Two-component powder coating composition having a separated catalyst system

Abstract

The present invention relates to a two-component powder coating composition AB comprising coating component A and coating component B, the powder coating composition AB comprising a crosslinkable composition formed by a crosslinkable donor component (i) and a crosslinkable acceptor component (ii) capable of crosslinking by a true Michael addition (RMA) reaction, and a catalyst system comprising a catalyst precursor (P) and a catalyst activator (C), the catalyst precursor (P) and the catalyst activator (C) being separated such that coating component A comprises the catalyst precursor (P) and coating component B comprises the catalyst activator (C), and optionally the donor component (i), the acceptor component (ii), the catalyst precursor (P), and the catalyst activator (C). and a non-RMA-reactive component (iii) which is different from the catalyst system, the crosslinkable composition, and, if present, the non-RMA-reactive component (iii) and is not a pigment or a filler, wherein the coating composition AB comprises a crystalline component CC present in an amount of 1 to 50 wt. % based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA-reactive component (iii), and at least a portion of the donor component (i) and / or the acceptor component (ii) and / or the non-RMA-reactive component (iii) is the crystalline component CC, and wherein both paint components A and B comprise the donor component (i) and the acceptor component (ii).

Description

[Technical Field]

[0001] The present invention relates to a two-component powder coating composition AB comprising a crosslinkable composition crosslinkable via true Michael addition (RMA) and a separate catalyst system comprising a precursor P and an activator C, a method for preparing the two-component powder coating composition, a method for coating an article with the powder coating composition, and the coated article. [Background technology]

[0002] Powder coatings are dry, finely divided, free-flowing materials that are solid at room temperature and have recently become more popular than liquid coatings. Powder coatings are typically cured at elevated temperatures, typically between 120°C and 200°C, more commonly between 140°C and 180°C. High temperatures are necessary not only to allow the binder to flow sufficiently to allow film formation and achieve a good coating surface appearance, but also to achieve high reactivity in the crosslinking reaction. At lower curing temperatures, reaction kinetics can be encountered that do not allow for short cure times if sufficient mechanical and resistance properties are desired. On the other hand, in systems where high reactivity of components can be produced, the relatively high viscosity of such systems at these lower temperatures tends to result in poor coating appearance, which rapidly increases as the curing reaction proceeds; i.e., the time-integrated flow of such systems is too low to achieve adequate planarization (see, for example, Progress in Organic Coatings, 72, pp. 26-33 (2011)).

[0003] Patent application WO 2019 / 145472 describes a powder coating composition that provides a glossy coating on substrates, such as medium density fiberboard (MDF), wood, plastics, and certain metal alloys, which are heat-sensitive substrates, and can be cured at low temperatures. The coating composition is curable by RMA using a catalyst system consisting of a catalyst precursor and a catalyst activator.

[0004] Patent applications CN112457751 and CN112457752 describe low-temperature RMA curable compositions containing a donor, an acceptor and a (semi-)crystalline component, and an RMA catalyst activator is added as a separate compound to the coating components containing the RMA donor, the RMA acceptor and the RMA catalyst precursor, resulting in powder coatings with not too low gloss values.

[0005] Many powder coating compositions provide coatings with high gloss after curing. There is a growing demand for powder coatings and resins that provide coatings with excellent quality and exhibit reduced gloss. Furthermore, it would be advantageous to be able to apply such types of coatings to heat-sensitive substrates such as medium density fiberboard (MDF), wood, plastics, and certain metal alloys.

[0006] Therefore, there is a need for a powder coating composition that has excellent properties, such as being able to cure at low temperatures, providing a very low gloss, dead matte coating while maintaining excellent mechanical and chemical resistance, adhesion and flow upon cure, and ensuring a long shelf life upon storage, being able to react quickly, and the coating having a smooth finish. Summary of the Invention

[0007] The present invention addresses one or more of the above problems by providing a two-component powder coating composition AB as set forth in claim 1.

