Powder Coatings and Crystalline Precursor Catalysts

Abstract

The present invention relates to a powder coating composition comprising a crosslinkable composition and a catalyst system, the crosslinkable composition being formed by a crosslinkable donor component A and a crosslinkable acceptor component B which are crosslinkable by a true Michael Addition (RMA) reaction via the catalyst system, the catalyst system being capable of catalyzing the RMA crosslinking reaction at curing temperatures below 140° C., the catalyst system comprising a (semi-)crystalline precursor P, an activator C and optionally a retarder T.

Description

[Technical field]

[0001] The present invention relates to a powder coating composition comprising a crosslinkable composition crosslinkable by Real Michael Addition (RMA) and a catalyst system having a precursor P and an activator C, and optionally a retarder T, a method for preparing the powder coating composition, a method for coating an article with said powder coating composition, the coated article, and the retarder T and precursor P for use in the catalyst system. [Background technology]

[0002] Powder coatings are finely divided, free-flowing solid materials that dry at room temperature and have gained popularity over liquid coatings in recent years. 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 necessary to provide sufficient flow of the binder to allow film formation and achieve good coating surface appearance, as well as high reactivity for crosslinking reactions. At lower curing temperatures, reaction kinetics that do not allow for short curing times may be encountered when demanding full mechanical and resistance property development. On the other hand, in systems where high reactivity of the components may be created, the coating may have poor appearance due to the relatively high viscosity of such systems at such low temperatures, which increases rapidly further as the curing reaction proceeds, and the time-integrated fluidity of such systems is too low to achieve sufficient leveling (see, for example, Progress in Organic Coatings, Vol. 72, pp. 26-33 (2011)). Appearance may be limited, especially when thinner films are targeted. Furthermore, very high reactivity can lead to problems due to premature reaction when compounding powder coatings in an extruder. Moreover, highly reactive formulations may have limited storage stability.

[0003] Patent application WO 2019 / 145472 describes a powder coating composition that can provide a coating on substrates, such as heat-sensitive substrates such as medium density fiberboard (MDF), wood, plastics and certain metal alloys, and can be cured at low temperatures. The coating composition is curable by RMA using a catalyst system having only amorphous compounds.

[0004] However, the powder compositions described in the prior art provide coatings that leave room for improvement with respect to flexibility, adhesion to metals etc. and storage stability.

[0005] Thus, there remains a need for powder coating compositions that have good mechanical properties, can be cured at low temperatures with high cure rates, provide excellent adhesion to substrates such as metals, and provide long-term storage stability. Summary of the Invention

[0006] The present invention addresses one or more of the above problems by providing a powder coating composition as claimed in claim 1.

[0007] Thus, a first aspect of the present invention is a powder coating composition, a crosslinkable composition and a catalyst system, wherein the crosslinkable composition is formed by a crosslinkable donor component A and a crosslinkable acceptor component B crosslinkable by a true Michael addition (RMA) reaction via a catalyst system, the catalyst system being capable of catalysing the RMA crosslinking reaction at a curing temperature of less than 140°C, 130 or even 120°C, 110°C or 100°C, preferably at least 70°C, preferably at least 80, 90 or 100°C, The crosslinkable composition comprises a) a crosslinkable donor component A having at least two acidic CH donor groups in an activated methylene or methine; b) a crosslinkable acceptor component B having at least two activated unsaturated acceptor groups C=C which react with component A by true Michael addition (RMA) to form a crosslinked network; Including, the catalytic system comprises a (semi-)crystalline precursor P, an activator C and, optionally, a retarder T, the (semi-)crystalline precursor P is a weak base whose protonated form has a pKa of more than 2 units, preferably more than 3 units, more preferably more than 4 units, even more preferably at least 5 units lower than the pKa of the activated CH group in the donor component A, and an activator C is capable of reacting with P at the curing temperature to generate a strong base (CP) capable of catalyzing the Michael addition reaction between A and B, the retarder T is preferably a (semi)crystalline retarder, the retarder T being an acid having a pKa more than 2 points, more preferably more than 3 points, even more preferably more than 4 or 5 points lower than the pKa of the activated CH in A, which upon deprotonation generates a weak base capable of reacting with the activator C and a strong base capable of catalyzing the Michael addition reaction between the crosslinkable compositions A and B, It relates to powder coating compositions, crosslinkable compositions and catalyst systems.

[0008] In a second aspect, the present invention relates to a (semi-)crystalline catalyst retarder T or precursor P for use in a catalyst system for crosslinking a crosslinkable composition via a true Michael Addition (RMA) reaction to obtain a powder coating composition according to any one of claims 1 to 18, wherein the catalyst retarder T and / or precursor P are (ia) reacting HDI with a compound (i) which is a diol and a compound (ii) which contains a hydroxyl carboxylic acid group to obtain a carboxylic acid-based (semi-)crystalline retarder T; (ib) neutralizing a carboxylic (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iia) reacting HDI with a stoichiometric excess of compound (i), which is a diol, to obtain a hydroxyl-terminated urethane intermediate; (iib) reacting the hydroxyl urethane intermediate with a cyclic anhydride to obtain a carboxylic acid-based (semi-)crystalline retarder T; (iic) neutralizing a carboxylic (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iiia) reacting HDI with a compound (i) containing a diol and a compound (iii) having hydroxyl and carboxylic acid ester functional groups to obtain a (semi-)crystalline urethane ester; (iiib) hydrolysis of the ester groups of the (semi-)crystalline urethane ester with a hydroxide to obtain a (semi-)crystalline precursor P; (iiic) optionally acidifying said (semi-)crystalline precursor to obtain a crystalline retarder T; (iva) reacting HDI with a compound (i) containing a diol and a compound (ii) containing hydroxyl and tertiary amine functional groups to obtain a tertiary amine-based (semi-)crystalline precursor P; (ivb) protonating a tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T, or (va) reacting HDI with a compound (i) containing a diol and a compound (ii) containing hydroxyl and acrylate functional groups to obtain an acrylate-functional (semi-)crystalline intermediate; (vb) reacting the acrylate group of the acrylate-functional (semi)crystalline intermediate with a secondary amine to obtain a tertiary amine-functional semi-crystalline precursor P; (vc) protonating a tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T The present invention relates to a (semi-)crystalline catalyst retarder T or precursor P prepared by

[0009] In a third aspect, the present invention provides a method of powder coating a substrate, comprising the steps of: a. applying a layer comprising a powder coating composition according to an embodiment of the first aspect to a substrate surface, the substrate being preferably a temperature sensitive substrate, preferably a temperature sensitive metal substrate such as MDF, wood, plastic, composite or alloy; b. heating, preferably using infrared heating, to a curing temperature Tcur of 75-200°C, preferably 80-180°C, more preferably 80-160, 150, 140, 130 or even 120°C, wherein the melt viscosity at the curing temperature Tcur is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas; c. Curing at Tcur for a cure time of preferably less than 40, 30, 20, 15, 10, or even 5 minutes; The present invention relates to a method comprising the steps of:

[0010] In a fourth aspect, the present invention relates to an article coated with a powder comprising a powder coating composition according to an embodiment of the first aspect, preferably having a temperature sensitive substrate, preferably selected from the group of MDF, wood, plastic or metal alloys, preferably having a crosslink density XLD of at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / ml (as determined by DMTA), preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / ml.

[0011] Detailed Description of the Invention The inventors have surprisingly found that the powder coating compositions according to the invention, in which the precursor of the catalyst system is (semi)crystalline, provide powder coatings with very good adhesive properties, such as on metal substrates. Furthermore, the powder coatings provide a low melt viscosity upon application and during curing, which leads to better flow behavior and provides coatings with a better appearance. The powder coating compositions according to the invention also provide crystallization after extrusion, which has a positive effect on the storage stability of the powder coatings. Without being bound by theory, the plasticizing effect (reduction of Tg) in the cured film contributes to improved mechanical properties, such as flexibility and adhesion to metals.

[0012] In the context of the present invention, the term "(semi)crystalline compound" is a compound that has a melting temperature Tm above which the compound is liquid. In the context of the present invention, the "melting temperature" of a (semi)crystalline compound is the temperature at which the compound melts completely when present in a composition comprising at least a crosslinkable system and a catalyst system as described in the present invention, unless otherwise specified in the following description as the melting temperature of the compound itself. The melting temperatures reported herein are determined from differential scanning calorimetry (DSC) using a heating rate of 10°C / min. [Brief description of the drawings]

[0013] [Figure 1] 1 is a plot of a DSC temperature scan for PW2 between −30 and 210° C. at a rate of 10° C. / min. [Diagram 2] 1 is a plot of a DSC temperature scan for PW5 between −30 and 210° C. at a rate of 10° C. / min. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Catalyst system In an embodiment of the first aspect, the catalyst system is capable of crosslinking a crosslinkable composition comprising a crosslinkable donor component A and a crosslinkable acceptor component B by true Michael addition (RMA), whereby the catalyst system comprises a (semi-)crystalline precursor P and an activator C.

[0015] Precursor P is a weak base whose protonated form has a pKa that is more than 2 units, preferably more than 3 units, more preferably more than 4 units, and even more preferably at least 5 units lower than the pKa of the activated CH group in donor component A. Activator C can react with precursor P at cure temperatures to produce a strong base (CP) that can catalyze the Michael addition reaction between A and B.

[0016] The catalyst system may optionally further comprise a retarder T, which is preferably (semi-)crystalline and is an acid having a pKa more than 2 points, more preferably more than 3 points, even more preferably more than 4 or 5 points lower than the pKa of the activated CH in A, which upon deprotonation generates a weak base capable of reacting with the activator C and generating a strong base capable of catalyzing the Michael addition reaction between the crosslinkable compositions A and B.

[0017] In one embodiment, the (semi)crystalline precursor and / or retarder is in a partially crystalline state and has a melting temperature below 140°C, preferably below 130°C, or below 120°C, 110°C or 100°C, for example between 80 and 10°C, preferably between 80 and 120°C.

