BR112020013015B1 - POWDER COATING COMPOSITION, PROCESS FOR PREPARING A POWDER COATING COMPOSITION, METHOD FOR POWDER COATING, COATED ARTICLES, USE OF A CATALYST SYSTEM - Google Patents

Abstract

The invention relates to powder coating compositions suitable for low temperature powder coating crosslinking, typically at a curing temperature between 75 and 140°C, which can be used for powder coating of temperature sensitive substrates, such as MDF, wood, plastic or temperature-sensitive metal alloys. The powder coating compositions comprise a crosslinkable component A having at least 2 acidic C-H donor groups in activated methylene or methine, a crosslinkable component B having at least 2 activated C=C unsaturated acceptor groups that react with component A by Michael addition. real under the action of a catalyst system C which is preferably a latent catalyst system. The invention also relates to a process for manufacturing such powder coating compositions, processes for coating articles using said powder coating composition and the resulting coated articles. The invention also relates to specific polymers for use in powder coatings and to the use of specific catalyst systems in such powder coating compositions.

Description

BASICS OF THE INVENTION

[001] The invention relates to powder coating compositions that are curable at low curing temperatures, to processes for manufacturing such powder coating compositions, to processes for coating articles using said powder coating composition and to resulting coated articles. The invention also relates to specific polymers and catalyst systems for use in powder coating compositions.

DESCRIPTION OF RELATED TECHNIQUE

[002] Powder coatings are dry, finely divided, free-flowing solid materials at room temperature and have gained popularity in recent years over liquid coatings. Powder coatings are generally cured at elevated temperatures between 120°C and 200°C, more typically between 140°C and 180°C. High temperatures are required to provide sufficient flow of the binder to allow film formation and obtain a good surface appearance of the coating, but also to achieve high reactivity for a cross-linking reaction. At low curing temperatures, one may face reaction kinetics that will not allow short curing times by requiring the full development of mechanical and strength properties; on the other hand, for systems where high component reactivity can be created, the coatings are likely to have a poor appearance due to the relatively high viscosity of these systems at lower temperatures, increasing rapidly as the curing reaction proceeds: the integrated fluidity in the time of such systems is too low to achieve sufficient leveling (see, for example, Progress in Organic Coatings, 72 pp. 26-33 (2011)). Especially when bleaching thinner films, appearance can be limiting. Furthermore, very high reactivities can lead to problems due to premature reactions when formulating powder coatings in an extruder.

[003] As a result of this temperature restriction, powder coatings are not easily used in coating heat-sensitive substrates, such as medium density fiberboard (MDF), wood, plastics and certain metal alloys. Developments are underway to reduce curing temperatures, with a focus on green technologies and the corresponding push to reduce energy costs and be able to coat temperature-sensitive substrates. There is also an advantage to having powder coatings that cure at low temperatures when applied to solid metal components, as these components are slow to heat up.

[004] Recently, there has been a great effort to find powder coatings that cure at lower temperatures. Therefore, the term “lower” temperatures in the field of powder coatings generally implies a temperature significantly greater than room temperature, but less than 160°C, preferably less than 150°C, more preferably less than 140°C, even more preferably less than 140°C, even more preferably less than 130°C or even below 120°C. In general, it has been found that it is difficult to achieve high enough reactivity to obtain the film crosslinking density required for performance within an acceptable cure time window when using low cure temperatures, typically below 150°C and especially at or below 140°C, to achieve adequate chemical resistance, mechanical properties such as impact resistance, flexibility, surface hardness and weathering properties and at the same time also to achieve good coating appearance and flow.

[005] There are systems that cure at very low temperatures in the range between 120 and 130°C. These tend to be epoxy-cured polyester systems (e.g., triglycidyl isocyanurate (TGIC)). Generally, these systems suffer from poor appearance and are only used to produce textured coatings. Appearance can be improved by allowing lower Tg powders (requiring refrigerated storage) or by designing powder coatings with crystalline components that melt between the Tg and curing temperature, but both approaches have complications.

[006] Another approach to enabling low temperature curing of powder coatings is the use of UV-initiated radical curing for crosslinking. This provides an opportunity to combine low temperature curing and still look good in limited curing time windows; Still, this approach suffers from disadvantages such as the need for a radiation curing setup, inhomogeneous irradiation for substrates of complex shapes, potential problems with limited penetration depth in pigmented systems, and relatively high costs associated with binders and photoinitiators.

[007] A general problem with the prior art crosslinkable low temperature curable compositions described is that the cure rate is low or if the cure rate is higher, the appearance of the resulting coating is poor and may provide complications during the formulation of extrusion or that the components are expensive or less environmentally desirable. The combination of all demands requires a system that intrinsically has the appropriate level of reactivity required, and whose curing kinetics can be controlled with a high level of detail to enable good appearance in combination with the full build-up of chemical and mechanical resistance within challenging combinations of cure time, cure temperature and film thickness.

[008] Therefore, there remains a desire for a powder coating composition that can cure at low temperatures with a high cure rate to obtain acceptable curable times, but still with a sufficiently long open time to allow flow and coalescence and obtain good film formation with good coating appearance. “Open time” here refers to the time at the curing temperature before the progress of the reaction increases the viscosity to the point where further paint flow becomes negligible.

BRIEF SUMMARY OF THE INVENTION

[009] The present invention addresses one or more of these problems by providing a powder coating composition comprising one or more crosslinkable components and a catalyst distinguished by the fact that the one or more crosslinkable components are crosslinkable by the real Michael addition reaction (RMA ), the powder coating composition comprising a. a crosslinkable component A having at least 2 acidic C-H donor groups in activated methylene or methine, b. a crosslinkable component B having at least 2 activated unsaturated acceptor groups C=C, which react with component A by real Michael addition (RMA) to form a crosslinked network, c. a latent catalyst system C comprising a strong base or a strong base precursor for catalyzing the RMA cross-linking reaction with a delay at a curing temperature below 200°C, preferably below 175°C, more preferably below 150°C, 140, 130 or even 120°C and preferably at least 70°C, preferably at least 80, 90 or 100°C, wherein the catalyst system C is an LC latent catalyst system selected from the group from to. a latent LCC catalytic system with chemical latency comprising components that react at the curing temperature to initiate the reaction between the crosslinkable components A and B with a delay, said latent LCC catalytic system comprising In the LCC1 embodiment: a) a weak base C2, b ) a C1 activator reactive with C2 or a protonated C2 at the curing temperature, c) optionally additionally comprising a C3 acid, preferably a protonated C2 d) which in the case of the LCC2 modality: a) the weak base C2 is a Michael addition donor S2 and b) the activator C1 is a Michael acceptor S1 comprising an activated unsaturated group C=C reactive with S2 at the curing temperature, c) optionally further comprising an acid C3 being an acid S3, the corresponding base of which is also an addition donor. Michael, preferably a protonated S2, wherein if S1 is an acrylate, S2 has a pKa of the conjugate acid below 8, preferably below 7 and most preferably below 6, wherein pKa is defined as the value in an aqueous environment, and if S1 is a methacrylate, fumarate, itaconate or maleate, S2 has a pKa of the conjugate acid below 10.5, preferably below 9, more preferably below 8 or combinations of modalities LCC1 and LCC2, b. an LCE latent catalyst system with evaporative latency comprising a base blocked with a volatile acid or a weak base which on protonation forms a volatile acid and which volatile acid evaporates at the curing temperature and preferably additional free volatile acid. w. an LCP latent catalyst system with physical latency in which a catalytic system, preferably a strong base or a latent catalyst system, is present, which is physically separate and inaccessible for chemical reaction in the powder at or below a composition temperature and which is accessible for chemical reaction at the curing temperature, preferably chosen from a) an LCP1 latent catalyst system comprising a strong base catalyst having a melting temperature below the curing temperature and above the compounding temperature, preferably above 70, 80, 90 or 100°C or b) an LCP2 latent catalyst system comprising an active strong base catalyst species that is encapsulated or mixed with a material that releases the catalyst at a temperature below the curing temperature and above the compounding temperature at that preferably the material has a melting temperature or, in the case of an amorphous material, a glass transition temperature, below the curing temperature and above the compounding temperature, c) an LCP3 latent catalyst system comprising a generator component based on photo that releases a base upon irradiation with an appropriate wavelength, or combinations of LCC, LCE and LCP catalyst systems.

[0010] The inventors have found that the RMA powder coating composition is very suitable for powder coatings that can be cured at low temperatures with a relatively high cure speed, acceptable curable times, but still with a sufficiently long open time to allow film formation and obtain good crosslinking with good coating appearance using any of the latent base catalyst systems, as described in more detail below.

[0011] In another aspect, the invention relates to a process for preparing a powder coating composition according to the invention and to a method for powder coating a substrate. In the method, the curing temperature Tcur is chosen between 75 and 200°C, preferably between 80 and 180°C and more preferably between 80 and 160, 150, 140, 130 or even 120°C and preferably also uses infrared heating, Curing is preferably distinguished by a curing profile, determined by measuring the conversion of the unsaturated C=C bonds of component B as a function of time by FTIR, wherein the ratio of time to go from 20% to 60% C= conversion C for the time to reach 20% conversion is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably the time to reach 60% conversion less than 30, 20, 10 or 5 min and preferably with the time to reach 20% conversion of at least 1, preferably at least 2, 3, 5, 8 or 12 minutes when cured at 100°C. Preferably, the melt viscosity at the curing temperature is less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas. Melt viscosity can, for example, be measured with a Brookfield CAP 2000 cone and plate rheometer in accordance with ASTM D4287, using spindle #5 and should be measured at the start of the reaction or in the powder coating composition without catalyst activity.

[0012] The powder coating composition has the particular advantage that it can be used at low curing temperatures and therefore the method for powder coating a substrate, preferably a temperature sensitive substrate, preferably uses a curing temperature between 75 and 140°C, preferably between 80 and 130 or 120°C, more preferably between 100 and 120°C. This makes it possible to use the method for powder coating temperature-sensitive substrates, preferably substrates made of MDF, wood, plastic or temperature-sensitive metals such as alloys. The invention also relates in particular to articles coated with a powder coating composition according to the invention. It was found that good coating properties could be obtained with good XLD crosslinking density and resulting good coating properties.

[0013] In another aspect, the invention relates to the use of latent catalyst systems as described herein for the preparation of RMA crosslinkable powder coating compositions to catalyze the crosslinking reaction in RMA crosslinkable powder coating compositions. at curing temperatures below 200°C, preferably below 180°C, more preferably below 160, 140 or even 120°C and above 75, 80, 90 or 100°C.

[0014] In yet another aspect, the invention relates to an RMA-crosslinkable polymer and the use of said RMA-crosslinkable polymer in RMA-crosslinkable powder coatings. This RMA-crosslinkable polymer is an RMA-crosslinkable donor polymer. This RMA crosslinkable polymer is preferably chosen from the group of acrylic, polyester, polyester-amide and polyester-urethane polymers, comprising a. one or more components A comprising at least 2 acidic CH donor groups in activated methylene or methinO in a Z1(-C(-H)(-R)-)Z2 structure wherein R is hydrogen, a hydrocarbon, an oligomer or polymer, and wherein Z1 and Z2 are the same or different electron-withdrawing groups, preferably chosen from keto, ester or cyano or aryl groups, preferably an activated CH derivative with a structure according to formula 1: wherein R is hydrogen or an optionally substituted alkyl or aryl and Y and Y' are identical or different substituent groups, preferably alkyl, aralkyl or aryl or alkoxy or wherein in formula 1 the —C(=O)-Y and/or —C(=O)-Y' is substituted with CN or aryl, not more than one aryl or where Y or Y' can be NRR' (R and R' are H or optionally substituted alkyl), but preferably not both, said component A being preferably malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate groups, and more preferably malonate providing at least 50, preferably 60, 70 or even 80% of the total acidic CH groups in the crosslinkable component A, wherein R, Y or Y' provide connection to the polymer, b. optionally one or more components B comprising at least 2 activated unsaturated RMA acceptor groups, preferably acryloyl, methacryloyl, itaconate, citraconate, crotonate, cinnamate, maleate or fumarate functional groups, forming an A/B hybrid polymer, and c. optionally one or more components of the catalytic system C, wherein the polymer a. has a number average molecular weight Mn, as determined with GPC, of at least 450 g/mol, preferably at least 1000, more preferably at least 1500 and most preferably at least 2000 g/mol, b. has a weight average molecular weight Mw, as determined with GPC, of at most 20000 g/mol, preferably at least 15000, more preferably at most 10000 and most preferably at most 7500 g/mol, c. preferably has a Mw/Mn molecular weight distribution below 4, more preferably below 3, d. has an EQW equivalent weight in CH of at least 150, 250, 350, 450 or 550 g/mol and preferably at most 2500, 2000, 1500,1250 or 1000 g/mol and a numerical average functionality of CH reactive groups between 1 to 25, more preferably 1.5 to 15, even more preferably 2 to 15, more preferably 2.5 to 10 CH groups per molecule, e.g. preferably it has a melt viscosity at a temperature in the range between 100 and 140°C of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas f. preferably comprises amide, urea or urethane linkages and/or comprises high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers chosen from the group of 1,4-dimethylol cyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol, g. has a Tg above 25°C, preferably above 35°C, more preferably above 40, 50 or even 60°C, as determined by DSC at a heating rate of 10°C/min or is a crystalline polymer with a melting temperature between 40°C and 150, preferably 130°C, preferably at least 50 or even 70°C and preferably less than 150, 130 or even less than 120°C (as determined by DSC at a heating rate of 10°C/min).

