric polyisocyanates, with other polyisocyanate adducts or with NCO prepolymers. These other polyisocyanate adducts include those containing isocyanurate, biuret, and urethane groups. Examples

include the isocyanurate of hexamethylene diisocyanate, the isocyanurate of isophorone diisocyanate, and the adduct of trimethylolpropane and m- tetramethylxylylene diisocyanate.

The NCO prepolymers are prepared from the previously described monomeric polyisocyanates or polyisocyanate adducts, preferably monomeric diisocyanates, and organic compounds containing at least two isocyanate-reactive groups, preferably at least two hydroxy groups. These organic compounds include high molecular weight compounds having number average molecular weights of 400 to about 6,000, preferably 800 to about 3,000, and optionally low molecular weight compounds with molecular weights below 400. Products obtained by reacting polyisocyanates exclusively with low molecular weight compounds are polyisocyanates adducts containing urethane groups and are not considered to be NCO prepolymers. Examples of the high molecular weight compounds are polyester polyols, polyether polyols, polyhydroxy polycarbonates, polyhydroxy polyacetals, polyhydroxy polyacrylates, polyhydroxy polyester amides and polyhydroxy polythioethers. The polyester polyols, polyether polyols and polyhydroxy polycarbonates are preferred. Further details concerning the low molecular weight compounds and the starting materials and methods for preparing the high molecular weight polyhydroxy compounds are disclosed in U. S 4,701,480. These NCO prepolymers are prepared in known manner by the reaction of the above-mentioned starting materials at an NCO/OH equivalent ratio of about 1.05: 1 to 10: 1 preferably about 1.1: 1 to 3: 1. This reaction may take place in a suitable solvent which may optionally be removed by distillation after the reaction along with any unreacted volatile starting polyisocyanates still present.

The isocyanate functional compounds comprising a uretdione and/or an allophanate structure should be present in an amount of at least 5% by weight, preferably at least 10% by weight, based on the solids content of the polyisocyanate component.

Optionally other compounds may be present in the coating composition according to the present invention. Such compounds may be main binders and/or reactive diluents comprising reactive groups which may be cross- linked with the aforesaid oxazolidine functional compounds and/or isocyanate functional compounds comprising a uretdione and/or allophanate structure. Examples include hydroxyl-functional binders, e. g., polyester polyols such as described in H. Wagner et al., Lackkunstharze, 5th ed., 1971 (Carl Hanser Verlag, Munich), polyether polyols, polyacrylate polyols, polyurethane polyols, cellulose acetobutyrate, hydroxyl-functional epoxy resins, alkyds, and dendrimeric polyols such as described in WO 93/17060. Also, hydroxyl-functional oligomers and monomers, such as castor oil and trimethylolpropane may be present. Finally, ketone resins, aspargyl acid esters, and latent or non-latent amino-functional compounds such as ketimines, aldimines, diimines, secondary amines, and polyamines may be present. These and other compounds are known to the skilled person and are mentioned, int. al., in US 5,214,086.

The ratio of isocyanate groups to isocyanate-reactive groups is 0.25 to 1.5, preferably 0.75 to 1.25. At least 20 wt% of the compounds comprising isocyanate-reactive groups consists of oxazolidine functional compounds, preferably at least 30 wt%.

The coating composition may also contain catalysts to accelerate the reaction rate of oxazolidine and isocyanate functional compounds. The catalysts used may be aromatic or aliphatic carboxylic acids, arylsulphonic acids, and organometal compounds. Acids which are useful are formic acid, acetic acid, mono-, di, and trichloro acetic acid, oxalic acid, maleic acid, malonic acid, fumaric acid, heptanoic acid, pelargonic acid, isononanoic acid, benzoic acid, 4-hydroxybenzoic acid, mono-, di-, and trichlorobenzoic acid, and salicylic acid and anhydrides thereof. Preferred acids are acetic acid, heptanoic acid, and benzoic acid. Useful organometal compounds include zinc alkanoate, such as zinc octoate, dibutyltin dilaurate, dibutyltin (bis) mercaptide, dibutyltin diacetate, and dibutyltin sulphide. Preferred is dibutyltin dilaurate. Also mixtures of the above- mentioned catalysts may be used.

