Non-aqueous crosslinkable composition

Abstract

The present invention discloses a crosslinkable composition comprising a) at least one isocyanate-reactive compound, b) at least one polyisocyanate crosslinker having free isocyanate groups, c) at least one thermolatent metal-based catalyst for catalysing the reaction between the isocyanate-reactive groups of the isocyanate-reactive compound a) and the isocyanate groups of said polyisocyanate crosslinker b), d) at least one aromatic carboxylic acid, and / or at least one tertiary carboxylic acid. The present invention also discloses a coating composition comprising said crosslinkable composition and a method for applying said coating composition.

Description

[0001] NON-AQUEOUS CROSSLINKABLE COMPOSITION

[0002] Field of the Invention

[0003] The invention relates a crosslinkable composition comprising an isocyanate-reactive compound having free reactive groups, a polyisocyanate crosslinker, and a particular catalyst, and its use in coatings.

[0004] State of the Art

[0005] Two component polyurethane coatings are well-known in the art. Usually, they are formulated as two-pack systems, the first pack normally containing a polyol resin and the second pack comprising a crosslinking agent, often a polyisocyanate. Two component crosslinkable compositions, especially those that comprise a polyol and a polyisocyanate, are widely used in Automotive OEM coatings, especially clearcoats. These compositions are usually appreciated for their good flexibility, hardness, chemical resistance and appearance. In Automotive OEM, these two-component crosslinkable compositions are in general cured at 140 °C for 24 minutes, after which they display good resistance to chemicals and have good hardness.

[0006] Increasingly, high hardness values are also required shortly after curing. Such a high early hardness will enable earlier handling of an object treated with the crosslinkable composition and thus increasing the productivity. Preferably, use of highly toxic materials should be avoided. Because of economic and environmental reasons there is a tendency in the market to develop coatings which can be cured at lower temperatures (e.g. 80°C or lower) without substantially sacrificing the good resistance to chemicals and good hardness.

[0007] Formulations comprising polyols, polyisocyanates, a catalyst and an acid have been known since long and are for example disclosed in US 3808162, WO 2005 / 019362, WO 2007 / 020270 and WO 2013 / 131835.

[0008] WO2019072433 discloses fast curing systems comprising: a) at least one polyol having free -OH groups, b) at least one polyisocyanate crosslinker having free -NCO groups, c) at least one catalyst for catalysing the reaction between -OH groups and -NCO, d) at least one tertiary acid of formula RR'R"CCOOH (I), wherein each R, R' and R" group, independently, is an alkyl, alkenyl, aryl or aralkyl group containing at least one carbon atom, with the proviso that two or three of the R, R’ and R” groups can be linked to form a ring structure and wherein the R, R’ and / or R” groups can be substituted, and wherein the total number of carbon atoms in the R, R' and R" groups is the range of from 3 to 40, and e) optionally, at least one complexing agent containing at least one -SH group, wherein the tertiary acids perform as potlife extender. The claimed systems require a high level of tin-catalyst and still are characterized by a limited potlife.

[0009] US10815330 and WO2011051247 describe systems comprising a thermolatent catalyst enabling curing at 80 °C. Acidic compounds, such as 2-ethylhexanoic acid may be added to the crosslinkable compositions, which has a radiant man label for potentially damaging an unborn child, which is often unacceptable in today’s standards.

[0010] US10815330 provides a two-component system comprising:

[0011] • a component A) comprising at least one NCO-reactive compound and

[0012] • a component B) comprising at least one polyisocyanate and • at least one thermolatent inorganic tin-containing catalyst, wherein component A) comprises between 400 and 9500 ppmw of water based on the total weight of component A). An extended pot life without adversely affecting the catalytic activity of the thermolatent catalyst, for curing the applied two-component system by increasing the temperature, is claimed.

[0013] WO2011051247 provides a system comprising: a) at least one aliphatic, cycloaliphatic, araliphatic and / or aromatic polyisocyanate; b) at least one NCO-reactive compound; c) at least one thermolatent inorganic tin-containing catalyst; d) optionally further catalysts and / or activators different from c) and e) optionally fillers, pigments, additives, thickeners, defoamers and / or other auxiliaries and additives, with which it is possible to produce coatings based on polyisocyanate polyaddition products which, on preparation of the 2K mixture (generally at room temperature), have an open time which is not reduced or is reduced only slightly as compared with the uncatalyzed system but, after application to the substrate, cures in an accelerated manner as a result of a temperature increase and yields a coating which has the high level of qualities known for polyurethane systems.

[0014] Without questioning the positive properties of coating systems comprising the prior art crosslinkable compositions, there is still a need for improvement of Automotive OEM coatings, especially Automotive OEM clear coats, cured at temperatures below 100 °C when dealing with a combination of chemical resistance, coating hardness build-up, potlife and appearance.

[0015] Aim of the Invention

[0016] The present invention aims to provide a non-aqueous crosslinkable composition for coating compositions that do not present the limitations of the current state of the art coating systems.

[0017] It is the aim of the present invention to provide a non-aqueous crosslinkable composition for coating compositions which upon curing result in coatings characterized by an improved chemical resistance and hardness, said coating compositions further being characterized by an increased potlife, combined with a low temperature cure profile and an improved film hardness build-up.

[0018] Summary of the Invention.

[0019] The present invention discloses a crosslinkable composition comprising: a) at least one isocyanate-reactive compound, b) at least one polyisocyanate crosslinker having free isocyanate groups, c) at least one thermolatent metal-based catalyst for catalysing the reaction between the isocyanate-reactive groups of the isocyanate-reactive compound a) and the isocyanate groups of said polyisocyanate crosslinker b), said thermolatent metal-based catalyst comprising cyclic metal compounds, d) at least one aromatic carboxylic acid, and / or at least one tertiary carboxylic acid of formula RR'R"CCOOH wherein each R, R' and R" group, independently, is an alkyl, alkenyl, aryl or aralkyl group containing at least one carbon atom, wherein the total number of carbon atoms in the R, R' and R" groups is in the range of from 3 to 40, and wherein two or three of the R, R’ and R” groups optionally are linked to form a ring structure, and / or optionally are substituted by an hydroxyl- and / or a carboxyl group, wherein the amount of the at least one aromatic carboxylic acid and / or the at least one tertiairy carboxylic acid d) is in the range of 0.02 to 0.3 mmol per gram of isocyanatereactive compound a).

[0020] Preferred embodiments of the crosslinkable composition of the present invention disclose one or more of the following features:

[0021] - the thermolatent metal-based catalyst c) is a tin-based catalyst comprising cyclic tin compounds, wherein the tin atom is part of one or more ring structure(s), said ring structures being at least five-membered;

[0022] - the carboxylic acid d) is a tertiary carboxylic acid with general formula RR'R"CCOOH wherein the total number of carbon atoms in the R, R' and R" groups is in the range of from 3 to 30;

[0023] - the tertiary carboxylic acid d) has the general formula RR'R"CCOOH , wherein R is a methyl or ethyl group, and where the total number of carbon atoms of groups R’ and R” is from 2 to 17, and where R’ and / or R” is non-substituted or substituted with only one hydroxyl group;

[0024] - the isocyanate-reactive compound a) is a polyol, comprising:

[0025] • from 70 to 100% by weight of a polymeric polyol selected from the group consisting of polyester polyols, polyacrylate polyols, polycarbonate polyols, polyether polyols, polyurethane polyols, melamine polyols, and mixtures and hybrids thereof, and having a hydroxyl value in the range of 20 to 1 ,000 mg KOH per gram and an acid value of 15 mg KOH per gram or less, and

[0026] • from 0 to 30% by weight of one or more reactive diluents selected from the group consisting of monomeric and oligomeric compounds, and mixtures thereof, wherein the monomeric and oligomeric compounds comprise 2 to 5 hydroxyl groups, the oligomeric compounds being characterized by a degree of polymerization of at most 15, the sum of the weight percentages of the polymeric polyol and the reactive diluent not exceeding 100 % by weight;

[0027] - the polyisocyanate crosslinker b) is selected from the group consisting of aliphatic polyisocyanates, cycloaliphatic polyisocyanate, the adducts of aliphatic isocyanates, the adducts of cycloaliphatic polyisocyanates, and mixtures thereof, the adducts being selected from the group consisting of biurets, isocyanurates, imino-oxadiazinediones, allophanates, uretdiones, homopolymers of polyisocyanates, and mixtures thereof;

[0028] - the crosslinkable composition comprises:

[0029] • from 9 to 90 % of weight of at least one isocyanate-reactive compound a),

[0030] • from 9 to 90 % of weight of at least one polyisocyanate crosslinker b),

[0031] • from 0,01 to 10 % of weight of at least one thermolatent metal-based catalyst c), and

[0032] • from 0.001 to 10 % of weight of at least one aromatic carboxylic acid and / or tertiary carboxylic acid d), based on the total amount of isocyanate-reactive compound a), polyisocyanate crosslinker b), thermolatent metal-based catalyst c), aromatic and / or tertiary carboxylic acid d), the total amount being 100% by weight.

[0033] The present invention also discloses a coating composition comprising at least 30% by weight of non-volatile compounds and at most 70% by weight of water-free volatile organic solvents, the sum of the weight percentages of the non-volatile compounds and the water-free volatile organic solvents not exceeding 100% by weight of the coating composition; the non-volatile compounds comprising from 20 to 98% by weight of the crosslinkable composition of the present invention and from 2 to 80% by weight of one or more additives and auxiliaries, the sum of the weight percentages of the crosslinkable composition and the one or more additives and auxiliaries not exceeding 100% by weight of non-volatile compounds.

[0034] Preferred embodiments of the coating composition of the present invention disclose one or more of the following features:

[0035] - the one or more additives and auxiliaries are selected from the group consisting of pigments, dyes, surfactants, pigment dispersion aids, levelling agents, wetting agents, anticratering agents, antifoaming agents, matting agents, sag control agents, other rheology control agents, heat stabilizers, light stabilizers, UV absorbers, antioxidants, radical inhibitors, and fillers, and mixtures thereof;

[0036] - the coating composition comprises from 0.1 to 3 % by weight of sag control agent, relative to the total weight of the crosslinkable composition of the present invention;

[0037] - the sag control agent is a polyurea-based sag control agent.

[0038] The present invention further discloses a kit of parts for preparing a coating composition according to the present invention, said kit of parts comprising:

[0039] • a binder module i) comprising at least one isocyanate-reactive compound a), at least one carboxylic acid compound d), optionally at least one thermolatent catalyst c), optionally one or more additives and auxiliaries, and optionally water-free volatile organic solvents,

[0040] • a crosslinker module ii) comprising at least one polyisocyanate crosslinker b) optionally at least one thermolatent catalyst c), optionally one or more additives and auxiliaries, and optionally water-free volatile organic solvents, wherein

[0041] - the thermolatent metal-based catalyst is present in at least binder module i) and / or crosslinker module ii); and o in a preferred embodiment the carboxylic acid d) of binder module i) is a tertiary carboxylic acid d), o in another preferred embodiment binder module i) comprises sag control agents;

[0042] - the isocyanate-reactive compound a) is provided to binder module i) either

[0043] • as a solution in water-free volatile organic solvent comprising carboxylic acid d), or

[0044] • as a solution in water-free volatile organic solvent comprising sag control agents, or

[0045] • as a solution in water-free volatile organic solvent comprising carboxylic acid d) and sag control agents.