Detailed description of the invention

[0015] The inventors have found that the RMA powder coating composition of the invention can, in comparison with conventional powder coating compositions, be cured at relatively low temperatures with a high curing speed. The latent base catalyst system provides open time and good leveling at low temperatures. A latent catalyst system is a catalyst system that provides a delay in the initial stages of curing at the curing temperature. The delay is controlled by the choice of components of the catalytic system and is chosen for a particular chosen combination of RMA crosslinkable components A and B, in order to provide a preferred curing profile, as described below. The RMA cross-linking reaction between components A and B requires the presence of a base, typically defined here as a “strong base”. This strong base is a base capable of catalyzing RMA in Tcur. In the present invention, as will be explained herein below in more detail, this strong base is generated through a latent catalyst system C. This latent catalyst system C may be a chemical latent system LCC (LCC1 and/or LCC2), a latent system evaporative LCE or a physical latent system LCP or a combination of at least 2 of the systems mentioned.

[0016] In a preferred embodiment, the powder coating composition has an LCC catalyst system with chemical latency. Suitable catalyst system LCC1 comprises In embodiment LCC1: a) a weak base C2, b) an activator C1 reactive with C2 or a protonated C2 at the curing temperature, c) optionally further comprising a C3 acid, preferably a protonated C2.

[0017] Chemical latency is obtained by the time required for the chemical reaction of the weak base C2 with the activator C1 or S1 and, preferably including an acid C3 to further increase the latency.

[0018] In a preferred embodiment, the powder coating composition comprises an embodiment of LCC1 chemical latent catalyst system, wherein — activator C1 is selected from the group of functional components epoxide, carbodiimide, oxetane, oxazoline or aziridine, preferably an epoxide or carbodiimide, and wherein — the weak base C2 preferably has a pKa of the conjugate acid greater than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic CH groups of the majority component A and wherein C2 is preferably a weak base nucleophile anion chosen from the anions of the carboxylate, phosphonate, sulfonate, halide or phenolate group or salts thereof or a nonionic nucleophile, preferably a tertiary amine, more preferably the weak base C2 is a weak base nucleophilic anion chosen from the salts of the carboxylate, halide or phenolate group or 1,4-diazabicyclo-[2.2.2]octane (DABCO) and - the latent catalyst system preferably also comprises C3 acid with a pKa of more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H groups of the majority component A, wherein the C3 acid is preferably a protonated C2.

[0019] In an alternative embodiment, the powder coating composition comprises an embodiment of LCC2 chemical latent catalyst system comprising: a) the weak base C2 is a Michael addition donor S2 and b) the activator C1 is a Michael acceptor S1 comprising an activated unsaturated C=C group reactive with S2 at the curing temperature, c) optionally further comprising a C3 acid being an S3 acid, the corresponding base of which is also a Michael addition donor, preferably a protonated S2, in which case S1 is an acrylate, S2 has a pKa of the conjugate acid below 8, preferably below 7 and more preferably below 6, where pKa is defined as the value in an aqueous environment, and if S1 is a methacrylate, fumarate, itaconate or maleate , S2 has a pKa of the conjugate acid below 10.5, preferably below 9, more preferably below 8

[0020] Combinations of LCC1 and LCC2 modalities are also possible. Preferably the powder coating composition comprises an LCC2 embodiment of the latent catalyst system, wherein -the weak base S2 is preferably selected from the group of phosphines, N-alkylimidazoles and fluorides or is a weak base nucleophilic anion an acidic X-H group containing compound in which X is N, P, O, S, or C, in which the anion conjugate acid also comprises acid S3 with a pKa of more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H groups of the majority component A, wherein the acid S3 is preferably an S2 protonated.

[0021] For components S3, or their deprotonated versions S2, in the LCC2 modality, in order to provide an adequate kinetic profile, it is important that the reaction of these components with Michael addition acceptor groups can occur at an appropriate rate, to avoid a reaction very fast and be able to provide a significant delay in curing under thermal conditions relevant to powder coatings. Finding a suitable reactivity window requires choosing a suitable combination of S3XH (or S2X-) components and acceptor functional groups for use in powder coating compositions.

[0022] W02014/16680 describes compositions that are crosslinkable by RMA using as catalyst C a combination of acid X-H and the anion X- of an acid in which the anion X- is also a Michael addition donor reactive to component B. use in powders is mentioned, however the document focuses on solvent-based compositions curable at room temperature (22°C according to the examples) and does not describe powder coating compositions curable at high temperature (i.e., the temperatures greater than ambient temperature). For these solvent-based, room temperature curable compositions, combinations of acrylate acceptor groups with X-H components have been reported using X-H/X- components such as succinimide, 1,2,4-triazole and benzotriazole as catalysts. However, it has been found that these combinations do not work for high temperature curable powder paint compositions because they do not provide the desired amount of delay, as the reactivity of the X- anions towards acrylates is too high.

[0023] It has been found that for powder paint compositions comprising the LCC2 acrylate acceptor group catalyst system, wherein the S1 components are acrylate acceptor groups and the S2 and S3 components are X-/X-H components with pKa acid below 8, more preferably below 7, 6 or even 5.5. Examples of useful X-H components for powder paint compositions containing acrylate acceptor include cyclic 1,3-diones such as 1,3-cyclohexanedione (pKa 5.26) and dimedone (5,5-dimethyl-1,3cyclohexanedione , pKa 5.15), ethyl trifluoroacetoacetate (7.6), Meldrum's acid (4.97). Preferably, components X-H are used which have a boiling point of at least 175°C, more preferably at least 200°C.

[0024] It has further been found that for powder paint compositions comprising methacrylate, fumarate, maleate or itaconate acceptor groups, an LCC2 catalyst system can be used, wherein the S1 components are acceptor groups as listed above, preferably groups methacrylate, itaconate or fumarate, and components S2 and S3 are X-/X-H components with acidic pKa below 10.5, more preferably below 9.5, 8 or even below 7.

[0025] The pKa values referred to are aqueous pKa values under ambient conditions (21°C). They can be easily found in the literature and, if necessary, determined in aqueous solution by procedures known to those skilled in the art. A list of the pKa values of the relevant components is given below.

[0026] A more preferred C1 activator in the LCC1 modality is an epoxy group. Suitable choices for epoxide as the preferred C1 activator are cycloaliphatic epoxides, epoxidized oils, and glycidyl-type epoxides. Suitable C1 components are described in US4749728 Col 3 of Line 21 to 56 and include C218 alkylene oxides and oligomers and/or polymers with epoxide functionality including multiple epoxy functionality. Particularly suitable alkylene oxides include 1,2-hexylene oxide, tert-butyl glycidyl ether, phenyl glycidyl ether, glycidyl acetate, glycidyl esters of versatile esters, glycidyl methacrylate and glycidyl benzoate. Useful multifunctional epoxides include bisphenol A diglycidyl ether, as well as larger homologues of these BPA epoxy resins, diglycidyl adipate, 1,4-diglycidyl butyl ether, glycidyl ether from Novolac resins, glycidyl esters of diacids such as Araldite PT910 and PT912 (Huntsman) , TGIC and other commercial epoxy resins. Bisphenol A diglycidyl ether, as well as its higher molecular weight solid counterparts, are preferred epoxides. Acrylic (co)polymers with epoxide functionality derived from glycidyl methacrylate are also useful. In a preferred embodiment, the epoxy components are oligomeric or polymeric components with an Mn of at least 400 (750, 1000, 1500). Other epoxide compounds include 2-methyl-1,2-hexene oxide, 2-phenyl-1,2-propene oxide (alpha-methyl-styrene oxide), 2-phenoxy-methyl-1,2-propene oxide, oils epoxidized unsaturated or fatty esters, and 1-phenylpropene oxide. Useful and preferred epoxides are glycidyl esters of a carboxylic acid, which may be in a carboxylic acid functional polymer or preferably in a highly branched hydrophobic carboxylic acid such as Cardura E10P (VersaticTM 10 acid glycidyl ester). Most preferred are the typical powdered crosslinking epoxy components: triglycidyl isocyanurate (TGIC), Araldite PT910 and PT912 and phenolic glycidyl ethers which are solid in nature at room temperature.

[0027] Suitable examples of weak base C2 in the LCC1 modality are weak base nucleophilic anions chosen from the group of carboxylate, phosphonate, sulfonate, halide or phenolate anions or salts thereof or a nonionic nucleophile, preferably a tertiary amine and for the LCC catalyst system according to embodiment 1, C2 is preferably a weak base nucleophilic anion chosen from salts of the carboxylate, halide or phenolate group, more preferably carboxylate salts, or is 1,4diazabicyclo[2.2.2]octane (DABCO). The C2 component is capable of reacting with the C1 group, preferably epoxy, to yield a strongly basic anionic adduct that can, in principle, initiate the reaction of the crosslinkable components. Alternatively, it may react via its conjugated acid form to produce a non-acidic adduct. Preferably, the weak base group C2 does not have substantial basicity relative to the acidic C-H groups of the crosslinkable component A, but is reactive to the epoxide under low temperature crosslinking conditions (e.g., typically with an average value of less than 30, preferably 15 minutes at desired curing temperature).

[0028] Another suitable example of a weak base C2 is a weak base nucleophile anion selected from the weak base anion group or C, wherein the anion X- is a Michael addition donor that can react with the activator C1 and the anion X- is distinguished by a pKa of the corresponding conjugate acid 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H groups of the majority component A. These C2 components are specified as S2 for reaction with C=C S1 acceptor groups in the LCC2 modality, but can also act as C2 nucleophiles in reaction with C1 activating components in the LCC1 modality, for example with epoxy, which can provide 2 pathways to react according to the LCC1 and LCC2 modality.

[0029] The C2 group preferably reacts with the C1 groups at temperatures below 150°C, preferably 140, 130, 120 and preferably at least 70, preferably at least 80 or 90°C on the time scale of the curing window. The reaction rate of the C2 group with the C1 group at the curing temperature is low enough to provide a useful open time and high enough to allow sufficient curing in the intended time window.

[0030] The weak base C2, if an anion, is preferably added as a salt comprising a cation that is not acidic. Non-acidic means not having a hydrogen that competes for the base with component A and therefore does not inhibit the cross-linking reaction at the intended curing temperature. The cation is preferably substantially unreactive towards any components in the crosslinkable composition. The cations can, for example, be alkali metals, ammonium or quaternary phosphonium, but also protonated 'superbases' that are not reactive towards any of the components A, B or C in the crosslinkable composition. Suitable superbases are known in the art.

[0031] Preferably the salt comprises alkali or alkaline earth metal, in particular lithium, sodium, or potassium cation or, preferably, a quaternary ammonium or phosphonium cation according to the formula Y(R')4, where Y represents N or P, and wherein each R' may be the same or different alkyl, aryl or aralkyl group possibly attached to a polymer or wherein the cation is a protonated very strong basic amine, which very strong basic amine is preferably selected from the amidine group; preferably 1,8-diazabicyclo (5.4.0)undec-7-ene (DBU), or guanidines; preferably 1,1,3,3-tetramethylguanidine (TMG). R' can be replaced with substituents that do not interfere substantially or not with RMA crosslinking chemistry, as is known to the skilled artisan. More preferably, R' is an alkyl of 1 to 12, more preferably 1 to 4 carbon atoms.

[0032] Document EP0651023 describes a catalyst system for RMA crosslinkable solvent-based compositions comprising a catalyst C comprising quaternary ammonium or phosphonium salt of Cl, Br, I, salicylate, a polybasic carboxylate, nitrate, sulfonate, sulfate, sulfite, phosphate, or an acidic phosphate ester anion in combination with an epoxy compound.

[0033] More preferably the powder coating composition comprises an LCC latent catalyst system further comprising C3 acid with a pKa of more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units less than the pKa of the acidic C-H groups of the majority component A and wherein the C3 acid is preferably a protonated C2. Preferably, the C3 acid and the C2 conjugate acid have a boiling point of at least 120°C, preferably 130°C, 150, 175, 200 or even 250°C. Preferably, C3 is a carboxylic acid.

[0034] A preferred catalyst system is the LCC1 catalyst system, which comprises C1 epoxide groups, C2 weak base nucleophilic anion groups that react with the C1 epoxide group to form a strongly basic C1/2 anionic adduct and more preferably also groups C3 acids. In a suitable LCC1 catalyst system, C2 is a carboxylate salt and C1 is epoxide, carbodiimide, oxetane or oxazoline, plus epoxide or carbodiimide, or alternatively, C2 is DABCO and C1 is epoxy.

[0035] Without wishing to be bound by theory, it is believed that the nucleophilic anion C2 reacts with the activating epoxide C1 to provide a strong base, but that this strong base is protonated by the acid C3 to create a salt (similar in function to C2 ) which will not directly strongly catalyze the cross-linking reaction. The reaction scheme proceeds until substantially complete depletion of the C3 acid, which provides the open time because no significant amount of strong base is present during this time to significantly catalyze the reaction of the crosslinkable components. When the C3 acid is depleted, a strong base will be formed and survive to effectively catalyze the rapid RMA cross-linking reaction. Alternatively, the cycle can also function in a similar way when the activation reaction with C1 occurs with the protonated C2 species (C2 protonated as a result of the equilibrium of the acid base with the A component); Furthermore, this scheme will lead to the consumption of excess C3 acid and the availability of deprotonated species A when the cycle progresses.

[0036] The characteristics and advantages of the invention will be recognized by reference to the following exemplary reaction scheme.