Optionally pigments may be present in the coating composition of the present invention. Useful pigments are various types common to the art which include but are not limited to titanium dioxide, graphite, carbon black, zinc oxide, calcium sulphide, chromium oxide, zinc sulphide, zinc chromate, strontium chromate, barium chromate, lead chromate, lead cyanamide, lead silico chromate, yellow nickel titanium, yellow chromium titanium, red iron oxide, yellow iron oxide, black iron oxide, naphtol red and browns, anthraquinones, dioxa zinc violet, isoindoline yellow, arylide yellow and oranges, ultramarine blue, phthalocyanine complexes, amaranth, quinacridones, halogenated thioindigo pigments, extender pigments such as magnesium silicate, aluminium silicate, calcium silicate, calcium carbonate, fumed silica, barium sulphate, and zinc phosphate.

Preferably, the coating composition comprises less than 500 g/l of volatile organic solvent based on the total composition, more preferably less than 480 g/l, most preferably less than 420 g/l. The solid resin content preferably is higher than 50%, more preferably higher than 52%, most preferably higher than 58%.

Coating compositions described by the present invention find utility as clearcoat, basecoat, topcoat, and primer.

The coating composition of the present invention can be used in the preparation of coated substrates. These substrates include glass, ceramics, paper, wood, plastic and metal. The coating composition is especially useful in the refinish industry, in particular the body shop, to repair automobiles. The coating composition is also applicable in the automotive industry for the finishing of large transport vehicles, such as trains and buses, and can also be used on airplanes. The substrate may be uncoated material or can be primed. The substrate may also be coated with paint products applied at the time of manufacture or just prior to application of the compositions of the present invention. The coating composition can be applied using conventional spray equipment or high volume low- pressure spray equipment resulting in a high quality finish. Other modes of application are roller coating, brushing, sprinkling, flow coating, dipping, electrostatic spraying or electrophoresis, spraying being preferred.

Exemplary metal substrates include steel aluminium, copper, zinc, magnesium, and alloys thereof. Curing temperatures are preferably between 0 and 80°C, and more preferably between 20 and 60°C.

The invention is further illustrated by the following examples.

Examples Methods: The viscosity is measured in a DIN flow cup number 4 in accordance with DIN 53221-1987. The viscosity is given in seconds.

The VOC of the coating composition is measured in accordance with ASTM 3960-92.

The pot life is the time between the initial mixing of all components and the point where the viscosity has increased to 2 times the initial viscosity.

A coating is free to handle (FTH) when the mark from firm pushing with the thumb disappears after 1 or 2 minutes.

The hardness is measured using ISO 1522-1973, except that a steel plate, treated as indicated in the examples, is used instead of a glass plate.

The gloss is measured in accordance with ISO 2813: 1994 (angle 20°). The gloss is expressed in GU.

The Enamel Hold Out (EHO) is determined as the total visual appearance.

Each sample is rated for visual appearance on a scale of 1 to 10 (1= very bad appearance, 10 = excellent appearance) by a panel of at least 3 people. The determination takes into account gloss, wrinkling, flow and image clarity/distinctness of image. The average number will give the EHO.

DOI is determined by projecting a standard (original) image on a coating.

The sharpness of the reflected image and of the original image is compared. If the reflected image is (nearly) as sharp as the original image, the DOI of the coating is high. If the reflected image is much less sharp than the original image, the DOI of the coating is low.

The following compounds were used.

Pupox A (polyurethane oxazolidine) is the reaction product of 1 mole of isophorone diisocyanate and 2 moles of"INCOZOL@"3 available from Industrial Copolymers Ltd (Preston, Lancashire, UK), i. e. an oxazolidine produced from diethanolamine and isobutyraldehyde.

Pupox B (polyurethane oxazolidine) is the reaction product of 1 mole of 2,2,4-trimethyl hexane diisocyanate and 2 moles of"INCOZOL@"3.

Pupox C (polyurethane oxazolidine) is the reaction product of 1 mole of tetramethyl meta-xylylene diisocyanate and 2 moles of"INCOZOL"'3.

"INCOZOL@"LV is the reaction product of 1 mole of diallyl carbonate and 2 molesof"lNCOZOL@"3.

"ZOLDINE@"RD20 LC is 1-aza-3,7-dioxo-2,8-diisopropyl-5-ethyl bicyclo (3,3,0) octane available from Angus Chemical Company (Buffalo Grove, IL).

"DESMODUR""LS2138 is an isocyanate functional compound based on the allophanate of isophorone diisocyanate available from Bayer (Pittsburgh, PA) (solids content is 80% in butylacetate).