[0046] The present invention also discloses a method of providing a coating layer, said method comprising the steps of applying a coating composition according to the present invention to at least a part of an object, preferably the (exterior) surface of a transportation vehicle, and curing the applied coating composition, preferably in a temperature range of 5 to 180 °C. Detailed Description of the Invention.

[0047] In the present invention, it has been found that a crosslinkable composition comprising at least one isocyanate-reactive compound a), at least one isocyanate crosslinker b), at least one thermolatent metal-based catalyst c), and at least one aromatic carboxylic acid and / or at least one tertiary carboxylic acid d) provides a coating composition, which upon curing results in a coating having an improved chemical resistance and hardness, said coating composition being characterized by an increased potlife while being curable at low temperature, and an improved film hardness build-up.

[0048] Particularly, the crosslinkable composition according to the present invention comprises a) at least one isocyanate-reactive compound, b) at least one polyisocyanate crosslinker having free isocyanate groups, c) at least one thermolatent metal-based catalyst for catalyzing the reaction between the isocyanate-reactive groups of the isocyanate-reactive compound a) and the isocyanate groups of said polyisocyanate crosslinker b), said thermolatent metal-based catalyst comprising cyclic metal compounds, wherein the metal atom is part of one or more ring structure(s), said ring structures being at least five-membered, d) at least one aromatic carboxylic acid, and / or at least one tertiary carboxylic acid of formula RR'R"CCOOH, wherein each R, R' and R" group, independently, is an alkyl, alkenyl, aryl or aralkyl group containing at least one carbon atom, wherein the total number of carbon atoms in the R, R' and R" groups is in the range of from 3 to 40 and wherein two or three of the R, R' and R" groups optionally are linked to form a ring structure, and / or optionally are substituted by an hydroxyl- and / or a carboxyl group.

[0049] The crosslinkable composition according to the invention is a non-aqueous composition, though water may be present in one or more of its constituents, as they are technical grade constituents which, as generally known by the one skilled in the art, may contain up to 0.2% of water. Therefor by “non-aqueous crosslinkable composition” in the present invention is meant a crosslinkable composition containing at most 0.2% by weight of water, based on the total of crosslinkable composition (a), b), c), d)) and water, if present, being 100% by weight.

[0050] In the context of the invention the water content is determined by Karl Fischer titration as a volumetric method according to DIN 53715 (DIN 53715 was based on DIN 51777 part 1 (1973 edition)). The measurement range of the water content is 0.01% to less than 99% by weight.

[0051] The isocyanate-reactive compound a) of the crosslinkable composition according to the present invention comprises one or more functional groups selected from the group consisting of the hydroxyl-group, the thiol-group, the amine-group, the carboxylic acid-group, and combinations thereof. Preferably the isocyanate-reactive compound a) comprises one or more hydroxyl groups.

[0052] Preferably the isocyanate-reactive compound a) comprises a polymer comprising at least 2 hydroxyl groups, hereinafter referred to as the polymeric polyol, selected from the group consisting of polyester polyols, polyacrylate polyols, polycarbonate polyols, polyether polyols, polyurethane polyols, melamine polyols, and mixtures and hybrids thereof, wherein by mixtures a physical blend of two or more polymeric polyols of similar or different type is meant, whereas hybrids comprise the chemical reaction product of two or more polymer segments of different type linked through covalent bonds. Of the wide variety of potentially isocyanate-reactive compounds a), preferred polymeric polyols are the polyester polyols and polyacrylic polyols and mixtures and hybrids thereof wherein by mixtures a physical blend of polyester polyols and polyacrylate polyols is meant whereas hybrids comprise the chemical reaction product of polyacrylate and polyester, wherein polyester segments and polyacrylate segments are linked through covalent bonds and wherein the polyester segments and / or the polyacrylate segments comprise -OH groups, the resulting polyester-polyacrylate hybrid comprising at least two -OH groups.

[0053] Suitable polyester polyols can be obtained, for instance, by the polycondensation of one or more di- and / or higher functional hydroxyl compounds with one or more di- and / or higher functional carboxylic acids, optionally in combination with one or more monofunctional carboxylic acids and / or mono-hydroxyl functional compounds. As non-limiting examples, di- and / or higher functional hydroxyl compounds can be one or more alcohols selected from ethylene glycol, neopentyl glycol, trimethylol propane and pentaerythritol. As non-limiting examples, the di- and / or higher functional carboxylic acids are one or more carboxylic acids selected from the group consisting of adipic acid, 1 ,4-cyclohexyl dicarboxylic acid, hexahydrophthalic acid, succinic acid, and functional equivalents thereof. Alternatively, polyester polyols can be prepared from di- and / or higher functional hydroxyl compounds and from carboxylic acid anhydrides and / or C1-C4 alkyl esters of the carboxylic acids.

[0054] Suitable (meth)acrylic polyols can be obtained, for instance, by the (co)polymerization of one or more hydroxyl- functional (meth)acrylic monomers such as for example 2- hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4- hydroxybutyl (meth)acrylate, 2,3-dihydroxypropyl (meth)acrylate, polyethylene glycol esters of (meth)acrylic acid, polypropylene glycol esters of (meth)acrylic acid, and mixed polyethylene glycol and polypropylene glycol esters of (meth)acrylic acid, and one or more alpha, beta-ethylenically unsaturated monomers selected from the group consisting of alpha, beta-ethylenically unsaturated monoacids, such as (meth)acrylic acid, alkylesters of alpha, beta-ethylenically unsaturated monoacids, such as methyl (meth)acrylate, tert-butyl (meth)acrylate, isobornyl (meth)acrylate, isobutyl (meth)acrylate, (substituted) cyclohexyl (meth)acrylate, alpha, beta-ethylenically unsaturated diacids such as maleic acid, fumaric acid, itaconic acid, cratonic acid, mono and di-alkylesters of alpha, beta-ethylenically unsaturated diacids, such as monomethyl maleate, vinyl aromatic monomers, such as styrene, vinyl toluene, vinylalkanoates, such as vinyl isobutyrate, and mixtures thereof, preferably in the presence of a free radical initiator.

[0055] The polymeric polyol used in the crosslinkable composition according to the present invention preferably has a hydroxyl value of at least 20 mg KOH / g, more preferably of at least 50 mg KOH / g, most preferably of at least 100 mg KOH / g; preferably the polymeric polyol a) has a hydroxyl value of at most 1 ,000 mg KOH / g, more preferably of at most 500 mg KOH / g, most preferably of at most 250 mg KOH / g, the hydroxyl value being measured according to the method ASTM E222 - 17.

[0056] The polymeric polyol used in the crosslinkable composition according to the present invention preferably has an acid value of at most 15 mg KOH / g, more preferably of at most 10 mg KOH / g, even more preferably of at most 6 mg KOH / g, most preferably of at most 4 mg KOH / g; preferably the polymeric polyol a) has an acid value higher than 0 mg KOH / g ), more preferably higher than 1 mg KOH / g, most preferably higher than 2 mg KOH / g, the acid value being measured according to ISO 3682-1996.

[0057] The polymeric polyol used in the crosslinkable composition according to the invention further is characterized by: a number average molecular weight (Mn) of less than 10,000 Dalton, preferably less than 5,000, more preferably less than 3,000, most preferably less than 2,000 Dalton and of at least 600 Dalton, preferably at least 700 Dalton, more preferably at least 900 Dalton, most preferably at least 1 ,000 Dalton and / or a weight average molecular weight (Mw) of less than 15,000 Dalton, preferably less than 10,000, more preferably less than 8,000, most preferably less than 6,000, even less than 4,000 Dalton and of at least 900 Dalton, preferably at least 1 ,100 Dalton, more preferably at least 1 ,300 Dalton, most preferably at least 1 ,500 Dalton and / or a polydispersity Mw / Mn of higher than 1 , more preferably of from 1.1 to 6.6, most preferably of from 1 .4 to 4, as determined according to ASTM D 3593 by Gel Permeation Chromatography (GPC) using polystyrene standards, more particularly using size exclusion chromatography.

[0058] Preferably the polymeric polyol used in the crosslinkable composition according to the invention further is characterized by: a number average molecular weight (Mn) of less than 10,000 Dalton, preferably less than 5,000, more preferably less than 3,000, most preferably less than 2,000 Dalton and of at least 600 Dalton, preferably at least 700 Dalton, more preferably at least 900 Dalton, most preferably at least 1 ,000 Dalton, and a weight average molecular weight (Mw) of less than 15,000 Dalton, preferably less than 10,000, more preferably less than 8,000, most preferably less than 6,000, even less than 4,000 Dalton and of at least 900 Dalton, preferably at least 1 ,100 Dalton, more preferably at least 1 ,300 Dalton, most preferably at least 1 ,500 Dalton and a polydispersity Mw / Mn of higher than 1 , more preferably of from 1.1 to 6.6, most preferably of from 1 .4 to 4, as determined according to ASTM D 3593 by Gel Permeation Chromatography (GPC) using polystyrene standards, more particularly using size exclusion chromatography.

[0059] The polymeric polyol used in the crosslinkable composition according to the invention further is characterized by a glass transition temperature (Tg), as determined by Differential Scanning Calorimetry (DSC) according to DIN EN ISO 16805 and ISO 11357, of more than -80 °C, preferably of more than -40 °C, more preferably of more than -10 °C, and most preferably of more than 10 °C. The glass transition temperature of the polymeric polyol preferably is lower than 90 °C, more preferably lower than 75 °C, even more preferably lower than 60 °C, most preferably lower than 50 °C.

[0060] Preferably, the polymeric polyol used in the crosslinkable composition according to the invention further is characterized by:

[0061] - a number average molecular weight (Mn) of less than 5,000 Dalton, preferably less than 3,000, more preferably less than 2,000, and of at least 600 Dalton, preferably at least 700 Dalton, more preferably at least 900 Dalton, and

[0062] - a weight average molecular weight (Mw) of less than 10,000 Dalton, preferably less than 8,000, more preferably less than 6,000, most preferably less than 4,000, and of at least 900 Dalton, preferably at least 1 ,100 Dalton, more preferably at least 1 ,300 Dalton, and - a polydispersity Mw / Mn of higher than 1 , more preferably of from 1.1 to 6.6, most preferably of from 1.4 to 4, and

[0063] - a glass transition temperature (Tg) of more than -40 °C, preferably of more than -10 °C, more preferably of more than 10 °C; preferably of lower than 75 °C, more preferably lower than 60 °C, even more preferably lower than 50 °C, and

[0064] - an acid value of at most 10 mg KOH / g, more preferably of at most 6 mg KOH / g, even more preferably of at most 4 mg KOH / g, and

[0065] - a hydroxyl value of at least 50 mg KOH / g, more preferably of at least 100 mg KOH / g; preferably the polymeric polyol a) has a hydroxyl value of at most 500 mg KOH / g, more preferably of at most 250 mg KOH / g.

[0066] The isocyanate-reactive compound a) of the crosslinkable composition according to the present invention further may comprise one or more reactive diluents selected from the group consisting of monomeric compounds having 2 to 5 hydroxyl groups, aliphatic mono-alcohols, oligomeric compounds having on average 1 to 5 hydroxyl groups, and mixtures thereof.

[0067] Suitable monomeric compounds include, for instance, 1 ,2-ethylene glycol, 1 ,2-propylene glycol 1 ,3-propylene glycol, 1 ,4-butanediol, and 1 ,6 hexanediol.