[0018] In another embodiment, the (semi)crystalline precursor and / or retarder has a melting temperature of the compound itself, i.e. when not present in the coating composition, below 145° C., below 130° C., preferably below 120° C., below 110° C., or even below 100° C., for example between 80 and 130° C., preferably between 80 and 120° C. The melting temperature of the (semi)crystalline precursor and / or retarder itself can be slightly higher than the melting temperature when formulated in the paint and thus when present in the coating composition.

[0019] In another embodiment, the (semi-)crystalline precursor P and optionally the (semi-)crystalline retarder T comprise a urethane backbone. The urethane backbone is prepared by reacting an isocyanate, preferably a diisocyanate, with at least a compound (i) having at least two isocyanate-reactive groups, such as hydroxyls, and preferably a diol.

[0020] Surprisingly, it has been found that when the (semi-)crystalline precursor and optionally the retarder have a urethane backbone, in particular a urethane backbone prepared from hexamethylene diisocyanate (HDI), with a selected diol and a targeted molecular weight, it provides a powder coating composition that has a suitable melting temperature to recrystallize after extrusion, has a reduced melt viscosity compared to amorphous precursor / retarder systems, and provides a coating with better adhesion and flexibility compared to amorphous precursor / retarder systems.

[0021] In a preferred embodiment, the urethane backbone of the (semi-)crystalline precursor and / or retarder is prepared by reacting hexamethylene diisocyanate (HDI) with a compound (i) comprising at least two, preferably two, isocyanate-reactive groups, preferably an alcohol, more preferably a diol.

[0022] In another preferred embodiment, the diol has a linking chain between the hydroxyl groups that contains an ether or thioether group (CH2-O-CH2, CH2-S-CH2, CH2-SS-CH2), the linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between the hydroxyl groups, or having a linking chain between the -CH(CH3)- units or -CH(CH2CH3)- containing hydroxyl groups, preferably at a central position, whereby the linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between the hydroxyl groups; The hydroxyl groups are primary hydroxyl groups and the diol is not aromatic and is not alicyclic.

[0023] It has been found that such types of diols can provide the urethane backbone of a (semi-)crystalline precursor / retarder with the desired melting temperature and crystallization tendency.

[0024] Preferably, compound (i) is a diol selected from the group consisting of diethylene glycol; triethylene glycol; 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol; thiodiethanol; 2,2'-dithiodiethanol; tetraethylene glycol; di(1,3-propanediol); di(1,4-biutanediol).

[0025] In another embodiment, the (semi-)crystalline retarder and / or precursor comprises a urethane backbone, (ia) reacting HDI with a compound (i) which is a diol and a compound (ii) which contains a hydroxyl carboxylic acid group to obtain a carboxylic acid-based (semi-)crystalline retarder T; (ib) neutralizing a carboxylic (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iia) reacting HDI with compound (i), which is a diol, to obtain a hydroxyl-terminated urethane intermediate; (iib) reacting the hydroxyl urethane intermediate with a cyclic anhydride to obtain a carboxylic acid-based (semi-)crystalline retarder T; (iic) neutralizing a carboxylic (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iiia) reacting HDI with a compound (i) which is a diol and a compound (iii) which has a hydroxyl carboxylic acid ester group to obtain a (semi-)crystalline urethane ester; (iiib) hydrolysis of the ester groups of the (semi-)crystalline urethane ester with a hydroxide to obtain a (semi-)crystalline precursor P; (iiic) optionally acidifying the (semi-)crystalline precursor of (iiib) to obtain a crystalline retarder T; (iva) reacting HDI with a compound (i) containing a diol and a compound (iv) containing hydroxyl and tertiary amine functional groups to obtain a tertiary amine-based (semi-)crystalline precursor P; (ivb) protonating a tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T, or (va) reacting HDI with a diol component (i) and a compound (v) containing hydroxyl and acrylate functional groups to obtain an acrylate-functional (semi-)crystalline intermediate; (vb) reacting the acrylate group of the acrylate-functional (semi)crystalline intermediate with a secondary amine to obtain a tertiary amine-functional semi-crystalline precursor P; (vc) protonating a tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T It is prepared by:

[0026] The cyclic anhydride used in iib is preferably succinic anhydride or maleic anhydride, Compound (ii) contains both a hydroxyl group and a carboxylic acid group and can be, for example, lactic acid, glycolic acid, hydroxypivalic acid, hydroxybutyric acid.

[0027] Compound (iii) contains a hydroxyl and a carboxylic acid ester group and can be, for example, ethyl lactate, or an alkyl ester of a hydroxy acid as generally described for compound (ii).

[0028] The skilled person will understand that the hydrolyzed (semi-)crystalline precursor P can be acidified to obtain the crystallinity retarder T.

[0029] The compound (iv) containing hydroxyl and tertiary amine functions can be, for example, dimethylethanolamine.

[0030] In yet another embodiment, the (semi)crystalline precursor is prepared by the above process, Hydrolysis and / or neutralization may be a hydroxide salt of a non-acidic cation, preferably a cation according to the formula Y(R')4, where Y represents N or P and each R' can be the same or different alkyl, aryl or aralkyl that can be attached to a polymer, preferably a quaternary ammonium or phosphonium cation, preferably the tetrabutylammonium cation or the tetraethylammonium cation; or a very strong basic amine, preferably selected from the group of amidines; preferably 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) or guanidine; preferably 1,1,3,3-tetramethylguanidine (TMG), optionally in the presence of some water It is held.

[0031] In one embodiment, the number average molecular weight of the (semi)crystalline precursor is 300-4000, preferably 500-3000 g / mol, more preferably 1000-2000 g / mol. Preferably, an excess of isocyanate reactive groups over isocyanate groups is used. Thus, preferably, the ratio of isocyanate reactive groups of compound (i) and, if present, compounds (ii), (iii), (iv) or (v) to isocyanate groups is preferably greater than 1. More preferably, the molar ratio of isocyanate reactive groups to isocyanate groups is 1.0-1.5, more preferably 1.01-1.2.

[0032] Also disclosed are (semi)crystalline precursors P or retarders T which do not use compound (i) to prepare the urethane backbone.

[0033] 10. A powder coating composition according to any one of the preceding claims, wherein in one embodiment the catalyst system is a separated catalyst system in which the (semi-)crystalline precursor P and the activator C are macro-physically separated.

[0034] According to the present invention, the term "macro-physically separated" means that the reactable compounds P and C are essentially unavailable for chemical reaction in the powder coating composition below the curing temperature. This is because the semi-(crystalline) precursor P and the acceptor C are not melt mixed (also called extrusion) together when preparing the powder coating composition. This helps to provide a powder coating composition with a longer storage time and provides a coating with a matte appearance.

[0035] In one embodiment, the (semi)crystalline precursor P may be a salt formed by an anion and a cation that is not acidic. By not acidic, it is meant that it does not have hydrogens that compete with the crosslinkable donor component A for the base and therefore does not inhibit the crosslinking reaction at the intended curing temperature. Preferably, the cation is substantially unreactive towards any component in the crosslinkable composition. The cation may be, for example, an alkali metal, a quaternary ammonium or a phosphonium, but may also be a protonated "superbase" that is unreactive towards any of the components A, B or C in the crosslinkable composition. Suitable superbases are known in the art.

[0036] In yet another embodiment, the catalyst system comprises: an activator C in an amount of 1 to 600 μeq / gr, preferably 10 to 400, more preferably 20 to 200 μeq / gr, based on the total weight of the binder components A and B and the catalyst system; a (semi)crystalline precursor P in an amount of 1 to 300 μeq / gr, preferably 10 to 200, more preferably 20 to 100 μeq / gr, relative to the total weight of the binder components A and B and the catalyst system, optionally a retarder T in an amount of 1 to 500, preferably 10 to 400, more preferably 20 to 300 μeq / gr, most preferably 30 to 200 μeq / gr, relative to the total weight of the binder components A and B and the catalyst system, Preferably, the equivalents of C are (i) if present, it is preferably in an amount of from 1 to 300 μeq / gr, preferably from 10 to 200, more preferably from 20 to 100 μeq / gr, greater than the amount of T; (ii) preferably greater than the amount of P; (iii) More preferably, it is greater than the sum of the amounts of P and T.

[0037] In yet another embodiment, the catalyst system of the powder coating composition comprises a catalyst system: a. (Semi)crystalline precursors represent 10-100 equivalent % of the sum of P and T; b. Preferably, the amount of retarder T is 20-400 equivalent % of the amount of P, preferably 30-300 equivalent %; c. Preferably, the ratio of the equivalents of C to the sum of the amounts of P and T is at least 0.5, preferably at least 0.8, more preferably at least 1, preferably at most 3, more preferably at most 2; The ratio of C to dT is preferably at least 1, preferably at least 1.5, and most preferably at least 2.

[0038] In one embodiment, the catalyst system comprises a catalyst activator composition (C) preferably comprising an activator C1 selected from the group of epoxide, carbodiimide, oxetane, oxazoline or aziridine functional components, preferably epoxides or carbodiimides.