"DESMODUR@"N3400 is an isocyanate functional compound based on the uretdione of hexamethylene diisocyanate.

"DESMoDUR@"N3390 is an isocyanate functional compound based on the isocyanurate of hexamethylene diisocyanate (solids content is 90% in butylacetate).

"VESTANAR"T1890 is an isocyanate functional compound based on the isocyanurate of isophorone diisocyanate available from Huis (Chicago, IL) (solids content is 70% in butylacetate).

"DESMoDUR@"LS2025/1 is a low viscous isocyanate functional compound based on isocyanurate of hexamethylene diisocyanate.

"CYTHANE@"3160 is an isocyanate functional compound based on the adduct of trimethylolpropane and m-tetramethylxylylene diisocyanate available from Cytec Industries Inc. (West Paterson, NJ) (solids content is 80% in methyl ethyl ketone/butylacetate (1/1)).

"DESMODUR@"IL is an aromatic polyisocyanate based on toluene diisocyanate (solids content is 51% in butylacetate).

"MONDUR""MRS is an aromatic polyisocyanate based on diphenylmethane-4,4'-diisocyanate (Bayer).

PUPO is a polyurethane polyol being the reaction product of isophoronediisocyanate and 2-ethyl-2-butyl-1,3-propane diol having a viscosity of 2.8 Pa. s, a solids content of 60.8%, a hydroxyl value of about 136 mg KOH/g resin solids, an Mn of 1300 and a Mw 1800 (polystyrene standard on GPC). The PUPO was prepared as follows: Into a two liter round bottom reaction vessel equipped with a stirrer, packed column, condenser, heating mantle, thermometer, and nitrogen inlet, were charged: 426 g of 2-butyl-2-ethyl-1, 3-propanediol, 440 g of butyl acetate, and 0.11 g of dibutyltin dilaurate.

The mixture was heated under a nitrogen atmosphere to 55°C. Then 934 g of a 70% solution in butylacetate of the isocyanurate trimer of IPDI (available as"VESTANATE)"T 1890 E from Huis) were added over a period of about 60 minutes. During this addition the temperature was not allowed to exceed 70°C. After complete addition, the mixture was post-reacted at 70°C until the NCO-content, calculated on solid ingredients, dropped below 0.1 wt%. After cooling, a clear polyurethane polyol solution was obtained.

PE is a polyester polyol being the reaction product of hexahydrophthalic anhydride, trimethylol propane, isononanoic acid, and phthalic anhydride, having a solids content of 80.5. %, a viscosity of 7.5 Pa. s measured at 20 °C, an acid value or 9.3 mg KOH/g resin solids and a hydroxyl value of 145 mg KOH/g resin solids. The polyester polyol had an Mn of 1900 and an Mw of 4500 (as measured by gel permeation chromatography using polystyrene as a standard). The PE was prepared as follows: Into a 10 liter round bottom reaction vessel equipped with a stirrer, packed column, condenser, heating mantle, thermometer, and nitrogen inlet, were charged: 2608 g of hexahydrophthalic anhydride, 2981 g of trimethylol propane, 2015 g of isononanoic acid, 195 g of phthalic anhydride, and 9.2 g of an aqueous solution comprising 85% phosphoric acid.

The reaction mixture was heated under a nitrogen stream of 10 liter/hour.

The temperature of the mixture was gradually raised to 240°C. The reaction water was distille off at a rate such that the temperature at the top of the packed column did not exceed 103°C. After the reaction was run at 240°C for one hour, the nitrogen stream was increased to 50 liter/hour and the reaction continued at 240°C until an acid value of 9.3 was reached.

The reaction mixture was then cooled to 130°C and diluted with 1,817 g of butylacetate.

"DESMoPHEN@"670-80 is a polyester resin available from Bayer.

"JONCRYL"SCX 910 is an acrylic resin available from S. C. Johnson & Son (Racine, WI).

DBTL is dibutyl tin dilaurate.

"FASCAT3"4202 is a tin catalyst available from Elf Atochem (Philadelphia, PA).

"NUXTRA@"Zinc is a zinc catalyst (Huls).

The levelling agent is a 25 wt. % mixture of Byk 332 and Byk 355 (weight ratio 10/15) in butyl acetate.

Byk 332, Byk 333, Byk, 355, and Byk 358 are levelling agents available from Byk Chemicals (Wallington, CT).