[0068] Suitable aliphatic mono-alcohols include, for instance, n-butanol, 2-butanol, 2- ethylhexylalcohol, 1- or 2-octanol, nonylalcohol, 3,3,5-trimethylhexanol, decyl and lauryl alcohols, cyclopentanol, cyclohexylalcohol, and benzylalcohol.

[0069] Suitable oligomeric compounds include, for instance, low molecular weight hydroxyl functional polyesters, hydroxyl functional (meth)acrylic (co)polymers and polyether polyols, said oligomeric compounds being characterized by a degree of polymerization of at most 15.

[0070] The isocyanate-reactive compound a) of the crosslinkable composition according to the present invention preferably comprises at least 70% by weight, more preferably at least 80% by weight, most preferably at least 90% by weight of polymeric polyol, and preferably comprises at most 30% by weight, more preferably at most 20% by weight, most preferably at most 10% by weight of reactive diluent, based on the total amount of isocyanate-reactive compound a) being 100% by weight.

[0071] The isocyanate-reactive compound a) is present in the crosslinkable composition according to the present invention preferably in an amount of from 9 to 90% by weight, more preferably of from 19 to 80% by weight, most preferably of from 29 to 70% by weight, based on the total amount of the isocyanate-reactive compound a), the polyisocyanate crosslinker b), the thermolatent metal-based catalyst c), the carboxylic acid d), the total amount being 100% by weight.

[0072] The polyisocyanate crosslinker b) of the crosslinkable composition according to the present invention preferably is a polyisocyanate crosslinker having at least 2 free isocyanate groups.

[0073] The polyisocyanate crosslinker b) is preferably selected from the group consisting of hexamethylene diisocyanate, 2,4,4-trimethyl hexamethylene diisocyanate, 1 ,2-cyclohexylene diisocyanate, 1 ,4-cyclohexylene diisocyanate, 4,4'-dicyclohexylene diisocyanate methane, 3, 3'-dimethyl-4,4'-dicyclohexylene diisocyanate methane, norbornane diisocyanate, m- and p- phenylene diisocyanate, 1 ,3- and 1 ,4-bis (isocyanate methyl) benzene, xylylene diisocyanate, a,a,a',a'-tetramethyl xylylene diisocyanate (TMXDI), 1 ,5-dimethyl-2,4-bis (isocyanate methyl) benzene, 2,4- and 2,6-toluene diisocyanate, 2,4,6-toluene triisocyanate, 4,4'-diphenylene diisocyanate methane, 4,4'-diphenylene diisocyanate, naphthalene-1 ,5-diisocyanate, isophorone diisocyanate, 4-isocyanatomethyl-1 ,8-octamethylene diisocyanate, and mixtures thereof.

[0074] Other preferred isocyanate crosslinkers are the adducts of polyisocyanates, e.g., biurets, isocyanurates, imino-oxadiazinediones, allophanates, uretdiones, homopolymers of polyisocyanates, and mixtures thereof. Examples of such adducts are the adduct of two molecules of hexamethylene diisocyanate or isophorone diisocyanate to a diol such as ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate to 1 molecule of water, the adduct of 1 molecule of trimethylol propane to 3 molecules of isophorone diisocyanate, the adduct of 1 molecule of pentaerythritol to 4 molecules of toluene diisocyanate, the isocyanurate of hexamethylene diisocyanate (available under the trade name DESMODUR® (E) N3390 or TOLONATE™ HDT-LV, TOLONATE™ HDT-90, a mixture of the uretdione and the isocyanurate of hexamethylene diisocyanate, under the trade name DESMODUR® N3400, the allophanate of hexamethylene diisocyanate, available under the trade name DESMODUR® LS 2101 , and the isocyanurate of isophorone diisocyanate, available under the trade name VESTANAT® T1890. Furthermore, (co)polymers of isocyanate-functional monomers such as a,a'-dimethyl-m-isopropenyl benzyl isocyanate are suitable for use. If desired, it is also possible to use hydrophobically or hydrophilically modified polyisocyanates to impart specific properties to the coating.

[0075] Optionally the polyisocyanate crosslinker b) comprises blocked polyisocyanates when blocking agents having a sufficiently low deblocking temperature are used to block any of the polyisocyanate crosslinker b), mentioned above. In that case, polyisocyanate crosslinker b) is substantially free of unblocked isocyanate group-containing compounds and the crosslinkable composition can be formulated as one-component formulation. The blocking agents which can be used to prepare a blocked isocyanate component are well-known to the skilled person.

[0076] Preferably the polyisocyanate crosslinker b) is selected from the group consisting of aliphatic polyisocyanates, cycloaliphatic polyisocyanate, the adducts of aliphatic isocyanates, the adducts of cycloaliphatic polyisocyanates, and mixtures thereof.

[0077] The polyisocyanate crosslinker b) is present in the crosslinkable composition according to the present invention preferably in an amount of from 9 to 90% by weight, more preferably of from 19 to 80% by weight, most preferably of from 29 to 70% by weight based on the total amount of the isocyanate-reactive compound a), the polyisocyanate crosslinker b), the thermolatent metal-based catalyst c), and the carboxylic acid d), the total amount being 100% by weight.

[0078] The thermolatent metal-based catalyst c) of the crosslinkable composition according to the present invention comprises cyclic metal compounds wherein the metal is selected from the group consisting of tin, bismuth, zinc, zirconium, scandium, aluminium, and mixtures thereof.

[0079] Preferably the cyclic metal compounds comprise one or more at least five-membered ring structures, the metal atom being part of said ring structures.

[0080] Preferably the thermolatent metal-based catalyst c) is characterized by the absence of direct metal-carbon bonds.

[0081] In the context of the present invention “thermolatent metal-based catalyst c)” is especially understood to mean any catalyst that, in combination with aromatic and / or tertiary carboxylic acid d), does not accelerate or does not significantly accelerate the crosslinking reaction of the at least one polyisocyanate b) with the at least one isocyanate-reactive compound a) to form a urethane bond below 25° C, in particular below 30° C, preferably below 40° C, but significantly accelerates it above 60° C, especially above 70° C. “Does not significantly accelerate” here means that below 25° C, in particular below 30° C, preferably below 40° C, the presence of the thermolatent catalyst c), in combination with aromatic and / or tertiary carboxylic acid d) in the coating does not have any significant effect on the reaction rate of the reaction that proceeds in any case. A “significant acceleration” is understood to mean that above 60° C, in particular above 70° C, the presence of the thermolatent metal-based catalyst c) in combination with aromatic and / or tertiary carboxylic acid d) in the coating has a distinct effect on the reaction rate of the reaction that proceeds in any case. More specifically, in the present invention, with “thermolatent catalyst c)” is meant a catalyst which, added at 0.08% by weight to a stoichiometric mixture of isocyanate-reactive compound a) I isocyanate crosslinker b), in combination with 0.9% by weight of neodecanoic acid (tertiary carboxylic acid d) (the total of a), b), c) and d) being 100% by weight), diluted to a viscosity of 27 s Din Cup 4 with a 1 :1 mixture of methoxypropyl acetate and xylene leads to a viscosity increase of less than 30 s Din Cup 4 after 2 hours at a temperature of 25°C and to dry coatings after 30 minutes at 80°C.

[0082] Preferably the themolatent metal-based catalyst c) is a thermolatent tin-based catalyst comprising cyclic tin compounds of the formula I, II or III or mixtures thereof. wherein:

[0083] D represents — O — , — S — or — N(R1) wherein R1 represents a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical which has up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen or the radical or R1 and L3 together represent — Z-L5-;

[0084] D* represents — O — or — S — ;

[0085] X, Y and Z represent identical or different radicals selected from alkylene radicals having the formulae — C(R2)(R3)-, — C(R2)(R3)-C(R4)(R5)- or — C(R2)(R3)-C(R4)(R5)-C(R6)(R7)- or orthoarylene radicals having the formulae wherein R2 to R11 independently represent saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or are hydrogen;

[0086] L1 , L2 and L5 independently represent — O — , — S — , — OC(=O) — , — OC(=S) — SC(=O) — , — SC(=S)— , — OS(=O)2O— , — OS(=O)2— or — N(R12)-, wherein R12 represents a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical which has up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen;

[0087] L3 and L4 independently represent — OH, — SH, — OR13, -Hal, — OC(=O)R14, — SR15, — OC(=S)R16, — OS(=O)2OR17, — OS(=O)2R18 or — NR19R20, or L3 and L4 together represent -L1-X-D-Y-L2-, wherein R13 to R20 independently represent saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or are hydrogen.

[0088] D is preferably — N(R1)-, where the pair of lone pair electrons may be represented as forming a coordinate bond between the nitrogen and the metal atom;

[0089] R1 is preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 20 carbon atoms or the radical particularly preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 12 carbon atoms or the radical very particularly preferably hydrogen or a methyl, ethyl, propyl, butyl, hexyl or octyl radical, where propyl, butyl, hexyl and octyl are all isomeric propyl, butyl, hexyl and octyl radicals, or Ph-, CH3Ph- or the radical

[0090] D*is preferably — O — .

[0091] X, Y and Z are preferably the — C(R2)(R3), — C(R2)(R3)-C(R4)(R5)- or the ortho-arylene radical

[0092] R2 to R7 are preferably hydrogen or alkyl, aralkyl, alkaryl or aryl radicals having up to 20 carbon atoms, particularly preferably hydrogen or alkyl, aralkyl, alkaryl or aryl radicals having up to 8 carbon atoms, very particularly preferably hydrogen or alkyl radicals having up to 8 carbon atoms, yet more preferably hydrogen or methyl.

[0093] R8 to R11 are preferably hydrogen or aryl radicals having up to 8 carbon atoms, particularly preferably hydrogen or methyl.

[0094] L1 , L2 and L5 are preferably — NR12— , — S— , — SC(=S)— , — SC(=O)— , — OC(=S)— , — O — , or — OC(=O) — , particularly preferably — O — , or — OC(=O) — .

[0095] R12 is preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 20 carbon atoms, particularly preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 12 carbon atoms, very particularly preferably hydrogen or a methyl, ethyl, propyl, butyl, hexyl or octyl radical, where propyl, butyl, hexyl and octyl represent all isomeric propyl, butyl, hexyl and octyl radicals.

[0096] L3 and L4 are preferably — Hal, — OH, — SH, — OR13, — OC(=O)R14, where the R13 and R14 radicals have up to 20 carbon atoms, preferably up to 12 carbon atoms.

[0097] L3 and L4 are particularly preferably Cl — , MeO — , EtO — , PrO — , BuO — , HexO — , OctO — , PhO — , formate, acetate, propanoate, butanoate, pentanoate, hexanoate, octanoate, laurate, lactate or benzoate, where Pr, Bu, Hex and Oct are all isomeric propyl, butyl, hexyl and octyl radicals, yet more preferably Cl — , MeO — , EtO — , PrO — , BuO — , HexO — , OctO — , PhO — , hexanoate, laurate or benzoate, where Pr, Bu, Hex and Oct represent all isomeric propyl, butyl, hexyl and octyl radicals. R15 to R20 are preferably hydrogen or alkyl, aralkyl, alkaryl or aryl radicals having up to 20 carbon atoms, particularly preferably hydrogen or alkyl, aralkyl, alkaryl or aryl radicals having up to 12 carbon atoms, very particularly preferably hydrogen, methyl, ethyl, propyl, butyl, hexyl or octyl radicals, where propyl, butyl, hexyl and octyl represent all isomeric propyl, butyl, hexyl and octyl radicals.

