Uretdione-containing polyurethane-dispersions comprising hydrophilic groups

The present invention relates to a specific uretdione prepolymer, and an aqueous curable composition based on the specific uretdione prepolymer. Furthermore, it pertains to a process for curing said aqueous curable composition, the cured article obtained by this process and additionally to the use of said aqueous composition for coatings, adhesives and/or sealants.

Aqueous curable compositions based on specific uretdione prepolymers are for example known from DE 10 2005 036 654 Al. However, those compositions do not show a sufficient long-term stability. The hydrophilization of the polymer is obtained via ionogenic groups.

Therefore, it was an object of the present invention to provide an uretdione prepolymer, which provides an improved aqueous curable composition, which shows improved, preferably long-term, storage stability.

It has been surprisingly found by the present inventors that following uretdione prepolymer can overcome the above-mentioned deficiency:

An uretdione prepolymer, which comprises at least one uretdione group, and which is obtainable by reacting

Al) at least one uretdione polyisocyanate having an isocyanate functionality of at least 2.0, whereby said uretdione polyisocyanate is obtained from at least one aliphatic polyisocyanate, with

A2) at least one polyalkoxy ether derivative comprising at least two -OH groups, which are present on two different non-neighbouring atoms of the molecule and whereby at least one of the -OH groups is not a terminal -OH group,

and

A3) at least one reactant, which comprises at least one Zerewitinoff-active group and being different from A2 or which is ¾0,

preferably in the presence of at least one catalyst, to obtain the uretdione prepolymer;

wherein the prepolymer has an acid number of at most 4 mg KOH/g, preferably determined according to DIN EN ISO 2114:2002-06 as 37 wt.% aqueous dispersion.

When the uretdione prepolymer of the present invention is employed in aqueous curable compositions, the thus obtained compositions are homogenous after storage over a long time, can retain a high amount of uretdione groups, compared to the initially used ones, the uretdione groups can be reacted with alcohols or amines, whereby a crosslinking of the prepolymers is obtained, the reaction of the uretdione group with alcohol can be catalysed and the cured product obtained by these compositions show equivalent or even improved lacquer properties. Not to be bound by any theory it is assumed that the use of compounds A2 in the preparation of the prepolymer leads to this properties, since it promotes chain growth and provides a better cross-linking

In the present invention, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of " 1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In the present invention, a "monomer" is a low-molecular weight compound comprising functional moieties, wherein said monomer functions as a building block for polymers and has a defined molecular weight.

In the present invention the term„polymer“ refers to a compound, formed during a chemical reaction by linking several monomers (i.e. more than two monomers) of the same or different kind together via covalent bonding, wherein the resulting polymer can differ in its degree of polymerization, molecular weight distribution and chain length respectively. Hence, a polymer according to the present invention is a compound, comprising in its molecular structure at least one repeating unit, which was integrated in the polymer structure during polymer synthesis by repeatedly linking monomers together via covalent bonds to form said polymer structure. The number average molecular weight is preferably at least 250 g/mol, more preferably at least 1,000 g/mol.

The term "polymer" includes homopolymers, copolymers, block-copolymers and oligomers.

In the present invention, a "prepolymer" is a polymer with reactive groups. In analogy to the definition of the term„polymer“, the molecular structure of a prepolymer is formed by repeatedly linking more than two monomers of the same of different kind together. The prepolymer can participate in a subsequent formation of a polymer, which has a higher molecular weight than said prepolymer. The term“prepolymer” encompasses polymers, which are able to chemically react via at least one of its reactive groups, forming a repeating unit of a (preferably crosslinked) polymer. Therefore the term „prepolymer“ encompasses as well self-crosslinking polymers with at least two different kinds of reactive groups, wherein said groups are able to chemically react among themselves, so that the prepolymer molecules are able to crosslink.

According to this invention, if not otherwise specified, the average molecular weight is defined as the number average molecular weight Mn. As molecular weight of polymers the number average molecular weight Mn is applied. Mn is determined via gel permeation chromatography (GPC at 23°C) in tetrahydrofurane as the solvent. The measurement is performed as described in DIN 55672-1 (the DIN-version used was at the application date (or priority date if applicable) of the present invention, the latest version): "Gelpermeationschromatographie, Teil 1 - Tetrahydrofuran als Elutionsmittel" (SECurity GPC-System from PSS Polymer Service, flowrate 1,0 ml/min; colums: 2xPSS SDV linear M, 8x300 mm, 5 pm; RID-detector). Samples of polystyrene standards of known molecular weight were used for calibration. The calculation of the number average molecular weight was performed by software. Baseline values and evaluation threshold values were determined according to above referenced DIN 55672 Teil 1.

The term„low-molecular“ is defined to encompass a molecular weight up to 800 g/mol.

The term„high-molecular“ is defined to encompass a molecular weight above 800 g/mol.

An„organic compound" contains at least one moiety, comprising a carbon-hydrogen covalent bond.

According to this application the term„aliphatic" is defined as non-aromatic hydrocarbyl groups being saturated or unsaturated.

According to this application the term„araliphatic" is defined as hydrocarbyl moieties composed of a non-aromatic, as well as saturated or unsaturated hydrocarbyl group, which is directly bonded to an aromatic moiety.

According to this application the term "alicyclic" or "cycloaliphatic" are optionally substituted, carbocyclic or heterocyclic compounds or moieties, which are non-aromatic (like for example cycloalkanes, cycloalkenes or oxa-, thia-, aza- or thiazacycloalkanes). Particular examples are cyclohexyl groups, cyclopentyl groups, and their N- or O-heterocyclic derivatives like for example pyrimidine, pyrazine, tetrahydropyrane or tetrahydrofurane.

In case the groups or compounds are disclosed to be "optionally substituted" or "substituted", suitable substituents are -F, -Cl, -I, -Br, -OH, -OC¾, -OCH2CH3, -O-Isopropyl or -O-nPropyl, -OCF3, -CF3, -S-Ci- ₆ -Alkyl and/or (optionally via a hetero atom attached) a linear or branched, aliphatic and/or alicyclic structural unit with 1 to 12 carbon atoms, respectively functioning as a substitute for a carbon bound hydrogen atom of the molecule in question. Preferred substituents are halogen (especially -F, -Cl), Ci- ₆ -Alkoxy (especially methoxy and ethoxy), hydroxy, trifluoromethyl and trifluoromethoxy, respectively functioning as a substitute for a carbon bound hydrogen atom of the molecule in question. In a formula illustrating the structure of a chemical moiety, a covalent bond of said formula marked with a * defines the covalent bond, which connects said illustrated moiety to the rest of a more complex molecular structure.