[0008] Accordingly, a first aspect of the present invention is a two-component powder coating composition AB comprising a coating component A and a coating component B, said powder coating composition AB comprising: A crosslinkable composition formed by a crosslinkable donor component (i) and a crosslinkable acceptor component (ii) that are crosslinkable by a true Michael addition (RMA) reaction, The donor component (i) has at least two activated methylene or methine acidic CH donor groups, and The acceptor component (ii) has at least two activated unsaturated acceptor groups C=C that react with the donor component (i) via a true Michael addition (RMA) reaction via a catalytic system; a crosslinkable composition; A catalyst system comprising a catalyst precursor (P) and a catalyst activator (C), wherein the catalyst precursor (P) and the catalyst activator (C) are The coating material component A contains a catalyst precursor (P), The paint component B contains a catalyst activator (C). They are separated as follows: The catalyst precursor (P) is a weak base having a pKa of its protonated form more than 2 units lower than the pKa of the activated C-H group in the donor component (i), and the catalyst activator (C) is capable of reacting with P to produce a strong base (CP) at a curing temperature, T; A catalyst system; Optionally, a non-RMA reactive component (iii) different from the donor component (i), the acceptor component (ii), the catalyst precursor (P) and the catalyst activator (C); Including, coating composition AB comprises crystalline component CC present in an amount of 1 to 50 wt. %, preferably 2 to 40 wt. %, more preferably 4 to 30 wt. %, based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii); At least a portion of the donor component (i) and / or the acceptor component (ii) and / or the non-RMA reactive component (iii) is crystalline component CC; and Both coating components A and B comprise a donor component (i) and an acceptor component (ii); It relates to a two-component powder coating composition AB.

[0009] In a second aspect, the present invention provides a method for powder coating a substrate, comprising: a. applying a layer comprising the two-component powder coating composition AB 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 to a curing temperature Tcur of 75 to 150°C, preferably 90 to 140°C, more preferably 100 to 130°C; c.Cur for a cure time of preferably less than 40 minutes, more preferably less than 30 minutes, 20 minutes, or even less than 10 minutes.

[0010] In a third aspect, the present invention relates to an article coated with the two-component powder coating composition AB, said article having a temperature-sensitive substrate preferably selected from the group of MDF, wood, plastic or metal alloys, and having a gloss level of less than 20 gloss units (GU) at an angle of 60°.

[0011] Detailed Description of the Invention The inventors have surprisingly found that a two-component powder coating composition AB according to the present invention, in which the catalyst system is separated across paint components A and B (also referred to as macrophysically separated) and which comprises a crystalline component CC present in an amount of 1 to 50 wt%, provides a coating composition that can be cured at low temperatures with high cure rates, has a long shelf life, and provides a coating with a dead matte appearance, with a smooth finish and improved cure times.

[0012] According to the present invention, the term "separated" or "macrophysically separated" means that the reactable components, catalyst precursor (P) and catalyst activator (C), are essentially inaccessible for chemical reaction in the two-component powder coating composition below the curing temperature. This is because not all of the reactable components of the powder coating composition are melt-mixed (also referred to as extruded) together. In the present invention, the catalyst system is macrophysically separated.

[0013] The inventors have found that when components (P) and (C) are macro-physically separated and the powder coating composition AB further comprises a crystalline component (CC), it is possible to provide a coating that, after curing, is of good quality and has a dead matte appearance, i.e., a gloss level at an angle of 60° of less than 20 GU.

[0014] Furthermore, the macro-physical separation of components (P) and (C) provides a longer shelf life.

[0015] Furthermore, powder coating composition AB is suitable for powder coatings that can be cured at low temperatures with a relatively high curing rate, an acceptably short curing time, and can achieve excellent crosslinking with excellent coating appearance.

[0016] The powder coating composition AB according to the present invention can be cured at a curing temperature Tcur selected from 75°C to 200°C, preferably 80°C to 180°C, more preferably 100°C to 160, 150, 140, 130°C, or even 120°C, preferably also using infrared heating. Preferably, the melt viscosity at the curing temperature is less than 60 Pas, more preferably less than 40, 30, 20, 10, or even 5 Pas. The melt viscosity can be measured, for example, with a Brookfield CAP 2000 cone-plate viscometer according to ASTM D4287 using spindle #5, and should be measured at the start of the reaction or on the catalytically inactive powder coating composition AB.

[0017] The low curing temperature makes it possible to use the powder coating composition AB for powder coating temperature-sensitive substrates, preferably MDF, wood, plastic, composites, or temperature-sensitive metal substrates such as alloys. The present invention therefore particularly relates to such articles coated with the powder coating composition AB according to the present invention. It has been found that good coating properties are obtained with a good crosslink density XLD and the resulting good coating properties.

[0018] In the context of the present invention, the term "crystalline component" is a compound that has a melting temperature Tm above which the compound is liquid. "Crystalline component" also encompasses semi-crystalline components.