[0098] The units L1-X, L2-Y and L5-Z preferably represent — CH2CH2O — , — CH2CH(Me)O — ,

[0099] — CH(Me)CH2O— , — CH2C(Me)2O— , — C(Me)2CH2O— or — CH2C(=O)O—

[0100] The unit L1-X-D-Y-L2 preferably represents: HN[CH2CH2O— ]2, HN[CH2CH(Me)O— ]2,

[0101] HN[CH2CH(Me)O— ][CH(Me)CH2O— ], HN[CH2C(Me)2O— ]2,

[0102] HN[CH2C(Me)2O— ][C(Me)2CH2O— ], HN[CH2C(=O)O— ]2, MeN[CH2CH2O— ]2,

[0103] MeN[CH2CH(Me)O— ]2, MeN[CH2CH(Me)O— ][CH(Me)CH2O— ], MeN[CH2C(Me)2O]2, MeN[CH2C(Me)2O— ][C(Me)2CH2O— ], MeN[CH2C(=O)O— ]2, EtN[CH2CH2O— ]2, EtN[CH2CH(Me)O— ]2, EtN[CH2CH(Me)O— ][CH(Me)CH2O— ], EtN[CH2C(Me)2O]2, EtN[CH2C(Me)2O— ][C(Me)2CH2O-], EtN[CH2C(=O)O-]2, PrN[CH2CH2O— ]2, PrN[CH2CH(Me)O— ]2, PrN[CH2CH(Me)O— ][CH(Me)CH2O— ], PrN[CH2C(Me)2O— ]2, PrN[CH2C(Me)2O— ][C(Me)2CH2O— ], PrN[CH2C(=O)O— ]2, BuN[CH2CH2O— ]2, BuN[CH2CH(Me)O— ]2, BuN[CH2CH(Me)O— ][CH(Me)CH2O— ], BuN[CH2C(Me)2O— ]2, BuN[CH2C(Me)2O— ][C(Me)2CH2O— ], BuN[CH2C(=O)O]2, HexN[CH2CH2O— ]2, HexN[CH2CH(Me)O— ]2, HexN[CH2CH(Me)O— ][CH(Me)CH2O— ], HexN[CH2C(Me)2O— ]2, HexN[CH2C(Me)2O— ][C(Me)2CH2O— ], HexN[CH2C(=O)O— ]2, OctN[CH2CH2O— ]2, OctN[CH2CH(Me)O— ]2, OctN[CH2CH(Me)O— ][CH(Me)CH2O— ], OctN[CH2C(Me)2O— ]2, OctN[CH2C(Me)2O— ][C(Me)2CH2O— ], OctN[CH2C(=O)O— ]2, wherein Pr, Bu, Hex and Oct may represent any isomeric propyl, butyl and octyl radicals, PhN[CH2CH2O — ]2, PhN[CH2CH(Me)OP— ]2, PhN[CH2CH(Me)O— ][CH(Me)CH2O— ], PhN[CH2C(Me)2O— ]2, PhN[CH2C(Me)2O— ][C(Me)2CH2O— ], PhN[CH2C(=O)O— ]2,

[0104] Preferably the thermolatent tin-based catalyst c) is characterized by the absence of direct tincarbon bonds.

[0105] Processes for producing the thermolatent metal-based catalysts suitable according to the invention are described for example in: EP 2 900 716 A1 , EP 2 900 717 A1 , EP 2 772 496 A1 , EP 14182806, J. Organomet. Chem. 2009 694 3184-3189, Chem. Heterocycl. Comp. 2007 43 813-834, Indian J. Chem. 1967 5 643-645, and in the literature referenced therein, the disclosure content of which is hereby incorporated by reference in its entirety.

[0106] As is known to the person skilled in the art, tin compounds have a propensity to oligomerize, and so there are often polynuclear tin compounds or mixtures of mono- and polynuclear tin compounds. In the polynuclear tin compounds, the tin atoms are preferably connected to one another via oxygen atoms (‘oxygen bridges’). Typical oligomeric complexes (polynuclear tin compounds) form, through condensation of the tin atoms via oxygen or sulfur, for example where n>1 (cf. formula II). Cyclic oligomers are frequently encountered in the case of low degrees of oligomerization, linear oligomers with OH or SH end groups in the case of high degrees of oligomerization (cf. formula III).

[0107] Preferably the thermolatent tin-based catalyst is selected from the group of mono- or polynuclear tin compounds of the type:

[0108] • 1 ,1-di-“R”-5-“organyl”-5-aza-2,8-dioxa-1-stanna-cyclooctane,

[0109] • 1 ,1-di-“R”-5-(N-“organyl”)aza-3,7-di-“organyl”-2,8-dioxa-1-stanna-cyclooctane,

[0110] • 1 ,1-di-“R”-5-(N-“organyl”)aza-3,3,7,7-tetra-“organyl”-2,8-dioxa-1-stanna-cyclooctane,

[0111] • 4,12-di-“organyl”-1 ,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane,

[0112] • 4,12-di-“organyl”-2,6, 10,14-tetra-“organyl”-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,

[0113] • 4,12-di-“organyl”-2,2,6,6, 10,10,14,14-octa-“organyl”-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane, wherein “R” is D*, L3 or L4, as defined above, and “organyl” is R1 , as defined above.

[0114] More preferably the thermolatent tin-based catalyst is selected from:

[0115] • 4,12-d i-n - b uty I- 1 ,7,9,15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7]pentadecane,

[0116] • 4,12-di-n-butyl-2,6, 10, 14-tetramethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,

[0117] • 2,4,6,10,12,14-hexamethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,

[0118] • 4,12-di-n-octyl-2,6, 10,14-tetramethyl- 1 ,7,9, 15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,

[0119] • 4,12-d i-n -octyl- 1 ,7,9,15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7]pentadecane,

[0120] • 4,12-dimethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7]pentadecane,

[0121] • 1 ,1-dichloro-5-methyl-5-aza-2,8-dioxa-1 -stannacyclooctane,

[0122] • bis [1 ,1'-(butylimino-kappaN)bis (propane-2-olato-kappaO)] tin, and mixtures thereof.

[0123] The thermolatent tin-based catalyst c) is present in the crosslinkable composition according to the present invention preferably in an amount of from 0.01 to 10% by weight, more preferably of from 0.05 to 8% by weight, most preferably of from 0.1 to 7% by weight based on the total amount of the isocyanate-reactive compound a), the polyisocyanate crosslinker b), the thermolatent metal-based catalyst c), and the carboxylic acid d), the total amount being 100% by weight.

[0124] The carboxylic acid d) of the crosslinkable composition according to the present invention is selected from the group consisting of aromatic carboxylic acids, tertiary carboxylic acids, and mixtures thereof. By aromatic carboxylic acids is meant any carboxylic acid in which the carboxyl group is directly bonded to an aromatic ring.

[0125] The aromatic carboxylic acids d) of the crosslinkable composition according to the present invention preferably are selected from the group consisting of aromatic monocarboxylic acids, alkyl- or alkoxy- or hydroxy- substituted aromatic monocarboxylic acids, aromatic dicarboxylic acids, monoalkyl esters of aromatic dicarboxylic acids, alkyl- or alkoxy- or hydroxy substituted aromatic dicarboxylic acids, monoalkyl esters of alkyl- or alkoxy- or hydroxy-substituted of aromatic dicarboxylic acids, aromatic tricarboxylic acids, monoalkyl esters of aromatic tricarboxylic acids, dialkyl esters of aromatic tricarboxylic acids, aromatic tetracarboxylic acids, monoalkyl esters of aromatic tetracarboxylic acids, dialkyl esters of aromatic tetracarboxylic acids, trialkyl esters of aromatic tetracarboxylic acids, and mixtures thereof.

[0126] More preferably the aromatic carboxylic acid d) is selected from the group consisting of aromatic monocarboxylic acids, alkyl- or alkoxy- or hydroxy- substituted aromatic monocarboxylic acids, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, pyromellitic acid, and mixtures thereof.

[0127] Even more preferably the aromatic carboxylic acid d) is selected from the group consisting of aromatic monocarboxylic acids, alkyl- or alkoxy- or hydroxy- substituted aromatic monocarboxylic acids, phthalic acid, isophthalic acid, and mixtures thereof.

[0128] Most preferably the aromatic carboxylic acid d) is selected from the group consisting of benzoic acid, phthalic acid, isophthalic acid, and mixtures thereof.

[0129] Even most preferably the aromatic carboxylic acid d) is benzoic acid.

[0130] Preferably the carboxylic acid d) of the crosslinkable composition according to the present invention is a tertiary carboxylic acid or a mixture of (two or more) tertiary carboxylic acids.

[0131] The tertiary carboxylic acid d) used in the composition according to the present invention has the general formula RR'R"CCOOH wherein:

[0132] • each R, R' and R" group, independently, is an alkyl, alkenyl, aryl or aralkyl group containing at least one carbon atom,

[0133] • two or three of the R, R' and R" groups are optionally linked to form a ring structure and wherein the R, R’ and / or R” groups can be substituted, and

[0134] • the total number of carbon atoms in the R, R' and R" groups are in the range of from 3 to 40.

[0135] Preferred are tertiary carboxylic acids d) are those of the formula RR'R"CCOOH wherein the total number of carbon atoms in the R, R' and R" groups are in the range of from 3 to 30, more preferably from 3 to 18, and most preferably from 3 to 8. R, R’ and R” can be the same or can be different and include linear as well as branched groups as well as groups which are substituted with one or more functional groups such as -OH groups, primary, secondary or tertiary amine groups, carboxylic acids groups, ester groups, ether groups, -SH groups. Alternatively, one of R’ or R” can be a carboxylic acid group.

[0136] Preferred tertiary carboxylic acids d) are those of the formula RR'R"CCOOH wherein R, R' and R" are a linear or branched alkyl group, more preferably a methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-pentyl or i-pentyl group and wherein optionally at least one R, R' or R" may comprise one or more hydroxyl group. Particularly preferred tertiary carboxylic acids d) are those wherein R is a methyl or ethyl group and where the total number of carbon atoms of groups R' and R" is from 2 to 17, most preferred from 2 to 12, especially from 2 to 7, and where R' and / or R" is non-substituted or substituted with only one hydroxyl group.

[0137] Non-limiting examples of tertiary carboxylic acids d) that can be used in the crosslinkable composition according to the invention preferably are neodecanoic acid, 3- hydroxy-2, 2- dimethylpropionic acid, 2,2-bis(hydroxymethyl)propionic acid, abietic acid, dimetylmalonic acid, ethylmethylmalonic acid, diethylmalonic acid, 2,2-dimethylsuccinic acid, 2,2- diethylsuccinic acid, 2,2-dimethylglutaric acid, 2,2-dimethylpropionic acid, 2,2-dimethylbutyric acid, 2-ethyl-2-methylbutyric acid, 2,2-diethylbutyric acid, 2,2-dimethylvaleric acid, 2-ethyl-2- methylvaleric acid, 2,2-diethylvaleric acid, 2,2-dimethylhexanoic acid, 2,2-diethylhexanoic acid, 2,2-dimethyloctanoic acid, 2-ethyl-2,5-dimethylhexanoic acid, 3-methylisocitric acid, 4,4- dimethylaconitic acid, 1 -methylcyclopentane carboxylic acid, 1 ,2,2-trimethyl-1 ,3-cyclopentane dicarboxylic acid, 1 -methyl- 1 -cyclohexane carboxylic acid, 2-methylbicyclo[2.2.1]-5-heptene- 2-carboxylic acid, 2-methyl-7-oxabicyclo[2.2.1]-5-heptene-2-carboxylic acid, 1 -adamantane carboxylic acid, bicyclo[2.2.1]heptane-1 -carboxylic acid and bicyclo[2.2.2]octane-1-carboxylic acid, or mixtures thereof.