The term“transparent” preferably means that the coating (with a thickness of 45pm) is capable of transmitting rays of visible light so bodies situated beyond or behind can be distinctly seen. Transparent coatings according to this invention exhibit a Haze-value < 20 (Haze measurement instrument: DIN EN ISO 2813 (the DIN-version used at the application date (or at the priority date if applicable) of the present invention at the latest version).

The present invention in particular pertains to:

1. An uretdione prepolymer, which comprises at least one uretdione group, and which is obtainable by reacting

Al) at least one uretdione polyisocyanate having an isocyanate functionality of at least 2.0, whereby said uretdione polyisocyanate is obtained from at least one aliphatic polyisocyanate, with

A2) at least one polyalkoxy ether derivative comprising at least two -OH groups, which are present on two different non-neighbouring atoms of the molecule and whereby at least one of the -OH groups is not a terminal -OH group, and

A3) at least one reactant, which comprises at least one Zerewitinoff-active group and being different from A2 or which is ¾0,

preferably in the presence of at least one catalyst, to obtain the uretdione prepolymer;

wherein the prepolymer has an acid number of at most 4 mg KOH/g, preferably determined according to DIN EN ISO 2114:2002-06 as 37 wt.% aqueous dispersion.

2. The uretdione prepolymer according to aspect 1, characterized in that

in a first step, the at least one uretdione polyisocyanate Al is reacted, preferably in the presence of a catalyst, with the at least one polyalkoxy ether derivative A2, wherein after the first step the resulting intermediate product has preferably an isocyanate content of 0.5 to 10 wt.-%, preferably 1 to 6 wt.-%, more preferably 2 to 4 wt.-%, measured according to DIN EN ISO 11909:2007-05;

and in a second step the polymer obtained in the first step is reacted with the at least one reactant A3.

3. The uretdione prepolymer according to aspect 1, characterized in that

the components Al to A3 are reacted in a one-step process, preferably in the presence of a catalyst. The uretdione prepolymer according to aspect 1, characterized in that in a first step, the at least one uretdione polyisocyanate A1 is reacted with the at least one reactant A3 and in a second step the polymer obtained in the first step is reacted in a second step with the at least one polyalkoxy ether derivative A2, preferably in the presence of a catalyst. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione prepolymer is a nonionic prepolymer. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione prepolymer exhibits a zeta potential of at least -20 mV. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione prepolymer comprises at least one *-0-(CH ₂ CH ₂ 0) _n -R moiety, in which R is a hydrogen atom or a (Ci-C -alkyl group and n is a number from 3 to 100. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione polyisocyanate A1 is obtained from at least one cycloaliphatic polyisocyanate. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione polyisocyanate A1 is obtained from isophorone diisocyanate (IPDI), 1,6- diisocyanatohexane (HDI) or mixtures thereof. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione polyisocyanate A1 is prepared from at least 20 mol% isophorone diisocyanate (IPDI) based on the total amount of polyisocyanates used. The uretdione prepolymer according to any one of the above aspects, characterized in that said uretdione polyisocyanate A1 is prepared from isophorone diisocyanate as the only polyisocyanate used. The uretdione prepolymer according to any one of the above aspects, characterized in that the uretdione polyisocyanate A1 contains from 1 to 10 uretdione moieties. The uretdione prepolymer according to any one of the above aspects, characterized in that compound A2 is selected from compounds of formula (I):

characterized in that

X is H or alkyl, preferably H or Ci-20-alkyl, more preferably H or C2-io-alkyl;

R is a C14 alkylene group;

p is an integer of 2 to 50;

in each unit p

n is independently 0 or 1 and

m is independently 0 or 1,

with the proviso that at least one of n or m in each unit p is 1 ;

preferably characterized in that

X is H, methyl, ethyl, or propyl, preferably ethyl;

R is methyl;

p is an integer of 5 to 25;

in each unit p

n is independently 0 or 1 and

m is independently 0 or 1,

with the proviso that at least one of n or m in each unit p is 1 and the total amount of n > m, preferably the total amount of n is at least 2*m, more preferably n is at least 3*m, most preferably only n is present. The uretdione prepolymer according to any one of the above aspects, characterized in that compounds A3 is selected from at least one polyol which is different from A2, preferably selected from polyester polyols, polyether polyols, polyurethane polyols, polyacrylate polyols, polymethacrylate polyols, polycarbonate polyols or mixtures thereof, preferably A3 is selected from polyester polyols, polyether polyols, polycarbonate polyols, polyurethane polyols, polyacrylate polyols, polymethacrylate polyols, C2-C 10-hydrocarbons with at least two hydroxyl groups, or mixtures thereof, most preferably A3 is a polyester polyol. The uretdione prepolymer according to any one of the above aspects, characterized in that said compound A1 is used in an amount of 3.0 to 50.0 wt.% based on the total weight of compounds A1 to A3. The uretdione prepolymer according to any one of the above aspects, characterized in that said compound A2 is used in amount of 50 to 97 wt.-% based on the total weight of compounds A1 to A3. The uretdione prepolymer according to any one of the above aspects, characterized in that the weight ratio of A 1 to A2 is from 1 : 1 to 1 : 32.3. An aqueous, curable composition, comprising or consisting of

the uretdione prepolymer according to any one of aspects 1 to 17, and

optionally at least one compound, which comprises at least one Zerewitinoff- active group and/or

optionally at least one azolate-compound. The aqueous, curable composition according to aspect 18, characterized in that said uretdione prepolymer is a dispersed uretdione prepolymer, preferably characterized in that the uretdione prepolymer is suspended in the aqueous liquid. The aqueous, curable composition according to aspect 18 or 19, characterized in that said uretdione prepolymer is contained in a total amount of 3 to 40 wt.% based on the total weight of the composition. The aqueous, curable composition according to any one of aspects 18 to 20, characterized in that said composition is substantially free of compounds comprising at least one isocyanate moiety. The aqueous, curable composition according to any one of aspects 18 to 21, characterized in that said azolate-compound is selected from at least one triazolate-compound of formula (III) or salts thereof and formula (IV) or salts thereof