[0039] The most preferred catalyst activators C1 contain epoxy groups. Suitable choices of epoxides as preferred activators C1 are cycloaliphatic epoxides, epoxidized oils and glycidyl-type epoxides. Suitable components C1 include C10-18 alkylene oxides and oligomers and / or polymers with epoxide functionality, including multiple epoxy functionality, as described, for example, in US Pat. No. 4,749,728, column 3, lines 21-56. Particularly suitable monoepoxides include tert-butyl glycidyl ether, phenyl glycidyl ether, glycidyl acetate, glycidyl esters of versatic esters, glycidyl methacrylate (GMA) and glycidyl benzoate. Useful multifunctional epoxides include bisphenol A diglycidyl ether and higher homologs of such BPA epoxy resins, glycidyl ethers of hydrogenated BPA such as Eponex 1510 (Hexion), ST-4000D (Kukdo), aliphatic oxiranes such as epoxidized soybean oil, diglycidyl adipate, 1,4-diglycidyl butyl ether, glycidyl ethers of novolac resins, glycidyl esters of diacids such as Araldite PT910 and PT912 (Huntsman), TGIC and other commercially available epoxy resins. Bisphenol A diglycidyl ether and its solid high molecular weight homologs are preferred epoxides. Acrylic (co)polymers with epoxide functionality derived from glycidyl methacrylate are also useful. In a preferred embodiment, the epoxy component is an oligomeric or polymeric component 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 (α-methylstyrene oxide), 2-phenoxymethyl-1,2-propene oxide, epoxidized unsaturated oils or fatty esters, and 1-phenylpropene oxide.Useful and preferred epoxides are the glycidyl esters of carboxylic acids, which may be present on a carboxylic acid functional polymer or, preferably, on a highly branched hydrophobic carboxylic acid such as Cardura E10P (glycidyl ester of Versatic™ Acid 10). Most preferred are the typical powder crosslinker epoxy components: triglycidyl isocyanurate (TGIC), Araldite PT910 and PT912, and phenolic glycidyl ethers that are naturally solid at ambient temperature, or acrylic (co)polymers of glycidyl methacrylate.

[0040] Optionally, in some preferred embodiments, the catalyst system further comprises a retarder T, which is an acid having a pKa 2, preferably 3, more preferably 4, most preferably 5 points lower than the pKa of the activated CH in the crosslinkable donor component A, which upon deprotonation produces a weak base that can act as a P1 precursor, and which can react with the activator C1 to produce a strong base that can catalyze the Michael addition reaction between A and B. The retarder T is preferably the protonated precursor P1. The retarder T can be part of the catalyst precursor composition or the catalyst activator composition. It may be part of both the catalyst precursor composition and the catalyst activator composition. Preferably, the retarder T and the protonated precursor P1 have a boiling point of at least 120°C, preferably 130°C, 150, 175, 200 or even 250°C. Preferably, the retarder T is a carboxylic acid. The use of the retarder T can have a beneficial effect in delaying the crosslinking reaction to allow more interdiffusion of the components during curing before mobility limitations become significant.

[0041] The retarder is most preferably (semi)crystalline as described above.

[0042] The pKa values ​​referred to in this patent application are aqueous pKa values ​​at ambient conditions (21° C.). They can be readily found in the literature and, if necessary, can be determined in aqueous solution by procedures known to those skilled in the art.

[0043] The reaction of retarder T and its deprotonated version P1 with activator C1 should occur at an appropriate rate so as to provide a useful delay of the crosslinking reaction under the curing conditions.

[0044] A preferred catalyst system includes an epoxy as catalyst activator C1, a weakly basic nucleophilic anion group as catalyst precursor P1 that reacts with the epoxide group of C1 to form a strongly basic adduct C1, and most preferably also includes a retarder T. In a suitable catalyst system, P1 is a carboxylate salt, C1 is an epoxide, carbodiimide, oxetane or oxazoline, more preferably an epoxide or carbodiimide, and T is a carboxylic acid. Alternatively, P1 is a tertiary amine, C1 is an epoxy, and T is a carboxylic acid.

[0045] Without wishing to be bound by theory, it is believed that the nucleophilic anion P1 reacts with the activator epoxide C1 to produce a strong base which is immediately protonated by the retarder T to produce a salt (functionally similar to P1) that does not directly and strongly catalyze the crosslinking reaction. The reaction scheme is carried out until the retarder T is substantially completely depleted, which provides an open time since during that time there is no significant amount of strong base to significantly catalyze the reaction of the crosslinkable components A and B. Once the retarder T is depleted, a strong base is formed which remains to effectively catalyze the rapid RMA crosslinking reaction.

[0046] The features and advantages of the present invention will be understood with reference to the following illustrative reaction schemes. [ka]

[0047] Specifically, for carboxylates, epoxides and carboxylic acids as the P1, C1 and T species, this can be depicted as: [ka]

[0048] In some cases, the detailed mechanism of the reaction of activator C1 with precursor P1 may not be known or is under debate, and a reaction mechanism may be suggested that involves the protonated form of P1 actually participating in the reaction. The net effect of such a reaction sequence may be similar to the sequence described based on its progression through the deprotonated form of P1. Systems are included in the present invention where the reaction may be argued to proceed along the protonated P1 pathway. In this case, after the retarder T is depleted, C1 reacts with the protonated P1 generated from the acid-base equilibrium with Michael donor species A, which activates crosslinking due to this acid-base equilibrium being drawn to the deprotonated Michael donor side.

[0049] The reaction scheme when the activator reacts via the protonated form of P1H may be shown by the following scheme: [ka]

[0050] In one embodiment, the retarders T are protonated anionic groups P1, preferably carboxylic acids T and carboxylates P1, which can be formed, for example, by partial neutralization of an acid functional component, preferably a polymer containing an acid group as retarder T, to a partial conversion to an anionic group on P1, the partial neutralization being preferably carried out with a hydroxide cation or a (bi)carbonate, preferably a tetraalkylammonium or tetraalkylphosphonium cation. In another embodiment, the polymer-bound component P1 can be made by hydrolyzing the ester groups in the polyester with the aforementioned hydroxides.

[0051] crosslinking component The powder coating composition comprises a) a crosslinkable donor component A having at least two acidic CH donor groups in an activated methylene or methine; b) a crosslinkable acceptor component B having at least two activated unsaturated acceptor groups C=C which react with component A by true Michael addition (RMA) to form a crosslinked network; The present invention further includes a crosslinkable composition comprising:

[0052] In one particular embodiment, the crosslinkable donor component A and / or the crosslinkable acceptor B are (semi-)crystalline compounds, preferably having a urethane backbone, which is preferably prepared by reacting hexamethylene diisocyanate with a compound comprising at least two isocyanate-reactive groups, preferably an alcohol, more preferably a diol.

[0053] Preferably, the diol is or having a linking chain between the hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-SS-CH2-, the linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between the hydroxyl groups; having a linking chain between the -CH(CH3)- units or -CH(CH2CH3)- containing hydroxyl groups, preferably at a central position, whereby the linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between the hydroxyl groups; The hydroxyl groups are primary hydroxyl groups and the diol is not aromatic and is not alicyclic.

[0054] The diol is preferably selected from the group consisting of diethylene glycol; triethylene glycol; 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol; thiodiethanol; dithiodiethanol; tetraethylene glycol; di(1,3-propanediol) di(1,4-butanediol).

[0055] Without wishing to be bound by theory, it is assumed that if the backbone of the donor component A and / or the cross-linkable acceptor B is similar or the same as that from the crystalline precursor B, even at low concentrations, better (co)crystallization is achieved.

[0056] Therefore, in another preferred embodiment, the urethane backbone of the (semi-)crystalline donor component A and / or the (semi-)crystalline acceptor B and the (semi-)crystalline precursor (P) have a urethane backbone prepared by the same components, preferably the urethane backbone being prepared by reacting HDI with the same compound (i) having at least two isocyanate-reactive groups, preferably a diol, as described above.

[0057] In this embodiment, preferably at least the crosslinkable donor component A and / or at least the crosslinkable acceptor component B are (semi-)crystalline, A polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), is reacted with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; Compounds (iia) which contain at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group carrying at least one acidic CH donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A, or with a compound (iib) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B. The polyurethane backbone is formed by:

[0058] According to the present invention, "substantially" means that at least 95% of the polyisocyanate used is HDI.

[0059] In one embodiment, the crosslinking component A comprises at least two acidic CH donor groups in an activated methylene or methine in the structure Z1(-C(-H)(-R)-)Z2, where R is hydrogen, a hydrocarbon, an oligomer or a polymer, and Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from keto, ester or cyano or aryl groups, preferably represented by the formula 1 [ka] wherein R is hydrogen or optionally substituted alkyl or aryl, Y and Y' are the same or different substituents, preferably alkyl, aralkyl or aryl, or alkoxy, or wherein in formula 1 -C(=O)-Y and / or -C(=O)-Y' are CN or aryl, substituted with up to one aryl, or Y or Y' may be NRR' (R and R' are H or optionally substituted alkyl), but preferably not both, and R, Y or Y' optionally provide for linkage to an oligomer or polymer, said component A being preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, preferably providing at least 50, preferably 60, 70 or even 80% of the total of CH acid groups in the crosslinkable component A, b. component B comprises at least two activated unsaturated RMA acceptor groups, preferably derived from acryloyl, methacryloyl, itaconate, maleate or fumarate functional groups; Preferably at least one of components A or B, more preferably both, is polymeric; Preferably, the composition comprises a total amount of donor groups CH and acceptor groups C=C per gram of binder solids of from 0.05 to 6 meq / gr of binder solids, and preferably the ratio of acceptor groups C=C to donor groups CH is greater than 0.1 and less than 10. Preferably, at least one of components A or B, more preferably both, is polymeric.

[0060] Preferably, the crosslinkable composition comprises a total amount of donor groups CH and acceptor groups C=C per gram of binder solids of 0.05 to 6 meq / gr of binder solids, and preferably the ratio of acceptor groups C=C to donor groups CH is greater than 0.1 and less than 10.

[0061] True Michael Addition (RMA) crosslinkable coating compositions comprising crosslinkable components A and B have been generally described for use in solvent borne systems in EP 2556108, EP 0808860 or EP 1593727, the specific descriptions of which are deemed to be incorporated herein.

[0062] Components A and B each contain an RMA reactive donor and acceptor moiety that reacts upon curing to form a crosslinked network in the coating. Components A and B can be on separate molecules, but can also be on one molecule, referred to as a hybrid A / B component or combinations thereof.