[0019] In the context of the present invention, the "melting temperature" of a (semi-)crystalline component is the temperature at which the compound completely melts. The melting temperatures reported herein are determined from differential scanning calorimetry (DSC) using a heating rate of 10°C / min.

[0020] Aspects of the present invention will now be described in more detail, reference being made to the accompanying drawings, in which: [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 depicts the isothermal DSC analysis for powder coating composition PW2 and powder coating composition PW4 cured at 120°C. DETAILED DESCRIPTION OF THE INVENTION

[0022] Two-component powder coating composition AB The two-component powder coating composition AB comprises a coating component A and a coating component B, wherein coating component A comprises a catalyst precursor (P) and coating component B comprises a catalyst activator (C) such that the catalyst precursor (P) and the catalyst activator (C) are macro-physically separated.

[0023] Coating components A and B further comprise a donor component (i) and an acceptor component (ii). Coating components A and / or B further comprise a crystalline component CC. In a preferred embodiment, both coating components A and B comprise a crystalline component CC.

[0024] The catalyst system preferably further comprises a retarder (T). The retarder can be present in the coating component A and / or B. The retarder (T) is preferably present at least in the coating component B.

[0025] In a preferred embodiment, coating components A and B have a Tg greater than 35°C, preferably greater than 40°C, and preferably less than 60°C, more preferably less than 55°C, where Tg is the midpoint determined by differential scanning calorimetry (DSC) at a heating rate of 10°C / min.

[0026] In another embodiment, the two-component powder coating composition AB comprises melt-mixing components (i) and / or (ii) of the crosslinkable system with a catalyst precursor (P) and optionally a retarder T to obtain component A extrudates; melt-mixing components (i) and / or (ii) of the crosslinkable system with a catalyst activator (C) and optionally a retarder T to obtain component B extrudates; solidifying and granulating the component A extrudate and the component B extrudate to obtain the coating component A and the coating component B; Dry mixing of coating component A and coating component B to obtain a two-component powder coating composition AB It is prepared by

[0027] According to the present invention, standard methods typically used to manufacture powder resins can be used for melt mixing (also known as extrusion). After forming the extrudate in an extruder known to those skilled in the art, the extrudate is typically immediately solidified by forcing it onto a cooling band. The solidified extrudate 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 granulated, preferably by breaking it into small pieces (flakes) using a peg breaker. At this point, no significant shape control is applied to the granules. The granules can then optionally be transferred to a classifying micronizer, where they can be further crushed and classified. Coating components A and B are then blended to form a two-component powder coating composition AB. The solidified flakes from the component A extrudate and the component B extrudate are finally micronized together as a blend. Because the catalyst precursor P and catalyst activator C are not extruded together, they are macrophysically separated in the two-component powder coating composition AB.

[0028] In a preferred embodiment, the weight ratio of the coating components A and B is 0.1 to 10, preferably 0.2 to 5, more preferably 0.33 to 3, even more preferably 0.5 to 2, and most preferably 0.75 to 1.33.

[0029] Crystalline component CC The two-component powder coating composition AB according to the present invention comprises a crystalline component CC present in an amount of 1 to 50% by weight, preferably 2 to 40% by weight, more preferably 4 to 30% by weight, based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA-reactive component (iii). At least a portion of the donor component (i) and / or the acceptor component (ii) and / or the non-RMA-reactive component (iii) is the crystalline component CC. Most preferably, the crystalline component is the donor component (i) or the acceptor component (ii). Thus, the crystalline component CC according to the present invention is not a component that forms part of the catalyst system and is therefore not a catalyst precursor (P), a catalyst activator (C), or a catalyst retarder (T).

[0030] Crystalline component CC is also not a filler or pigment material.

[0031] Surprisingly, it has been found that the presence of crystalline component CC in a two-component powder coating composition that is RMA crosslinkable, thereby separating the catalyst system, provides a powder coating that has a dead matte and smooth appearance.

[0032] In one highly preferred embodiment, the two-component powder coating composition AB is melted at a temperature between 2 and 50°C, preferably between 3 and 40°C, more preferably between 4 and 30°C, at which point the maximum plasticizing effect (Tg store -Tg flow ) characterized by Tg store and Tg flow teeth,

number

[0033] Tg storerepresents the glass transition temperature of the two-component powder coating composition AB when CC is in the crystalline state and at a storage temperature well below the curing temperature. Only the Tg of each of the amorphous compounds is Tg store is used to calculate

[0034] Tg flow represents the glass transition temperature of the two-component powder coating composition AB under conditions where the crystalline component melts. When the composition melts, the crystalline component CC has a plasticizing effect on Tg. The crystalline component has a Tg much lower than the melting temperature Tm, and Tg can be less than 50°C, less than 40°C, less than 20°C, or even less than 0°C.