(III) (IV)

characterized in that

R ¹ , R ² , R ³ and R ⁴ are independently selected from a hydrogen atom, a halogen atom, a nitro group, a saturated or unsaturated, aliphatic or cycloaliphatic radical, an optionally substituted aromatic group comprising up to 20 carbon atoms and optionally up to 3 heteroatoms selected from oxygen, sulphur, nitrogen, an optionally substituted araliphatic group comprising up to 20 carbon atoms and optionally up to 3 heteroatoms selected from oxygen, sulphur, nitrogen, and whereby R ³ and R ⁴ of formula (IV) together with the carbon atoms of the 1,2,3-triazolate five-membered ring form fused rings with 3 to 6 carbon atoms. The aqueous, curable composition according to aspect 22, characterized in that said azolate- compound is selected from alkaline metal-l,2,4-triazolate, alkaline metal- 1,2,3-triazolate, alkaline metal-benzotriazolate, alkaline earth metal-l,2,4-triazolate, alkaline earth metal-1, 2,3- triazolate, alkaline earth metal-benzotriazolate. The aqueous, curable composition according to any one of aspects 18 to 23, characterized in that said at least one compound, which comprises at least one Zerewitinoff-active group is selected from polyester polyols, polyether polyols, polyurethane polyols, polyacrylate polyols, polymethacrylate polyols, or polycarbonate polyols and mixtures thereof. The aqueous, curable composition according to any one of aspects 18 to 24, characterized in that said uretdione prepolymer is contained in an amount of 1 to 50 wt.% and/or

said at least one compound, which comprises at least one Zerewitinoff-active group is contained in an amount of 0 to 80 wt.-% and/or

said triazolate-compound is contained in an amount of 0.1 to 10 wt.%, based on the total weight of the composition, respectively. The aqueous, curable composition according to any one of aspects 18 to 25, characterized in that the composition comprises water in an amount of 10 to 85 wt.%, based on the total weight of the composition. The aqueous, curable composition according to any one of aspects 18 to 26, characterized in that the pH-value at 20°C is from pH 5 to pH 13. Process for curing a liquid composition on a substrate, comprising

a) applying on a substrate an aqueous, curable composition according to any one of aspects 18 to 27; and

a) exposing the deposited aqueous, curable composition to a temperature of 60°C to

160°C to cure said deposited curing composition. A cured article obtainable by the process according to aspect 28. 30. Use of the composition according to any one of aspects 18 to 27 for coatings, adhesives and/or sealants.

Suitable uretdione polyisocyanates A1 are typically obtained by catalytic dimerization of polyisocyanates by methods which are known in the art. Examples of suitable polyisocyanates include diisocyanates such as linear aliphatic polyisocyanates, cycloaliphatic polyisocyanates and alkaryl polyisocyanates. Specific examples include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI), 2,4’- and/or 4,4

'-diisocyanatocyclohexylmethane (HMD1), isophorone diisocyanate (IPDI), 1,3- and 1,4- bisisocyanatomethylcyclohexane, 1,3- and 1,4-xylylene diisocyanates (XDI) and mixtures thereof.

Examples of dimerization catalysts are: trialkylphosphines, aminophosphines and aminopyridines such as dimethylaminopyridines, and tris(dimethylamino)phosphine, as well as any other dimerization catalyst known to those skilled in the art. The result of the dimerization reaction depends, in a manner known to the skilled person, on the catalyst used, on the process conditions and on the polyisocyanates employed. In particular it is possible for products to be formed which contain on average more than one uretdione group per molecule, the number of uretdione groups being subject to a distribution.

The uretdione polyisocyanate A1 preferably on average contains from 1 to 10 uretdione moieties.

Preferably said uretdione polyisocyanate A1 is prepared from at least one cycloaliphatic polyisocyanate. In another preferred embodiment, said uretdione polyisocyanate A1 is prepared from at least 20 mol% isophorone diisocyanate (IPDI) based on the total amount of polyisocyanates used. Said uretdione polyisocyanate A1 is most preferred prepared from isophorone diisocyanate as the only polyisocyanate used. Alternatively the uretdione polyisocyanate A1 is preferably prepared from isophorone diisocyanate (IPDI), 1,6- diisocyanatohexane (HDI) or mixtures thereof.

Preferred uretdione polyisocyanates are for example commercially available as Desmodur N3400 from Covestro Deutschland AG, Leverkusen, Germany.

Component A2 is at least one polyalkoxy ether derivative comprising at least two -OH groups, which are present on two different non-neighbouring atoms of the molecule and whereby at least one of the -OH groups is not a terminal -OH group. Preferred embodiments are defined in formula (I) above.

Preferred commercially available examples are Ymer™ N120 (CAS number: 131483-27-7) by Perstorp Holding AB, Malmo, Sweden and Tegomer® D 3403 (Evonik Industries AG, Essen, DE). Component A3 is at least one reactant, which comprises at least one Zerewitinoff-active group and being different from A2 or H2O; preferably at least one Zerewitinoff-active group and being different from A2.

A“Zerewitinoff-active group” is defined as a functional group, comprising at least one Zerewitinoff- active hydrogen atom, being an acidic hydrogen atom or active hydrogen atom. The abundance of such an active hydrogen atom is determined by a known reaction of the compound in question with a Grignard reagent. The amount of Zerewitinoff-active hydrogen atoms is typically determined by measuring the amount of released methane gas, and subsequently calculated in consideration of the stoichiometry of the following reaction equation, wherein for each mole of active hydrogen atoms of the compound in question (R-XH) one mole of methyl magnesium bromide (CEb-MgBr) is used and one mole of methane is released:

CHs-MgBr + R-XH -> CH ₄ + Mg (XR)Br

Zerewitinoff-active groups are in particular C-H active organic groups, -OH, -SH, -NH2 or -NHR‘ wherein R‘ denotes an organic moiety. Preferably Zerewitinoff-active groups are selected from -OH, -SH, -NH2 or -NHR‘ wherein R‘ denotes an organic moiety. Especially preferred, the Zerewitinoff- active groups according to the invention are

-OH. A particularly preferred uretdione prepolymer as component A+B) comprises as Zerewitinoff- active groups at least two hydroxy groups.

It was also found, that the curing time was improved by introducing hydrophilic groups as grafts or terminus into the structure of said uretdione prepolymer. It is preferred, when said hydrophilic groups do not comprise an ionic moiety. A preferred uretdione prepolymer comprises grafts with at least one hydrophilic group selected from polyoxyalkylene ether capped with methyl, ethyl, propyl or butyl, polyethyleneoxide capped with one methyl group, Polyethyleneoxide capped with one ethyl, propyl, or butyl group. Particularly preferred uretdione prepolymers comprise additionally on average at least one *-0-(CH ₂ CH ₂ 0)„-R moiety, in which R denotes a (Ci-C -alkyl group and n denotes a number from 3 to 100. n denotes preferably a number from 5 to 70, more preferably from 7 to 55. R is preferably a methyl group.

Said hydrophilic groups are introduced into the structure of said uretdione prepolymer by (preferably nonionic) hydrophilizing agents. Suitable nonionically hydrophilizing agents are, for example, polyoxyalkylene ethers which have isocyanate-reactive groups, such as hydroxy, amino or thiol groups. A preference is given to monohydroxy-functional poly alky lene oxide poly ether alcohols having, on statistical average, 5 to 70, preferably 7 to 55, ethylene oxide units per molecule, as are accessible in a manner known per se by alkoxylation of suitable starter molecules (e.g. in Ullmanns Encyclopadie der technischen Chemie [Ullmanns encyclopaedia of industrial chemistry], 4th edition, Volume 19, Verlag Chemie, Weinheim pp. 31-38). These are either pure polyethylene oxide ethers or mixed polyalkylene oxide ethers, where they contain at least 30 mol%, preferably at least 40 mol%, ethylene oxide units, based on all of the alkylene oxide units present.