[0063] Preferably, components A and B are separate molecules, each independently in the form of a polymer, oligomer, dimer or monomer. For coating applications, at least one of components A or B is preferably an oligomer or polymer. Note that the activated methylene group CH2 contains two CH acid groups. Even if after the reaction of the first CH acid group, the reaction of the second CH acid group is more difficult, the functionality of such an activated methylene group counts as 2, for example, in reaction with methacrylates, compared to acrylates. Reactive components A and B can also be combined into one A / B hybrid molecule. In this embodiment of the powder coating composition, both CH and C=C reactive groups are present in one AB molecule.

[0064] Preferably, component A is a polymer, preferably a polyester, polyurethane, acrylic, epoxy or polycarbonate, having as functional groups component A and optionally one or more components B, or components from catalyst system C. Mixtures or hybrids of these polymer types are also possible. Suitably, component A is a polymer selected from the group of acrylic, polyester, polyesteramide, polyester-urethane polymers.

[0065] Malonate or acetoacetate are the preferred donor types in component A. In view of the high reactivity and durability in the most preferred embodiment of the crosslinkable composition, component A is a malonate CH-containing compound. In the powder coating composition, it is preferred that the majority of the activated CH groups are malonate-derived, i.e., more than 50%, preferably more than 60%, more preferably more than 70%, and most preferably more than 80% of all activated CH groups in the powder coating composition are malonate-derived.

[0066] Oligomeric and / or polymeric malonate group-containing components are preferred, such as polyesters, polyurethanes, polyacrylates, epoxy resins, polyamides and polyvinyl resins or hybrids thereof that contain malonate-type groups in the backbone, pendant or both.

[0067] The total amount of donor groups CH and acceptor groups C=C per gram of binder solids, regardless of how they are distributed over the various crosslinkable components, is preferably between 0.05 and 6 meq / gr, more typically between 0.10 and 4 meq / gr, even more preferably between 0.25 and 3 meq / gr of binder solids, most preferably between 0.5 and 2 meq / gr. Preferably, the stoichiometry between components A and B is chosen such that the ratio of reactive C=C groups to reactive CH groups is greater than 0.1, preferably greater than 0.2, more preferably greater than 0.3, most preferably greater than 0.4, and in the case of acrylate functional groups B, preferably greater than 0.5, most preferably greater than 0.75, the ratio being preferably less than 10, preferably less than 5, more preferably less than 3, 2 or 1.5.

[0068] Malonate group-containing polyesters are preferably obtainable by transesterification of methyl or ethyl diesters of malonic acid with polyfunctional alcohols which may be of polymeric or oligomeric nature, but which may also be incorporated by Michael addition reaction with other components. Particularly preferred malonate group-containing components for use in the present invention are malonate group-containing oligomeric or polymeric esters, ethers, urethanes and epoxy esters as well as hybrids thereof, such as polyester-urethanes containing 1 to 50, more preferably 2 to 10, malonate groups per molecule. The polymer component A can also be prepared in known manner, for example by radical polymerization of ethylenically unsaturated monomers containing activated CH acid (donor) groups, preferably acetoacetate or malonate groups, such as (meth)acrylates, functionalized with moieties containing 2-(methacryloyloxy)ethyl acetoacetate 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, and most preferably 1,000 to 4,000, and an Mw (expressed in GPC polystyrene equivalent) of less than 20,000, preferably less than 10,000, and most preferably less than 6,000.

[0069] Suitable crosslinking component B can generally be an ethylenically unsaturated component whose carbon-carbon double bond is activated by an electron-withdrawing group, for example, a carbonyl group at the α position.Representative examples of such components are disclosed in US Pat. No. 2,759,913 (column 6, line 35 to column 7, line 45), DE-PS No. 835,809 (column 3, line 16 to line 41), US Pat. No. 4,871,822 (column 2, line 14 to column 4, line 14), US Pat. No. 4,602,061 (column 3, line 14, line 20 to column 4, line 14), US Pat. No. 4,408,018 (column 2, line 19 to line 68) and US Pat. No. 4,217,396 (column 1, line 60 to column 2, line 64).

[0070] Preferred are acrylates, methacrylates, itaconates, fumarates and maleates. Itaconates, fumarates and maleates can be incorporated into the backbone of polyesters or polyester-urethanes. Preferred exemplary resins include polyesters, polycarbonates, polyurethanes, polyamides, acrylics and epoxy resins (or their hybrids), polyethers and / or alkyd resins that contain activated unsaturated groups. These include, for example, urethane (meth)acrylates obtained by reacting polyisocyanates with hydroxyl group-containing (meth)acrylic acid esters, such as hydroxyalkyl esters of (meth)acrylic acid, or components prepared by esterification of poly-hydroxyl components with substoichiometric amounts of (meth)acrylic acid; polyether (meth)acrylates obtained by esterification of hydroxyl group-containing polyethers with (meth)acrylic acid; multifunctional (meth)acrylates obtained by reacting hydroxyalkyl (meth)acrylates with polycarboxylic acids and / or polyamino resins; poly(meth)acrylates obtained by reacting (meth)acrylic acid with epoxy resins, and polyalkylmaleates obtained by reacting monoalkylmaleate esters with epoxy resins and / or hydroxy-functional oligomers or polymers. Also, polyesters end-capped with glycidyl methacrylate are preferred examples. The acceptor component can contain multiple types of acceptor functional groups.

[0071] The most preferred activated unsaturated group-containing components B are unsaturated acryloyl, methacryloyl and fumarate functional components. Preferably, the number average functionality of activated C=C groups per molecule is 2-20, more preferably 2-10, most preferably 3-6. The equivalent weight (EQW: average molecular weight per reactive functional group) is 100-5000, more preferably 200-2000, and the number average molecular weight is preferably Mn200-10000, more preferably 300-5000, most preferably 400-3500 g / mol, even more preferably 1000-3000 g / mol.

[0072] Considering use in powder systems, the Tg of component B is preferably greater than 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 by DSC, midpoint, heating rate of 10°C / min. If one of the components has a Tg substantially higher than 50°C, the Tg of the other formulation components may be lower, as will be understood by those skilled in the art.

[0073] Suitable component B is a urethane (meth)acrylate prepared by reacting hydroxy- and (meth)acrylate functional compounds with isocyanates to form urethane bonds, the isocyanates being preferably at least partially di- or tri-isocyanates, preferably isophorone diisocyanate (IPDI). The urethane bonds introduce rigidity by themselves, but preferably high Tg isocyanates are used, such as cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic. The amount of such isocyanates used is preferably selected so that the (meth)acrylate functional polymer Tg is raised above 40°C, preferably above 45 or 50°C.

[0074] Powder coating compositions are preferably designed such that after curing they have a crosslink density (using DMTA) that can be determined to be at least 0.025 mmol / cc, more preferably at least 0.05 mmol / cc, and most preferably at least 0.08 mmol / cc, and typically less than 3, 2, 1 or 0.7 mmol / cc.

[0075] The powder coating composition should remain a free flowing powder at ambient conditions and therefore preferably have a Tg greater than 25°C, preferably greater than 30°C, more preferably greater than 35, 40, 50°C as a mean value as determined by DSC at a heating rate of 10°C / min.

[0076] As noted above, the preferred component A is a malonate-functional component. However, the incorporation of malonate moieties tends to lower the Tg, and providing a powder coating composition based on malonate as the primary component A with a sufficiently high Tg has been a challenge.

[0077] With a view to achieving a high Tg, the powder coating composition preferably comprises a crosslinkable composition, in which the crosslinkable donor component A and / or the crosslinkable acceptor component B, which may be in the form of a hybrid component A / B, comprise an amide, urea or urethane bond and / or thereby a high Tg monomer, preferably an alicyclic or aromatic monomer, or in the case of polyesters, one or more monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetra-methyl-cyclobutanediol.

[0078] Furthermore, with a view to achieving a high Tg, the powder coating composition comprises component B or hybrid component A / B which is a polyester (meth)acrylate, polyester urethane (meth)acrylate, epoxy (meth)acrylate or urethane (meth)acrylate, or is a polyester containing fumarate, maleate or itaconate units, preferably fumarate, or is a polyester endcapped with isocyanate or epoxy functional activated unsaturated groups.

[0079] Most preferably, the powder coating composition comprises an RMA crosslinkable composition having characteristics adapted for use in an RMA crosslinkable powder coating composition, in particular with a view to achieving good flow and leveling properties, as well as good chemical and mechanical resistance, preferably in the powder coating composition at least one of the crosslinkable components A or B or hybrid A / B is a polymer, preferably selected from the group of acrylic, polyester, polyesteramide, polyester-urethane polymers, said polymer being have a number average molecular weight Mn, measured by GPC, of ​​at least 450 gr / mol, preferably at least 1000, more preferably at least 1500 and most preferably at least 2000 gr / mol, have a weight average molecular weight Mw, measured by GPC, of ​​at most 20 000 gr / mol, preferably at most 15 000, more preferably at most 10 000 and most preferably at most 7500 gr / mol, has a polydispersity Mw / Mn preferably less than 4, more preferably less than 3, an equivalent weight EQW in CH or C=C of at least 150, 250, 350, 450 or 550 gr / mol, preferably at most 2500, 2000, 1500, 1250 or 1000 gr / mol, and a number average functionality of reactive groups CH or C=C of 1 to 25, more preferably 1.5 to 15, even more preferably 2 to 15 and most preferably 2.5 to 10 CH groups / molecule, preferably has a melt viscosity of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas at a temperature in the range of 100 to 140°C, preferably comprising amide, urea or urethane bonds and / or comprising high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol, and / or It has been found to be a crystalline polymer having a median Tg of more than 25°C, preferably more than 35°C, more preferably more than 40, 50 or even 60°C, as determined by DSC at a heating rate of 10°C / min, or a melting temperature of between 40°C and 150, preferably 130°C, preferably at least 50 or even 70°C, preferably less than 120°C (determined by DSC at a heating rate of 10°C / min).