[0035] According to the present invention, the maximum plasticizing effect means the theoretically calculated plasticizing effect. In practice, the plasticizing effect is usually lower than that calculated, so the theoretical effect is referred to as the maximum plasticizing effect.

[0036] Tg store and Tg flow The difference between σ and σ represents the maximum plasticizing effect due to the melting of the crystalline component CC, whereby this plasticization decreases the melt viscosity and increases the diffusion coefficient.

[0037] According to the present invention, the range of maximum plasticizing effect is 2 to 50°C. Below this range, plasticization may not be sufficient to effectively increase the diffusion coefficient, whereas above this range, the coating may be too soft after curing and may have poor mechanical or resistance properties. Those skilled in the art can use the Fox-Flory equation to determine the amount of crystalline component needed to produce the plasticizing effect within this range. A smaller amount of a crystalline component with a lower Tg is required to achieve the same effect than a component with a higher Tg.

[0038] In one embodiment, crystalline component CC can have a group crosslinkable via RMA, can have at least two activated methylene or methine acidic CH donor groups, or can have at least two activated unsaturated acceptor groups C=C that react with donor component (i). Crystalline component CC can also be non-RMA-reactive component (iii). Thus, in one embodiment, at least a portion of donor component (i), acceptor component (ii) and / or non-RMA-reactive component (iii) is crystalline component CC.

[0039] In another embodiment, crystalline component CC has a melting temperature of less than 140° C., preferably less than 120° C., even more preferably less than 110° C., or even less than 100° C. Preferably, crystalline component CC is present in both paint components A and B.

[0040] In yet another embodiment, the crystalline component CC has a number average molecular weight (Mn) greater than 500, 750, 1000 and less than 5000, 4000, 3000.

[0041] In a preferred embodiment, crystalline component CC is present in both coating components A and B in an amount such that the weight fraction of crystalline component CC based on the weight of coating component A and coating component B differs by less than 5% by weight. In this way, the plasticizing effect that crystalline component CC has on both coating components upon its melting is similar. Without being bound by theory, diffusion is increased by lowering the Tg upon cure, and if the diffusion coefficients of the two coating components A and B differ too much, this can ultimately lead to different cure rates and a hazy coating.

[0042] In another embodiment, the crystalline component CC is a polyurethane prepared by reacting a polyurethane compound, preferably hexamethylene diisocyanate, with an isocyanate-reactive group. Preferably, the isocyanate-reactive group is a diol, preferably selected from the group consisting of diethylene glycol, triethylene glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, thiodiethanol, dithiodiethanol, bis(hydroxyethyl)methylamine, tetraethylene glycol, di(1,3-propanediol), and di(1,4-butanediol), and preferably diethylene glycol or 3-methyl-1,5-pentanediol. The donor or acceptor functional group can be introduced as a terminal group or mid-chain portion.

[0043] Isolated catalyst system The catalyst system is a separated catalyst system comprising a catalyst precursor (P), which is a weak base having a pKa in its protonated form that is more than 2 points, preferably more than 3 points, more preferably more than 4 points, and even more preferably at least 5 points lower than the pKa of the activated C-H donor group in the activated methylene or methine of the crosslinkable donor component A, and a catalyst activator (C), which can react with P at cure temperatures to produce a strong base (CP) that can initiate the Michael addition reaction between (i) and (ii). The catalyst precursor composition (P) and the catalyst activator composition (C) are macrophysically separated.

[0044] In one embodiment, the activator (C) is present in an amount of 60 to 1200 meq / g, preferably 90 to 750, and even more preferably 180 to 390 meq / g, based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii).

[0045] In another embodiment, the precursor (P) is present in an amount of 20 to 400 meq / g, preferably 30 to 250 meq / g, more preferably 60 to 130 meq / g, based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii).

[0046] In a preferred embodiment, the catalyst system is formed by a catalyst precursor (P), a catalyst activator (C), and a catalyst retarder (T), where the retarder (T) is an acid having a pKa more than two points lower than the pKa of the activated CH of the donor component (i), which upon deprotonation generates a weak base capable of reacting with the catalyst activator C to generate a strong base capable of catalyzing the RMA reaction between components (i) and (ii).