Suitable starter molecules for such nonionic hydrophilizing agents are in particular saturated monoalcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomeric pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n- hexadecanol, n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols or hydroxymethylcyclohexane, 3-ethyl-3 -hydro xymethyloxetane or tetrahydrofurfuryl alcohol, diethylene glycol monoalkyl ethers, such as, for example, diethylene glycol monobutyl ether, unsaturated alcohols, such as allyl alcohol, 1,1-dimethylallyl alcohol or oleyl alcohol, aromatic alcohols, such as phenol, the isomeric cresols or methoxyphenols, araliphatic alcohols, such as benzyl alcohol, anisyl alcohol or cinnamyl alcohol, secondary monoamines, such as dimethyl amine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, bis(2-ethylhexyl)amine, N-methyl- and N-ethylcyclohexylamine or dicyclohexylamine, and also heterocyclic secondary amines, such as morpholine, pyrrolidine, piperidine or lH-pyrazole. Preferred starter molecules are saturated monoalcohols of the type specified above. Particular preference is given to using diethylene glycol monobutyl ether or n-butanol as starter molecules.

Alkylene oxides suitable for the alkoxylation reaction are in particular ethylene oxide and propylene oxide, which can be used in the alkoxylation reaction in any desired order or else in a mixture.

Particularly preferred nonionic hydrophilizing agents are monofunctional mixed polyalkylene oxide polyethers, which have 40 to 100 mol% ethylene oxide units and 0 to 60 mol% propylene oxide units.

Suitable polyol as compound A3 is preferred selected from polyester polyol, polyether polyol, polyurethane polyol, polycarbonate polyol, polyacrylate polyol, polymethacrylate polyol, C2-C10- hydrocarbon with at least two hydroxyl groups, or mixtures thereof.

The term "polyol" includes materials having an average of two or more primary hydroxyl groups per molecule. The polyols useful in the practice can be either low or high molecular weight materials and in general will have average hydroxyl values as determined by ASTM designation E-222-67, Method B, between about 1000 and 2, and preferably between about 500 and 2. The polyols include low molecular weight diols, triols and higher alcohols and polymeric polyols such as polyester polyols, polyether polyols, polyurethane polyols and hydroxy-containing (meth)acrylic polymers. The low molecular weight diols, triols and higher alcohols useful in the instant invention are known in the art. For the most part they are monomeric and have hydroxy values of 200 and above, usually within the range of 1500 to 200. Such materials include aliphatic polyols, particularly alkylene polyols containing from 2 to 18 carbon atoms. Examples include ethylene glycol, 1,4-butanediol, 1,6- hexanediol; cycloaliphatic polyols such as cyclohexane dimethanol. Examples of triols and higher alcohols include trimethylol propane and pentaerythritol. Also useful are polyols containing either linkages such as diethylene glycol and triethylene glycol.

The most suitable polymeric polyols are those having hydroxyl values less than 200, such as 10 to 180. Examples of polymeric polyols include polyalkylene ether polyols, polyester polyols including hydroxyl-containing polycaprolactones, hydroxy-containing (meth)acrylic polymers, polycarbonate polyols and polyurethane polyols.

Examples of polyether polyols are poly(oxytetramethylene) glycols, poly(oxyethylene) glycols, poly(oxypropylene) glycols, and the reaction product of ethylene glycol with a mixture of propylene oxide and ethylene oxide.

Also useful are polyether polyols formed from the oxyalkylation of various polyols, for example, glycols such as ethylene glycol, 1 ,4-butane glycol, 1 ,6-hexanediol, and the like, or higher polyols, such as trimethylol propane, pentaerythritol and the like. One commonly utilized oxyalkylation method is by reacting a polyol with an alkylene oxide, for example, ethylene oxide in the presence of an acidic or basic catalyst.

Polyester polyols can also be used as a polymeric polyol component in the practice of the invention. The polyester polyols can be prepared by the polyesterification of organic polycarboxylic acids or anhydrides thereof with organic polyols. Usually, the polycarboxylic acids and polyols are aliphatic or aromatic dibasic acids and diols.

The diols which are usually employed in making the polyester include alkylene glycols, such as ethylene glycol and butylene glycol, neopentyl glycol and other glycols such as cyclohexane dimethanol, caprolactone diol (for example, the reaction product of caprolactone and ethylene glycol), polyether glycols, for example, poly(oxytetramethylene) glycol and the like. However, other diols of various types and, as indicated, polyols of higher functionality can also be utilized. Such higher polyols preferably include, for example, trimethylol propane, trimethylol ethane, pentaerythritol, and the like, as well as higher molecular weight polyols such as those produced by oxyalkylating low molecular weight polyols. A particularly preferred example of such high molecular weight polyol is the reaction product of 20 moles of ethylene oxide per mole of trimethylol propane. The acid component of the polyester polyols consists primarily of monomeric carboxylic acids or anhydrides having 2 to 18 carbon atoms per molecule. Among the acids which are useful are phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, glutaric acid, chlorendic acid, tetrachlorophthalic acid and other dicarboxylic acids of varying types. Also, there may be employed higher polycarboxylic acids such as trimellitic acid and tricarballylic acid (where acids are referred to above, it is understood that the anhydrides of those acids which form anhydrides can be used in place of the acid). Also, lower alkyl esters of acids such as dimethyl glutarate can be used.

Besides polyester polyols formed from polybasic acids and polyols, polycaprolactone-type polyesters can also be employed. These products are formed from the reaction of a cyclic lactone such as epsilon- caprolactone with a polyol with primary hydroxyls such as those mentioned above. Such products are described in U.S. Pat. No. 3,169,945 to Hostettler.

In addition to the polyether polyols and polyester polyols, hydroxy-containing (meth)acrylic polymers or (meth)acrylic polyols can be used as the polyol component.

Among the (meth)acrylic polymers are polymers of about 2 to 20 percent by weight primary hydroxy- containing vinyl monomers such as hydroxyalkyl acrylate and methacrylate having 2 to 6 carbon atoms in the alkyl group and 80 to 98 percent by weight of other ethylenically unsaturated copolymerizable materials such as alkyl (meth)acrylates; the percentages by weight being based on the total weight of the monomeric charge.

Examples of suitable hydroxy alkyl (meth)acrylates are hydroxyl ethyl and hydroxy butyl (meth)acrylate. Examples of suitable alkyl acrylates and (meth)acrylates are lauryl methacrylate, 2-ethylhexyl methacrylate and n-butyl acrylate.