[0080] The polymer properties Mn, Mw and Mw / Mn are selected taking into account the desired powder stability on the one hand, the desired low melt viscosity on the other hand, as well as the envisaged coating properties. A high Mn is preferred to minimize the Tg-decreasing effect of end groups, and a low Mw is preferred on the other hand, since the melt viscosity is very much related to Mw and low viscosity is desirable. Thus, a low Mw / Mn is preferred.

[0081] With a view to achieving a high Tg, the RMA crosslinkable polymers preferably contain amide, urea or urethane bonds and / or contain high Tg monomers, preferably cycloaliphatic or aromatic monomers, or in the case of polyesters, monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), TCD diol, isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol.

[0082] If the RMA crosslinkable polymer is an A / B hybrid polymer, it is further preferred that the polymer also comprises one or more component B groups selected from the group of acrylate or methacrylate, fumarate, maleate and itaconate, preferably (meth)acrylate or fumarate. Furthermore, when used as a crystalline material, it is preferred that the RMA crosslinkable polymer has a crystallinity with a melting temperature (determined by DSC at a heating rate of 10° C. / min) between 40° C. and 130° C., preferably at least 50° C. or even 70° C., preferably 150, less than 130° C. or even 120° C. Note that this is the melting temperature of the (pure) polymer itself, not the melting temperature of the polymer in the composition.

[0083] In a preferred embodiment, an RMA crosslinkable polymer comprising polyesters, polyesteramides, polyester-urethanes or urethane-acrylates comprising urea, urethane or amide bonds derived from cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic isocyanates, has a Tg of at least 40°C, preferably at least 45 or 50°C, maximum 120°C and a number average molecular weight Mn of 450 to 10000, preferably 1000 to 3500 gr / mol, preferably a maximum Mn of 20000, 10000 or 6000 gr / mol, the polymer being provided with RMA crosslinkable components A or B or both. The polymer can be 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 such isocyanates added or urea / urethane bonds formed is selected such that the Tg is increased to at least 40°C, preferably at least 45 or 50°C.

[0084] Preferably, the RMA crosslinkable polymer is a polyester or polyester-urethane comprising malonate as main component A, containing a number average malonate functionality of 1-25, more preferably 1.5-15, even more preferably 2-15 and most preferably 2.5-10 malonate groups per molecule, having a GPC weight average molecular weight of 500-20000, preferably 1000-10000, most preferably 2000-6000 gr / mol, and prepared by reacting a hydroxy- and malonate-functional polymer with an isocyanate to form a urethane bond.

[0085] Furthermore, the polymer may be an amorphous or (semi)crystalline polymer or a mixture thereof. Semi-crystalline means partially crystalline and partially amorphous. (Semi)crystallinity is defined by the DSC melting endotherm, with the target crystallinity being defined as having a DSC peak melting temperature Tm of at least 40°C, preferably at least 50°C, more preferably at least 60°C, preferably up to 130, 120, 110 or 100°C. The DSC Tg of such components in a completely amorphous state is preferably below 40°C, more preferably below 30, 20 or even 10°C.

[0086] (Semi)crystalline retarders and precursors In a second aspect, the present invention relates to a (semi-)crystalline catalyst retarder T or precursor P for use in a catalyst system for crosslinking a crosslinkable composition via a true Michael addition (RMA) reaction to obtain a powder coating composition according to any one of claims 1 to 18, the catalyst retarder T precursor being (ia) reacting HDI with compound (i) which is a diol and compound (ii) which contains hydroxyl and carboxylic acid groups to obtain a carboxylic acid-based (semi-)crystalline retarder T; (ib) neutralizing a carboxylic (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iia) reacting HDI with an excess of compound (i), which is a diol, to obtain a hydroxyl-terminated urethane intermediate; (iib) reacting the hydroxyl urethane intermediate with a cyclic anhydride to obtain a carboxylic acid-based (semi-)crystalline retarder T; (iic) neutralizing a carboxylic (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iiia) reacting HDI with a compound (i) containing a diol and a compound (iii) having hydroxyl and carboxylic acid ester groups to obtain a (semi-)crystalline urethane ester; (iiib) hydrolysis of the ester groups of the (semi-)crystalline urethane ester with a hydroxide to obtain a (semi-)crystalline precursor P; (iiic) optionally acidifying said (semi-)crystalline precursor to obtain a crystalline retarder T; (iva) reacting HDI with a diol component (i) and a compound (ii) containing hydroxyl and tertiary amine functional groups to obtain a tertiary amine-based (semi-)crystalline precursor P; (ivb) protonating a tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T, or (va) reacting HDI with a diol component (i) and a compound (ii) containing hydroxyl and acrylate functional groups to obtain an acrylate-functional (semi-)crystalline intermediate; (vb) reacting the acrylate group of the acrylate-functional (semi)crystalline intermediate with a secondary amine to obtain a tertiary amine-functional semi-crystalline precursor P; (vc) protonating a tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T The present invention relates to a (semi-)crystalline catalyst retarder T or precursor P prepared by

[0087] The embodiments and preferences described for the (semi-)crystalline precursor and the retarder in the first aspect of the invention also apply to the second aspect of the invention.

[0088] Substrates and Coatings The present invention also provides a method of powder coating a substrate, comprising the steps of: a. providing a powder coating composition according to the present invention; b. applying a layer of powder to a substrate surface; c. heating, preferably using infrared heating, to a curing temperature Tcur of 75°C to 140°C, preferably 80°C to 130, 120, 110°C or even 100°C; d. Curing at Tcur for a cure time preferably less than 40, 30, 20, 15, 10 or even 5 minutes. The present invention relates to a method comprising the steps of:

[0089] The powder coating composition at Tcur preferably has a melt viscosity at the curing temperature of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas. The melt viscosity is measured at the very start of the reaction or without C2 of the catalyst system.

[0090] In a preferred embodiment of the method, the curing temperature is between 75°C and 140°C, preferably between 80°C and 120°C, and the catalyst system C is a latent catalyst system as described above that allows the powder coating of temperature-sensitive substrates, preferably MDF, wood, plastics, composites, or temperature-sensitive metal substrates such as alloys.

[0091] The present invention therefore also relates to an article, preferably having a temperature sensitive substrate like MDF, wood, plastic or metal alloy, coated with the powder coating composition of the present invention, preferably wherein the crosslink density XLD of the coating is at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / cc (determined by DMTA), and preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / cc.

[0092] The powder coating composition may further comprise additives such as additives selected from the group of pigments, dyes, dispersants, degassing aids, leveling additives, matting additives, flame retardant additives, additives for improving film forming properties, additives for the optical appearance of the coating, additives for improving mechanical properties, adhesion, or additives for stability properties such as color and UV stability. These additives may be melt mixed with one or more of the components of the powder coating composition.

[0093] Powder paints can also be designed to produce matte coatings using similar means as conventional powder coating systems, relying on additives or by deliberate heterogeneous crosslinking using either powder blend systems or systems based on blends of polymers of different reactivity.

[0094] Standard powder coating processes can be used, which typically involve solidifying the extrudate immediately after it leaves the extruder by forcing it to spread over a cooling band. The extruded paint can take the form of a solidified sheet as it travels along the cooling band. At the end of the band, the sheet is then broken into small pieces, preferably via a peg breaker, into granules. At this point, no significant shape control is applied to the granules, although a statistical maximum size is preferred. The paint granules are then transferred to a classifying microniser, which breaks down the paint to a very precise particle size distribution. The product then becomes the finished powder coating paint.

[0095] The invention is illustrated by the following non-limiting examples.

[0096] example OH value The OHV was determined by manual titration of prepared blank and sample flasks. The indicator solution is composed by dissolving 0.80 g of thymol blue and 0.25 g of cresol red in 1 L of methanol. Ten drops of indicator solution are added to the flask and then titrated with a standardized 0.5 N methanolic potassium hydroxide solution. The end point is reached when the color changes from yellow to gray to blue and a blue coloration occurs that is maintained for 10 seconds. The hydroxyl value is then calculated according to the following: Hydroxy value = (BS) x N x 56.1 / M + AV During the ceremony, B = ml of KOH used for blank titration S = ml of KOH used in sample titration N = normality of potassium hydroxide solution M = weight of sample (base resin) AV = Acid value of base resin Net hydroxy value is defined as follows: Net OHV = (BS) x N x 56.1 / M

[0097] Amine Number A freshly prepared solvent blend of 3:1 xylene:ethanol propanol is prepared. A certain amount of resin is accurately weighed into a 250 ml Erlenmeyer flask. Then, 50-60 ml of 3:1 xylene:ethanol is added. The solution is gently heated until the resin is completely dissolved, being careful not to allow the solution to boil. The solution is then cooled to room temperature and titrated potentiometrically with 0.1 M hydrochloric acid until after the equivalence point.

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

[0099] DSC Tg Resin and coating glass transition temperatures reported herein are those of the midpoint Tg determined from differential scanning calorimetry (DSC) using a heating rate of 10° C. / min.

[0100] Shock-resistance Impact testing was performed on powder coated panels on both the coated and reverse sides according to ASTM D 2794. The maximum impact that does not cause the coating to crack is recorded in inch-pounds (in.lb).