[0138] More preferably the tertiary carboxylic acid d) is neodecanoic acid, abietic acid, 1-methyl-1- cyclohexane carboxylic acid, 3-hydroxy-2,2-dimethylpropionic acid, 2,2-dimethylpropionic acid, or 2,2-dimethylbutyric acid, or mixtures thereof. Most preferred the tertiary carboxylic acid is neodecanoic acid.

[0139] Preferably the carboxylic acid d) of the crosslinkable composition according to the present invention is a tertiary carboxylic acid selected from the group consisting of neodecanoic acid, abietic acid, 1-methyl-1 -cyclohexane carboxylic acid, 3-hydroxy-2,2-dimethylpropionic acid, 2,2-dimethylpropionic acid, or 2,2-dimethylbutyric acid and mixtures thereof.

[0140] The amount of carboxylic acid d) incorporated in the crosslinkable composition according to the present invention preferably ranges from 0.005 to 0.5 mmole, per gram of isocyanatereactive compound a), viz. per gram of polyol a).

[0141] More preferably, the amount of carboxylic acid d) ranges from 0.02 to 0.3 mmole, most preferably from 0.04 to 0.25 mmole, per gram of isocyanate-reactive compound a), viz. per gram of polyol a).

[0142] The carboxylic acid d) is present in the crosslinkable composition according to the present invention, preferably in an amount of from 0.001 to 10% by weight, more preferably of from 0.002 to 5% by weight, most preferably of from 0.01 to 2.5% by weight based on the total amount of the isocyanate-reactive compound a), the polyisocyanate crosslinker b), the thermolatent metal-based catalyst c), and the carboxylic acid d), the total amount being 100% by weight.

[0143] Optionally the crosslinkable composition according to the present invention may comprise primary and / or secondary, preferably non-polymer bonded, carboxylic acids, in addition to the carboxylic acid d). If used, the quantity of primary and / or secondary acid is preferably present in the range of from 0.01 to 1 mole, more preferably in the range of from 0.01 to 0.5 mole, most preferably in the range of from 0.01 to 0.2 mole per mole of carboxylic acid d), the total amount of the isocyanate-reactive compound a), the polyisocyanate crosslinker b), the thermolatent metal-based catalyst c), the carboxylic acid d), and primary and / or secondary acid, if present, constituting 100% by weight of crosslinkable composition. Examples of primary and secondary acids are acetic acid, propionic acid, isononanoic acid, 2-ethylhexanoic acid, pentanoic acid and 3-methylbutanoic acid, 7,7-dimethyloctanoic acid, and mixtures thereof.

[0144] The crosslinkable composition of the present invention forms the basis for water-free coating compositions preferably comprising at least 30% by weight, more preferably at least 40% by weight, most preferably at least 50% by weight of non-volatile compounds, and preferably at most 70% by weight, more preferably at most 60% by weight, most preferably at most 50% by weight of volatile organic compounds, the sum of the weight percentages of the non-volatile compounds and the water-free volatile organic solvents not exceeding 100% by weight.

[0145] By “water-free” in the present invention is meant that there is no intentional addition of water neither to the non-volatile compounds nor to the volatile organic solvents and that both, the water-free non-volatile compounds and the water-free volatile organic solvents are technical grade non-volatile compounds I volatile organic solvents, used as such without further purification and or drying. As is generally known by the one skilled in the art technical grade compounds I organic solvents can comprise up to 0.2% by weight of water. Therefor by “water-free coating composition” in the present invention is meant a coating composition containing at most 0.2% by weight of water, based on the total of coating composition and water, if present, being 100% by weight.

[0146] Examples of suitable volatile organic compounds are hydrocarbons, such as toluene, xylene, SOLVESSO™ 100, ketones, terpenes, such as dipentene or pine oil, halogenated hydrocarbons, such as dichloromethane, ethers, such as ethylene glycol dimethyl ether, esters, such as ethyl acetate, ethyl propionate, n-butyl acetate or ether esters, such as methoxypropyl acetate or ethoxyethyl propionate. Also mixtures of these compounds can be used.

[0147] Further one or more so-called "exempt solvents" may be part of the coating composition. Examples of exempt solvents that are approved for use in paints and coatings include acetone, methyl acetate, parachlorobenzotrifluoride (commercially available under the name OXSOL®100), and volatile methyl siloxanes. Also tertiary butyl acetate is being considered as an exempt solvent.

[0148] The coating composition according to the invention also may be used and applied without volatile organic compounds, in particular in case where the viscosity of the coating composition is adjusted through the use of one or more reactive diluents in the crosslinkable composition or in applications where higher application viscosity is appropriate.

[0149] On the other hand, volatile organic compounds can be omitted and viscosity of the coating composition can be adjusted through the addition of compounds having hydroxyl- and / or other reactive groups for crosslinking with the isocyanate-reactive compounds a) and / or isocyanate crosslinkers b) of the crosslinkable composition. Examples of such other compounds are ketone resins, and latent amino-functional compounds such as oxazolidines, ketimines, aldimines, and diimines. These and other compounds are known to the skilled person and are mentioned, inter alia in US 5214086.

[0150] The non-volatile compounds of the coating composition according to the present invention preferably comprise from 20 to 98% by weight, more preferably from 30 to 95% by weight, most preferably from 40 to 90% by weight, of the crosslinkable composition of the present invention comprising a), b), c) and d), and preferably from 2 to 80% by weight, more preferably from 5 to 70% by weight, most preferably from 10 to 60% by weight, of one or more additives and auxiliaries, the sum of the weight percentages of the crosslinkable composition and the one or more additives and auxiliaries not exceeding 100% by weight of non-volatile compounds.

[0151] In a particular embodiment of the present invention, one or more additives or auxiliaries may be part of one or more components of the crosslinkable composition, which means that one or more additives or auxiliaries are incorporated into one or more components of the crosslinkable composition such as for example into the isocyanate-reactive compound a); nevertheless, the one or more additives or auxiliaries, and the one or more components of the crosslinkable composition, are considered separately when it comes to their weight percentages in the non-volatile compounds.

[0152] The one or more additives or auxiliaries being part of the non-volatile compounds of the coating composition according to the present invention are selected from the group consisting of pigments, dyes, surfactants, pigment dispersion aids, levelling agents, wetting agents, anticratering agents, antifoaming agents, matting agents, sag control agents, other rheology control agents, complexing agents, heat stabilizers, light stabilizers, UV absorbers, antioxidants, radical inhibitors, and fillers.

[0153] Antioxidants optionally used in coating compositions are well known and are generally chosen from phenolic type anti-oxidants, phosphite based antioxidants, phosphonite type anti-oxidant, thioethers and blends thereof. The coating composition according to the invention preferably comprises at least one anti-oxidant of the phosphite or phosphonite type.

[0154] Radical scavengers optionally used in coating compositions are well known. The coating composition can comprise any type of radical scavenger; preferably the coating composition according to the present invention comprises a radical scavenger based on a sterically hindered phenol moiety, more preferably based on esters comprising a 3-(3,5-d i-tert-butyl-4- hydroxyphenyl)propionate fragment.

[0155] Optionally the coating composition of the present invention comprise at least one hindered amine light stabilizer(s) and / or one or more benzotriazole-based UV absorbers, well known in the art.

[0156] Complexing agents, optionally used in coating compositions according to present invention, in general are organic compounds preferably containing one or more -SH groups. Preferred complexing agents are those of the general formula R-SH, wherein R can be an alkyl, alkenyl, aryl or aralkyl group. The -SH group can be a primary, secondary or tertiary -SH group. R can be a linear, cyclic or branched group and can comprise one or more other functional groups such as for example hydroxyl groups, primary, secondary or tertiary amine groups, silane or siloxane groups, ether groups, ester groups, carboxylic acid groups. Preferably R is a linear or branched alkyl group of the general formula -CnH2n+iwherein n is from 4 to 40, more preferably from 8 to 30. Examples are n-Ci2H25SH, n-Ci6H33SH , linear or branched molecules of formula CnH23SH , CI2H25SH and CI3H27SH, as well as mixtures thereof, and (CH3)2(iPr)C- C(CH3)2-C(CH3)2SH. If R contains more than one other functional groups, these can be different or the same. Particularly hydroxyl or ester groups are preferred as other functional group. In case of R containing an ester group, R preferably has the general formula - (CH2)n(C=O)O-R'. Herein, n can be chosen in the range of 1 - 20, preferably in the range of 1 - 10 and particularly preferred n is 1 or 2. R' can be any alkyl, alkenyl, aryl or aralkyi group, preferably containing from 1 to 24 carbon atoms, such as for example butyl, 2-ethylhexyl, iso-octyl, tridecyl, octadecyl. Particularly preferred are complexing agents of formula HS-(CH2)n(C=O)O-R', wherein n is 1 or 2 and wherein R' is an alkyl group containing from 3 to 20 carbon atoms. The complexing agent e) can contain multiple -SH groups. Preferred are those of formula HS- (CH2)X-SH wherein x = 1 to 20, those of formula (HSCH2)4-mC(CH2SCH2CH2SH)mwherein m = 1 to 4 and similar compounds such as for example described in patents EP 0665219 and EP 0435306. Other complexing agents e) which are particularly preferred are esters from SH- functional acids, especially SH-functional carboxylic acids, and a polyol. Not necessarily limiting to condensation reaction synthesis only, such products can be obtained by the formation of (poly)ester bonds between for example HS(CH2)nCOOH (wherein n = 1 to 20) and a polyol. Preferred are those which are the reaction products of carboxylic acids of formula HS(CH2)nCOOH wherein n is from 1 to 20 and a polyol having an OH-functionality of 2 or more. In this case, the polyol has usually an OH-functionality of 2 or more and can be monomeric, oligomeric or polymeric. Non-limiting examples of such polyols can be glycol, glycerol, trimethylolpropane, neopentyl glycol, pentaerythritol, dipentaerythritol, ethoxylated trimethylolpropane, tri(hydroxyethy I) isocyan urate, castor oil, OH functional polyester, OH functional polyacrylate, polycaprolactone, OH functional polycarbonate, polymers based on diepisulphide monomers as described in patent US 6486298. Mixtures of different complexing agents e) can be used, including mixtures of compounds e) having one SH moiety with those containing more than one sulphur-hydrogen bond.

[0157] The amount of complexing agent in the coating composition according to the invention is generally such that the molar equivalents of -SH groups per molar equivalent of metal in the metal-based catalyst c) is in the range of 1 to 20 molar equivalents of SH per equivalent of metal from the metal-based catalyst c), preferably in the range of 2 to 10 molar equivalents of SH per equivalent of metal from the metal-based catalyst.

[0158] The complexing agent is preferably used in an amount of 0.001 to 1%, more preferably of 0.01 to 0.5%, most preferably from 0.02 to 0.3%, by weight relative to the total weight of a), b), c), d), and complexing agent.

[0159] Preferably the coating composition of the present invention comprises one or more sag control agents.

[0160] Sag control agents are Theologically active compounds providing thixotropic properties to the coating composition. Sag control agents are well known and are generally chosen from clay sag control agents, silica-based sag control agents, microgel sag control agents, amide-based sag control agents or sag control agents based on polyurea products.