[0047] In one embodiment, the retarder (T) is present in an amount of 10 to 800, 15 to 500, 30 to 260 meq / g based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii).

[0048] In one embodiment, the catalyst system comprises a catalyst activator (C), preferably selected from the group of an epoxide, a carbodiimide, an oxetane, a vinyl ether, an oxazoline, or an aziridine functional component, preferably an epoxide or a carbodiimide, and a catalyst precursor (P), preferably a weakly basic nucleophile anion selected from the group of a carboxylate, a phosphonate, a sulfonate, a halide, or a phenolate anion, or a non-ionic nucleophile, preferably a tertiary amine or a phosphine, more preferably a weakly basic nucleophile anion selected from the group of a carboxylate, a halide, or a phenolate anion, or 1,4-diazabicyclo-[2.2.2]-octane (DABCO) or an N-alkylimidazole, most preferably a carboxylate.

[0049] In another embodiment, the isolated catalyst system comprises a catalyst precursor P that is also a Michael addition donor, and a catalyst activator (C) that is a Michael acceptor containing an activated unsaturated group C=C reactive with P. In such an embodiment, when the activator (C) is an acrylate, (P) has a pKa of the conjugate acid of less than 8, preferably less than 7, more preferably less than 6, where pKa is defined as the value in an aqueous environment, and when (C) is a methacrylate, fumarate, itaconate, or maleate, (P) has a pKa of the conjugate acid of less than 10.5, preferably less than 9, more preferably less than 8. The Michael acceptor activator (C) can be of the same type as defined as the acceptor component (ii), or can be of a different (more reactive) nature.

[0050] Within this embodiment, the catalyst precursor (P) is a weak base preferably selected from the group of phosphines, N-alkylimidazoles and fluorides, or a weak base nucleophile anion X from an acidic XH group-containing compound. - wherein X is N, P, O, S or C, and the anion X - is an activator (C) and a reactive Michael addition donor.

[0051] The most preferred catalyst activator (C) contains an epoxy group. Suitable choices of epoxides for the preferred activator (C) are cycloaliphatic epoxides, epoxidized oils, and glycidyl-type epoxides. Suitable components (C) are described, for example, in U.S. Pat. No. 4,749,728, column 3, lines 21-56, and include C10-18 alkylene oxides and oligomers and / or polymers having epoxide functionality (including multiple epoxy functionality). 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 its higher homologs of BPA epoxy resins, glycidyl ethers of hydrogenated BPA such as Eponex 1510 (Hexion) and 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 (alpha-methylstyrene oxide), 2-phenoxymethyl-1,2-propene oxide, epoxidized unsaturated oils or fatty esters, and 1-phenylpropene oxide.Useful and preferred epoxides are glycidyl esters of carboxylic acids and can 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 representative powder crosslinker epoxy components: triglycidyl isocyanurate (TGIC), Araldite PT910 and PT912, and acrylic (co)polymers of phenolic glycidyl ethers or glycidyl methacrylate that are essentially solid at ambient temperatures.

[0052] In a preferred embodiment, the activator (C) is an epoxide or a carbodiimide from the group of epoxides, carbodiimides, oxetanes, vinyl ethers, oxazolines or aziridine functional components, preferably an epoxide or a carbodiimide, preferably an epoxide from the group of TGIC, GMA acrylics, other glycidyl esters or phenolic glycidyl ethers.

[0053] Preferred examples of catalyst precursor (P) are weakly basic nucleophilic anions selected from the group consisting of carboxylate, phosphonate, sulfonate, halide, or phenolate anions or their salts, or nonionic nucleophiles, preferably tertiary amines or phosphines. More preferably, the weak base is a weakly basic nucleophilic anion selected from the group consisting of carboxylate, halide, or phenolate salts, most preferably carboxylate salts, or 1,4-diazabicyclo[2.2.2]octane (DABCO) or N-alkylimidazole. The catalyst precursor (P) reacts with the catalyst activator (C), preferably an epoxy, to produce a strongly basic anionic adduct capable of initiating the reaction of the crosslinkable components (i) and (ii). When a retarder (T) is present, the retarder (T) is preferably a protonated version of the precursor (P).

[0054] Another suitable example of the catalyst precursor (P) is a weak base nucleophile anion, which is selected from the group of weak base anions X- from acidic XH group-containing compounds, where X is N, P, O, S or C, and the anion X- is a Michael addition donor capable of reacting with a Michael acceptor activator C, wherein the anion X- is characterized by a pKa of the corresponding conjugate acid XH of less than 8, preferably less than 7, more preferably less than 6, where pKa is defined as the value in an aqueous environment, and when C is methacrylate, fumarate, itaconate or maleate, P has a pKa of the conjugate acid of less than 10.5, preferably less than 9, more preferably less than 8.