[0101] Solvent resistance The solvent resistance of the cured film is measured by rubbing twice with a small cotton ball saturated with methyl ethyl ketone (MEK) and judged using the following rating system (0-5, best to worst): 0. No noticeable change. Cannot scratch with fingernail 1. Slight loss of gloss 2. Some loss of gloss 3. The coating is very dull and can be scratched with fingernails 4. The coating is very dull and very soft 5. The coating is cracked

[0102] Abbreviation [Table 1] [Table 1-2]

[0103] Preparation of amorphous materials Preparation of malonate donor resin M-1 A 5 liter round bottom reactor equipped with a 4-way cap, metal anchor stirrer, Pt-100, packed column with top thermometer, condenser, distillate collection vessel, thermocouple and N2 inlet was charged with 1300 g of isosorbide (80%), 950 g of NPG and 1983 g of TPA. The temperature of the reactor was gently increased to about 100°C and 4.5 g of Ken-React® KR46B catalyst was added. The reaction temperature was further increased gradually to 230°C and polymerization was allowed to proceed under nitrogen with continuous stirring until the reaction mixture became clear and the acid number was less than 2 mg KOH / g. During the last part of the reaction, a vacuum was applied to complete the reaction. The temperature was reduced to 120°C and 660 g of diethyl malonate was added. The temperature of the reactor was then increased to 190°C and maintained until no more ethanol was formed. Again, a vacuum was applied to complete the reaction. After the transesterification reaction was complete, the hydroxyl number of the polyester was measured: final OHV was 27 mg KOH / g, GPC Mn was 1763 and Mw was 5038, Tg(DSC) was 63°C.

[0104] Preparation of urethane acrylate acceptor resin UA-1 A urethane-acrylate based on IPDI, hydroxypropyl acrylate, glycerol is prepared with the addition of a suitable polymerization inhibitor, for example as described in EP 0585742. A 5 liter reactor equipped with a thermometer, stirrer, dosing funnel and gas bubbling inlet is charged with 1020 parts of IPDI, 1.30 parts of DBTL and 4.00 parts of hydroquinone. 585 parts of hydroxypropyl acrylate are then charged, avoiding the temperature rising above 50°C. Once the addition is complete, 154 parts of glycerin are added. 15 minutes after the exothermic reaction has subsided, the reaction product is cast on a metal tray. The resulting urethane acrylate is characterized by a GPC Mn of 744 and Mw of 1467, a Tg (DSC) of 51°C, a residual isocyanate content of less than 0.1%, and a theoretical unsaturation EQW of 392 g / mol.

[0105] Preparation of Carboxylate-Terminated Retardant Resin T-1 A 5 liter round bottom reactor equipped with a 4-way top, metal anchor stirrer, Pt-100, packed column with top thermometer, condenser, distillate collection vessel, thermocouple and N2 inlet was charged with 1180 g of NPG and 2000 g of IPA. The temperature of the reactor was increased to 230°C and the polymerization was allowed to proceed under nitrogen with continuous stirring until the reaction mixture became clear. The final product obtained has an AV of 48 mg KOH / g and a Tg (DSC) of 55°C.

[0106] Preparation of catalyst precursor P-1 To prepare the catalyst precursor, carboxylate-terminated polyester resin (AV 48) was melted and mixed with an aqueous solution of tetraethylammonium bicarbonate TEAHCO3 (41%) using a Leistritz ZSE 18 twin-screw extruder. The extruder contained a barrel housing nine successive heating zones set to maintain the following temperature profile from inlet to outlet: 30-50-80-120-120-120-120-100-100 (in °C). Solid polyester resin was added at a rate of 2 kg / hr through the first zone, and liquid TEAHCO3 was injected at 0.60 kg / hr through the second zone. Mixing was performed between zones 4-7, with the screws set to rotate at 200 rpm. Volatiles and water evolved from the acid-base neutralization were removed using a vacuum in zone 7. After leaving the die, the extruded strands were immediately cooled and collected. The final product obtained has an AV of 11 mg KOH / g, an amine value of 33 KOH / g and a Tg(DSC) of 48°C.

[0107] Preparation of (semi)crystalline materials Preparation of (semi)crystalline urethane acrylate resin CUA-1 504.6 g HDI, 1 g DBTL and 5 g butylated hydroxytoluene (BHT) were charged into a 2 liter round bottom reactor and heated to 50° C. under dry air. A mixture of 288.3 g hydroxybutyl acylate and 212.2 g DEG was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120° C. The resulting (semi)crystalline urethane acrylate product has maximum and end DSC melting temperatures of 106° C. and 113° C., respectively. Theoretical unsaturation EQW=506 g / mol.

[0108] Preparation of the (semi)crystalline acid retarders and corresponding catalyst precursors according to the invention CT-1&CP-1 379.3 g of DEG and 1 g of DBTL were charged into a 2 liter round bottom reactor and heated to 50°C. Then 497.9 g of HDI was added dropwise to the reactor to initiate the reaction under nitrogen protection, maintaining the process temperature below 120°C. After that, 122.8 g of succinic anhydride was charged into the reactor. The reaction is allowed to proceed at 120°C until the desired acid number is achieved. The resulting final product CT-1 has an AV of 69 mg KOH / g, a Tg(DSC) of -5°C, and maximum and end DSC melting temperatures of 115°C and 125°C, respectively.

[0109] To prepare the corresponding catalyst precursor CP-1, 1790 g of CR-1 was charged into a reactor and melted by heating to 125°C. Then, 842.5 g of tetraethylammonium hydroxide (TEAOH) aqueous solution (35%) was slowly added to the reactor and mixed with the molten crystalline acid resin under continuous stirring. The volatiles and water evolved from the acid-base neutralization were removed using vacuum. The resulting final product CP-1 has an AV of 36 mg KOH / g, an amine value of 44 mg KOH / g, a Tg(DSC) of -5°C, and maximum and end DSC melting temperatures of 110°C and 120°C, respectively.

[0110] CT-2&CP-2 324.3g of DEG and 1g of DBTL were charged into a 2 liter round bottom reactor and heated to 50°C. Then, 401.2g of hexamethylene diisocyanate (HDI) was added dropwise into the reactor to initiate the reaction under nitrogen protection, and the process temperature was maintained below 120°C. After that, 136.8g of hydroxypivalic acid was charged into the reactor and the reaction was allowed to proceed at 120°C until complete homogenization was achieved. Finally, another portion of 166.3g of HDI was slowly charged into the reactor over a period of 30 minutes. The resulting final product CT-2 has an AV of 64mgKOH / g, a Tg(DSC) of 10°C, and maximum and end DSC melting temperatures of 120°C and 128°C, respectively.

[0111] To prepare the corresponding catalyst precursor CP-2, 700 g of CR-1 was charged into a reactor and melted by heating to 125°C. Then, 169.7 g of tetraethylammonium hydroxide (TEAOH) aqueous solution (35%) was slowly added to the reactor and mixed with the molten crystalline acid resin under continuous stirring. The volatiles and water evolved from the acid-base neutralization were removed using vacuum. The resulting final product CP-2 has an AV of 23 mg KOH / g, an amine value of 29 mg KOH / g, a Tg(DSC) of 10°C, and maximum and end DSC melting temperatures of 121°C and 128°C, respectively.

[0112] CT-3 41.68 g of hydroxybipallic acid and 100.5 g of 3-methyl-1,5-pentanediol were charged into a 2 liter round bottom reactor. The mixture was mixed and heated to 60°C. Then 172.8 g of HDI was added dropwise to the reactor to initiate the reaction under nitrogen protection. The reaction was allowed to proceed at about 110°C until all the isocyanate groups had reacted. The resulting final product, CT-3, has an AV of 63 mg KOH / g, a Tg(DSC) of 9°C, and maximum and end DSC melting temperatures of 88°C and 99°C, respectively.

[0113] CT-4 324.3 g of DEG, 136.8 g of hydroxypivalic acid and 1 g of DBTL were charged into a 2 liter round bottom reactor and heated to 50° C. Then, 401.2 g of hexamethylene diisocyanate (HDI) was added dropwise to the reactor to initiate the reaction under nitrogen protection, and the process temperature was maintained below 120° C. until all the isocyanate groups had reacted. The resulting final product, CT-4, has a theoretical AV of 64 mg, maximum and final DSC melting temperatures of 116° C. and 122° C., respectively.

[0114] CP-5 The (semi)crystalline catalyst precursor CP-5 was prepared by a two-step route. In the first step, 0.029 g DBTL, 32.3 g ethyl lactate, and 75.5 g DEG were charged to the reaction vessel. The reaction mixture was at 60° C. when HDI feed was started. A total of 142.2 g HDI was fed dropwise and the temperature was slowly increased to 110° C. over 1 h. Towards the end of the reaction, when some crystallization was visible, additional heat was added to increase the temperature to 120° C. The reaction was then allowed to proceed at 120° C. for 20 min after HDI addition was complete. The theoretical Mn of this product is expected to be 1800 and the EQW of the ester is expected to be 900 g / mol. DSC analysis showed maximum and final melting temperatures of 133° C. and 140° C., respectively. In the second step, 127.9 g of the product obtained in the first step was charged into a reactor equipped with a stirrer, thermometer, dropping funnel and distillation apparatus. The crystalline polyurethane was carefully melted to a temperature of 135°C. Then, 44 g of tetraethylammonium hydroxide (TEAOH) aqueous solution (35%) was slowly added to the reactor and mixed with the molten crystalline acid resin under continuous stirring. Volatiles (water and ethanol) were removed with the aid of some N2 flow to the reaction mass. The feeding and distillation steps took about 1 hour, during which the temperature was maintained at 125-135°C. The final product obtained, CP-5, has an amine value of 24 mg KOH / g, maximum and end DSC melting temperatures of 109°C and 123°C, respectively.

[0115] CP-6 The reaction vessel was charged with a mixture of 6 mg DBTL, 14.3 g DEG and 6.87 g dimethylethanolamine and heated to 60° C. At this point, HDI (total 29.1 g) was fed to begin. The reaction mass was slowly ramped up to 105° C. over the course of the feeds, over the course of 50 minutes. At the end of the feed step, when crystallization was visible, additional heat was added to raise the temperature to 120° C. Heating was continued for an additional 20 minutes after the feeds were complete. The resulting final product, CP-6, has a ttheoretical expected Mn of 1300, an amine EQW of 650 g / mol, and maximum and end DSC melting temperatures of 110° C. and 117° C., respectively.