[0161] The coating composition of the present invention preferably comprises a sag control agent based on a polyurea product, more preferably a polyurea product typically prepared from the reaction of a polyisocyanate with a monoamine, most preferably a polyurea product prepared from the reaction of benzylamine, S-alpha methyl benzyl amine or 3-methoxypropyl amine and the adducts (or derivatives) of hexamethylene diisocyanate.

[0162] A polyurea product based sag control agent is typically prepared by the reaction of a polyisocyanate or its isocyanurate, biuret or uretdione derivative with at least one mono-amine or, alternatively, by the reaction of effectively mono-isocyanates (including diisocyanates that have been selectively reacted at one side) with polyamines. It is noted that when a polyurea product is prepared by the reaction product of amines with a polyisocyanate, it is preferred to prepare a di-urea product or a tri-urea product. In the present application, polyurea product based sag control agent is also referred to as polyurea-based sag control agent.

[0163] Polyisocyanates used for the preparation of the polyurea product based sag control agent are preferably selected from the group consisting of aliphatic, cycloaliphatic, aralkylene, and arylene polyisocyanates, more preferably from the group consisting of substituted or unsubstituted linear aliphatic polyisocyanates (and their isocyanurates, biurets, uretdiones), and substituted or unsubstituted aralkylene and cyclohexylene polyisocyanates. Optionally, the polyisocyanate may contain other functional groups such as for example ether functionalities, ester functionalities or urethane functionalities. The polyisocyanate usually contains 2 to 40 and preferably 4 to 12 carbon atoms between the NCO groups. The polyisocyanate preferably contains at most on average four isocyanate groups, more preferably at most on average three isocyanate groups, and most preferably on average two isocyanate groups. It is even more preferred to use a symmetrical aliphatic or cyclohexylene diisocyanate. Suitable diisocyanates are preferably selected from the group consisting of tetramethylene-1 ,4-diisocyanate, pentamethylene-1 ,5-diisocyanate, hexamethylene-1 ,6- diisocyanate (HMDI), trans-cyclohexylene-1 ,4-diisocyanate, dicyclohexylmethane-4,4'- diisocyanate, 1 ,5-dimethyl-(2,4-[omega]-diisocyanato methyl) benzene, 1 ,5-dimethyl(2,4- [omega]-diisocyanatoethyl) benzene, 1 ,3,5-trimethyl(2,4-[omega]diisocyanato-methyl) benzene, 1 ,3,5-triethyl(2,4-[omega]-diisocyanatomethyl) benzene, meta-xylylene diisocyanate, para-xylylene diisocyanate, dicyclohexyl-dimethylmethane-4,4'-diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and diphenylmethane-4,4'-diisocyanate (MDI).

[0164] Preferred polyisocyanates are selected from the group consisting of hexamethylene-1 , 6- diisocyanate (HMDI), condensed derivatives of hexamethylene-1 , 6-diisocyanate (HMDI), such as uretdiones, biurets, isocyanurates (trimers), and asymmetrical trimers, many of which are marketed as DESMODUR® N and TOLONATE™ HDB and TOLONATE™ HDT.

[0165] Particularly preferred polyisocyanates are selected from the group consisting of HMDI, its isocyanurate trimer and its biuret, trans-cyclohexylene-1 , 4-diisocyanate, para- and meta- xylylene diisocyanate, and toluene diisocyanate. Most preferred polyisocyanate is HMDI or its isocyanurate.

[0166] As will be understood by the person skilled in the art, it is also possible to use conventionally blocked polyisocyanates which generate two or more isocyanates in situ, as long as the blocking agent, after splitting, does not prevent the formation of the sag control agent. The term “polyisocyanate” thus stands for polyisocyanates and polyisocyanate-generating compounds.

[0167] In accordance with a preferred embodiment of the invention the amines used to prepare polyurea product based sag control agent comprise mono-amines. Many monoamines can be used in combination with the polyisocyanates to create polyurea reaction products. Primary and secondary aliphatic as well as aromatic amines can be used. Preferably, primary amines are used; of these n-alkylamines and ether-substituted n-alkylamines are particularly useful in accordance with this invention. Optionally, the amines may comprise other functional groups, such as hydroxy groups, ester groups, urethane groups. Preferred monoamines include n- aliphatic amines, especially n-alkylamines such as hexylamine; cyclohexylamine; benzylamine; 3-methoxypropylamine; S-alpha-methylbenzylamine and 2-phenethylamine, as well as mixtures thereof. Specifically preferred polyurea product based sag control agent are the adducts of (derivatives of) HMDI and benzylamine, the adducts of (derivates of ) HMDI and S-alpha-methylbenzylamine, the adducts of (derivatives of) HMDI and 3- methoxypropylamine, or mixtures thereof.

[0168] The use of diamines (e.g. ethylenediamine) as component next to mono-amines may also be an option to create high melting point polyureas. The monoamine or part of the monoamine used to prepare the polyurea product based sag control agent can be a chiral monoamine. Thixotropic agents comprising polyurea products as claimed in U.S. Pat. No. 8,207,268 are considered to be part of this invention.

[0169] The polyurea formation reaction may be carried out in the presence of an inert solvent, for example acetone, methyl isobutyl ketone, N-methyl pyrrolidone, benzene, toluene, xylene, butyl acetate or an aliphatic hydrocarbon such as petroleum ether, alcohols, and water, or mixtures thereof. Here the term “inert” indicates that the solvent does not significantly interfere in the process of polyurea formation, which means that the amount of polyurea formed when solvent is present is at least 80% of the amount produced when no solvent is present.

[0170] Alternatively the polyurea formation reaction may be carried out in the presence of any component of the coating composition in particular in the presence of isocyanate-reactive compound a) or in the presence of polyisocyanate crosslinker b). Preferably, the polyurea formation reaction is carried out in the presence of isocyanate-reactive compound a).

[0171] It will be obvious that if the isocyanate-reactive compound a) is highly reactive with either the isocyanate or the amine, the isocyanate-reactive compound a) and that particular highly reactive isocyanate or amine cannot be premixed. As the polyisocyanate crosslinker b) is highly reactive with the amine, the polyisocyanate crosslinker b) and that amine cannot be premixed. By the term “highly reactive” is meant that more than 30% of the isocyanate or amine reacts with the isocyanate-reactive compound a) or the polyisocyanate crosslinker b), respectively, before the complementary amine or isocyanate, required for the polyurea synthesis, are mixed.

[0172] According to a preferred embodiment of the invention, the polyurea product based sag control agent is prepared in the presence of isocyanate-reactive compound a). This can be done by mixing a mixture of the isocyanate-reactive compound a) and isocyanate with the amine, or by mixing the isocyanate with a mixture of the isocyanate-reactive compound a) and amine, or by mixing a mixture of isocyanate-reactive compound a) and amine with a mixture of isocyanate-reactive compound a) and isocyanate, or by mixing the isocyanate and the amine with the isocyanate-reactive compound a) simultaneously.

[0173] It is also possible that small amounts of coreactive components are intentionally employed in the preparation reaction of the polyurea product based sag control agent to act as crystallization modifiers, and more particularly to modify the crystal sizes upon precipitation or the colloidal stability of the resulting crystals. Equally, dispersant and other adjuvants may be present in any of these introduction steps.

[0174] The preparation of the polyurea product based sag control agent may be carried out in any convenient manner, generally with the reactants being vigorously stirred, in a batch or in a continuous process. Amine components may be added to isocyanate or isocyanate may be added to amine components, whichever is most convenient. Alternatively the polyurea product based sag control agent can be formed in a separate reaction and mixed with the isocyanate-reactive compound a), usually under proper stirring.

[0175] The relative molar ratio amine / isocyanate is usually between 0.9 and 1.1 , preferably between 0.95 and 1.05.

[0176] The particle size of polyurea product is preferably less than 15 pm as determined by ISO 1524.

[0177] The sag control agent is preferably used in an amount of 0.1 to 5% by weight , more preferably from 0.15 to 4% by weight, most preferably from 0.2 to 3% by weight, relative to the total weight of a), b), c), d) and sag control agent(s).

[0178] In a particular embodiment of the present invention, the at least one sag control agent is part of one or more components of the crosslinkable composition, which means that the at least one sag control agent is incorporated into one or more components of the crosslinkable composition such as for example the isocyanate-reactive compound a); nonetheless, the at least one sag control agent and the one or more components of the crosslinkable composition are considered separately when it comes to their weight percentages in the non-volatile compounds.

[0179] In a preferred embodiment of the present invention the at least one sag control agent is part of the isocyanate-reactive compound a); the values of their relative weight percentages in the non-volatile compounds of the coating composition are such as if they are considered separately.

[0180] In a preferred embodiment of the present invention the isocyanate-reactive compound a) comprises from 0.1 to 10% by weight of one or more polyurea product based sag control agent, the weight percentages of isocyanate-reactive compound and polyurea product based sag control agent being 100% by weight.

[0181] As is usual with coating compositions comprising a crosslinkable composition comprising an isocyanate-reactive compound and a polyisocyanate crosslinker, the coating composition according to the invention has a limited pot-life. Therefore, the crosslinkable composition is suitably provided as a multi- component composition, for example as a two-component composition or as a three-component composition, wherein the isocyanate-reactive compound a) and the polyisocyanate crosslinker b) are parts of at least two different components. Therefore, the invention also relates to a kit of parts for preparing a coating composition, comprising: i. a binder module comprising at least one isocyanate-reactive compound a), at least one carboxylic acid d), optionally at least one thermolatent metal-based catalyst c), and optionally at least one sag control agent, ii. a crosslinker module comprising at least one polyisocyanate crosslinker b), and optionally at least one thermolatent metal-based catalyst c), wherein

[0182] - the thermolatent metal-based catalyst is present in at least binder module i) and / or crosslinker module ii); and o in a preferred embodiment the carboxylic acid d) of binder module i) is a tertiary carboxylic acid d), o in another preferred embodiment binder module i) comprises sag control agents. Preferably a kit of parts for preparing a coating composition, comprises: i. a binder module comprising at least one isocyanate-reactive compound a), at least one carboxylic acid d), and optionally at least one sag control agent, ii. a crosslinker module comprising at least one polyisocyanate crosslinker b), and at least one thermolatent metal-based catalyst c), wherein in a preferred embodiment the carboxylic acid d) of binder module i) is a tertiary carboxylic acid d), in another preferred embodiment binder module i) comprises sag control agents.

[0183] Alternatively, the kit of parts may comprise three components, comprising: i. a binder module comprising the isocyanate-reactive compound a), ii. a crosslinker module comprising the polyisocyanate crosslinker b), and

[0184] Hi. a diluent module comprising a volatile organic diluent,

[0185] - wherein carboxylic acid d) may be distributed over modules i), and / or iii), and

[0186] - wherein at least one of the modules comprises carboxylic acid d);

[0187] - wherein in a preferred embodiment carboxylic acid d) is a tertiary carboxylic acid d);

[0188] - wherein the thermolatent metal-based catalyst c), and optionally one or more sag control agent, may be distributed over modules i), ii), and / or iii);

[0189] - wherein at least one of the modules, preferably crosslinker module ii), comprises the thermolatent metal-based catalyst c); and

[0190] - wherein in a preferred embodiment at least one of the modules, preferably binder module i), comprises sag control agents.