Besides the acrylates and methacrylates, other copolymerizable monomers which can be copolymerized with the hydroxyalkyl (meth) acrylates are ethylenically unsaturated materials such as monoolefinic and diolefinic hydrocarbons, halogenated monoolefinic and diolefinic hydrocarbons, unsaturated esters of organic and inorganic acids, amides and esters of unsaturated acids, nitriles and unsaturated acids and the like. Examples of such monomers include styrene, 1,3-butadiene, acrylamide, acrylonitrile, alpha-methyl styrene, alpha-methyl chlorostyrene, vinyl butyrate, vinyl acetate, alkyl chloride, divinyl benzene, diallyl itaconate, triallyl cyanurate and mixtures thereof. Usually these other ethylenically unsaturated materials are used in admixture with the above- mentioned acrylates and methacrylates. The mean weight average molecular weight M _w of the uretdione prepolymer, measured with GPC as described above, but with N,N-dimethylacetamide instead of tetrahydrofurane as solvent and calculated as M _w is preferably in the range of 20,000 to 800,000 g/mol, particular preferred in the range of 100,000 to 500,000 g/mol.

The uretdione prepolymer exhibits an acid number of at most 4 mg KOH/g, preferably at most 3.5 mg KOH/g, particularly preferably 3.0 mg KOH/g, most preferably at most 2.5 mg KOH/g (each determined according to DIN EN ISO 2114:2002-06). This significantly reduces the curing time of the aqueous composition. The acid number is measured according to DIN EN ISO 2114:2002-06. The sample for determining the acid number essentially consists (or consists) of 37 wt.% uretdione prepolymer and water and instead of a mixture of toluene and ethanol as described in DIN EN ISO 2114:2002-06, a mixture of acetone and ethanol in a weight ratio of 2: 1 was used.

The uretdione prepolymer preferably exhibits a zeta potential of -20 mV or higher. The zeta potential of the uretdione prepolymer is preferably determined from a dispersion of uretdione prepolymer in water as the sample. One drop of a preformed dispersion of the uretdione prepolymer is highly diluted with 20 ml of demineralized water and homogenized by stirring, leading to the sample. Subsequently the zeta potential is determined at 23°C in the Malvern Nanosizer ZS90 instrument (Malvern Instruments, Herrenberg, Germany). The given values of the zeta potential are always related to said sample of the dispersed uretdione polymer.

The uretdione prepolymer comprises on average at least one uretdione group. It is preferred, that the uretdione prepolymer comprises on average at least two uretdione groups. Preferred uretdione prepolymers of this invention are self-curing prepolymers. It is preferred, that the uretdione prepolymer comprises on average at least two Zerewitinoff-active groups. During heat induced curing, the uretdione prepolymer will (self-)crosslink via reaction of said uretdione groups with said Zerewitinoff-active groups. The more uretdione groups and Zerewitinoff-active groups are on average comprised in said uretdione prepolymer (or said reactant), the better.

It was found, that it was even possible to cure at low temperature uretdione prepolymers, which were prepared from at least one aliphatic uretdione polyisocyanate (especially cycloaliphatic uretdione polyisocyanate), preferably from at least 20 mol% aliphatic uretdione polyisocyanate based on the total amount of polyisocyanates used, particularly preferred only from aliphatic uretdione polyisocyanates.

The uretdione polyisocyanate A1 is used in an amount of 3 to 50 wt.-% based on the total amount of reactants used for preparation of said uretdione prepolymer. The sum of compounds A2 and A3 is preferably used in an amount of 50 to 97 wt.-% based on the total amount of reactants used for preparation of said uretdione prepolymer.

For preparation of said uretdione prepolymer it is particularly preferred to use the uretdione polyisocyanate A1 in relation to said compound A2 in a weight ratio from 1 : 1 to 1 : 32.3.

Most preferably, compound A2 is used in a total amount of 1 to 25 wt.-%, preferably 5 to 20 wt.-% and compound A3 is used in a total amount of 20 to 70 wt.-%, preferably 35 to 65 wt.-%, based on the total amount of reactants used for preparation of said uretdione prepolymer.

The aqueous, curable composition preferably comprises less organic solvents compared to conventional curing compositions. According to the invention, water is used in the composition as a component (preferably as the main component) of the liquid continuous phase of the dispersion. Replacement of organic solvents, especially of low-VOC compounds, by water leads to more ecologically friendly compositions. Preferred compositions according to the invention are characterized in that they comprise water preferably in an amount of 10 to 85 wt.%, particularly preferred in an amount of 30 to 75 wt.%, most preferred in an amount of 50 to 70 wt.%, also preferred in an amount from 40 to 70 wt.%, most preferred in an amount of 60 to 70 wt.%, based on the total weight of the composition respectively.

The aqueous, curable compositions of the invention have a preferred pH- value at 20°C of from pH 5 to pH 13, more preferred from pH 6 to pH 12, even more preferred from pH 7 to pH 9.

In order to further improve the physiological compatibility, the composition of the invention is preferably substantially free of compounds comprising at least one isocyanate group. Due to the water present in the composition, the majority up to all isocyanate groups will hydrolyze. Preferably the content of the isocyanate groups (expressed as NCO, M.G. 42g/mol) is below 0.05 wt.-%. Particularly preferred, the composition of the invention is free of compounds comprising at least one isocyanate moiety. Unless expressly mentioned otherwise, NCO contents were determined volumetrically in accordance with DIN-EN ISO 11909 (the DIN-version used at the application date (or at the priority date if applicable) of the present invention at the latest version).

In a preferred embodiment, the composition comprises said uretdione prepolymer in a total amount of 1 to 50 wt.%, preferably 3 to 40 wt.% and most preferred 30 to 40 wt.%, based on the weight of the total composition. Preferred compositions of this embodiment of the invention comprise at least one Zerewitinoff-active compound. Suitable compounds are the compounds as disclosed above for A2 and A3. Preferred compound are selected from polyester polyol, polyether polyol, polycarbonate polyol, polyurethane polyol, polyacrylate polyol, polymethacrylate polyol, C ₂ -Cio-hydrocarbon with at least two hydroxyl groups, or mixtures thereof.

The aqueous, curable composition of this invention preferably comprises at least one azolate - compound. According to the Hantzsch-Widman-nomenclature (IUPAC-rule RB-1.2, R-2.3.3.1) an azole is the generic term for unsaturated five-membered heterocyclic compounds, comprising in the cycle one nitrogen atom and in addition to that optionally at least one or more further hetero atoms including nitrogen atom. An azolate-compound according to this invention comprises an azole-anion (azolate).