[0116] Preparation of Powder Coating Compositions To prepare the powder coating compositions, the raw materials were first premixed in a high speed Thermoprism Pilot Mixer 3 premixer at 1500 rpm for 20 seconds and then extruded in a Baker Perkins (formerly APV) MP19 25:1 LD twin screw extruder. The extruder speed was 250 rpm and the four extruder barrel zone temperatures were set at 15, 25, 100 and 100°C to extrude amorphous resins, or 15, 25, 120 and 100°C to extrude (semi)crystalline resins. After extrusion, the extrudate was ground using a Retsch GRINDOMIX GM 200 knife mill. The ground extrudate was sieved to less than 100 μm using a Russel Finex 100 micron mesh Demi Finex laboratory vibrating sieve.

[0117] result PW1 (comparative) and PW2-PW5 (inventive) are examples of powder coatings stoichiometrically formulated to have a reactive acryloyl / C-H2 ratio of 1.5:1, 50 meq of catalyst precursor, 50 meq of acid retarder and 200 meq of activator, as listed in Table 2. All coatings were sprayed on aluminum and steel panels at 80-100 μm film thickness and cured at 120 °C for 22 minutes. Coating analysis and application results are summarized in Table 3.

[0118] [Table 2]

[0119] PW1 is a comparative benchmark paint prepared with only amorphous components. The paint has a Tg of 56°C and can be cured well after 22 minutes at 120°C, as evidenced by good solvent resistance. However, it has no adhesion or impact resistance to both aluminum and steel substrates.

[0120] PW2 was prepared by replacing the amorphous catalyst precursor P-1 with the (semi)crystalline CP-1. The effect of the (semi)crystalline material on the coating Tg was negligible, and a decrease in the coating Tg per 1 °C was determined by DSC analysis. This is strong evidence that most of the (semi)crystalline catalyst precursor recrystallized in the coating after extrusion. The DSC scan of the PW2 coating (Figure 1) shows a melting peak in the same melting range as CP-1 (delta H due to melting = 0.24 J / g). This also suggests that most of the (semi)crystalline catalyst precursor is in the form of crystals within the amorphous matrix of the coating. The cure rate is comparable to the amorphous catalyst, since good solvent resistance can be achieved. The (semi)crystalline precursor CP-1 significantly improved the adhesion of the coating on the metal substrate, with perfect adhesion being obtained. In addition, the mechanical properties of the film are slightly improved in terms of impact resistance. This is probably because CP-1 plasticized the cured film, as evidenced by a 2°C decrease in the cured film Tg.

[0121] PW3 was formulated with both the (semi)crystalline acid retarder CT-1 and the precursor CP-1. As the majority of the (semi)crystalline components are believed to have recrystallized in the coating after extrusion, the coating still has a relatively high Tg. This is evidenced by an increase in delta H to 0.31 J / g. Application results show good solvent resistance. Adhesion and impact resistance are also improved compared to PW1. [Table 3]

[0122] PW4 was prepared using an alternative (semi)crystalline catalyst precursor, CP-2. CP-2 has the same backbone as CP-1, but the terminal carboxylate was prepared by reacting a hydroxyl acid with an isocyanate group. The coating has a slightly lower Tg due to the higher amount of (semi)crystalline in the formulation. It is still believed that most of the CP-2 recrystallized in the coating after extrusion, and the delta H increased to 0.46 J / g. Compared to the fully amorphous formulation PW1, the coating results also showed advantages for adhesion and impact resistance.

[0123] PW5 was prepared with the (semi)crystalline urethane acrylate acceptors CUA-1 and CP-2. Compared to PW4, the further addition of the (semi)crystalline acceptors did not decrease the Tg of the paint. It is believed that CUA-1 and CP-2 can recrystallize together in the paint since they have similar backbone structures. The DSC scan of PW5 (Figure 2) clearly demonstrates the presence of crystals in the amorphous matrix of the paint, with the melting peaks in good agreement with the melting ranges of CUA-1 and CP-2.

Claims

1. A powder coating composition comprising a crosslinkable composition and a catalyst system, said crosslinkable composition being formed by a crosslinkable donor component A and a crosslinkable acceptor component B crosslinkable by a true Michael addition (RMA) reaction via said catalyst system, said catalyst system being capable of catalysing said RMA crosslinking reaction at a curing temperature below 140°C, preferably below 120°C, even more preferably below 110°C or below 100°C, preferably at least 70°C, preferably at least 80, 90 or 100°C, The crosslinkable composition comprises: a) a crosslinkable donor component A having at least two acidic C—H donor groups in activated methylene or methine; b) said crosslinkable acceptor component B having at least two activated unsaturated acceptor groups C=C which react with component A by true Michael addition (RMA) to form a crosslinked network; Including, said catalytic system comprising a (semi-)crystalline precursor P, an activator C and optionally a retarder T, said (semi-)crystalline precursor P is a weak base whose protonated form has a pKa of more than 2 units, preferably more than 3 units, more preferably more than 4 units and even more preferably at least 5 units lower than the pKa of the activated C-H groups in said donor component A, and said activator C is capable of reacting with P at the curing temperature to produce a strong base (CP) capable of catalysing said Michael addition reaction between A and B, said retarder T is preferably a (semi)crystalline retarder, said retarder T being an acid having a pKa of more than 2 points, more preferably more than 3 points, even more preferably more than 4 or 5 points lower than the pKa of the activated C-H in A, which upon deprotonation generates a weak base capable of reacting with said activator C and a strong base capable of catalyzing said Michael addition reaction between said crosslinkable compositions A and B, Powder coating compositions.

2. 2. The powder coating composition according to claim 1, wherein the (semi-)crystalline precursor and / or the (semi-)crystalline retarder are in a partially crystalline state and have a melting temperature below 140, 130°C, preferably below 120°C, 110°C or even below 100°C, and wherein the precursor and / or retarder comprise a urethane backbone.

3. 2. The powder coating composition according to claim 1, wherein the (semi-)crystalline precursor P and / or the (semi-)crystalline retarder T have a urethane backbone prepared by reacting hexamethylene diisocyanate (HDI) with at least a compound (i) comprising at least two, preferably two, isocyanate-reactive groups, preferably hydroxyls, more preferably a diol.

4. The (semi)crystalline retarder T and / or precursor P contain a urethane skeleton, (ia) reacting HDI with compound (i) which is a diol and compound (ii) which contains hydroxyl and carboxylic acid functional groups to obtain a carboxylic acid-based (semi-)crystalline retarder T; (ib) neutralizing said carboxylic acid-based (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iia) reacting HDI with a stoichiometric excess of compound (i), which is a diol, to obtain a hydroxyl-terminated urethane intermediate; (iib) reacting said hydroxyl urethane intermediate with a cyclic anhydride to obtain a carboxylic acid-based (semi-)crystalline retarder T; (iic) neutralizing said carboxylic acid-based (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iiia) reacting HDI with compound (i), which is a diol, and compound (iii), which has hydroxyl and carboxylic acid ester functional groups, to obtain a (semi-)crystalline urethane ester; (iiib) hydrolyzing the ester groups of said (semi-)crystalline urethane ester with a hydroxide to obtain a (semi-)crystalline precursor P; (iiiic) optionally acidifying said (semi)crystalline precursor of (iiib) to obtain a crystalline retarder T; (iva) reacting HDI with compound (i), which is a diol, and compound (iv), which contains hydroxyl and tertiary amine functional groups, to obtain a tertiary amine-based (semi-)crystalline precursor P; (ivb) protonating said tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T, or (va) reacting HDI with compound (i), which is a diol, and compound (v), which contains hydroxyl and acrylate functional groups, to obtain an acrylate-functional (semi-)crystalline intermediate; (vb) reacting the acrylate groups of said acrylate-functional (semi)crystalline intermediate with a secondary amine to obtain a tertiary amine-functional semi-crystalline precursor P; (vc) protonating said tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T; 10. The powder coating composition of claim 1 prepared by:

5. The (semi)crystalline precursor P is prepared according to claim 4, wherein the hydrolysis and / or neutralization is - hydroxide salts of non-acidic cations, preferably cations according to formula Y(R')4, where Y represents N or P and each R' can be the same or different alkyl, aryl or aralkyl that can be bonded to a polymer, preferably quaternary ammonium or phosphonium cations, preferably the tetrabutylammonium or tetraethylammonium cations; or a very strong basic amine, preferably selected from the group of amidines; preferably 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) or guanidine; preferably 1,1,3,3-tetramethylguanidine (TMG), optionally in the presence of some water The powder coating composition of claim 4 .

6. The diol (i) is having a linking chain between said hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-S-S-CH2-, said linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between said hydroxyl groups; or having linking chains between said hydroxyl groups containing -CH(CH3)- units or -CH(CH2CH3)-, preferably at a central position, whereby said linking chains have a chain length with an uneven number of less than 6 carbon atoms and / or heteroatoms between said hydroxyl groups; the hydroxyl groups are primary hydroxyl groups, and the diol is non-aromatic and non-alicyclic; The powder coating composition of claim 3.

7. 4. The powder coating composition of claim 3, wherein the compound (i) containing at least two isocyanate reactive groups is a diol selected from the group consisting of diethylene glycol, triethylene glycol, 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol, 2,2'-thiodiethanol, 2,2'-dithiodiethanol, tetraethylene glycol, di-1,3-propanediol, di(1,4-butanediol).

8. 4. A powder coating composition according to claim 3, wherein the ratio of said isocyanate reactive groups of compound (i) and, if present, compounds (ii), (iii), (iv) or (v) to said isocyanate groups is preferably greater than 1, more preferably the molar ratio of said isocyanate reactive groups to isocyanate groups is from 1.0 to 1.5, more preferably from 1.01 to 1.

2.

9. 2. Powder coating composition according to claim 1, wherein the (semi)crystalline retarder has a number average molecular weight of 300-4000, preferably 500-3000, more preferably 1000-2000 g / mol.