[0055] The catalyst precursor, which is a weak base P, preferably reacts with the catalyst activator C during the curing process at temperatures below 150° C., preferably below 140° C., 130° C., 120° C., preferably at least 70° C., preferably at least 80° C. or 90° C. The reaction rate of the weak base P with the activator C at the curing temperature is low enough to provide a useful open time and high enough to provide sufficient curing in the desired time window.

[0056] If the catalyst precursor P is an anion, it is preferably added as a salt containing 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 (i) for the base and therefore does not inhibit the crosslinking reaction at the intended curing temperature. Preferably, the cation is substantially unreactive with any of the components in the crosslinkable composition. The cation can be, for example, an alkali metal, quaternary ammonium, or phosphonium, but can also be a protonated "superbase" that is unreactive with either component (i) or (ii) in the crosslinkable composition. Suitable superbases are known in the art.

[0057] Preferably, the salt comprises an alkali metal or alkaline earth metal, particularly a lithium, sodium, or potassium cation, or more preferably a quaternary ammonium or phosphonium 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 group, optionally linked to the polymer, or the cation is a protonated superbasic amine, preferably selected from the group of amidines, preferably 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) or guanidines, preferably 1,1,3,3-tetramethylguanidine (TMG). As known to those skilled in the art, R' can be substituted with substituents that do not interfere or substantially do not interfere with the RMA crosslinking chemistry. Most preferably, R' is an alkyl having 1 to 12 carbon atoms, most preferably 1 to 4 carbon atoms.

[0058] Optionally, in some preferred embodiments, the isolated catalyst system further comprises a retarder T, which is an acid having a pKa that is 2, preferably 3, more preferably 4, and most preferably 5 points lower than the pKa of the activated CH in the crosslinkable donor component (i), which upon deprotonation produces a weak base that can act as a P precursor and react with the activator C to produce a strong base that can catalyze the Michael addition reaction between (i) and (ii).

[0059] The retarder T is preferably a protonated precursor P. Preferably, the retarder T and the protonated precursor P have a boiling point of at least 120°C, preferably 130°C, 150°C, 175°C, 200°C or even 250°C. Preferably, the retarder T is a carboxylic acid. The use of a retarder T can have a beneficial effect in slowing the crosslinking reaction to allow more interdiffusion of components during cure before mobility limitations become significant.

[0060] In one specific embodiment, the catalyst activator C is an acrylate acceptor group and components P and T are selected from X having a pKa (in acid form) of less than 8, more preferably less than 7, 6 or even 5.5. - The XH component is preferably a carboxylate / carboxylic acid compound. Examples of useful XH components for acrylate acceptor-containing powder coating compositions include cyclic 1,3-diones such as 1,3-cyclohexanedione (pKa 5.26) and dimedone (5,5-dimethyl-1,3-cyclohexanedione, pKa 5.15), ethyl trifluoroacetoacetate (pKa 7.6), and Meldrum's acid (pKa 4.97). Preferably, an XH component having a boiling point of at least 175°C, more preferably at least 200°C, is used.

[0061] In another embodiment, the catalyst activator C is a methacrylate, fumarate, maleate or itaconate acceptor group, preferably a methacrylate, itaconate or fumarate group, and components P and T are selected from X having an acid pKa of less than 10.5, more preferably less than 9.5, less than 8, or even less than 7. - / XH component.

[0062] The pKa values ​​referred to in this patent application are aqueous pKa values ​​at ambient conditions (21° C.) These values ​​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.

[0063] The reaction of the retarder T and its deprotonated version P with the activator C should occur at an appropriate rate in order to be able to provide a beneficial delay of the crosslinking reaction under the curing conditions.

[0064] A preferred isolated catalyst system comprises an epoxy as the catalyst activator C, a weakly basic nucleophilic anion group as the catalyst precursor P (which reacts with the epoxide group of C to form a strong base adduct C), and most preferably also a retarder T. In a suitable isolated catalyst system, P is a carboxylate salt, C is an epoxide, carbodiimide, oxetane, vinyl ether, or oxazoline, more preferably an epoxide or carbodiimide, and T is a carboxylic acid. Alternatively, P is DABCO, C is an epoxy, and T is a carboxylic acid.