Preferred azolate compound comprise a five-membered N-heterocycle. The ring of said preferred N- heterocycle contains an amount of n nitrogen atoms with n = 1, 2 or 3 and an amount of (5-n) carbon atoms. In addition to that, the five membered ring of said N-heterocycle comprises two endocyclic double bonds. Said endocyclic double bonds are preferably conjugated double bonds. The five- membered N-heterocycle is negatively charged. Said negative charge is delocalized. Preferably, the endocyclic double bonds contribute to the delocalization of the negative charge.

Preferred compositions comprise at least one azolate-compound of formula (II)

wherein

one, two or three moieties of X ¹ , X ² , X ³ and X ⁴ independently of one another represent the moiety “-N=" wherein the rest of the moieties of X ¹ , X ² , X ³ and X ⁴ independently of one another represent "-CR=", wherein R independently represents H, Ci to C ₂₀ alkyl, C ₃ to C ₂₀ cycloalkyl C ₆ to C ₂₀ aryl, Ci to C ₂ alkoxy, -NR ₂ (R'=Ci to C ₂₀ alkyl), -NO ₂ , fluorine, chlorine, bromine, fluorinated Ci-C ₆ -alkyl, fluorinated Ci-C ₆ -alkoxy, cyano, carboalkoxy, -S-R" (R"=Ci to C ₂₀ alkyl), and/or -S-(C ₆ to C ₂₀ aryl) and in the event two adjacent subsitutents of X ¹ to X ⁴ represent "-CR=", the substituents R of these substituents together with the C-atoms of these substituents may form a further annellated carbo- or heterocyclic, n-membered ring system where n=3 to 10, wherein the annellated carbo- or heterocyclic ring system may, independently of one another, contain one or more heteroatoms (N, 0, S) and may be substituted independently of one another by one or more the same or different substituents from the following group: H, Ci to C20 alkyl, C3 to C20 cycloalkyl C ₆ to C20 aryl, Ci to C2 alkoxy, -NR' ₂ (R'=Ci to C20 alkyl), -NO2, fluorine, chlorine, bromine, fluorinated Ci-C ₆ -alkyl, fluorinated Ci-C ₆ -alkoxy, cyano, carboalkoxy, -S-R" (R"=Ci to C20 alkyl), and/or -S-(C ₆ to C20 aryl), Cat ⁺ is a counterion.

The cycle of formula (II) represents a p-system, comprising the two endocyclic double bonds and the delocalized charge.

The azolate compounds are usually prepared by deprotonation of a neutral azole compound. Deprotonation is achieved preferably with a base, preferably with alkaline alkoxides like sodium methanolate, alkaline earth alkoxides, alkaline hydroxides or alkaline earth hydroxides. The azolate compound of formula (II) is prepared by deprotonization of neutral compounds of formula (II- 1) with a base, preferably with at least one of the above mentioned preferred bases,

wherein X ¹ , X ² , X ³ and X ⁴ are defined according to formula (II).

Other suitable neutral compounds for preparation of the azolate compound according to the invention include pyrrole, substituted pyrroles and carbocyclic and/or heterocyclic annellated derivatives of pyrrole.

Other suitable neutral compounds for preparation of the azolate compound according to the invention include pyrazole and/or imidazole, substituted pyrazoles and/or imidazoles and carbocyclically and/or heterocyclically annellated derivatives of pyrazole and/or imidazole.

Other suitable neutral compounds for preparation of the azolate compound according to the invention include triazole, preferably selected from 1,2,3- and 1,2,4-triazoles, substituted species of 1,2,3- and 1,2,4-triazoles and carbocyclically and/or heterocyclically annellated species of 1,2,3- and 1,2,4- tri azoles.

To produce the azolate compound, in principle all five-membered N-heterocycles may be used which carry at least one hydrogen atom bound to a ring nitrogen atom. Examples of these include pyrrole, indole, carbazole and substituted derivatives such as 5-nitroindole or 5-methoxyindole, pyrazole, indazole and substituted derivatives such as 5-nitroindazole, imidazole and substituted derivatives such as 4-nitroimidazole or 4-methoxyimidazole, benzimidazole or substituted benzimidazoles, for example 5-nitrobenzimidazole, 5-methoxybenzimidazole, 2-trifluoromethylbenzimidazole, hetero aromatic annellated imidazoles such as pyridinoimidazole or purine, 1,2,3-triazole and substituted derivatives such as 4-chloro-5-carbomethoxy-l, 2, 3-triazole or 4-chloro-5-cyano-l, 2, 3-triazole, 1,2,4- triazole and substituted derivatives such as 3, 5-dibro mo triazole, 1,2,3-benzotriazole and substituted

1.2.3-benzotriazole such as 5-fluor- 1,2,3-benzotriazole, 5-trifluoromethyl-l,2,3-benzotriazole, 5-nitro-

1.2.3-benzotriazole, 5-methoxy-l,2,3,-benzotriazole, 5-chloro- 1,2,3-benzotriazole, 5- tetrafluoroethoxy- 1,2,3-benzotriazole, 5-trifluorothio- 1,2,3-benzotriazole, 4,6-bis-(trifluoromethyl)-

1.2.3-benzotriaole, 4-trifluoromethoxy-5-chloro- 1,2,3-benzotriazole and heteroaromatic annellated

1.2.3-triazoles such as the isomeric pyridinotriazoles, for example the lH-l,2,3-triazolo[4,5-b]pyridine - referred to in the remainder of the text as pyridinotriazole- and azapurine.

In particularly preferred compositions of the invention, the composition comprises at least one triazolate-compound as component C).

Said triazolate-compound is most preferably selected from at least one triazolate-compound of formula (III) or their corresponding salts and formula (IV) or their corresponding salts

(III) (IV)

wherein

R ¹ , R ² , R ³ and R ⁴ independent from one another denote a hydrogen atom, a halogen atom, a nitro group, a saturated or unsaturated, aliphatic or cycloaliphatic radical, an optionally substituted aromatic group comprising up to 20 carbon atoms and optionally up to 3 heteroatoms selected from oxygen, sulphur, nitrogen, an optionally substituted araliphatic group comprising up to 20 carbon atoms and optionally up to 3 heteroatoms selected from oxygen, sulphur, nitrogen,

and where R ³ and R ⁴ of formula (IV) together with the carbon atoms of the 1,2,3-triazolate five- membered ring form fused rings with 3 to 6 carbon atoms.

Said triazolate-compound is particularly preferred selected from alkaline metal-l,2,4-triazolate, alkaline metal- 1,2,3-triazolate, alkaline metal-benzotriazolate, alkaline earth metal-l,2,4-triazolate, alkaline earth metal- 1,2,3-triazolate, alkaline earth metal-benzotriazolate. Especially preferred, the triazolate-compound is selected from alkaline metal- 1,2, 4-triazolate, alkaline metal- 1,2,3-triazolate, alkaline metal-benzotriazolate. Sodium 1,2, 4-triazolate, potassium 1,2, 4-triazolate, sodium 1,2,3- triazolate, potassium 1,2,3-triazolate, sodium benzotriazolate, potassium benzotriazolate and mixtures thereof are the most preferred triazolate-compounds.