[0037] Specifically for the case of carboxylates, epoxides and carboxylic acids such as C2, C1 and C3 species, this can be established as:

[0038] The reaction scheme, if the activator reacts through the protonated form of C2, would be illustrated by the next scheme:

[0039] The open time can be adjusted by the amount of acid (C3) and also by choosing the quantities and reactivity of the reagents C1 and C2. C1 epoxide must be available to initiate the reaction and it is preferable that the molar amount of epoxide is greater than the molar amount of C3 acid.

[0040] In one embodiment, the C3 acid group is a C2 protonated anion group, preferably C3 carboxylic acid and C2 carboxylate, which for example can be formed by partially neutralizing an acid functional component, preferably a polymer comprising C3 acid groups to partially convert into C2 anionic groups, in which partial neutralization is preferably carried out by a cation hydroxide, preferably tetraalkylammonium or tetraalkylphosphonium hydroxide. In another embodiment, a polymer-bound C2 component can be produced by hydrolysis of an ester group in a polyester with hydroxides mentioned above.

[0041] Ethyl triphenyl-phosphonium acid acetate is known as a catalyst for cross-linking functional epoxy polymers, as described in “ETPPAAc Solutions Ethyl triphenyl-phosphonium Acid Acetate”, April 20, 2007 (2007-04-20), pages 1-2, XP055319211. The use of this compound is not known as component C2 and C3 in RMA crosslinkable powder coating compositions. Furthermore, it is preferred that the boiling point of the C3 component and the C2 conjugate acid be above the anticipated curing temperature of the powder coating composition to avoid less well-controlled evaporation of these components from the catalyst system during the curing conditions. . Formic acid and acetic acid are less preferred C3 acids as they can evaporate during curing. Preferably, for an LCC-type system, the C3 component and the conjugate acid of C2 have a boiling point greater than 120°C.

[0042] The LCC1 catalyst system is preferably a catalyst composition comprising individual components C1, C2 and optionally C3. This is most convenient to mix with a specific combination of donor and acceptor polymers of your choice. Alternatively, at least one of C1, C2 or C3 of the LCC1 catalyst system is a group in crosslinkable components A or B or both. In this case, if one or more but not all of the groups C1, C2 and C3 are in the crosslinkable components A or B or both, the remaining component will be added separately. In this case, typically and preferably C2 and C3 are in a polymer and C1 is added separately or C1 and C3 are in a polymer and C2 is added separately. The advantage is flexibility in optimizing reactivity parameters by simply adjusting the catalyst composition. In a convenient embodiment, C2 and C3 are in the crosslinkable polymeric component A and/or B and C2 is preferably formed by partially neutralizing an acid functional polymer comprising C3 acid groups with a base comprising a cation as described above to partially convert the C3 acid groups into C2 anionic groups. Another embodiment would have component C2 formed by hydrolysis of a polyester, for example, a polyester of component A, and be present as a polymeric species.

[0043] In an alternative embodiment, the powder coating composition comprises a latent catalytic system LCC2, in which the weak base C2 is selected from the group of phosphines, N-alkylimidazoles, fluorides and a weak base anion from an acidic X-H group containing the compound in which X is N, P, O, S or C, in which the anion by a pKa of the corresponding conjugate acid C2 with an unsaturated group with Michael acceptor characteristics (51, which may be the same as B, but may be another species of Michael addition acceptor) triggers the generation of more catalytically active strong basic species to accelerate the reaction between the components A and B.

[0044] In yet another embodiment, the powder coating comprises the latent catalyst system is an LCE latent catalyst system with evaporative latency, in which the reaction is delayed by a step of slow evaporation of an acidic species. In this embodiment, comprising 1) a base, preferably a strong base, blocked with a volatile acid or alternatively 2) comprising a weak base C2 which, upon protonation by excess weakly acidic species A, forms a volatile acid and in which the latent catalyst optionally further comprises additional volatile acid C3, which volatile acids evaporate at the curing temperature Tcur, wherein the boiling point of the acid is less than 300°C, preferably below 250°C, 225, 200 or 150°C and preferably above 100°C or 120°C. Quaternary ammonium or phosphonium salts of carboxylic acids with a boiling point as specified above are preferred.

[0045] The powder coating composition preferably comprises a. In the case of the LCC1 catalyst system, an activator C1 in an amount of between and 600 μeq/g, preferably between 10 and 400, more preferably between 20 and 200 μeq/g, wherein μeq/g is μeq relative to the total weight of the binder components A and B and LCC catalyst system or, in the case of the LCC2 catalyst system, an activator S1 in an amount of at least 1 μeq/g, preferably at least 10, more preferably at least 20, even more preferably at least 40 μeq/g, b. the weak base C2 in an amount between 1 and 300 μeq/g, preferably between 10 and 200, more preferably between 20 and 100 μeq/g relative to the total weight of the binder components A and B and LC catalyst system, c. optionally, a C3 acid in an amount between 1 and 500, preferably between 10 and 400, more preferably between 20 and 300 μeq/g and most preferably between 30 and 200 μeq/g, d. wherein preferably the amount of C1 or, respectively, S1 i. is greater than the amount of C3, preferably in an amount between 1 and 300 μeq/g, preferably between 10 and 200, more preferably between 20 and 100 μeq/g and ii. is preferably greater than the amount of C2 and iii. is preferably greater than the sum of the amount of C2 and C3.

[0046] In the case of the LCC2 catalyst system for S1, there is no relevant upper concentration limit, as S1 can also be component B. The catalyst also works with the amount of C1 lower than that of C2. However, this is less preferred as it can be a waste of C2. In case the amount of C1, in particular epoxide, is greater than the amount of C2, the disadvantages are limited, as they can react with C2 and C3 or other nucleophilic residues, but still maintain basicity after the reaction or can be left in the network, without many problems. However, excess C1 may be disadvantageous in view of the cost for non-epoxy C1. It should be noted that a combination of LCC1 and LCE modalities is possible, in which case C2 may be greater than C1 if C2 is also forming an evaporative acid and therefore is also conducting catalysis as an LCE-type catalyst. Furthermore, in case the C3 acid is a volatile acid, it provides additional initial latency by evaporation of the C3 retardant acid. This is a combination of the LCC and LCE latent catalyst system. In this case, above requirement d.i does not apply.

[0047] Additionally, it is preferred that in the powder coating composition a. the weak base C2 represents between 10 and 100 mol% of the sum of C2 and C3, b. preferably the amount of C3 acid is 20 to 400 mol%, preferably 30 to 300 mol% of the amount of C2, c. wherein preferably the ratio of the molar amount of C1 to the sum of the amount of C2 and C3 is at least 0.5, preferably at least 0.8, more preferably at least 1 and preferably at most 3, more preferably at most 2, d. the ratio of C1 to C3 is preferably at least 1, preferably at least 1.5, more preferably at least 2.

[0048] In an alternative embodiment, the powder coating composition comprises an LCP latent catalyst system with physical latency in which a catalytic system, preferably a strong base or a latent catalyst system, is present, which is physically separate and inaccessible to chemical reaction in the powder at or below a composition temperature Tcomp and which is accessible for chemical reaction at the curing temperature, preferably chosen from a) an LCP1 latent catalyst system comprising a catalyst with a melting temperature below the curing temperature and above the composition temperature, preferably above 70, 80, 90 or 100°C or b) an LCP2 latent catalyst system comprising an active catalyst species that is encapsulated or mixed with a material that releases the catalyst at a temperature below the curing temperature and above the compounding temperature wherein preferably the material has a melting temperature or, in the case of an amorphous material, a glass transition temperature, below the curing temperature and above the compounding temperature, or c) a LCP3 latent catalyst system comprising a photo-based generator component that releases a base upon irradiation with an appropriate wavelength,

[0049] It should be noted that combinations of LCC, LCE and LCP catalyst systems are possible.

[0050] Document EP1813630 describes encapsulated base catalysts and processes for preparing them for RMA-crosslinkable adhesives which are included here by reference. Capsules can be made from base catalysts using paraffin and microcrystalline waxes to provide a shell or matrix. Document EP6224793 describes an encapsulated active agent comprising an active agent encapsulated in a crystallizable or thermoplastic polymer. The melting or glass temperature of the encapsulation is chosen here between Tcomp and Tcur.

[0051] In the alternative LCP3 embodiment, the latency of the catalyst system for RMA curing powder coatings due to the high curing temperature can be provided by photobased generator components (PBGs) that release a base upon irradiation with a wavelength appropriate. The generated base is preferably a strong base, that is, strong enough to catalyze the RMA reaction between A and B or it may be a weak base that is used as a C2 component in combination with a chemically latent LCC catalytic system.

[0052] PBGs for Michael addition reaction systems are described, for example, in EP3395800, in Progr. Coat Org. (2019) 127, 222-230, in Polymer (2017) 113 193-199, in React. Funct. Polym. (2018) 122 60-67. Photobase generators offer high levels of reactivity control similar to radical photoinitiators; they also face similar complications such as potential problems with uniform irradiation of substrates with complex shapes, radiation penetration issues with pigmented coatings, and expensive dedicated setup requirements. The PBGs described herein can be used if the base generated has the pKa and nucleophilicity values required for the envisioned latent catalyst system. Preferably, high basicity species such as amidine, guanidine or carbanion are generated.

[0053] The powder coating composition with RMA-crosslinkable components A and B and LC latent catalyst system, preferably LCC catalyst system and more preferably LCC1 catalyst system, as described above, allows curing temperatures as targeted are low curing temperatures compared to competitive powder systems. Low curing temperatures generally range between 75 and 150°C, preferably 80 to 130°C, more preferably 80 to 120°C or 80 to 110°C, the curing temperature is chosen within this range, for example, taking into account takes into account the temperature sensitivity of the substrates. Curing time depends on the chosen curing temperature. Curing time is the time during which heat is applied to the curing temperature, for example in an oven, to obtain sufficient cure before being cooled to room temperature. Within the indicated curing temperature ranges, this curing time typically varies between 1 or 2 and 50, preferably between 2 or 5 and 40 and generally and most preferably between 5 or 10 and 30 minutes. Curing may occur in an oven and may also preferably be assisted by infrared radiative heating.

[0054] The powder coating composition according to the invention preferably has a kinetic curing profile, as can be determined by measuring the conversion of the unsaturated C=C bonds of component B as a function of time by FTIR, at a temperature of cure chosen between 80, 90, 100 and 200, 150, 135 or 120°C, where the ratio of the time to go from 20% to 60% C=C conversion and the time to reach 20% conversion (as determined by FTIR) is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably with the time to reach 60% conversion being less than 30 or 20 or 10 min. Preferably, the powder paint has a kinetic curing profile such that the time to reach 20% conversion at 100°C is at least 1 minute, preferably at least 2, 3, 5, 8 or 12 minutes. The curing profile is defined by the choice of catalytic system components for the chosen combination of reagents A and B and the curing temperature.

[0055] The powder coating process involves heating substrates to curing temperature, which involves a significant energy cost. The coating process using the powder coating composition of the invention is more energy efficient as it operates at low temperatures, allowing sufficient curing preferably within 50, 30, 20 or even 15 minutes of curing time and with the longest possible open time of the applied coating film (pre-gelation). The composition is preferably distinguished by a sigmoidal cure profile with an onset that provides an initial period of maximum fluidity and low reaction conversion (open time), followed by a sharp increase to ensure sufficient final conversion within limited cure times. The long period of open time maximizes flow before gelling, which benefits the development of a good appearance of the coating. In addition to coating properties, the powder coating composition may be especially advantageous for use in low temperature curing powders, where due to the kinetic profile of the catalyst system, a premature cross-linking reaction and premature molecular weight or viscosity, during composition and mixing of components in the extruder is limited.

[0056] The powder coating composition according to the invention is further preferably distinguished by the fact that a. the crosslinkable component A comprises at least 2 acidic CH donor groups in activated methylene or methinO in a Z1(-C(-H)(-R)-)Z2 structure wherein R is hydrogen, a hydrocarbon, an oligomer or polymer, and wherein Z1 and Z2 are the same or different electron-withdrawing groups, preferably chosen from keto, ester or cyano or aryl groups, and preferably comprises an activated CH derivative with a structure according to formula 1: wherein R is hydrogen or an optionally substituted alkyl or aryl and Y and Y' are identical or different substituent groups, preferably alkyl, aralkyl or aryl or alkoxy or wherein in formula 1 the —C(=O)-Y and/or —C(=O)-Y' is substituted with CN or aryl, not more than one aryl or where Y or Y' can be NRR' (R and R' are H or optionally substituted alkyl), but preferably not both, wherein R, Y or Y' optionally provides connection to an oligomer or polymer, said component A being preferably malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, preferably providing at least 50, preferably 60, 70 or even 80% of the total of acidic CH groups in the crosslinkable component A, b. component B comprising at least 2 activated unsaturated RMA acceptor groups preferably comes from acryloyl, methacryloyl, itaconates, maleate or fumarate functional groups, wherein preferably at least one, more preferably both, of components A or B is a polymer and wherein preferably the composition comprises a total amount of CH donor groups and C=C acceptor groups per gram of binder solids of 0.05 to 6 meq/g of binder solids and preferably the ratio of C=C acceptor groups and CH donor groups is greater than 0.1 or less than 10.

[0057] Real Michael addition (RMA) crosslinkable coating compositions comprising crosslinkable components A and B are generally described for use in solvent-based systems in EP2556108, EP0808860 or EP1593727 whose specific description for crosslinkable components A and B are considered here in annex.