"SOLVESSO"100 is a solvent blend available from Exxon (Houston, TX).

"EXXATEO"600 is a solvent blend (Exxon).

Example 1 and Comparative Example A A two-component polyurethane primer"AUToCRYL@"filler 3+1 available from Akzo Nobel Coatings, Inc. (Norcross, GA) was applied by spraying onto a sanded steel panel. After sanding of the filler, a metallic solvent borne basecoat"AUToBASE@"MM metallic basecoat (Akzo Nobel Coatings Inc.) was sprayed onto it. After the basecoat was dried at room

temperature for 30 minutes, a clearcoat composition according to the present invention was applied by being sprayed on top of it. The coating was cured at room temperature and at elevated temperature (at 60°C). The dry-layer thickness of the clearcoat was 60 microns. For comparison, a clearcoat composition comprising an isocyanate functional compound having an isocyanurate structure instead of a uretdione structure was also prepared. The coating compositions and their properties are listed in Table 1. All amounts are given in grams. The ratio of isocyanate groups to isocyanate-reactive groups is 1 for both compositions.

Table 1 Example 1 Example A Pupox A 75. 0 50 Desmodur N 3400 96. 9---- DesmodurX N 3390 73.5 DBTL (10% xylene/butyl acetate (1/1)) 3. 4 1. 1 acetic acid (10% in butyl acetate) 3.4 1.1 levelling agent 2. 3 1.5 ethyl amyl ketone 53. 5 52.6 Properties Example 1 Example A | VOC (theor) (g/l) 354 432 VOC (ASTM) (g/ 315 389 Viscosity (sec.) 16.1 17.5 potlife (min.) 150 75 Drying (RT); FTH (min.) 56 82 Drying (60°C); FTH (min.) 20 20 Potlife/FTH (drying at 60°C) 7. 5 3 75 Gloss (20°, in GU) 85 85 DOI 70 70

The comparison shows that the use of an isocyanate having a uretdione structure result in a clearcoat composition having a lower VOC at the same viscosity and that the pot life drying balance is far better than clearcoat compositions comprising an isocyanate functional compound having an isocyanurate structure. Other paint properties are on the same level.

Example 2 and Comparative Example B Steel panels coated with a filler and a basecoat were prepared as described in Example 1. A clearcoat composition according to the invention and a comparative clearcoat composition were applied by spraying on top of the basecoat. The coating was cured at room temperature and at elevated temperature (at 60°C). The coating compositions and their properties are listed in Table 2. All amounts are given in grams. The ratio of isocyanate groups to isocyanate-reactive groups is 1 for both compositions.

Table 2

Example 2 Example B Pupox B 50 50 Desmodut""LS2138 124. 1---- Vestanat T1890----119 DBTL (10% xylene/butyl acetate (1/1)) 2. 3 1. 1 acetic acid (10% in butyl acetate) 2. 3 1. 1 levelling agent 3. 8 3.8 ethyl amyl ketone 50. 5 50.6 Properties Example 2 Example B VOC (theor) (g/ 402 457 VOC (ASTM) (g/1) 359 380 Viscosity (sec.) 16.6 16.4 potlife (min.) 240 240 Drying (RT); FTH (min.) 88 95 Drying (60°C); FTH (min.) 40 45 Potlife/FTH (drying at 60°C) 6 5. 3 Gloss (20°, in GU) 85 85 DOI 80 80 The comparison shows that the use of an isocyanate having an allophanate structure result in a clearcoat composition having a lower VOC at the same viscosity and that the pot life drying balance is far better than clearcoat compositions comprising an isocyanate functional compound

having an isocyanurate structure. Other paint properties are on the same level.

Example 3 and Comparative Example C Steel panels coated with a filler and a basecoat were prepared as described in Example 1. A clearcoat composition according to the invention and a comparative clearcoat composition were applied by spraying on top of the basecoat. The coatings were cured at room temperature. The coating compositions and their properties are listed in Table 3. All amounts are given in grams. The ratio of isocyanate groups to isocyanate-reactive groups is 1 for both compositions Table 3 Example 3 Example C incozol LV 63. 4 63.4 DesmodurN3400/185. 4'1 Cythanee 3160 (1/1 wt ratio on solids) Desmodurs LS2025/1/182.8 Cythane 3160 (1/1 wt ratio on solids) DBTL (10% xylene/butyl acetate (1/1)) 3. 2 3. 2 acetic acid (10% in butyl acetate) 1.6 1.6 levelling agent 3 3 butyl acetate/Solvesso 100/41. 1 65.4 ethoxyethyl propionate (1/1/1 wt. ratio) Properties Example 3 Example C VOC (theor) (g/l) 297 352 Viscosity (sec.) 17.9 17.4 potlife (min.) >180 >180 Drying (RT); FTH (min.) 270 >300 EHO 9 7 Persoz Hardness after 1 week 164 184 Gloss (20°, in GU) 86 86 DOI 95 90