It was proven advantageous to preferably apply curable compositions, which comprise said azolate- compound, preferably said triazolate-compound, in an amount of 0.1 to 10.0 wt.%, particularly preferred of 0.3 to 3 wt.%, based on the weight of the composition respectively. Particularly preferred curable compositions of the invention comprise said uretdione prepolymer in an amount of 1 to 50 wt.%, preferably 3 to 40 wt.% and most preferred 30 to 40 wt.% and said azolate-compound, preferably said triazolate-compound, in an amount of 0.1 to 10.0 wt.%, preferably 0.3 to 3 wt.-%, based on the weight of the composition respectively.

In addition to the ingredients mentioned the composition above may contain various optional ingredients. Examples of these are dyes, pigments, fillers and reinforcing agents, for example calcium carbonate, silicates, talc, kaolin, mica and barium sulfate. Other additives, for example plasticizers, lubricants and rheological additives and solvent or diluent may be included in the compositions. When present, these optional ingredients may constitute up to 50% by weight of the composition based on total weight of the composition.

Of particular interest is the use of the compositions of the invention for preparing coatings on substrates of all kinds. Such coatings are preferably protective and decorative coatings such as exterior coatings on substrates of all kinds, for example buildings, fences, chipboard panels, and as a coating on stone, concrete or metal, for the coating of vehicles, for example, such as cars, railways or aircraft. The compositions may likewise be used in automotive OEM finishing and automotive refinish, and also for the finishing of car bodies, plastic parts for cars and body-mounted car parts.

The compositions of the invention can also be used as sealants or adhesives.

Furthermore, the present invention pertains to a process for curing a liquid composition on a substrate, comprising

a) applying on a substrate an aqueous, curable composition according to the present invention; and

b) exposing the deposited aqueous, curable composition to a temperature of 60°C to 160°C to cure said deposited curing composition.

Using known coating processes, the aqueous, curable composition may be applied uniformly to a substrate, for example by spin coating, dip coating, knife coating, curtain coating, brushing, spraying— especially electrostatic spraying— and reverse roll coating. Said coating compositions can be used as a primer, color coat or as a clear coat.

The previously described preferred embodiments of said aqueous, curable composition are of course also preferably used in the process of this invention.

The choice of diluent and the concentration depend predominantly on the choice of coating ingredients and the coating process. The diluent should preferably be inert. In other words, it should not undergo any chemical reaction with the components and should be capable of being removed after the coating operation in the curing process. Surprisingly it was found, that especially water is an appropriate diluent. Examples of suitable diluents are water, ketones, ethers and esters, such as methyl ethyl ketone, isobutyl methyl ketone, cyclopentanone, cyclohexanone, N-methylpyrrolidone, dioxane, tetrahydrofuran, 2-methoxy ethanol, 2-ethoxy ethanol, l-methoxy-2-propanol, 1 ,2-dimethoxy ethane, ethyl acetate, n-butyl acetate and ethyl 3-ethoxypropionate. It is particularly preferred to use water as diluent.

It is particularly preferred, that the deposited aqueous curable composition coalesces to form a coating. The coating thickness upon drying is typically from 0.5 to 46 pm. If the coating is a base coat, the coating thickness upon drying is preferably 15 to 20 pm. If the coating is a top coat, the coating thickness upon drying is preferably 45 to 50 pm.

The deposited aqueous, curable composition is preferably exposed to a temperature of 60 to 120°C, preferably 80 to 100°C, to cure said deposited curing composition.

According to the process of the invention, the deposited aqueous, curable composition is preferably exposed to said temperature for a period of 20 to 45 minutes to cure said deposited curing composition. It is particularly preferred to expose the deposited aqueous, curable composition to a temperature of 60 to 120°C, preferably 80 to 100°C, for a period of 20 to 45 minutes.

It is also preferred to cure said deposited, aqueous curable composition by preheating the deposited, curable composition to a temperature of 30°C to below 60°C for a period of 2 to 10 minutes. Said preheating is particularly preferred followed by increasing the temperature to 60 to 160°C (preferably to 60 to 120°C, most preferred to 80 to 100°C) and exposing for another period of 20 to 45 minutes at said increased temperature. The preheating step is advantageous, since the amount of water is reduced in the deposited, curable composition prior to curing. The subsequent curing reaction at 60°C to 160°C is thereby enhanced. Preferably, the cured aqueous curable composition forms a crosslinked film on the substrate, preferably forms a transparent solid on the substrate, that shows excellent mechanical and optical properties and a high resistance against chemicals and solvents.

Examples:

Compounds:

Ymer N120 (CAS number: 131483-27-7), a linear, trimethylolpropane started polyethylene glycol monomethyl ether, OH number 100-120 mg KOH/g) was acquired from Perstorp Holding AB, Malmo, Sweden.

Polyester 1 OH-functional polyester prepared from 3039 g adipic acid, 4041 g isopthalic acid, 267 g 1,2-propylene glycol, 4773 g neopentyl glycol and 1419 g trimethylol propane (OH number: 181 mg KOH/g, acid number < 3 mg KOH/g)

Other chemicals were - unless otherwise stated - purchased at Sigma-Aldrich Chemie GmbH, Munich, Germany

IPDI uretdione (“IPDI-dimer”): To 1000 g (4.50 mol) of isophorone diisocyanate (IPDI) were added at room temperature under dry nitrogen and stirring 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed from volatile components without prior addition of a catalyst poison with the aid of a thin-film evaporator at a temperature of 160 ° C and a pressure of 0.3 mbar.

This gave a pale yellow uretdione with a content of free NCO groups of 17.0%, a content of monomeric IPDI of 0.4% and a viscosity (according to DIN EN ISO 3219: 1994-10) of more than 200,000 mPas (23 °C). Measurement methods:

Unless noted otherwise, all of the analytical measurements refer to measurements at temperatures of 23 °C.

All percentages refer, unless otherwise stated, to the weight.

The solids contents (non-volatile contents) were determined by heating a weighed sample (approx lg) at 105 °C to constant weight. At constant weight, the solid-body content is calculated by reweighing the sample.

The pendulum hardness by the Konig method was measured on a glass plate according to DIN EN ISO 1522:2007-04.

NCO contents were determined volumetrically in accordance with DIN-EN ISO 11909:2007-05. The control on free NCO groups was carried out by means of IR spectroscopy (band at 2260 cm ¹ ).