[0058] Components A and B, respectively, comprise the RMA-reactive donor and acceptor portions that upon curing react to form the cross-linked network in the coating. Components A and B can be present in separate molecules, but they can also be present in a molecule, called a hybrid component A/B, or combinations thereof. Preferably, components A and B are separate molecules and each independently in the form of polymers, oligomers, dimers or monomers. For coating applications, it is preferred that at least one of components A or B is preferably oligomers or polymers. It should be noted that an activated methylene group CH2 comprises 2 acidic C-H groups. Even after the reaction of the first acidic C-H group, the reaction of the second acidic C-H group is more difficult, for example, for the reaction with methacrylates, compared with acrylates, the functionality of this activated methylene group is counted as 2. The reactive components A and B can also be combined into an A/B hybrid molecule. In this embodiment of the powder coating composition, both C-H and C=C reactive groups are present in an A-B molecule.

[0059] It is envisaged that one or more components of the catalyst system C may also be combined into a molecule optionally in combination with component A and/or B, although this component should not be an active catalyst component or a combination of two components that can form the catalytic active component to avoid premature reaction in the synthesis, formulation and powder formation stage. For example, the polymer may comprise groups C1, C2 and/or C3, but not the combination C1 and C2. From the standpoint of flexibility in formulating the composition, the components of the catalyst system C are most preferably added as separate components.

[0060] Preferably, component A is a polymer, preferably a polyester, polyurethane, acrylic, epoxy or polycarbonate, having as a functional group a component A and, optionally, one or more components B or components of the catalytic system C. Furthermore, Mixtures or hybrids of these types of polymers are possible. Suitably, component A is a polymer chosen from the group of acrylic, polyester, polyester amide, polyester-urethane polymers.

[0061] Malonates or acetoacetates are preferred types of donors in component A. In view of the high reactivity and durability in a more preferred embodiment of the crosslinkable composition, component A is a C-H malonate-containing compound. It is preferred that in the powder coating composition the majority of activated C-H groups are malonate, i.e. more than 50%, preferably more than 60%, preferably more than 70%, more preferably more than 80% of all C-H groups. activated in the powder coating composition is malonate.

[0062] The advantages of the invention are particularly manifest in critically difficult compositions, with relatively high concentrations and functionalities of functional groups, for example, in the case where component A is a compound, in particular an oligomer or polymer, comprising an average of 2 to 30, preferably 3 to 20 and more preferably 4 to 10 C-H activated per polymer chain. Components containing oligomeric and/or polymeric malonate groups are preferred, such as, for example, polyesters, polyurethanes, polyacrylates, epoxy resins, polyamides and polyvinyl resins or hybrids thereof, containing malonate-type groups in the main chain, pendant or both.

[0063] The total amount of C-H donor groups and C=C acceptor groups per gram of binder solids, regardless of how they are distributed among the various crosslinkable components, is preferably between 0.05 to 6 meq/g, more typically 0.10 to 4 meq/g, even more preferably 0.25 to 3 meq/g of binder solids, more preferably between 0.5 to 2 meq/g. Preferably, the stoichiometry between components A and B is chosen such that the ratio of reactive C=C groups to reactive C-H groups is greater than 0.1, preferably greater than 0.2, more preferably greater than 0.3, more preferably greater than 0.4 and, in the case of acrylate B functional groups, preferably greater than 0.5 and more preferably greater than 0.75, and the ratio is preferably less than 10, preferably 5, more preferably less than 3, 2 or 1.5.

[0064] Polyesters containing malonate group can be obtained preferably by transesterification of a methyl or ethyl diester of malonic acid, with multifunctional alcohols that can be of polymeric or oligomeric nature, but can also be incorporated through a Michael addition reaction with other components. Especially preferred malonate group-containing components for use with the present invention are oligomeric or polymeric malonate group-containing esters, ethers, urethanes and epoxy esters and hybrids thereof, for example polyester-urethanes, containing 1 to 50, more preferably 2 to 10, malonate groups per molecule. The polymeric components A can also be made in a known manner, for example, by radical polymerization of ethylenically unsaturated monomers comprising monomers, for example (meth)acrylate, functionalized with a moiety comprising activated acidic (donor) C-H groups, preferably an acetoacetate group. or malonate, in particular 2(methacryloyloxy)ethylacetoacetate or - malonate. In practice, polyesters, polyamides and polyurethanes (and hybrids thereof) are preferred. It is also preferred that such malonate group-containing components have a number average molecular weight (Mn) in the range of about 100 to about 10,000, preferably 500 to 5,000, more preferably 1,000 to 4,000; and a Mw less than 20000, preferably less than 10000, more preferably less than 6000 (expressed in GPC polystyrene equivalents).

[0065] Suitable crosslinkable components B can generally be ethylenically unsaturated components in which the carbon-carbon double bond is activated by an electron-withdrawing group, for example, a carbonyl group in the alpha position. Representative examples of such components are described in US2759913 (column 6, line 35 to column 7, line 45), DE-PS-835809 (column 3, lines 16 to 41), US4871822 (column 2, line 14 to column 4, line 14), US4602061 (column 3, line 14 20 to column 4, line 14), US4408018 (column 2, lines 19 to 68) and US4217396 (column 1, line 60 to column 2, line 64).

[0066] Acrylates, methacrylates, itaconates, fumarates and maleates are preferred. Itaconates, fumarates and maleates can be incorporated into the main chain of a polyester or polyester-urethane. Examples of preferred resins may be mentioned, such as polyesters, polycarbonates, polyurethanes, polyamides, acrylic and epoxy resins (or their hybrids), polyethers and/or alkyd resins containing activated unsaturated groups. These include, for example, urethane (meth)acrylates obtained by reacting a polyisocyanate with a hydroxyl group containing (meth)acrylic ester, for example, a hydroxyalkyl ester of (meth)acrylic acid or a component prepared by the esterification of a polyhydroxyl component with less than a stoichiometric amount of (meth)acrylic acid; polyether (meth)acrylates obtained by esterification of a polyether containing a hydroxyl group with (meth)acrylic acid; Polyfunctional (meth)acrylates obtained by reacting a hydroxyalkyl (meth)acrylate with a polycarboxylic acid and/or a polyamino resin; poly(meth)acrylates obtained by reacting (meth)acrylic acid with an epoxy resin and polyalkyl maleates obtained by reacting a monoalkyl maleate ester with an epoxy resin and/or a hydroxy functional oligomer or polymer. Furthermore, polyesters end-coated with glycidyl methacrylate are a preferred example. It is possible for the acceptor component to contain several types of acceptor functional groups.

[0067] The most preferred activated unsaturated B components containing group B are the unsaturated functional components acryloyl, methacryloyl and fumarate. Preferably, the number average functionality of the activated C=C groups per molecule is 2 to 20, more preferably 2 to 10, more preferably 36. The equivalent weight (EQW: average molecular weight per reactive functional group) is 100 to 5000, more preferable 200 to 2000, and the number average molecular weight is preferably Mn 200 to 10000, more preferably 300 to 5000, more preferably 400 to 3500 g/mol, even more preferably 1000 to 3000 g/mol.

[0068] In view of use in powder systems, the Tg of component B is preferably above 25, 30, 35, more preferably at least 40, 45, most preferably at least 50°C or even at least 60°C, due to the need for powder stability. Tg is defined as measured with DSC, midpoint, heating rate 10°C/min. If one of the components has a Tg substantially greater than 50°C, the Tg of the other components may be lower, as will be understood by those skilled in the art.

[0069] A suitable component B is a urethane (meth)acrylate that has been prepared by reacting a hydroxy functional compound and (meth)acrylate with isocyanate to form urethane bonds, wherein the isocyanates are preferably at least in part di or triisocyanates, preferably isophorone diisocyanate (IPDI). The urethane linkages introduce rigidity by themselves, but preferably high Tg isocyanates are used as cyclo-aliphatic or aromatic isocyanates, preferably cyclo-aliphatic. The amount of isocyanates used is preferably chosen so that said Tg of the (meth)acrylate functional polymer is increased above 40, preferably above 45 or 50°C.

[0070] The powder coating composition is preferably designed in such a way that, after curing, a crosslink density (using DMTA, as described below) of at least 0.025 mmol/cc, more preferably at least 0, can be determined. 05 mmol/cc, more preferably at least 0.08 mmol/cc and typically less than 3, 2, 1 or 0.7 mmol/cc.

[0071] The powder coating composition must retain free-flowing powder under ambient conditions and therefore preferably has a Tg above 25°C, preferably above 30°C, more preferably above 35, 40, 50° C as the midpoint value determined by DSC at a heating rate of 10°C/min.

[0072] As described above, the preferred component A is a malonate functional component. However, the incorporation of malonate moieties tends to reduce Tg and it has been a challenge to provide powder coating compositions based on malonate as the dominant component A with sufficiently high Tg.

[0073] In order to achieve high Tg, the powder coating composition preferably comprises a crosslinkable component A, a component B or a hybrid component A/B comprising amide, urea or urethane bonds and/or comprises high Tg monomers, preferably cycloaliphatic or aromatic monomers or in the case of polyesters, one or more monomers chosen from the group 1,4-dimethylol cyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetra-methyl- cyclobutanediol.

[0074] Furthermore, in order to achieve high Tg, the powder coating composition comprises component B or the hybrid component A/B, being a polyester (meth-)acrylate, a polyester urethane (meth-)acrylate , an epoxy (meth-)acrylate or a urethane (meth-)acrylate, or is a polyester comprising fumarate, maleate or itaconate units, preferably fumarate or is a polyester with an end coated with an activated unsaturated isocyanate or epoxy functional group.

[0075] The measures mentioned above to achieve high Tg in crosslinkable components A or B or hybrid A/B can be advantageously combined with the presence of crystalline components. The components in the powder coating composition may be amorphous or crystalline. In case the components in the composition are completely amorphous, the Tg of these components must be sufficiently high, but this may be difficult to obtain in combination with a low melt viscosity at low temperatures. Therefore, it may be preferred that the powder coating composition comprises one or more components, preferably crosslinkable components A or B or hybrid A/B or catalyst system components C or different separate plasticizers that are in a (semi)crystalline state in the powder coating composition and have a melting temperature between 40 and 150°C, preferably 50 to 130°C, more preferably 60 or 70 to 120°C, most preferably 60 to 110°C. Preferably, one or more components A or B or components of the catalyst system C are (semi)crystalline or a mixture of amorphous and (semi)crystalline components, but the crystalline components may also be additives without additional role in the crosslinking reaction. The crystalline components preferably have a Tg when melted below 50°C or more preferably below 30, 20 or even 10°C and a Tm, when crystallized in the paint composition, in the indicated range. Crystalline components have a lower melt viscosity when melted, but do not decrease Tg when in the crystalline state. An advantage of the (semi)crystalline polymer is that a higher Tg of the composition can be achieved, in combination with a lower melt viscosity at the curing temperature due to the melt plasticization effect. The amount of crystalline components is chosen together with other Tg influencing parameters to obtain a correct balance of melt viscosity at the expected curing temperature of less than 60 Pas, more preferably less than 50, 40, 30, 20, 10 or even 5 Pas and a Tg powder paint, preferably above 35°C. Care must be taken in the preparation process that the crystallizable components are in the crystalline state of the powder paint as used.

[0076] More preferably, the powder coating composition comprises an RMA crosslinkable polymer according to another aspect of the invention, which has characteristics adapted for use in an RMA crosslinkable powder coating composition. In particular, with a view to obtaining good flow and leveling properties, and good chemical and mechanical resistance, it has been found that, preferably in the powder coating composition, at least one of the crosslinkable components A or B or hybrid A/B is a polymer, preferably chosen from the group of polymers of acrylic, polyester, polyester amide, polyester-urethane, which polymer a) has a number average molecular weight Mn, as determined with GPC, of at least 450 g/mol, preferably at least 1000, more preferably at least 1500 and most preferably at least 2000 g/mol, b) has a weight average molecular weight Mw, as determined with GPC, of at most 20000 g/mol, preferably at least 15000, more preferably at most 10000 and more preferably at most 7500 g/mol, c) preferably has a molecular weight distribution Mw/Mn below 4, more preferably below 3, and of course above 1, d) has an equivalent weight EQW in C-H or C= C of at least 150, 250, 350, 450 or 550 g/mol and preferably at most 2500, 2000, 1500,1250 or 1000 g/mol and a numerical average functionality of C-H or C=C reactive groups between 1 to 25, more preferably 1.5 to 15, even more preferably 2 to 15, more preferably 2.5 to 10 C-H groups per molecule, e) preferably has a melt viscosity at a temperature in the range between 100 and 140°C less than 60 Pas , more preferably less than 40, 30, 20, 10 or even 5 Pas f) preferably comprises amide, urea or urethane linkages and/or comprises high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers chosen from the group of 1,4-dimethylol cyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol, g) has a Tg above 25°C, preferably above 35°C, more preferably above 40, 50 or even 60°C, such as the midpoint value determined by DSC at a heating rate of 10°C/min or is a crystalline polymer with a melting temperature between 40°C and 150, preferably 130°C, preferably at least 50 or even 70°C and preferably less than 150, 130 or even 120°C (as determined by DSC at a heating rate of 10°C/min).

[0077] It may be noted that RMA is also used to prepare the coating from liquid (powder-free) compositions. For example, W02016166371 describes RMA-crosslinkable coating compositions using a catalyst system based on a strong base catalyst blocked by carbon dioxide, a reactive component A, for example, a malonated polyester, and a reactive component B.