10. 2. The powder coating composition according to claim 1, wherein the catalyst system is a separated catalyst system in which the (semi-)crystalline precursor P and the activator C are macro-physically separated.

11. said activator C is selected from the group consisting of epoxide, carbodiimide, oxetane, oxazoline or aziridine functional components, preferably epoxides or carbodiimides; said (semi)crystalline precursor P is a carboxylate or a tertiary amine, said retarder T is preferably a protonated precursor P; The powder coating composition of claim 1.

12. an activator C in an amount of 1 to 600 μeq / gr, preferably 10 to 400, more preferably 20 to 200 μeq / gr, relative to the total weight of the binder components A and B and the catalyst system; a (semi)crystalline precursor P in an amount of 1 to 300 μeq / gr, preferably 10 to 200, more preferably 20 to 100 μeq / gr, relative to the total weight of the binder components A and B and the catalyst system; optionally a retarder T in an amount of 1 to 500, preferably 10 to 400, more preferably 20 to 300 μeq / gr, most preferably 30 to 200 μeq / gr, relative to the total weight of the binder components A and B and the catalyst system, Preferably, the equivalents of C are (i) when present, preferably in an amount of from 1 to 300 μeq / gr, preferably from 10 to 200, more preferably from 20 to 100 μeq / gr, greater than the amount of T; (ii) preferably greater than the amount of P; (iii) more preferably, greater than the sum of the amounts of P and T; The powder coating composition of claim 1.

13. a. each of said (semi)crystalline precursors P represents 10-100 equivalent % of the sum of P and T; b. Preferably, the amount of retarder T is 20-400 equivalent percent, preferably 30-300 equivalent percent, of the amount of P; c. Preferably, the ratio of the equivalents of C to the sum of the amounts of P and T is at least 0.5, preferably at least 0.8, more preferably at least 1, preferably at most 3, more preferably at most 2; d. The ratio of C to T is preferably at least 1, preferably at least 1.5, and most preferably at least 2; The powder coating composition of claim 1.

14. 2. Powder coating composition according to claim 1, wherein the crosslinkable donor component A and / or the acceptor component B are (semi-)crystalline compounds, preferably having a urethane backbone, which are preferably prepared by reacting hexamethylene diisocyanate with a compound comprising at least two isocyanate-reactive groups, preferably an alcohol, more preferably a diol.

15. the urethane skeleton of the (semi-)crystalline donor component A and / or the (semi-)crystalline acceptor B and the (semi-)crystalline precursor (P) has a urethane skeleton prepared by reacting HDI with at least a compound (i) having at least two isocyanate-reactive groups that are the same as those of the (semi-)crystalline precursor (P) and the (semi-)crystalline donor component A and / or the (semi-)crystalline acceptor B, The compound (i) is preferably a diol, and the diol is having a linking chain between said hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-S-S-CH2-, said linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between said hydroxyl groups; or having a linking chain between said hydroxyl groups containing -CH(CH3)- units or -CH(CH2CH3)-, preferably at a central position, whereby said linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between said hydroxyl groups; the hydroxyl groups are primary hydroxyl groups, and the diol is non-aromatic and non-alicyclic; 15. The powder coating composition of claim 14.

16. a. the crosslinkable component A comprises at least two acidic C—H donor groups in activated methylene or methine in the structure Z1(—C(—H)(—R)—)Z2, where R is hydrogen, hydrocarbon, oligomer or polymer, Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from keto, ester or cyano or aryl groups, preferably represented by the formula 1 【Chemistry 1】 wherein R is hydrogen or optionally substituted alkyl or aryl, and Y and Y' are the same or different substituents, preferably alkyl, aralkyl or aryl, or alkoxy, or in which in formula 1 -C(=O)-Y and / or -C(=O)-Y' may be CN or aryl, substituted with up to one aryl, or Y or Y' may be NRR', where R and R' are H or optionally substituted alkyl, but preferably not both, and R, Y or Y' optionally provide for linkage to an oligomer or polymer, said component A being preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, preferably providing at least 50, preferably 60, 70 or even 80% of the total of the C-H acidic groups in the crosslinkable component A, b. component B comprises said at least two activated unsaturated RMA acceptor groups, preferably derived from acryloyl, methacryloyl, itaconate, maleate or fumarate functional groups; Preferably at least one of components A or B, more preferably both, is polymeric; 2. A powder coating composition according to claim 1, wherein the composition preferably comprises a total amount of donor groups C-H and acceptor groups C=C per gram of binder solids of from 0.05 to 6 meq / gr of binder solids, and preferably the ratio of acceptor groups C=C to donor groups C-H is greater than 0.1 and less than 10.

17. At least one crosslinkable component A or B or hybrid A / B is preferably a polymer selected from the group of acrylic, polyester, polyesteramide, polyester-urethane polymers, said polymer being having a number average molecular weight Mn, measured by GPC, of ​​at least 450 gr / mol, preferably at least 1000, more preferably at least 1500 and most preferably at least 2000 gr / mol; have a weight average molecular weight Mw of at most 20 000 gr / mol, preferably at most 15 000, more preferably at most 10 000 and most preferably at most 7 500 gr / mol, as determined by GPC; has a polydispersity Mw / Mn preferably less than 4, more preferably less than 3, an equivalent weight EQW in C—H or C═C of at least 150, 250, 350, 450 or 550 gr / mol, preferably at most 2500, 2000, 1500, 1250 or 1000 gr / mol, and a number average functionality of reactive groups C—H or C═C of from 1 to 25, more preferably from 1.5 to 15, even more preferably from 2 to 15 and most preferably from 2.5 to 10 C—H groups per molecule, preferably has a melt viscosity of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas at a temperature in the range of 100 to 140°C; preferably comprising amide, urea or urethane bonds and / or comprising high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol, and / or - is a (semi)crystalline polymer with a mean Tg, determined by DSC at a heating rate of 10°C / min, of more than 25°C, preferably more than 35°C, more preferably more than 40, 50 or even 60°C, or a melting temperature (determined by DSC at a heating rate of 10°C / min) of between 40°C and 150, preferably 130°C, preferably at least 50 or even 70°C, preferably less than 120°C; The powder coating composition of claim 1.

18. 2. The powder coating composition of claim 1, wherein the acceptor component B is a polyester (meth)acrylate, polyester urethane (meth)acrylate, epoxy (meth)acrylate or urethane (meth)acrylate, or a polyester containing fumarate, maleate or itaconate units, preferably fumarate, or a polyester endcapped with isocyanate or epoxy functional activated unsaturated groups.

19. A (semi)crystalline catalyst retarder T or precursor P suitable for use in a catalyst system for crosslinking a crosslinkable composition via a true Michael Addition (RMA) reaction to obtain a powder coating composition according to claim 1, said catalyst retarder T and / or precursor P being: (ia) reacting HDI with a compound (i) which is a diol and a compound (ii) which contains a hydroxyl carboxylic acid group to obtain a carboxylic acid-based (semi-)crystalline retarder T; (ib) neutralizing said carboxylic acid-based (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iia) reacting HDI with compound (i), which is a diol, to obtain a hydroxyl-terminated urethane intermediate; (iib) reacting said hydroxyl urethane intermediate with a cyclic anhydride to obtain a carboxylic acid-based (semi-)crystalline retarder T; (iic) neutralizing said carboxylic acid-based (semi-)crystalline retarder T to obtain a (semi-)crystalline precursor P, or (iiia) reacting HDI with a compound (i) which is a diol and a compound (iii) which has a hydroxyl carboxylic acid ester group to obtain a (semi-)crystalline urethane ester; (iiib) hydrolyzing the ester groups of said (semi-)crystalline urethane ester with a hydroxide to obtain a (semi-)crystalline precursor P; (iiiic) optionally acidifying said (semi)crystalline precursor of (iiib) to obtain a crystalline retarder T; (iva) reacting HDI with a diol component (i) and a compound (iv) containing hydroxyl and tertiary amine functional groups to obtain a tertiary amine-based (semi-)crystalline precursor P; (ivb) protonating said tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T, or (va) reacting HDI with a diol component (i) and a compound (v) containing hydroxyl and acrylate functional groups to obtain an acrylate-functional (semi-)crystalline intermediate; (vb) reacting the acrylate groups of said acrylate-functional (semi)crystalline intermediate with a secondary amine to obtain a tertiary amine-functional semi-crystalline precursor P; (vc) protonating said tertiary amine-based (semi-)crystalline precursor P to obtain a (semi-)crystalline retarder T; 4. A (semi)crystalline catalyst retarder T or precursor P prepared by:

20. 20. The (semi)crystalline catalyst retarder T or precursor P according to claim 19, wherein the (semi)crystalline precursor and / or the (semi)crystalline retarder has a melting temperature of the compound itself which is below 145°C, below 130°C, preferably below 120°C, below 110°C or below 100°C, for example between 80 and 130°C, preferably between 80 and 120°C.

21. A (semi-)crystalline catalyst retarder T or (semi-)crystalline precursor P as described in claim 19, having the characteristics as described in claim 1.

22. 1. A method of powder coating a substrate, comprising: a. applying a layer comprising the powder coating composition of claim 1 to a substrate surface, said substrate being preferably a temperature sensitive substrate, preferably a temperature sensitive metal substrate such as MDF, wood, plastic, composite or alloy; b. heating, preferably using infrared heating, to a curing temperature Tcur of 75-140°C, more preferably 80-130, 120, 110 or even 100°C, wherein said melt viscosity at said curing temperature Tcur is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas; c. Curing at Tcur for a cure time of preferably less than 40, 30, 20, 15, 10, or even 5 minutes. A method comprising:

23. A powder coated article having the powder coating composition according to claim 1, preferably having a temperature sensitive substrate, preferably selected from the group of MDF, wood, plastic, composites or metal alloys, preferably having a crosslink density XLD of at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / ml (as determined by DMTA), preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / ml.

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