[0065] Without wishing to be bound by theory, it is believed that the nucleophilic anion P reacts with the activator epoxide C to generate a strong base, which is immediately protonated by the retarder T to generate a salt (similar in function to P) that does not directly and strongly catalyze the crosslinking reaction. The reaction scheme is carried out until substantially complete depletion of the retarder T, which results in an open time because during that time there is no significant amount of strong base to significantly catalyze the reaction of the crosslinkable components (i) and (ii). Once the retarder T is depleted, a strong base is formed, which remains to effectively catalyze the rapid RMA crosslinking reaction.

[0066] In one embodiment, the retarders T are protonated anionic groups P, preferably carboxylic acids T and carboxylates P, which can be formed, for example, by partial neutralization of an acid-functional component (preferably a polymer containing acid groups as retarder T) to partially convert them to anionic groups on P, preferably with a cationic hydroxide or (bi)carbonate (preferably a tetraalkylammonium or tetraalkylphosphonium cation). In another embodiment, the polymer-bound component P can be made by hydrolysis of ester groups in polyesters with the aforementioned hydroxides.

[0067] Preferably, the boiling points of the conjugate acids of components T and P are above the intended cure temperature of powder coating composition AB to prevent uncontrolled evaporation of these catalyst system components during the cure conditions. Formic acid and acetic acid are less preferred retarders T because they may evaporate during cure. Preferably, the conjugate acids of retarders T and P have boiling points greater than 120°C.

[0068] Although less preferred, at least one of components P, C, or T of the separated catalyst system can be a group on one or both of crosslinking components (i) or (ii). In that case, care must be taken to ensure that P and C are macrophysically separated in the two-component powder coating composition AB. One or more, but not all, groups of P, C, and T can be on RMA crosslinking component (i) or (ii), or both. In an advantageous embodiment, both P and T are on RMA crosslinking component (i) and / or (ii), with P preferably being formed by partial neutralization of an acid-functional polymer containing the acid groups of T with a base containing the cations described above to partially convert the acid groups on T to anionic groups on P. Another embodiment has component P formed by hydrolysis of a polyester, such as the polyester of component (i), and present as a polymeric species.

[0069] The powder coating composition AB preferably comprises, in the case of an isolated catalyst system: a. an activator C in an amount of 1 to 600 μeq / gr, preferably 10 to 400, more preferably 20 to 200 μeq / gr, where μeq / gr is the μeq relative to the total weight of binder components (i) and (ii) and the separated catalyst system; b. a precursor which is a weak base P in an amount of 1 to 300 μeq / gr, preferably 10 to 200, more preferably 20 to 100 μeq / gr, based on the total weight of the binder components (i) and (ii) and the separated catalyst system; c. optionally a retarder T in an amount of 1 to 500, preferably 10 to 400, more preferably 20 to 300 μeq / gr, and most preferably 30 to 200 μeq / gr; Including, d. Preferably, the equivalents of C are more than the equivalent of iT, preferably 1 to 300 μeq / gr, more preferably 10 to 200, most preferably 20 to 100 μeq / gr, ii. preferably greater than the equivalent of P, and iii. Preferably greater than the sum of the P and T equivalents.

[0070] However, if the activator C is a Michael acceptor containing an activated unsaturated group C=C reactive with P, then there is no reasonable upper limit to the concentration, since in this case C can also be component (ii).

[0071] It is also possible for the isolated catalyst system to function with a lower amount of C than the amount of P. However, this is less preferred as it leaves unreacted P. If the amount of C, especially epoxide, is greater than the amount of P, the drawbacks are limited since C may react with P and T or other nucleophilic residues but may still remain basic after the reaction, or C may be left in the network without too much problem. Nevertheless, excess C may be disadvantageous in terms of the cost of C other than the epoxy.

[0072] Furthermore, in the powder coating composition AB, a. The precursor P is equivalent to 10-100 equivalent percent of the sum of P and T; b. Preferably, the amount of retarder T is 20-400 eq.%, preferably 30-300 eq.%, of the amount of P; c. Preferably, the ratio of the equivalents of C to the sum of the equivalents 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 equivalents of C to dT is preferably at least 1, preferably at least 1.5, most preferably at least 2; It is preferable.