[0191] Preferably the binder module comprises:

[0192] - from 50 to 94 % by weight, preferably from 55 to 89 % by weight, more preferably from 60 to 89 % by weight, of isocyanate-reactive compound a);

[0193] - from 5 to 50 % by weight, preferably from 10 to 45 % by weight, more preferably from 10 to 40% by weight, of water-free volatile organic solvent;

[0194] - from 0.05 to 12 % by weight, preferably from 0.1 to 6 % by weight, more preferably from 0.2 to 3.0 % by weight, of aromatic carboxylic acid and / or tertiary carboxylic acid d); and optionally from 0.1 to 4 % by weight, preferably from 0.15 to 3.5 % by weight, more preferably from 0.2 to 3 % by weight, of at least one sag control agent, preferably a polyurea-based sag control agent; optionally from 0.001 to 10 % by weight, preferably from 0.002 to 5 % by weight, more preferably from 0.005 to 1 % by weight, of thermolatent metal-based catalyst c); wherein the total of a), d), water-free volatile organic solvent, optional c),and optional polyurea sag control agent is 100% by weight.

[0195] Preferably, the isocyanate-reactive compound a) is provided to binder module i) either as a solution in water-free volatile organic solvent comprising carboxylic acid d), or as a solution in water-free volatile organic solvent comprising sag control agent, or as a solution in water-free volatile organic solvent comprising carboxylic acid d) and sag control agent.

[0196] The other components of the coating composition may be distributed in different ways over the modules as described above, as long as the modules exhibit the required storage stability. Components of the coating composition which react with each other upon storage are preferably not combined in one module. If desired, the components of the coating composition may be distributed over even more modules, for example 4 or 5 modules.

[0197] The coating composition of the invention, characterized by an extended potlife and accelerated film hardness build-up at low baking conditions, provides coatings with improved chemical resistance, film hardness and appearance.

[0198] The coating compositions of the invention can be applied to any substrate such as for example, metal, e.g., iron, steel, tinplate and aluminum, plastic, wood, glass, synthetic material, paper, leather, concrete or another coating layer, said another coating layer can be comprised of the coating composition of the present invention or it can be a different coating composition. The coating compositions of the present invention show particular utility as clear coats, base coats, pigmented top coats, primers, and fillers.

[0199] The coating composition according to the invention is very suitable for use as a clear coat. A clear coat is essentially free of pigments and is transparent for visible light. However, the clear coat composition may comprise matting agents, for example silica based matting agents, to control the gloss level of the coating.

[0200] The coating composition according to the present invention was found to be particularly suitable for use in crosslinkable clear coat compositions used in coating processes using different coating layers wherein the number of bake curing steps is reduced compared to a standard multilayer coating process. The coating processes with reduced number of bake curing steps are more economic with regard to paint and energy consumption compared to standard ways of application, in which usually a primer layer is applied on an electrodeposition coating, followed by a first bake curing step, and subsequent application of an aqueous basecoat layer, flash-off, application of a clear coat layer and second bake curing. In contrast, a process with reduced number of bake curing steps is often characterized in elimination of the primer layer as well as the first bake curing step. Instead, in a coating process with reduced number of bake curing steps, a first aqueous colored layer is applied on a substrate such as a metal, optionally comprising an electrodeposition layer, followed by flash-off, application of an aqueous basecoat layer , another flash-off and application of a clear coat layer followed by one bake curing step for all layers simultaneously.

[0201] It was particularly surprising to find that use of the crosslinkable compositions according to the invention yielded coating compositions, more particularly clear coat compositions, with very good chemical resistance and hardness and good appearance in a coating process with reduced number of bake curing steps.

[0202] The coating composition of the current invention is also suitable as pigmented topcoat for coating objects such as bridges, pipelines, industrial plants or buildings, oil and gas installations, or ships. The compositions are also suitable for finishing and refinishing automobiles and large transportation vehicles, such as trains, trucks, buses, and airplanes. In general, the coating composition of the current invention can be applied by spraying, brushing, draw-down or any other method to transfer a composition to a substrate.

[0203] The invention also relates to a method of providing a coating, preferably a coating for at least a part of a transportation vehicle, more preferably a coating for at least one part of the exterior surface of a transportation vehicle, wherein the method comprises the steps of applying a coating composition according to the invention to at least a part of a transportation vehicle, and curing the applied coating composition, preferably in a temperature range of 5 to 180° C, more preferably of 40 to 140° C, or most preferably of 60 to 120° C.

[0204] Examples

[0205] The following illustrative examples are merely meant to exemplify the present invention but they are not intended to limit or otherwise define the scope of the present invention.

[0206] Paint formulations were prepared according to the compositions as listed in Table 1 and Table 2 wherein example 1 to 6 are according to the invention, comprising thermolatent tin-based catalyst and aromatic carboxylic acid (Ex. 1) or comprising thermolatent tin-based catalyst and tertiary carboxylic acid (Ex.2 to Ex.6). Comparative examples 1 to 4 comprise a thermolatent tin-based catalyst in combination with a secondary carboxylic acid (Comp. Ex. 1) or with primary carboxylic acid (Comp. Ex. 2 and 3) or without carboxylic acid (Comp. Ex.4); while comparative example 5 comprises tertiary carboxylic acid and dibutyl tin dilaurate (being a non-thermolatent catalyst).

[0207] In these tables:

[0208] • SETALUX® 61230 BA-60 is an acrylic polyol with 3.5 % OH, modified with a polyurea- based sag control agent.

[0209] • SETALUX® 1232 is an acrylic polyol with 3.6% OH providing fast drying and good hardness.

[0210] • SETAL® 1624 is a polyester polyol with 6.5 % OH providing good hardness.

[0211] • SOLVESSO™ 100 is a mixture of aromatic solvents.

[0212] • TINUVIN® 292 is a mixture of two active tertiary amine ingredients: bis(1 ,2, 3, 6, 6- pentramethyl-4- piperidyl)sebacate and methyl(1 ,2,2,6,6-pentamethyl-4- piperidyl)sebacate.

[0213] • TINUVIN® 1130 is a benzotriazole-based UV absorber.

[0214] • MODAFLOW® 9200 is a low-viscosity flow modifier available from allnex.

[0215] • ADDITOL® XL 123N is a flow agent and defoamer based on a modified silicone oil available from allnex.

[0216] • Tinstab BL-277 is dibutyltin dilaurate.

[0217] • TOLONATE™ HDT- LV is a solvent free low viscosity aliphatic polyisocyanate based on hexamethylene diisocyanate.

[0218] • Hardener solution is a mixture of 90% by weight of homopolymer of hexamethylene-1 ,6- diisocyanate, 0.3% by weight of thermolatent tin-based catalyst with CAS N° 1622456- 43-2 and 9.7% by weight of butylacetate.

[0219] In the above SETALUX and SETAL polyols, x% OH means that out of 100 grams of polyol, x grams are coming from OH groups; the values may be converted in hydroxyl values (mg KOH / g) using the formula (561.x) / 17.

[0220] Table 1.

[0221]

[0222] Table 2

[0223] Coating formulations, prepared according to the compositions of table 1 , were applied directly onto glass by draw-down application and after a flash-off for 10 minutes at room temperature, dried for 30 minutes at 80 °C. Coatings were analyzed for Martens and Persoz hardness, as well as resistance against xylene (drop resistance), and pancreatine (gradient oven test). Coating properties of the coatings obtained from curing the coating compositions of table 1 are reported in table 3.

[0224] Table 3 Table 3 clearly demonstrates that coatings obtained from coating compositions according to the invention (Ex. 1 , Ex. 2 and Ex. 3), comprising an aromatic acid or a tertiary acid, display higher hardness and much improved xylene resistance compared to coatings obtained from similar coating compositions not according to the invention comprising primary acid or no acid (Comp Ex. 2, Comp Ex. 3 and Comp Ex. 4). Because the xylene resistance after 2 h was unacceptable for coatings obtained from coating compositions of comparative Examples 2, 3 and 4, no gradient oven tests were performed. Surprisingly, the coatings obtained from the coating compositions according to the invention (Ex. 1 , Ex. 2 and Ex. 3) comprising an aromatic acid or a tertiary acid displayed significantly improved pancreatin resistance, used to simulate bird excreta resistance, compared to a coating obtained from the coating composition of Comp Ex. 1 not according to the invention, comprising a secondary acid. Overall, the compositions according to the invention displayed much better coating properties compared to compositions not according to the invention.

[0225] Coating composition of Comparative Example 4 (comprising thermolatent tin-based catalyst but without tertiary carboxylic acid) had a potlife of more than 2.5 h, comparable to coating compositions of Example 4, 5 and 6, according to the invention, comprising thermolatent tin- based catalyst and tertiary carboxylic acid. Surprisingly FTIR analysis revealed an isocyanate conversion of 28.4 % after 30 minutes at 60°C and an isocyanate conversion of 33.1 % after 30 minutes at 80°C for the coating composition of Comparative Example 4, while an isocyanate conversion of respectively 79.2 % and 90.7 % for was measured for the coating composition of Example 2, according to the invention, the coating composition of Example 2 showing considerably improved Martens hardness, Persoz hardness, xylene an pancreatine resistance (table 3).

[0226] Coating compositions, prepared according to the compositions listed in Table 2, were sprayed on a black waterborne basecoat and after a flash-off for 10 minutes at room temperature, dried for 30 minutes at 80 °C.

[0227] Coatings compositions were analyzed for potlife; the coatings were evaluated for Kbnig hardness, DOI and long wave. Coating composition potlife and coating properties of the coatings obtained from the coating compositions of table 2 are reported in table 4.

[0228] Table 4

[0229] Table 4 clearly demonstrates that coating compositions (Examples 4, 5 and 6) according to the invention have good potlife while the coatings obtained from said coating compositions prove an outstanding appearance, whereas the coating composition of Comparative Example 5 displays unacceptably short potlife while the derived coating shows a mediocre appearance as judged by the low DOI. Furthermore, the longwave of the coatings of examples 4, 5 and 6 is better and the hardness is significantly higher compared to the results obtained for the coating obtained from the coating compositions of comparative Example 5, not according to the invention. Therefore, it is clear that the paint formulation of Comparative Example 5 does not provide an acceptable solution to the problem solved by the formulations according to the invention. In table 3 and table 4:

[0230] • Martens hardness was determined according to ISO 14577.

[0231] • Persoz hardness and Konig hardness were measured in a climatized room at 23° C, and 55+ / -5% relative humidity. Hardness was measured with a pendulum according to Persoz or Konig as described in ASTM D 4366 and ISO 1522-1973.

[0232] • Pancreatin resistance was determined using a gradient oven test according to ISO 2812- 5:2018.

[0233] • Xylene resistance was determined according to ISO 2812.

[0234] • DOI and longwave were measured using a Byk Wavescan Dual. • For determination of pot-life, the viscosity of the reacting paint before spraying was measured in time with a DIN Flow Cup 4 according to DIN 53211 and is indicated in seconds. The pot-life is the time required until the viscosity was doubled relative to the initial viscosity.

[0235] The above examples clearly demonstrate that the coating compositions according to the present invention display longer potlife; the coatings obtained from the coating compositions of the present invention show an improved combination of properties more particularly an improved chemical resistance, higher hardness, and improved appearance compared to the prior art coating compositions.