[0078] The polymer characteristics Mn, Mw and Mw/Mn are chosen taking into account, on the one hand, the desired powder stability and, on the other hand, the desired low melt viscosity, but also the anticipated coating properties. A high Mn is preferred to minimize the Tg lowering effects of the end groups, on the other hand, low Mw are preferred because the melt viscosity is closely related to the Mw and a low viscosity is desired; therefore low Mw/Mn is preferred.

[0079] In order to achieve a high Tg, the RMA crosslinkable polymer preferably comprises amide, urea or urethane bonds and/or comprises high Tg monomers, preferably cycloaliphatic or aromatic monomers, or in the case of polyester comprises monomers chosen from the group of 1,4-dimethylol cyclohexane (CHDM), TCD diol, isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol.

[0080] In case the RMA crosslinkable polymer is an A/B hybrid polymer, it is further preferred that the polymer also comprises one or more B component groups chosen from the group of acrylate or methacrylate, fumarate, maleate and itaconate, preferably (meth) acrylate or fumarate. Furthermore, if used as a crystalline material, it is preferred that the RMA crosslinkable polymer has crystallinity with a melting temperature between 40°C and 130°C, preferably at least 50 or even 70°C and preferably less than 150, 130 or even 120°C (as determined by DSC at a heating rate of 10°C/min). It should be noted that this is the melting temperature of the polymer itself (pure) and not the polymer in a blend.

[0081] In a preferred embodiment, the RMA crosslinkable polymer comprising polyester, polyester amide, polyester-urethane or a urethane acrylate comprising urea, urethane or amide linkages derived from cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic isocyanates, said polymer with a Tg of at least 40°C, preferably at least 45 or 50°C and at most 120°C and a number average molecular weight Mn of 450 to 10000, preferably 1000 to 3500 g/mol and preferably a maximum Mw of 20000, 10000 or 6000 g/mol and whose polymer is provided with components crosslinkable by RMA A or B or both. The polymer is obtained, for example, by reacting a precursor polymer comprising said RMA-crosslinkable groups with an amount of cycloaliphatic or aromatic isocyanates to increase the Tg. The amount of these added isocyanates, or urea/urethane bonds formed, is chosen so that the Tg is increased to at least 40°C, preferably at least 45 or 50°C.

[0082] Preferably, the RMA crosslinkable polymer is a polyester or polyester-urethane comprising a malonate as the dominant component A and comprising a number average malonate functionality between 1 and 25, more preferably 1.5 to 15, even more preferably 2 to 15, more preferably 2.5 to 10 malonate groups per molecule, with a weight average molecular weight GPC between 500 and 20000, preferably 1000 to 10000, more preferably 2000 to 6000 g/mol, which was prepared by reacting a functional polymer of hydroxy and malonate with isocyanate to form urethane bonds.

[0083] Furthermore, the polymer can be an amorphous or (semi)crystalline polymer or a mixture thereof. Semicrystalline means being partially crystalline and partially amorphous. (Semi)crystallinity should be defined by DSC melting endotherms, target crystallinity defined as having a DSC peak melting temperature Tm of at least 40°C, preferably at least 50°C, preferably at least 60°C and more preferably at least 60°C and preferably at least 130, 120, 110 or 100°C. The DSC Tg of that component in a fully amorphous state is preferably below 40°C, more preferably below 30, 20 or even 10°C.

[0084] In order to improve the shelf life of the powder coating composition, it has been found to be advantageous to use C2 and C3 functionalities linked to polymers, in particular a polymer comprising carboxylate and optionally also C2 and C3 carboxylic acid components. Lifespan is believed to be improved by reduced mobility and the impact of Tg. An additional advantage is that polymer components with high EQWs compared to low EQW components are more easily mixed into the powder coating composition, for example when formulations are prepared in an extruder, and the risk of inhomogeneities is reduced.

[0085] The invention therefore also relates to a polymer (C3/2 polymer) and its use as a latent base catalyst component in RMA crosslinkable coating compositions, said polymer comprising the weak base groups C2 and optionally C3 acid groups, wherein the C2 weak base groups are preferably formed by partially or fully neutralizing C3 acid groups in the polymer, wherein C2 and C3 are preferably carboxylate and carboxylic acid groups, wherein the polymer is preferably chosen from the group of acrylic, polyester, polyester-amide and polyester-urethane polymers, wherein the polymer optionally comprises C-H donor groups, C=C acceptor groups or both, wherein the polymer preferably has a) an acidic value in unneutralized form of at least 3, more preferably 5, 7, 10, 15 or up to 20 mg KOH/g, and preferably less than 100, 80, 70, 60 mg KOH/g, b) a quaternary ammonium or phosphonium cation, preferably a tetrabutyl or ethylammonium cation c) a Mn of at least 500, preferably at least 1000 or up to 2000, and Mw of no more than 20,000, preferably no more than 10,000 or 6000, d) in the case of C-H donor and/or acceptor groups C=C are present; an equivalent weight of reactive C-H donor or C=C acceptor of at least 150, acceptors at least 250, 350 or even 450 g/mol and not more than 2000, acceptors not more than 1500, 1200 or 1000 g/mol, e) if no C-H donor and C=C acceptor groups are present with an acid value in unneutralized form of at least 10, more preferably 15, 20 mg KOH/g and preferably less than 100, 80, 70, 60 mg KOH/g .

[0086] Preferably, the donor CH groups are malonate-type functionalities. The unsaturated acceptor groups are preferably acrylate, methacrylate, fumarate, maleate or itaconate groups. It is further preferred that the C3/2 polymer described above has high Tg or crystallinity, as specified above for the RMA crosslinkable polymer, comprising high Tg monomer components and/or rigid bonds.

[0087] The invention also relates to the use of the RMA-crosslinkable polymer in RMA-crosslinkable powder coatings. The invention further relates to a method for preparing a powder coating composition comprising the step of a. provision of component A, component B, catalyst system C and optional additives, b. extrusion of the components, preferably at a temperature Tcomp below 140°C, more preferably below 120, 100, 90 or even below 80°C c. cooling, d. shaping the extruded mixture to form a granulate, before, during or after cooling and. optional addition of other additives f. grinding the granulate into powder.

[0088] Optionally added coating additives are typically one or more additives selected from the group of pigments, dyes, dispersants, degassing aids, leveling additives, matting additives, flame retardant additives, additives for improving the properties of film formation, for optical appearance of the coating, to improve mechanical properties, adhesion or for stability properties such as color and UV stability.

[0089] Powder coatings can also be designed to produce matte coatings, using similar paths as conventional powder coating systems, relying on additives or through intentional inhomogeneous crosslinking using powder mixing systems or mixture-based systems. of polymers of different reactivity.

[0090] Standard powder coating processing can be used, typically involving solidifying the extrudate immediately after leaving the extruder by forcibly spreading the extrudate over a cooling strip. The extruded ink may take the form of a solidified sheet as it travels along the cooling track. At the end of the strip, the sheet is then divided into small pieces, preferably using a pin breaker, down to a granulate. At this point, there is no meaningful shape control applied to the beads, although a statistical maximum size is preferred. The paint granulate is then transferred to a classifying micronizer, where the paint is milled to a very precise particle size distribution. This product is then the finished paint for powder coating. If crystalline components are used, care must be taken that the crystallizable components are present in the crystalline state of the powder paint. This may, for example, imply choosing Tcomp below the melting temperatures Tm of the crystallizable components or, in the case of Tcomp being above Tm, allowing the components to crystallize on cooling.

[0091] The invention also relates to a method for powder coating a substrate comprising a. providing a powder with the powder coating composition according to the invention or as obtained in the process as described above, b. applying a layer of the powder to a substrate surface and c. heat to a curing temperature Tcur between 75 and 200°C, preferably between 80 and 180°C and more preferably between 80 and 160, 150, 140, 130 or even 120°C, optionally and preferably using infrared heating, d. and curing in Tcur for a curing time preferably less than 40, 30, 20, 15, 10 or even 5 minutes.

[0092] In the method, curing at Tcur is preferably distinguished by a curing profile, determined by measuring the conversion of the unsaturated C=C bonds of component B as a function of time by FTIR, where the ratio of time to go is 20 % to 60% C=C conversion for the time to reach 20% conversion is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably the time to reach 60% conversion rate of less than 30 or 20 or 10 min and the powder coating composition at Tcur preferably has a melt viscosity at curing temperature of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas. Melt viscosity must be measured at the beginning of the reaction or without C2 from the catalysis system.

[0093] In a preferred embodiment of the method, the curing temperature is between 75 and 140°C, preferably between 80 and 120°C and the catalyst system C is a latent catalyst system as described above, which allows coating in powder from a temperature-sensitive substrate, preferably MDF, wood, plastic or temperature-sensitive metal substrates such as alloys.

[0094] Therefore, the invention also relates to articles coated with a powder coating composition of the invention, with preferably a temperature-sensitive substrate such as MDF, wood, plastic or metal alloys and wherein preferably the XLD crosslinking density of the coating is at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol/cc (as determined by DMTA) and is preferably less than 3, 2, 1.5, 1 or even 0.7 mmol/cc.

[0095] The invention also relates to the use of a catalyst system C, as described above, to catalyze the crosslinking reaction in RMA crosslinkable powder coating compositions at curing temperatures below 200°C, preferably below 180°C. °C, more preferably below 160, 140 or even 120°C.

[0096] The invention relates to powder coating compositions suitable for low temperature powder coating crosslinking, typically at a curing temperature between 75 and 140°C, which can be used for powder coating of heat-sensitive substrates. temperature, such as MDF, wood, plastic or temperature-sensitive metal alloys. The powder coating compositions comprise a crosslinkable component A having at least 2 activated methylene or methine acidic C-H donor groups, a crosslinkable component B having at least 2 activated C=C unsaturated acceptor groups that react with component A by Michael addition. real under the action of a catalyst system C which is preferably a latent catalyst system. The invention also relates to a process for manufacturing such powder coating compositions, processes for coating articles using said powder coating composition and the resulting coated articles. The invention also relates to specific polymers for use in powder coatings and to the use of specific catalyst systems in such powder coating compositions.

[0097] The invention will be illustrated by the following examples.

Test Methods

[0098] The molar mass distribution of the polymers was determined with Gel Permeation Chromatography (GPC) on Perkin-Elmer HPLC series 200 equipment, using a refractive index (RI) detector and PLgel column, using THF as eluents, using calibration by polystyrene standards. Experimental molecular weights are expressed as polystyrene equivalents.

[0099] The resin and paint glass transition temperatures reported here are the midpoint Tg determined from Differential Scanning Calorimetry (DSC) using a heating rate of 10°C/min. Melting points are also determined with DSC using the same scan rate. To determine the heat of reaction evolved over time, DSC is used isothermally, after rapid heating (60C/min) to the curing temperature to be studied.

[00100] XLD was measured by measuring DTMA on an independent coating film prepared by applying the powder coating composition to PTFE coated panels and cured according to the chosen curing profile. The cured coating can be easily peeled off the panel to produce a self-contained coating film. From the freestanding film, a sample was cut for DMTA measurements of 3 mm wide and 30 mm long. The length between the clamps of the DMTA traction bench was 30 mm. A DMTA measurement was performed at 11 Hz and a heating rate of 5°C/min, from which the XLD crosslink density parameter (in mmol/cc) was evaluated as known in the art. The crosslink density parameter Modified Rheovibron (Toyo Baldwin type DDVII-C) at a frequency of 11 Hz with a dynamic tensile strength of 0.03%. All measurements are carried out in traction mode and at each temperature the traction storage modulus E', the traction loss modulus E” and tanδ (tanδ = E”/E') are determined. DMTA is run on a self-contained cured coating of about 30 to 50 μm layer thickness prepared on a non-stick substrate. For unfilled coatings, the crosslink density can be calculated directly from the minimum tensile storage modulus E'min and the temperature Tmin (in Kelvin) at which this minimum modulus E'min is found: where R is the gas constant (8.314 J/mol/K) and ve is the crosslink density (= number of moles of elastically effective network chains per volume). The Tg of the film can be determined from the DMTA curve as associated with the maximum tan δ or as the value associated with the maximum E”.

[00101] Gel times: a gel tester from Coesfeld Material is used to determine the gel time. Before testing, the gel tester is adjusted to the required temperature and allowed to stabilize. A controlled amount of ground powder is placed on the hot plate of the gel tester and the timer is started. When the sample begins to melt, the material is compounded with a wooden stick using a circular motion. As the sample reacts, the viscosity increases until it reaches a point where the material stops flowing freely and begins to form a sticky cohesive ball. The end point is reached when the sample is in this condition and is able to detach from the tip of the toothpick or the surface of the heating plate. The test is repeated until at least two sets of results are consistent.

[00102] Solvent resistance for the coating films was evaluated by placing a cotton pad over the ball head of a nominal 1 lb (0.454 kg) ball head hammer. This is covered with a 5 cm square of suitable fabric. The block and cotton fabric are attached to the hammer with a clamp, ensuring that the fabric is taut and free of wrinkles, creases or gaps. Sufficient methyl ethyl ketone (MEK) is applied to the fabric to completely moisten the cotton without leaving excess solvent. The ball head of the hammer is placed on the painted surface of a prepared panel of the paint to be tested. The hammer is pushed across the width of the panel and then pulled back to its original position. Care is taken to ensure that no upward or downward pressure is exerted on the hammer during this action. This constitutes a double rub and should take approximately 1 second. This is repeated 300 times, or until the coating fails (the coating rubs off the metal surface), whichever is sooner. The number of double rubs to rub, or 300 if no rub is observed.