The comparison shows that the use of an isocyanate having a uretdione structure results in a clearcoat composition having a lower VOC at the same viscosity and that the pot life drying balance is far better than clearcoat compositions comprising an isocyanate functional compound having an isocyanurate structure. Other paint properties are on the same level.

Examples 4 and 5 Steel panels coated with a filler and a basecoat were prepared as described in Example 1. Two clearcoat compositions according to the invention were applied by spraying on top of the basecoat. The coating was cured at room temperature and at elevated temperature (at 60°C). The coating compositions and their properties are listed in Table 4. All amounts are given in grams. The ratio of isocyanate groups to isocyanate-reactive groups is 1 for both compositions.

Table 4 Example 4 Example 5 Pupox A 50---- Pupox C----75 Desmodur N3400/Desmodur LS2025/1 77.7 112.1 (1/1 wt ratio on solids, SC is 82% in butyl acetate) DBTL (10% xylene/butyl acetate (1/1)) 2. 3 3. 5 acetic acid (10% in butyl acetate) 1.1 1.7 levelling agent 1.5 2.3 butyl acetate/Solvesso 100/ethoxyethyl 21 26.7 propionate (1/1/1 wt. ratio)

Properties Example 4 Example 5 VOC (theor) (g/l) 370 350 Viscosity (sec.) 19 19 potlife (min.) 150 200 Drying (RT); FTH (min.) 150 150 Drying (60°C); FTH (min.) 30 30 EHO 7 8 Persoz Hardness after 2 weeks 105 72 Gloss (20°, in GU) 90 90 DOI 80 90

Example 6 A steel panel coated with a filler and a basecoat were prepared as described in Example 1. A clearcoat composition according to the invention was applied by spraying on top of the basecoat. The coating was cured at room temperature. The coating compositions and their properties are listed in Table 5. All amounts are given in grams. The ratio of isocyanate groups to isocyanate-reactive groups is 1.

Table 5 Example 6 Incozols LV 50 PUPO 100 Desmoduro N3400/Desmodur LS2025/1 159.2 (1/1 wt ratio on solids, SC is 82% in butyl acetate) DBTL (10% xylene/butyl acetate (1/1)) 1. 2 acetic acid (10% in butyl acetate) 1.6 levelling agent 3.0 butyl acetate/Solvesso 100/ethoxyethyl propionate (1/1/1 wt. 39.6 ratio) Properties Example 6 VOC (theor) (g/ 364 Viscosity (sec.) 17 potlife (min.) 60 Drying (RT); FTH (min.) 280 EHO 7 Persoz Hardness after 2 weeks 120 DOI 75

Example 7 A clearcoat according to the present invention was prepared as follows. All amounts in Table 6 are given in weight percentage. The ratio of isocyanate groups to isocyanate-reactive groups is 0.83. The components are listed in order of addition. All components were added while stirring and were mixed on an air mixer for a minimum of 20 minutes after the addition was complet.

Table 6 Component A Example 7 PE 42.97 PUPO 13.55 Byk 358 0.23 Byk 333 0.28 Fascat 4202 0.10 Nuxtra Zinc 0.65 ButylAcetate 13.81 Exxate 600 5.35 methyl isobutyl ketone 6.42 ButylCellosolveAcetate 2.14 dibasic ester aliphatic 1.66 methyl amyl ketone 12.87 Component B Example 7 Desmodurs N 3390 53.73 Vestanates T1890 34.51 Desmodur'N 3400 10. 89

Component C Example 7 Zoldinee RD20 LC 66.00 Incozols LV 34.00 The components A, B and C were mixed by weight in the following amounts 40.00 grams A, 91.00 grams B, and 41.81 grams C. To the

mixture of Example 7,15.20 grams of butyl acetate were added in order to bring the viscosity below 20 seconds. The VOC of the composition was 285 g/l.