Claims

CLAIMS1 . A crosslinkable composition comprising a) at least one isocyanate-reactive compound, b) at least one polyisocyanate crosslinker having free isocyanate groups, c) at least one thermolatent metal-based catalyst for catalysing the reaction between the isocyanate-reactive groups of the isocyanate-reactive compound a) and the isocyanate groups of said polyisocyanate crosslinker b), said thermolatent metalbased catalyst comprising cyclic metal compounds, d) at least one aromatic carboxylic acid, and / or at least one tertiary carboxylic acid of formula RR'R"CCOOH, wherein each R, R' and R" group, independently, is an alkyl, alkenyl, aryl or aralkyl group containing at least one carbon atom, i. wherein the total number of carbon atoms in the R, R' and R" groups is in the range of from 3 to 40, and ii. wherein two or three of the R, R’ and R” groups optionally are linked to form a ring structure, and / or optionally are substituted by an hydroxyl- and / or a carboxyl group,Hi. wherein the amount of the at least one aromatic carboxylic acid and / or the at least one tertiary carboxylic acid d) is in the range of 0.02 to 0.3 mmol per gram of isocyanate-reactive compound a).

2. The crosslinkable composition according to claim 1 , wherein the thermolatent metalbased catalyst c) is a tin-based catalyst comprising cyclic tin compounds of formula I, II or III or mixtures thereof:where n > 1 where:D represents — O — , — S — or — N(R1) wherein R1 represents a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic radical, or an optionally substituted aromatic or araliphatic radical,which has up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or is hydrogen or the radicalor R1 and L3 together represent — Z-L5-;D* represents — O — or — S — ;X, Y and Z represent identical or different radicals selected from alkylene radicals having the formulae — C(R2)(R3)-, — C(R2)(R3)-C(R4)(R5)- or — C(R2)(R3)- C(R4)(R5)-C(R6)(R7)- or orthoarylene radicals having the formulaewherein R2 to R11 independently represent saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and may optionally contain heteroatoms from the group of oxygen, sulfur, nitrogen, or are hydrogen;L1 , L2 and L5 independently represent — O — , — S — , — OC(=O) — , — OC(=S) — SC(=O)— , — SC)=S)— , — OS(=O)2O— , — OS(=O)2— or — N(R12)-, wherein R12 represents a saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical which has up to 20 carbon atoms and may optionally contain heteroatoms selected from the group consisting of oxygen, sulfur, nitrogen, or is hydrogen;L3 and L4 independently represent — OH, — SH, — OR13, -Hal, — OC(=O)R14, — SR15, — OC(=S)R16, — OS(=O)2OR17, — OS(=O)2R18 or — NR19R20, or L3 and L4 together represent -L1-X-D-Y-L2-, wherein R13 to R20 independently represent saturated or unsaturated, linear or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and may optionally contain heteroatoms selected from the group consisting of oxygen, sulfur, nitrogen, or are hydrogen.

3. The crosslinkable composition according to any of claims 1 or 2, wherein the thermolatent tin-based catalyst is selected from the group consisting of• 4,12-d i- n- b uty I- 1 ,7,9,15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7]pentadecane,• 4,12-di-n-butyl-2,6, 10, 14-tetramethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,• 2,4,6,10,12,14-hexamethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,• 4,12-di-n-octyl-2,6, 10,14-tetramethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8- stannaspiro[7.7]pentadecane,• 4,12-di-n-octyl- 1 ,7,9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7]pentadecane,• 4,12-dimethyl-1 ,7,9,15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7]pentadecane,• 1 ,1-dichloro-5-methyl-5-aza-2,8-dioxa-1 -stannacyclooctane,• bis [1 ,1'-(butylimino-kappaN)bis (propane-2-olato-kappaO)] tin, and• mixtures thereof.

4. The crosslinkable composition according to claim 1 , wherein the carboxylic acid d) is a tertiary carboxylic acid with general formula RR'R"CCOOH wherein the total number of carbon atoms in the R, R' and R" groups is in the range of from 3 to 30.

5. The crosslinkable composition according to claim 4, wherein the tertiary carboxylic acid d) has the general formula RR'R"CCOOH , wherein R is a methyl or ethyl group, and where the total number of carbon atoms of groups R’ and R” is from 2 to 17, and where R’ and / or R” is non-substituted or substituted with only one hydroxyl group.

6. The crosslinkable composition according to claim 4 or 5, wherein the tertiary acid d) is selected from the group consisting of neodecanoic acid, abietic acid, 3- hydroxy-2, 2- dimethylpropionic acid, 2,2-bis(hydroxymethyl)propionic acid, 1 -methyl cyclohexanoic acid, dimetylmalonic acid, ethylmethylmalonic acid, diethylmalonic acid, 2,2- dimethylsuccinic acid, 2,2-diethylsuccinic acid, 2,2-dimethylglutaric acid, 2,2- dimethylpropionic acid, 2,2-dimethylbutyric acid, 2-ethyl-2-methylbutyric acid, 2,2- diethylbutyric acid, 2,2-dimethylvaleric acid, 2-ethyl-2-methylvaleric acid, 2,2- diethylvaleric acid, 2,2-dimethylhexanoic acid, 2,2-diethylhexanoic acid, 2,2- dimethyloctanoic acid, 2-ethyl-2,5-dimethylhexanoic acid, 3-methylisocitric acid, 4,4- dimethylaconitic acid, 1 -methylcyclopentane carboxylic acid, 1 ,2,2-trimethyl-1 ,3- cyclopentane dicarboxylic acid, 2-methylbicyclo[2.2.1]-5-heptene-2-carboxylic acid, 2- methyl-7-oxabicyclo[2.2.1]-5-heptene-2-carboxylic acid, 1 -adamantane carboxylic acid, bicyclo[2.2.1]heptane-1 -carboxylic acid, and bicyclo[2.2.2]octane-1 -carboxylic acid, and mixtures thereof.

7. The crosslinkable composition according to claim 1 , wherein the carboxylic acid d) is an aromatic carboxylic acid selected from the group consisting of aromatic monocarboxylic acids, alkyl- or alkoxy- or hydroxy- substituted aromatic monocarboxylic acids, aromatic dicarboxylic acids, monoalkyl esters of aromatic dicarboxylic acids, alkyl- or alkoxy- or hydroxy substituted aromatic dicarboxylic acids, monoalkyl esters of alkyl- or alkoxy- or hydroxy-substituted of aromatic dicarboxylic acids, aromatic tricarboxylic acids, monoalkyl esters of aromatic tricarboxylic acids, dialkyl esters of aromatic tricarboxylic acids, aromatic tetracarboxylic acids, monoalkyl esters of aromatic tetracarboxylic acids, dialkyl esters of aromatic tetracarboxylic acids, trialkyl esters of aromatic tetracarboxylic acids, and mixtures thereof, wherein the aromatic carboxylic acid is selected from the group consisting of benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, and pyromellitic acid, and mixtures thereof.

8. The crosslinkable composition according to any of claims 1 to 7, wherein the amount of aromatic carboxylic acid and / or tertiary carboxylic acid d) in the composition is in the range of 0.04 to 0.25 mmol per gram of isocyanate-reactive compound a).

9. The crosslinkable composition according to claim 1 , wherein the isocyanate-reactive compound a) is a polyol, comprising:• from 70 to 100% by weight of a polymeric polyol selected from the group consisting of polyester polyols, polyacrylate polyols, polycarbonate polyols, polyether polyols, polyurethane polyols, melamine polyols, and mixtures and hybrids thereof, and having a hydroxyl value in the range of 20 to 1 ,000 mg KOH per gram and an acid value of 15 mg KOH per gram or less, and• from 0 to 30% by weight of one or more reactive diluents selected from the group consisting of monomeric and oligomeric compounds, and mixtures thereof, wherein the monomeric and oligomeric compounds comprise 2 to 5 hydroxyl groups, the oligomeric compounds being characterized by a degree of polymerization of at most 15, the sum of the weight percentages of the polymeric polyol and the reactive diluent not exceeding 100 % by weight.

10. The crosslinkable composition according to claim 1 , wherein the polyisocyanate crosslinker b) is selected from the group consisting of aliphatic polyisocyanates, cycloaliphatic polyisocyanate, the adducts of aliphatic isocyanates, the adducts of cycloaliphatic polyisocyanates, and mixtures thereof, the adducts being selected from the group consisting of biurets, isocyanurates, imino-oxadiazinediones, allophanates, uretdiones, homopolymers of polyisocyanates, and mixtures thereof.11 . The crosslinkable composition according to any of claims 1 to 10, comprising:• from 9 to 90 % of weight of at least one isocyanate-reactive compound a),• from 9 to 90 % of weight of at least one polyisocyanate crosslinker b),• from 0,01 to 10 % of weight of at least one at least one thermolatent metal-based catalyst c), and• from 0.001 to 10 % of weight of at least one aromatic carboxylic acid and / or tertiary carboxylic acid d), based on the total amount of isocyanate-reactive compound a), polyisocyanate crosslinker b), thermolatent metal-based catalyst c), aromatic and / or tertiary carboxylic acid d), the total amount being 100% by weight.

12. A coating composition comprising at least 30% by weight of non-volatile compounds and at most 70% by weight of water-free volatile organic solvents, the sum of the weight percentages of the non-volatile compounds and the water-free volatile organic solvents not exceeding 100% by weight of the coating composition; the non-volatile compounds comprising from 20 to 98% by weight of the crosslinkable composition of claims 1 to 11 and from 2 to 80% by weight of one or more additives and auxiliaries, the sum of the weight percentages of the crosslinkable composition and the one or more additives and auxiliaries not exceeding 100% by weight of non-volatile compounds.

13. The coating composition according to claim 12, wherein the one or more additives and auxiliaries are selected from the group consisting of pigments, dyes, surfactants, pigment dispersion aids, levelling agents, wetting agents, anti-cratering agents, antifoaming agents, matting agents, sag control agents, other rheology control agents, heat stabilizers, light stabilizers, UV absorbers, antioxidants, radical inhibitors, and fillers, and mixtures thereof.

14. The coating composition according to claim 12 or 13 comprising from 0.1 to 5 % by weight of sag control agent, relative to the total weight of the crosslinkable composition of claim 11.

15. The coating composition according to claim 13 or 14, wherein the sag control agent is a polyurea-based sag control agent.

16. Kit of parts for preparing a coating composition according to any of claims 12 to 15 comprising:• a binder module i) comprising at least one isocyanate-reactive compound a), at least one carboxylic acid compound d), optionally at least one thermolatent catalyst c), optionally one or more additives and auxiliaries, and optionally water- free volatile organic solvents,• a crosslinker module ii) comprising at least one polyisocyanate crosslinker b), optionally at least one thermolatent catalyst c), optionally one or more additives and auxiliaries, and optionally water-free volatile organic solvents, wherein- the thermolatent metal-based catalyst is present in at least binder module i) and / or crosslinker module ii); and- the carboxylic acid d) of binder module i) is preferably a tertiary carboxylic acid d), binder module i) preferably comprises sag control agents, binder module i) preferably comprises water-free volatile organic solvents.

17. Kit of parts according to claim 16 wherein the isocyanate-reactive compound a) is provided to binder module i) either as a solution in water-free volatile organic solvent comprising carboxylic acid d), or as a solution in water-free volatile organic solvent comprising sag control agents, or as a solution in water-free volatile organic solvent comprising carboxylic acid d) and sag control agents.

18. A method of providing a coating layer comprising the steps of applying a coating composition according to any of claims 12 to 15, or a coating composition prepared using the kit of parts according to claim 16, to at least a part of an object, preferably the (exterior) surface of a transportation vehicle, and curing the applied coating composition, preferably in a temperature range of 5 to 180 °C.

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