[00103] Solvent resistance for the coating film was also evaluated by the acetone test. A 50 μl drop of acetone was placed on the panel for 30 seconds, and then the panels were visually inspected for signs of corrosion. Test panels were visually rated on a scale of 0 to 5. Rating; 0: no damage; 1: excellent, 2: good, 3: sufficient, 4: poor, 5: total destruction of the coating layer.

[00104] To evaluate flow and appearance, powder coated test panels are compared to a set of Powder Coating Institute (PCI) standard panels. These panels represent the degrees of smoothness achievable with powder coatings and have graduated degrees of orange peel (flow) and powder smoothness from rough to smooth. Standard panels consist of ten 4x6 inch panels painted black and labeled with the corresponding orange peel (flow) rating from 1 (poor) to 10 (excellent). Test panels are compared to standard panels to visually evaluate the appearance of the painted test panels. The test panels are assigned the flow value that most closely matches the value of the standard panels.

[00105] To follow the acryloyl conversion, a Nicolet iC10 FTIR instrument was used, equipped with a Specac Golden Gate ATR installation with diamond ATR crystal embedded in a hot stage. The formulated paint, dissolved in solvent or as powder paint, was applied directly to the hot stage at the desired curing temperature. The conversion was followed as a function of time, using the integration of the acryloyl peak at 810 cm-1, using the absorbance range 1760 C=O as a reference. Abbreviations Table 1: description of abbreviations used in the examples.

Preparation of materials Preparation of M-1 malonate resin

[00106] A 2-liter round bottom reactor equipped with a 4-neck lid, metal anchor stirrer, Pt-100, Dean-Stark pickup with cooler and an N2 inlet was charged with 510 g of CHDM and 153, 7 g of IPA. The reactor temperature was gently increased to about 100°C and 0.26 g of Fascat 4101 was added. The temperature was further increased to 200°C and the reaction was continued until the acid value was below 0.50 mg of KOH/g. During the last part of the reaction, a stream of nitrogen was used to bring the reaction to completion. The temperature was lowered to 50°C and 134.2 g of diethylmalonate were added. The reactor temperature was increased to 170°C and maintained until no more ethanol was formed. After transesterification was complete, the hydroxyl value of the polyester was measured. Then, the vessel temperature was set at 60°C and 284.40 g of IPDI were added over a period of 3 to 4 hours, in which the temperature increased to 155°C due to the exothermic reaction. After all the IPDI was added, the reaction was held for 30 minutes at 155°C to complete the reaction. The final OHV was 46 mg KOH/g, with a Mn GPC of 3343 and a Mw of 7372 and a Tg (DSC) of 64°C. The acid value is less than 1 mg KOH/g.

Preparation of M-2 malonate resin

[00107] A 5-liter round bottom reactor equipped with a 4-neck lid, metal anchor stirrer, Pt-100, column packed with top thermometer, condenser, distillate collection vessel, thermocouple and an N2 inlet was loaded with 2900 g of CHDM and 2300 g of IPA. The reactor temperature was gently increased to about 100°C and 3 g of Fascat 4101 catalyst was added. The reaction temperature was further increased gradually to 230°C, and the polymerization was progressed under nitrogen with continuous stirring until mixture of reaction is clear and the acid value is below 2 mg KOH/g. Depending on the measured OHV and the theoretical target OHV (88 mg KOH/g), a calculated amount of CHDM was added to the reactor to compensate for any loss of glycol during polymerization. During the last part of the reaction, vacuum was applied to bring the reaction to completion. The temperature was lowered to 120°C and 406 g of diethylmalonate were added. The reactor temperature was then increased to 190°C and maintained until no more ethanol was formed. Again, vacuum was applied to bring the reaction to completion. After transesterification was complete, the hydroxyl value of the polyester was measured. The final OHV was 35 mg KOH/g, with a Mn GPC of 2150 and a Mw of 5750 and a Tg (DSC) of 42°C. The AV is less than 1 mg KOH/g.

Preparation of M-3 malonate resin

[00108] M-3 was prepared in a similar process to M-2. 1970 g of NPG, 1800 g of TPA and 600 g of IPA were charged into the reaction vessel and condensed to a very low acid value. 674 g of diethylmalonate was added to this oligomer resin and further condensed by removing ethanol from the mixture. After stopping transesterification, the M-3 malonate resin obtained was distinguished by a final OHV of 16 mg KOH/g, with a Mn GPC of 3776, Mw 9774 and a Tg (DSC) of 37°C. The EQW of malonate is 1000, the acid value is less than 1 mg KOH/g.

Preparation of M-4 malonate resin

[00109] M-4 was prepared in a similar process to M-2. 1840 g of NPG, 2455 g of isosorbide (80 wt%), 2746 g of TPA and 1000 g of IPA were charged into the reaction vessel and condensed with 7.50 g of titanate catalyst to a very low acid value. 1247 g of diethylmalonate was added to this oligomer resin and further condensed by removing ethanol from the mixture. After stopping transesterification, the M-4 malonate resin obtained was distinguished by a final OHV of 21 mg KOH/g, with a Mn GPC of 2183, Mw of 5448 and a Tg (DSC) of 61°C. The EQW of malonate is 1000, the acid value is less than 1 mg KOH/g.

Preparation of acid functional malonate resin modified with AHM-4 anhydride

[00110] 700 g of M-4 malonate and 20.74 g of phthalic anhydride were added to a reaction vessel equipped with a mechanical stirrer. The reaction was continued at 170°C with continuous stirring for 2.5 hours. The final product has an AV of 16 mg KOH/g. The Mn by GPC was 1591 and the Mw was 4084, with a Tg (DSC) of 49°C.

Preparation of malonate polymer - carboxylate MC

[00111] A polymeric malonate-carboxylate polymer was prepared by hydrolyzing an M-2 malonate polyester resin (Mn = 2150) using TBAOH solution (55% by weight in water) at elevated temperature. Briefly, 45.3 g of M-2 malonate resin was first melted in a three-neck round-bottom flask equipped with a condenser. Once the resin was completely melted, 4.71 g of TBAOH solution was added dropwise to the flask at 140°C. The water was distilled out of the vessel until it was complete. The final product has a Mn per GPC of 797 and a Mw of 2772, and a base (carboxylate) concentration of 0.374 mol/kg.

MB-1 Standard Mix Resin Preparation

[00112] For the synthesis of the standard mix resin, 1000 g of M-4 malonate polyester resin and 750 g of CRYLCOAT® 1622-0 were charged into a 3 liter reaction vessel. The resin mixture was then melted at 170°C and homogenized with stirring. After that, the complete homogenized resin mixture was cooled to 150°C, followed by the addition of 343 g of TBAOH solution (55 wt% in H2O). The water was distilled out of the vessel. Finally, vacuum was applied for 15 minutes to push residual water out of the resin mixture. The final product has an AV of 28 and Tg (DSC) of 36°C. The theoretical carboxylate concentration is 0.217 mmol/g.

Preparation of AA-1 acetoacetate resin

[00113] AA-1 was prepared by starting with the condensation of 484.1 parts of NPG (90% by weight of water), 21.40 parts of trimethylpropane, 681.5 parts of IPA and 0.55 parts of Fascat 4100 as a catalyst at 235°C, in the last stages with vacuum, at an acid value below 1 mg KOH/g. To 2500 g of this material, 327.80 g of tBAA were added dropwise at 170°C. Tert-butanol was distilled while the reaction proceeded at 170°C until no more volatile was generated. Finally, excess tBAA was removed under vacuum. The final OHV was 3 mg KOH/g, with a Mn per GPC of 2150 and a Mw of 15800 and a Tg (DSC) of 44°C. The acid value is negligible; the EQW of acetoacetate is 2000 g/mol.

Preparation of urethane acrylate UA-1

[00114] For the synthesis, a 0.5 liter round bottom reactor with 4 necks is charged with 116.10 g of 2-hydroxyethyl acrylate (purified over basic Al2O3), 0.30 g of 2,6-di -tert-butyl-4-methylphenol and 0.30 g of dibutyltin dilaurate. The reactor temperature was increased to 55°C and 111.2 g of IPDI was added over a period of 2.5 hours. After all the isocyanate was added, the reaction temperature was maintained at 55°C for 1 hour to complete the reaction. The resulting urethane-acrylate has an acryloyl functionality of two.

Preparation of urethane acrylate UA-2

[00115] A urethane-acrylate based on IPDI, hydroxypropyl-acrylate, glycerin is prepared with the addition of suitable polymerization inhibitors, as described in, for example, EP0410241A2 and EP0585742. In a 5-liter reactor equipped with a thermometer, stirrer, dosing funnel and gas bubble inlet, 1020 parts of IPDI, 1.30 parts of di-butyltin dilaurate and 4.00 parts of hydroquinone are charged. Then, 585 parts of hydroxypropylacrylate are administered, preventing the temperature from rising above 50°C. Once the addition is complete, 154 parts of glycerin are added. Fifteen minutes after the exothermic reaction disappears, the reaction product is melted in a metal tray. The resulting urethane acrylate is distinguished by a Mn per GPC of 744 and Mw of 1467, Tg (DSC) of 51°C, residual isocyanate content < 0.1% and theoretical unsaturation EQW of 392.

Preparation of semi-crystalline urethane acrylate UA-3

[00116] In a 5-liter reactor equipped with a thermometer, stirrer, dosing funnel and gas bubble inlet, 833 parts of IPDI, 913 parts of HDI, 4.20 parts of di-butyl-tin-dilaurate and 5.00 parts butylated hydroxytoluene (BHT). Then, 395 parts of hydroxypropylacrylate are administered over 60 minutes, preventing the temperature from rising above 35°C. Once the addition is complete, 896 parts of 1.6—HD and 5 parts of BHT are added. Fifteen minutes after the exothermic reaction disappears, the reaction product is melted in a metal tray. The semi-crystalline urethane-acrylate obtained has a melting point of 125°C, Tg (DSC) of 17.7°C and theoretical unsaturation EQW of 1004.

Preparation of EA-1 epoxy-acrylate resin

[00117] 640 g of bisphenol A epoxy resin (Mn ~ 1075), 3.20 g of 4-methoxyphenol (MEHQ), 3.20 g of β-lonol and 4.73 g of ethyltriphenylphosphonium bromide were loaded into a 3-liter reaction vessel and heated to 135°C with stirring. In a separate flask, 81.50 g of acrylic acid was mixed with 0.08 g of MEHQ and 0.03 g of phenothiazine and then added to the reaction vessel over a period of 30 minutes. The reaction was allowed to proceed for another 5 hours at 130°C until completion (AV = 0). The final product has a Mn per GPC of 1399, a Mw of 4956, a Tg (DSC) of 39°C and a theoretical unsaturation EQW of 637.

Preparation of epoxy-acrylate resin with acid functionality modified with AHEA-1 anhydride

[00118] 137.10 g of epoxy-acrylate EA -1 and 16.20 g of phthalic anhydride were added to a reaction vessel equipped with a mechanical stirrer. The reaction was carried out at 140°C with continuous stirring for 3 hours. The final product has AV of 30, Tg (DSC) of 36°C, Mn by GPC was 2509 and Mw was 11770.

Preparation of Fumarate FP-1 Polyester Resin

[00119] A 5 liter round bottom reactor equipped with a 4 neck lid, metal anchor stirrer, Pt-100, column packed with top thermometer, condenser, distillate collection vessel, thermocouple and an N2 inlet it was loaded with 1563 g of NPG and 2150 g of IPA. The reactor temperature was gently raised to about 100°C and 3.5 g of monobutyltin oxide (MBTO) catalyst was added. The reaction temperature was further increased gradually to 210 ° C, and the polymerization was progressed under nitrogen with continuous stirring until the reaction mixture was clear and the AV was below 8 mg KOH/g. In the 2nd step, 1060 g of fumaric acid, 1.5 g of MEHQ and 1.05 g of phosphoric acid were added to the reaction vessel. Polymerization was carried out under vacuum until the AV was below 5 mg KOH/g. The final product obtained has AV of 4.4 mg KOH/g, OHV of 46.3 mg KOH/g, Tg (DSC) of 37°C and EQW of theoretical unsaturation of 500.

Preparation of tetrabutylammonium benzoate

[00120] 104.79 g of TBAOH solution (55% by weight in H20) and 48.85 g of benzoic acid were charged into a 250 ml round bottom flask and mixed until all solids were dissolved. Depending on the pH of the solution, additional TBAOH or benzoic acid was added to adjust the pH level to 7. The solution was then concentrated by partial evaporation of the water and cooled to allow crystallization. After crystallization was completed, the obtained TBA benzoate was dried in a vacuum oven.

Catalyst System Curing Profile

[00121] In examples 1 to 9 the following were used: malonate resin M-1 (12.0 g; 21.8 meq C-H reactive) and urethane acrylate UA-1 (4.46 g; 19.6 meq acryloyl) and solvent of butylacetate (11.1 g). Other components as well as reaction times are listed in Table 2. Catalyst component C1 is CarduraTM E10P (CE-10), catalyst component C2 is tetrabutylammonium benzoate, catalyst component C3 is benzoic acid or lauric. The compositions were cured at temperatures 95 and 102°C.

[00122] The conversion was measured as a function of time to determine the reaction's kinetic form factor 60-20/20 (SF60) and the form factor 8020/20 (SF80). The conversion is measured after applying the composition to a heated ATR-FTIR stage, and measuring the conversion of the acryloyl groups, focusing on the 809 cm-1 band characteristic of the acryloyl moiety. The results are summarized in Table 2 below.