The stated viscosities were determined by means of rotary viscometry in accordance with DIN 53019:2008-09 at 23 °C using a rotary viscometer with a shear rate of 186 1/s, from Anton Paar Germany GmbH, Ostfildern, Germany.

The average particle sizes (the number-average is given) of the polyurethane dispersions were determined following dilution with deionized water by means of laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malver Inst. Limited, London, UK).

Zeta potential was measured by diluting one drop of the sample with 20 ml demineralized water and homogenized by stirring. Subsequently the zeta potential is determined at 23°C in the Malvern Nanosizer ZS90" (Malvern Instruments, Herrenberg, Germany).

Acid number of the respective dispersion was determined according to DIN ISO 2114 1:2006-11. Instead of a mixture of toluene and ethanol - as described in DIN ISO 2114 1:2006-11- a mixture of acetone and ethanol (2: 1 by weight) was used as solvent. The unit of the acid number is mg KOH per g of the analyzed sample.

Solvent resistance and water resistance:

The cured coating films were tested for their resistance to xylene and water. A piece of cotton wool soaked with the test substance was placed on the coating surface and covered with a watch glass. After the specified exposure time, the cotton wool was removed; the exposed site was dried and immediately inspected. The evaluation of the softening or discoloring of the coating surface was carried out following the DIN EN ISO 4628-1 :2016-07:

0: unchanged, i.e. no perceptible change

1 : very slight, i.e. barely perceptible change

2: slight, i.e. clearly perceptible change

3: moderate, i.e. very clearly perceptible change

4: considerable, i.e. pronounced change

5: very marked change

Infrared measurements:

The uretdione ring opening was characterized by an FT-IR spectrometer (tensor P with Platinum ATR unit (diamond crystal) from Bruker). The spectra were recorded in a wave number range of (4000-400) cm ¹ . The maximum of the uretdione peak (about 1760 cm ¹ ) was evaluated. Peak heights to comparative systems were compared with an initial value set to 100% (uretdione film without catalyst, dried at room temperature) and variations relative to this (ratio formation). Uretdione peak height of films cured for 30 min at 180 °C were set to 0%. When measuring on an ATR crystal, the intensity of the spectrum depends on the occupation of the crystal surface. Since a comparable coverage of the crystal surface cannot be ensured in the case of different measurements by the sample preparation, a correction of this effect must be made for the ratio formation by normalizing all spectra on the peak of the CH stretching vibration (wave number range (3000-2800 cm ¹ ). In the case of the evaluation of peak heights as described above, a baseline correction of the spectra is additionally carried out.

Preparation of uretdione prepolymer dispersion A (according to the invention)

149.0 g of“IPDI uretdione” were dissolved in 580 g acetone at 50°C in a standard stirring apparatus. 64.6 g of Ymer N120 and 0.53 g of tin neodecanoate were added and the mixture was stirred at reflux under atmospheric pressure until the NCO content of 2.5% was reached. Then 213.2 g of polyester 1 were added and the mixture was stirred under reflux at atmospheric pressure until the NCO content dropped below 0.5%. The mixture was then dispersed by adding 213.2 g of water. The solvent was removed by distillation in vacuum; solid content was adjusted by addition of water.

The resulting white dispersion had the following properties:

Solids content: 37%

Average particle size (LCS): 107 nm

Viscosity (viscometer, 23 °C): 118 mPas

pH (23 °C): 5.3

Acid number: 0.9 mg KOH/g

Zeta potential: - 16.4 mV Comparative Dispersion 1:

149.1 g of“IPDI-dimer” were dissolved in 580 g acetone at 50°C in a standard stirring apparatus. 63.4 g of Poly(ethylene glycol) methyl ether with an average Mn of 500 g/mol, 214.24 g of a OH- functional polyester 1 and 0.53 g of tin neodecanoate were added and the mixture was stirred at reflux under atmospheric pressure until the NCO content dropped below 0.5%. Then 794 g of water were added. The acetone was removed by distillation in vacuum; solid content was adjusted by addition of water.

The resulting white dispersion had the following properties:

Solids content: 35.7%

Average particle size (LCS): 166 nm

Viscosity (viscometer, 23 °C): 20 mPas

pH (23 °C): 5.4

Preparation of anionic uretdione prepolymer dispersion (comparative example)

Comparative Dispersion 2:

150.3 g of“IPDI-dimer” were dissolved in 594 g acetone at 50°C in a standard stirring apparatus. 12.8 g of dimethylol propionic acid, 201.3 g of a OH-functional polyester 1 and 0.55 g of tin neodecanoate were added and the mixture was stirred at reflux under atmospheric pressure until the NCO content dropped below 0.5%. Then 8.5 g N,N-dimethylamino-ethanol and 670 g of water were added. The acetone was removed by distillation in vacuum; solid content was adjusted by addition of water.

The resulting white dispersion had the following properties:

Solids content: 35.6%

Average particle size (LCS): 108 nm

Viscosity (viscometer, 23 °C): 5 mPas

pH (23 °C): 8.5

Acid number: 7.3 mg KOH/g

Zeta potential: - 45.7 mV

Tests of the coatings

Clear coatings were prepared from the following composition:

100 weight percent (20 g) of urethane prepolymer dispersion A (or comparative) was mixed with 6 weight percent (1.2 g) of a solution consisting of 0.12 g 1,2,4-Triazolate-Na and 1.08 g water.

The mixture was applied to glass or coil (CS-300570 coil coating test panel, purchased from Zanders PBL) using a coating squeegee with a layer thickness of 150-180 pm (wet). The plates were dried at room temperature for 5 minutes and then baked at various temperatures for 30 minutes. The obtained films were evaluated at 23°C at 50% relative humidity by pendulum hardness, water resistance and solvent resistance and an IR spectrum was recorded.

The following table shows the coating properties of the corresponding films.

Requirements for coatings:

- Pendulum hardness > 100 s

- Xylene test: < 4

- 10 weeks stable at room temperature and 40°C

Inventive Examples Exl (with catalyst) and Ex 2 (without catalyst):

Clear coat of the following compositions:

Coating Properties (before storage):

Coating properties of inventive dispersion (Ex 1) which were stored beforehand at room temperature and at 40 °C:

Comparative examples 1 and 2: Comparative Dispersion 1:

Clearcoat of the following compositions:

Coating Properties (before storage):

Comparative examples 3 and 4: Comparative Dispersion 2:

Clearcoat of the following compositions:

Coating Properties (before storage):

Coating properties of non-inventive dispersions after storage at 40 °C or with catalyst could not be performed due to instability of these dispersions.

Stability Measurements of Examples and Comparative Example 1:

Dispersions were stored at room temperature or in a 40 °C oven with or without catalyst for 10 weeks. Stability of dispersion was evaluated by IR measurement before/after storage.