Example 8 A primer according to the present invention was prepared. The composition is provided in Table 7. All amounts in Table 7 are given in weight percentage. The ratio of isocyanate groups to isocyanate-reactive groups is 1.1.

Table 7 Desmophens670-80 4 Joncryls SCX 910 4 Zoldine'RD20 LC 12. 8 IncozolsLV 4.2 Desmodurs IL 14 Mondurs MRS 15.8 Desmodurs N 3400 3 Pigments 20.8 Flowagent 4.7 Solvents 16.8

The primer was prepared as follows. Into a clean, dry tank were charged and mixed: 776.7115 g DISPERBYK-110 (dispersant) (Byk) 268.0569 g butyl acetate

While mixing, the following were added: 650.6976 g DESMOPHEN 670A-80 650.6976 g JONCRYL SCX 910 The following were then added under mixing: <BR> <BR> <BR> <BR> 53.4307 g COSMIC BLACK D-2 (carbon black) (Ebonex,<BR> <BR> <BR> Melvindale, MI)<BR> <BR> <BR> <BR> 379.9135 g BLANC FIXE MICRO (filler pigment) (Sachtleben Chemie, Duisburg, Germany) 975.1328 g TALC 399 LO MICRON MAGNESIUM SILICATE (filler pigment) (Barretts Minerals, Bethlehem, PA) 703.8150 g WOLLASTOCOAT 10ES (filler pigment) (Nyco, Willsboro, NY) <BR> <BR> <BR> <BR> 703.8755 g TI-PURE R-902 28 (TiO2) (DuPont, Wilmington, DE)<BR> <BR> <BR> <BR> 626.4065 g HALOX CW 491 (anticorrosive pigment) (Halox Corp., Hammond, IN) Mixing was continued for five minutes, then DYNOMILL ground to 20-25 microns, as verified by a quality control grind check. The following was then added while mixing: 600.0000 g butyl acetate A quality control check was made of 1 quart to check the percentage of <BR> <BR> <BR> non-volatiles (acceptable is 81.8 2.0). Also checked was Stormer<BR> <BR> <BR> viscosity (95-100 Krebs units) and density (14.07 + 0.5 Ibs./gal). It is important that the tank be kept closed during this quality control check.

The batch must be filled within 24 hours. The batch was filtered through a 100 micron bag.

Activator Into a clean, dry tank were charged: <BR> <BR> <BR> <BR> <BR> 200.7000 g ZOLDINE RD-20<BR> <BR> <BR> <BR> <BR> <BR> 66.6700 g INCOZOL LV This was mixed on low speed for 5 minutes. Then the following was added and mixed together for 30 minutes: <BR> <BR> <BR> <BR> <BR> 1.4400 g DESMOPHEN 670A-80<BR> <BR> <BR> <BR> <BR> <BR> 0.3600 g MULTIFLOW (flow and leveling agent) (Monsanto, St. Louis, MO) <BR> <BR> <BR> <BR> <BR> 37.5000 g methyl amyl ketone<BR> <BR> <BR> <BR> <BR> <BR> 37.5000 g ethyl amyl ketone<BR> <BR> <BR> <BR> <BR> <BR> 88.8900 g butyl acetate A 1 quart sample was subject to a quality control check for density (7.42 0.5) and viscosity in a # 4 cup at 77°F (12.0 2.0). It is important that the tank be kept closed during the quality control check.

Hardener Under conditions to minimize moisture content, into a clean, dry, closed tank blanketed with nitrogen, were dosed and mixed on low speed for 10 minutes: 4.5359 lb DESMODUR IL 5.1454 lb MONDUR MRS 0.9681 lb DESMODUR 3400 Water content was checked on a 4 oz. sample. Water content should be less than 1500 ppm. Then was added: 0.1817 lb n-butyl acetate 0.0872 lb DOWANOL PMA (Dow, Midland, MI) 0.0654 lb butyl cellosolve acetate 0.0291 lb Aromatic 100 (Exxon) Water content was again checked. The solvent blend was mixed on low speed for 30 minutes. A 1 quart sample was subject to a quality control check for density (9.65 0.5), percentage non-volatiles (75.1 2.0) and viscosity with #4 cup at 77°F (60.0 3.0). It is important that the tank be kept closed during the quality control check. The batch must be filled within 24 hours and filtered through a 10 micron bag. The VOC of the composition was 2.8 Ib/gal. (335 g/I)