[00123] Shape factors are a characteristic of the reaction kinetics of the crosslinkable composition. The 60-20/20 form factor is the ratio of the time to convert 20% to 60% acryloyl and the time to reach 20% conversion. Likewise, the 80-20/20 form factor is the ratio of the time to go from 20% to 80% acryloyl conversion to the time to reach 20% conversion. Preferably, this form factor is low, indicating that there is a substantial and long open time, providing film-forming flow, good coating appearance, and a small amount of time to achieve cure of 20 to 60 or 80% of total conversion. .

[00124] An alternative method for determining an SF kinetic profile shape factor (DSC) is to use DSC (Differential Scanning Calorimetry). In this method, we measure the reaction exotherm of a powder paint composition at a relevant temperature as a function of time in an isothermal scan. The sample is heated to the curing temperature of interest at a rate of 60°C/min, and the heat evolved is measured as a function of time from that moment on (t0). An exothermic peak is observed, typically after a certain induction time, and can be integrated to obtain a total AH. This exotherm can be replaced after integration as the accumulated heat evolved after t0, and we can determine the times needed to reach 20% or 60% of AHtotal in this isothermal run (t20 and t60). An SF form factor (DSC) can be determined from the ratio of the time from 20 to 60% exothermic heat evolved (t60 - t20) to the time to reach 20% exothermic heat evolved (t20 - t0). SF(DSC)=(t60 - t20)/ (t20 - t0)

[00125] This shape factor preferably has a value less than 1, more preferably less than 0.8, even more preferably less than 0.6, 0.4, more preferably less than 0.3. Furthermore, the kinetics are preferably chosen so that the (t20 - t0), when tested at 100°C, is preferably greater than 1 minute, more preferably greater than 2,3,5,8,12 minutes. Table 2: Healing characteristics of examples 1 to 9

[00126] The examples show the advantage of catalyst latency due to the presence of C3. Preferably, the form factor 60-20/20 (SF60) is below 1, more preferably below 0.8, 0.6, 0.4 or 0.3 and preferably also the SF80 is below 1.5, preferably below 1, 0.5 or even below 0.35.

[00127] In example 10-11, the malonate resin M-4 (5 g), urethane acrylate UA-2 (3.92 g) and the C1 catalyst component Araldite® GT 7004 (1.14 g) were dissolved in acetone. To prepare catalyst component C2, TBAOH (0.24 g, 55 wt% in water) or TEAOH (0.33 g, 40 wt% in water) was neutralized with excessive amount of benzoic acid respectively in a separate flask. . The amount of each catalyst component in the formulation after neutralization is summarized in Table 3. The two solutions were then combined and a thin film was cast onto a polypropylene panel. Afterwards, the acetone was removed under vacuum at 50°C and the collected solids were measured on a DSC for isothermal analysis at 120°C. The results of the DSC isothermal scans, for example 10 and 11, show that approximately the same time is required to complete curing at 120°C as for examples 10 and 11.

[00128] In example 12, the acid functional malonate resin modified with AHM-4 anhydride (5.0 g) was first dissolved in acetone and then partially neutralized with TBA hydroxide (0.21 g, 55% by weight in water). In a separate flask, the urethane acrylate UA-2 (3.92 g) and the C1 catalyst component CE-10 (0.31 g) were also dissolved in acetone. The amount of each catalyst component in the formulation after neutralization is summarized in Table 3. The two solutions were then combined and a thin film was cast onto a polypropylene panel. Afterwards, the acetone was removed under vacuum at 50°C and the collected solids were measured on a DSC for isothermal analysis at 120°C.

[00129] In example 13, the M-4 malonate resin (5.0 g) and the C1 catalyst component Araldite® GT 7004 (1.76 g) were dissolved in acetone. In a separate flask, the anhydride-modified acid functional epoxyacrylate resin AHEA-1 (2.38 g) and the epoxyacrylate EA-1 (1.28 g) were also dissolved in acetone and then partially neutralized with hydroxide. of TBA (0.37 g, 55% by weight in water). The amount of each catalyst component in the formulation after neutralization is summarized in Table 3. The two solutions obtained were then combined and a thin film was cast on a polypropylene panel. Afterwards, the acetone was removed under vacuum at 50°C and the collected solids were measured on a DSC for isothermal analysis at 120°C. Table 3: Curing characteristics of examples 10 to 13

[00130] Examples 10 and 11 showed that TBA benzoate has similar reactivity to TEA benzoate at 120°C. This is also illustrated by similar times required to pass from 20% to 60% exothermic heat in isothermal runs.

[00131] Furthermore, the catalyst component C3 can be incorporated into the main chain of component A, as shown in example 12, or component B, as shown in example 13. The corresponding C2 anions were then formed by partial neutralization of C3 with cation hydroxide. The cure profile is illustrated by the DSC form factor. Powder paint formulations

[00132] Powder paint formulations P1-P11 were prepared and applied as powder paints. The coatings were formulated without pigments, at a stoichiometry to have an acryloyl/C-H2 reactive ratio of 2:1. Other components, including additives, are summarized in Table 4. Catalyst component C1 is Araldite® PT 912 or Araldite® GT 7004; the catalyst component C2 is tetrabutylammonium benzoate (TBA benzoate), the catalyst component C3 is benzoic acid. To prepare the RMA powder coatings, a double extrusion method was performed to ensure good mixing. First, the two resin components were pre-extruded at a relatively low extruder speed (100 rpm). The pre-extruded materials obtained were then crushed and mixed with the catalyst components and flow additive in a high-speed Thermoprism Pilot Mixer 3 premixer at 1500 rpm for 20 seconds, before extruding again at a relatively fast speed. extruder (250 rpm). For both extrusion steps, the four temperatures of the extruder barrel zone were set at 15, 25, 80 and 100°C. After extrusion, the coatings were milled using a Kemutec laboratory classifier micronizer. The classifier was set at 5.5 rpm, the rotor at 7 rpm, and the feed at 5.2 rpm. Coatings were sieved to 100 μm using Demel Finex Russell Finex laboratory vibrating sieves of 100 micron mesh. The formulation compositions (as parts by weight) for P1 to P11 are shown in Table 4. Table 4: Powder paint formulation of compositions P1 - P1

[00133] Powder paint formulations P12-P15 were prepared using the standard mixing resin MB-1 and the urethane-acrylate acceptor resin UA-2. Coatings P12-P14 were formulated without pigments, and in a stoichiometry to have an acryloyl/C-H2 reactive ratio of 2:1, 1:1 and 0.75:1, respectively. The P12 coating was formulated with 20% Kronos® 2160 pigment and at a stoichiometry to have an acryloyl/C-H2 reactive ratio of 1:1. The C1 catalyst component is Araldite® GT 7004. To prepare the RMA powder coatings, the resins and catalyst components were first crushed and mixed using a GRINDOMIX knife mill (5000 rpm) for 5 seconds. The mixture is then fed through a TSA twin screw extruder operated at 300 rpm. The temperature of the barrel zone of five extruders was set at 60, 100, 120, 120 and 120°C. After extrusion, the coatings were ground twice using a GRINDOMIX knife mill (10000 rpm) for 20 seconds. The coatings were then sieved using a 90 μm mechanical sieve.

[00134] Powder paint formulations P16-P19 were prepared using malonate resin M-4 and urethane-acrylate acceptor resin UA-2. Coatings P16-P19 were formulated without pigments, and at a stoichiometry to have an acryloyl/C-H2 reactive ratio of 2:1. Other components, including additives, are summarized in Table 5. For P16 and P17 paints, the catalyst system comprises a base blocked with weakly acidic species. For paint 16, component C1 is Araldite® GT 700; the C2 catalyst component is 1,4-diazabicyclo[2.2.2]octane (DABCO). For paint 17, component C1 is dicyclohexylcarbodiimide (DCC); the C2 catalyst component is TBA benzoate. In all of the above cases, the C3 catalyst component is benzoic acid. The RMA powder coatings were prepared using a similar process to the P1-P11 powder coating formulations. Table 5: Powder paint formulation of compositions P16 — P19

[00135] Powder paint formulations P20-P21 were prepared using malonate resin M-4 and urethane-acrylate acceptor resin UA-2. The P20 coatings were formulated without pigments, while the P21 coating was formulated with 20% Kronos® 2160 pigment. In both cases, a stoichiometry was formulated to have an acryloyl/C-H2 reactive ratio of 2:1 and was added approximately 10% MODAFLOW® P 6000 as flow additive. Catalyst component C1 is Araldite® PT 912; the C2 catalyst component is TBA benzoate, the C3 catalyst component is benzoic acid. Powder coatings by RMA P18 & P19 were prepared using a similar process to powder coating formulations P12-P15.

[00136] Powder paint formulations P22-P24 were prepared using the malonate resin M-4 and the urethaneacrylate acceptor resins UA-2 and semicrystalline UA-3. Coatings P21-P23 were formulated without pigments, and at a stoichiometry to have an acryloyl/C-H2 reactive ratio of 1.65:1. Other components, including additives, are summarized in Table 6. Catalyst component C1 is Araldite® GT 7004; the C2 catalyst component is TBA benzoate, the C3 catalyst component is benzoic acid. The RMA powder coatings were prepared using a similar process to the P1-P11 powder coating formulations. Table 6: Powder paint formulation of compositions P22 — P24

Powder coating evaluation

[00137] To evaluate the quality of the powder coating, the powders obtained were applied to the panels using a Nordson Surecoat corona gun. To evaluate appearance, the coatings were applied to 100 mm x 300 mm aluminum panels. Examples P1-P19 were cured at the indicated temperatures for 20 minutes. P4 ink was also cured for a curing time of less than 10 minutes at 120°C. Paints 20 and 21 were applied to MDF and cured using infrared heating at 130°C. In all cases, the thickness of the cured film was 60 to 80 μm. Samples were cooled to ambient conditions and appearance and solvent resistance were measured between 24 and 36 hours after curing. The coating evaluation results were summarized in Tables 7, 9, 10, 11 and 12. The numbers in the example codes correspond to the formulation numbers given above. Table 7. Summary of P1-P4 powder coating evaluation results.

[00138] The cure of coatings P1 to P4 was also measured with FTIR after curing at 120°C as a function of time to determine the reaction kinetic form factor 60-20/20 (SF60) and the form factor 8020/20 (SF80). The conversion is measured by measuring the conversion of the acryloyl groups in the composition by FTIR, focusing on the 809 cm-1 range that is characteristic of acryloyl. The results are summarized in Table 4 below. It can be seen that in all cases, most of the conversion occurred before 10 minutes, with the samples containing benzoic acids creating an induction time before the maximum cure rate developed. The results of this induction time can be seen as an improved appearance, as illustrated by the PCI rating in the table above. The shape factors of the conversion curves, introduced previously, are determined and listed below in Table 8. Table 8: Conversion kinetics of curing paint formulations P1 - P4

[00139] The data illustrates that the addition of the C3 benzoic acid component provides a latency for curing the powder paint, as illustrated by the shape factor. Table 9. Summary of P5-P11 powder coating evaluation results.

[00140] Examples P5-P11 show that variations in the RMA coating composition can be made for components A and B, while still obtaining good cure at relatively low temperature. This is illustrated by the achievement of good XLD crosslink density and solvent resistance results, as summarized in Table 9. PC8 was prepared with materials comprising isosorbide and consequently has much higher Tg than the rest of the examples. Table 10. Summary of powder coating evaluation results for P12-P15.

[00141] Example P12-P15 demonstrates that RMA coatings can be prepared with materials containing acid/carboxylate functional polyester to provide C2 and C3. The acryloyl/C-H2 ratio was varied in the formulation (PC12-PC14) and a pigmented RMA coating was also prepared (PC15). Relatively good curing can be achieved at 120°C in all of the above cases, as illustrated by the acetone test results shown in Table 10. Table 11. Summary of powder coating evaluation results for P16-P19.

[00142] PC16 and 17 demonstrated powder coatings by RMA with LCE catalyst system. This catalyst system is less preferred than LCC as evaporation of volatile acid is difficult to control during the curing process. At higher curing temperatures, faster acid evaporation at the film surface can lead to a gradient in curing speed. As a result, textured surfaces were observed under such conditions due to faster curing on the film surface.

[00143] It is possible to obtain a good cure for the LCC system using DABCO as component C2. This is illustrated by the good solvent resistance result obtained for PC18.

[00144] PC19 demonstrates that carbodiimide can be used as an alternative to epoxy as a C1 catalyst component in the LCC system to obtain good cure at 120 and 140°C. Table 12. Summary of powder coating evaluation results for P20 and P21.

[00145] The results shown in Table 12 were obtained from application tests on MDF panels. As can be seen from the results, good curing and solvent resistance were achieved in a short period of time using infrared heating. Table 13: Conversion kinetics of P22 - P24 curing paint formulations

[00146] Curing of coatings P22 to P24 was measured with DSC isothermal scans at 120°C to determine the kinetic form factor of the SF(DSC) 60-20/20 reaction. The results are summarized in Table 13 above. The data shows that the addition of the C3 benzoic acid component provides latency to the curing of the powder paint, as illustrated by the decrease in DSC form factor.

Curing characteristics of LCC2 latent catalyst system for acrylate component B

[00147] The model formulations were prepared in solvent butyl acetate using as LCC2 catalyst system a CO2 blocked base (Acure® 500) that deblocks very quickly at 100°C, which in combination with the S3 component creates a mixture S2/S3 of acid X-H and conjugate base X- in an LCC2 latent catalyst system.

[00148] The crosslinkable components used were 10 g of an Acure® 510-100 malonate functional polyester and 4.95 g of DTMPTA (acrylate functional). Then, 0.72 g of Acure® 500 catalyst was added with or without an S3 component. When XH S3 components were used, they were added at the 2 mmol level. The solutions were applied as thins (target dry film thickness 60 μm) onto an ATR crystal preheated to 100°C, and the acrylate concentration as a function of time was tracked using FTIR.

[00149] Without the S3 additive, the film was immediately cross-linked and removed from the ATR crystal before a first FTIR measurement was completed. Similar observations were obtained when S3 additives such as succinimide (pKa = 9.5) and 1,2,4-triazole (pKa = 10.4). Thus, it has been found that compounds X-H which are effective retardants for room temperature curing of acrylate-based compositions are not suitable for use at powder curing temperatures. Furthermore, when using ptoluenesulfonamide (pKa = 10.17) and 5,5-dimethylhydantoin (pKa = 9.19), insufficient delay was still observed.

[00150] Useful delayed curing under these 100°C curing conditions can be observed for S1 acrylate-based compositions comprising S3 components distinguished by lower pKa values. The table below indicates the times observed to reach 20, 50 and 60% C=C conversion. Table 14: Curing characteristics of S2 components of LCC2 for acrylate na: not determined

[00151] It has been found that for Michael acceptor S1 other than acrylates, for example methacrylates, fumarates and maleates, other requirements apply to the S3/S2 components to provide sufficient delay of the catalyst system.

Curing characteristics of LCC2 latent catalyst system for methacrylate component B

[00152] For the functional components in methacrylate B, FTIR experiments were carried out again in an ATR crystal preheated to 100°C, as described above. In this case, the same donor Acure® 510-100 (10g) was used mixed with the acceptor TMPTMA (acrylate functional) (2.4 g). Acure® 500 blocked base initiator was used in the formulation at 50 μeq/g of solid binders; when species X-H were used as S3 (forming S2 upon neutralization), the amount relative to the base is given in the table below. Experiments were conducted as described above.

[00153] For a composition based on S1/B methacrylate components, without any S3 component, we observed that curing for this composition with high concentrations of acceptor and donor groups is quite fast at 100°C and is completed within minutes. Using succinimide, 1,2,4-triazole or benzotriazole, a useful cure delay can be achieved at the practical levels indicated Table 15: Cure characteristics of S2 components of LCC2 for methacrylate

[00154] The examples show that compounds X-H with pKa above 8 do not delay efficiently when S1 (=B) is an acrylate. Therefore, in case S1 is acrylate in the LCC2 catalyst system, it is preferable to use as component S2 an X-H component with pKa < 8. If component S1 (=B) is methacrylate in the LCC2 catalyst system, it is preferable to use as component S2 an X-H component with pKa below 10.5.

Claims (18)

1. Powder coating composition comprising one or more crosslinkable components and a catalyst, characterized in that the one or more crosslinkable components are crosslinkable by real Michael addition reaction (RMA), the powder coating composition comprising a. a crosslinkable component A having at least 2 acidic C-H donor groups in activated methylene or methine, b. a crosslinkable component B having at least 2 activated unsaturated acceptor groups C=C, which react with component A by real Michael addition (RMA) to form a crosslinked network, c. a latent catalyst system C comprising a strong base or a strong base precursor for catalyzing the RMA cross-linking reaction with a delay at a curing temperature below 200°C, and at least 70°C, wherein the system catalyst C is an LC latent catalyst system selected from the group of a. a latent LCC catalytic system with chemical latency comprising components that react at the curing temperature to initiate the reaction between the crosslinkable components A and B with a delay, said latent LCC catalytic system comprising In the LCC1 embodiment: a) a weak base C2, b ) a C1 activator reactive with C2 or a protonated C2 at the curing temperature, c) optionally further comprising a C3 acid, wherein the C1 activator is selected from the group of epoxide, carbodiimide, oxetane, oxazoline or aziridine functional components , d) that in the case of the LCC2 modality: a) the weak base C2 is a Michael addition donor S2 and b) the activator C1 is a Michael acceptor S1 comprising an activated unsaturated group C=C reactive with S2 at the curing temperature, c ) optionally further comprising an acid C3 being an acid S3, the corresponding base of which is also a Michael addition donor, wherein if S1 is an acrylate, S2 has a pKa of the conjugate acid below 8, wherein pKa is defined as the value in an aqueous environment, and if S1 is a methacrylate, fumarate, itaconate or maleate, S2 has a pKa of the conjugate acid below 10.5, or combinations of LCC1 and LCC2 modalities, b. an LCE latent catalyst system with evaporative latency comprising a base blocked with a volatile acid or a weak base which on protonation forms a volatile acid and which the volatile acid evaporates at the curing temperature, c. an LCP latent catalyst system with physical latency in which a catalytic system, preferably a strong base or a latent catalyst system, is present that is physically separate and inaccessible for chemical reaction in the powder at or below a composition temperature and that is accessible for chemical reaction at the curing temperature, chosen from a) an LCP1 latent catalyst system comprising a strong base catalyst with a melting temperature below the curing temperature and above the composition temperature, or b) a latent catalyst system LCP2 comprising a kind of active strong base catalyst that is encapsulated or mixed with a material that releases the catalyst at a temperature below the curing temperature and above the composition temperature at which the material has a melting temperature or, in the case of an amorphous material, a glass transition temperature, below the curing temperature and above the composition temperature, c) an LCP3 latent catalyst system comprising a photo-based generating component that releases a base upon irradiation with an appropriate wavelength, or combinations of LCC, LCE and LCP catalyst systems. 2. Powder coating composition according to claim 1, characterized by the fact that in the LCC1 embodiment of the latent catalyst system — the weak base C2 has a pKa of the conjugate acid greater than 1 units lower than the pKa of the acidic C-H groups of the majority component A and wherein C2 is a weak base nucleophile anion chosen from the anions of the carboxylate, phosphonate, sulfonate, halide or phenolate group or salts thereof or a nonionic nucleophile, and — the latent catalyst system preferably also comprises C3 acid with a pKa of more than 1 units less than the pKa of the acidic C-H groups of the majority component A. 3. Powder coating composition according to claim 1, characterized by the fact that in the LCC2 embodiment of the latent catalyst system — the weak base S2 is selected from the group of phosphines, N-alkylimidazoles and fluorides or is an anion weak base nucleophile X- of an acidic X-H group containing compound in which is distinguished by a pKa of the corresponding conjugate acid 1 units smaller than the pKa of the acidic C-H groups of the majority component A. 4. Powder coating composition according to any one of claims 1 to 3, characterized in that the weak base C2 is added as a salt comprising a cation that is not acidic, wherein the cation is according to the formula Y(R')4, where Y represents N or P, and where each R' may be the same or different alkyl, aryl or aralkyl group possibly attached to a polymer or where the cation is a very strong protonated basic amine , whose very strong basic amine is selected from the group of amidines. 5. Powder coating composition according to claim 1, characterized by the fact that the latent catalyst system is an LCE latent catalyst system comprising 1) a base blocked with a volatile acid or alternatively 2) comprising a weak base that upon protonation forms a volatile acid and wherein the latent catalyst system further comprises additional volatile acid, which volatile acid evaporates at the curing temperature, wherein the boiling point of the acid is below 300°C. 6. Powder coating composition according to any one of claims 1 to 5, characterized in that it comprises a. In the case of the LCC1 catalyst system, a C1 activator in an amount between 1 and 600 μeq/g, where μeq/g is μeq in relation to the total weight of the binder components A and B and LCC catalyst system or, in the case of the LCC2 catalyst system, an activator S1 in an amount of at least 1 μeq/g, b. the weak base C2 in an amount between 1 and 300 μeq/g, relative to the total weight of the binder components A and B and LC catalyst system, c. optionally, a C3 acid in an amount between 1 and 500 μeq/g, d. where the amount of C1 or, respectively, S1 i. is greater than the amount of C3, in an amount between 1 and 300 μeq/g, and ii. is greater than the amount of C2 or iii. greater than the sum of the amount of C2 and C3. 7. Powder coating composition according to any one of claims 1 to 6, characterized by the fact that a. the weak base C2 represents between 10 and 100 mol% of the sum of C2 and C3, b. the amount of C3 acid is 20 to 400 mol% of the amount of C2, c. wherein the ratio of the molar amount of C1 to the sum of the amount of C2 and C3 is at least 0.5, and at most 3, d. the ratio of C1 to C3 is at least 1. 8. Powder coating composition according to any one of claims 1 to 7, characterized by the fact that it has a curing profile, determined by measuring the conversion of the unsaturated C=C bonds of component B as a function of time by FTIR, at a curing temperature chosen between 80 and 200°C, where the ratio of the time to go from 20% to 60% C=C conversion and the time to reach 20% conversion is less than 1, with the time to reach 60% conversion is less than 30 minutes and the time to reach 20% conversion at 100°C is at least 1 minute. 9. Powder coating composition according to any one of claims 1 to 8, characterized by the fact that a. the cross-linkable component A comprises at least 2 acidic C-H donor groups in activated methylene or methinO in a Z1(-C(-H)(-R)-)Z2 structure in which R is hydrogen, a hydrocarbon, an oligomer or polymer and in that Z1 and Z2 are the same or different electron-withdrawing groups, chosen from keto, ester or cyano or aryl groups, b. component B comprising at least 2 activated unsaturated RMA acceptor groups comes from acryloyl, methacryloyl, itaconates, maleate or fumarate functional groups, wherein at least one of components A or B is a polymer and wherein the composition comprises a total amount of C-H donor groups and C=C acceptor groups per gram of binder solids from 0.05 to 6 meq/g of binder solids and the ratio of C=C acceptor groups and C-H donor groups is greater than 0.1 or less than 10. 10. Powder coating composition according to claim 9, characterized in that the crosslinkable component A comprises an activated CH derivative with a structure according to formula 1: wherein R is hydrogen or an optionally substituted alkyl or aryl and Y and Y' are identical or different substituent groups, preferably alkyl, aralkyl or aryl or alkoxy or wherein in formula 1 the —C(=O)-Y and/or —C(=O)-Y' is substituted with CN or aryl, not more than one aryl or where Y or Y' can be NRR' (R and R' are H or optionally substituted alkyl), but preferably not both, wherein R, Y or Y' optionally provides connection to an oligomer or polymer, said component A being preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, preferably providing at least 50% of the total acidic CH groups in the crosslinkable component A. 11. Powder coating composition according to any one of claims 1 to 9, characterized in that at least one of the crosslinkable components A or B or hybrid A/B is a polymer, chosen from the group of acrylic, polyester polymers , polyester amide, polyester-urethane, polymer which a) has a number average molecular weight Mn, as determined with GPC, of at least 450 g/mol, b) has a weight average molecular weight Mw, as determined with GPC, of maximum 20000 g/mol, c) has a molecular weight distribution Mw/Mn below 4, d) has an EQW equivalent weight in C-H or C=C of at least 150. g/mol and maximum 2500g/mol and a numerical average functionality of C-H or C=C reactive groups between 1 and 25 C-H groups per molecule, e) has a melt viscosity at a temperature in the range between 100 and 140°C less than 60 Pas, f) comprises amide bonds, urea or urethane and/or comprises high Tg, cycloaliphatic or aromatic monomers, in particular polyester monomers chosen from the group of 1,4-dimethylol cyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethylcyclobutanediol, g) has a Tg above 25°C, as the midpoint value determined by DSC at a heating rate of 10°C/min or is a crystalline polymer with a melting temperature between 40°C and 150 (as determined by DSC at a heating rate of 10°C/min). 12. Powder coating composition according to any one of claims 1 to 10, characterized in that it comprises one or more components A or B or catalyst system components C or separate different plasticizers that are in a state (semi- ) crystalline in powder and have a melting temperature between 40 and 130°C. 13. Powder coating composition according to any one of claims 1 to 11, characterized by the fact that component B is a polyester (meth-)acrylate, a polyester urethane (meth-)acrylate, a (met -) epoxy acrylate or a urethane (meth-) acrylate is either a polyester comprising fumarate, maleate or itaconate units, or is a polyester coated with an activated unsaturated isocyanate or epoxy functional group. 14. Process for preparing a powder coating composition as defined in any one of claims 1 to 12, characterized in that it comprises step a. provision of component A, component B, catalyst system C and optional additives, b. extrusion of the components at a temperature Tcomp below 140°C, c. cooling, d. shaping the extruded mixture to form a granulate, before, during or after cooling and. optional addition of other additives f. grinding the granulate into powder. 15. Method for powder coating a substrate, characterized in that it comprises a. providing a powder with a powder coating composition as defined in any one of claims 1 to 13, or obtained in the process as defined in claim 14, b. applying a layer of powder to a surface of the substrate wherein the substrate is a temperature-sensitive substrate selected from MDF, wood, plastic or temperature-sensitive metal substrates, c. heat to a curing temperature Tcur between 75 and 200°C, d. wherein the melt viscosity at curing temperature Tcur is less than 60 Pas, e.g. and cure in Tcur for a curing time of less than 40 minutes. 16. Articles coated with a powder having a coating composition as defined in claims 1 to 13 or as obtained in the process as defined in claim 14, characterized in that they have a temperature-sensitive substrate, and in which the crosslinking density XLD is at least 0.01 mmol/ml (as determined by DMTA) and is less than 3 mmol. 17. Use of a catalyst system C as defined in any one of claims 1 to 8, characterized in that it is for the preparation of RMA crosslinkable powder coating compositions for catalyzing the crosslinking reaction in crosslinkable powder coating compositions by RMA at curing temperatures below 200°C. 18. Use according to claim 17, characterized by the fact that it is as a latent base catalyst component or in RMA crosslinkable powder coatings.