[0073] In one embodiment, the RMA crosslinkable composition comprises a polymer and its use as a latent base catalyst component in an RMA crosslinkable coating composition, said polymer comprising catalyst precursor groups P and optionally acid groups T, the P groups preferably being formed by partial or complete neutralization of acid groups T on the polymer, P and T preferably being carboxylate and carboxylic acid groups, the polymer preferably being selected from the group of acrylic, polyester, polyester-amide and polyester-urethane polymers, the polymer optionally comprising C-H donor groups, C=C acceptor groups or both, the polymer preferably being a) an acid number in the unneutralized form of at least 3 (more preferably 5, 7, 10, 15 or even 20) mg KOH / g, and preferably less than 100, 80, 70, or 60 mg KOH / g; b) a quaternary ammonium or phosphonium cation, preferably a tetrabutyl or ethylammonium cation; c) an Mn of at least 500, preferably at least 1000 or even 2000, and an Mw of not more than 20,000, preferably not more than 10,000 or 6000; d) when C-H donor groups and / or C=C acceptor groups are present, a reactive C-H donor or C=C acceptor equivalent weight of at least 150, preferably at least 250, 350 or even 450 g / mol and not more than 2000, preferably not more than 1500, 1200 or 1000 g / mol It has.

[0074] Crosslinkable Components (i) and (ii) the two-component powder coating composition AB further comprises a crosslinkable composition, the crosslinkable composition being formed by a crosslinkable donor component (i) and a crosslinkable acceptor component (ii) that are crosslinkable by a true Michael addition (RMA) reaction; a) the crosslinkable donor component (i) has at least two activated methylene or methine acidic CH donor groups; b) Crosslinkable acceptor component (ii) has at least two activated unsaturated acceptor groups C=C that react with component (i) by true Michael addition (RMA) to form a crosslinked network.

[0075] In a preferred embodiment, at least one of the crosslinkable components (i) or (ii) is a polymer, preferably the polymer is selected from the group of acrylic polymers, polyester polymers, polyesteramide polymers, polyesterurethane polymers, said polymer being have a number average molecular weight Mn, measured by GPC, of ​​at least 450 g / mol, preferably at least 1000, more preferably at least 1500, most preferably at least 2000 g / mol, have a weight average molecular weight Mw, measured by GPC, of ​​at most 20 000 g / mol, preferably at most 15 000, more preferably at most 10 000 and most preferably at most 7 500 g / mol, preferably has a polydispersity Mw / Mn of 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 g / mol, and preferably at most 2500, 2000, 1500, 1250 or 1000 g / 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 per molecule, preferably has a melt viscosity in the temperature range of 100 to 140°C of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas, 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 consisting of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, pentaspiroglycol or hydrogenated bisphenol A and tetramethylcyclobutanediol, and / or A crystalline polymer having a midpoint Tg of above 25°C, preferably above 35°C, more preferably above 40, 50 or even 60°C, as measured 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 and preferably below 120°C (measured by DSC at a heating rate of 10°C / min).

[0076] Preferably, the crosslinking component (i) comprises at least two activated methylene or methine acidic CH donor groups in the structure Z1(-C(-H)(-R)-)Z2, where R is hydrogen, hydrocarbon, oligomer or polymer, and Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from keto, ester or cyano or aryl groups. Also, the crosslinking component (i) preferably has a structure of formula 1: [ka] and an activated CH derivative having the structure 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 in formula 1, -C(=O)-Y and / or -C(=O)-Y' are replaced by CN or aryl, with not more than one aryl; or Y or Y' can be NRR' (R and R' are H or optionally substituted alkyl), but preferably not both, and R, Y or Y' optionally provides connection to an oligomer or polymer; and said component (i) is preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, preferably providing at least 50, preferably 60, 70 or even 80% of the total C-H acid groups in crosslinkable component (i).

[0077] The acceptor component (ii) preferably comprises at least two activated unsaturated RMA acceptor groups derived from acryloyl, methacryloyl, itaconate, maleate, or fumarate functional groups. Preferably, at least one of components (i) or (ii), more preferably both, is polymeric.

[0078] Preferably, the crosslinkable composition contains a total amount of donor groups C═C and acceptor groups C═C per gram of binder solids of 0.05 to 6 meq / gr, and preferably the ratio of acceptor groups C═C to donor groups C═C is greater than 0.1 and less than 10.

[0079] True Michael addition (RMA) crosslinkable coating compositions comprising crosslinkable components (i) and (ii) are generally described for use in solvent-borne systems in EP 2556108, EP 0808860 or EP 1593727, the specific descriptions of crosslinkable components (i) and (ii) in these patents being incorporated herein by reference.

[0080] Components (i) and (ii) each contain an RMA reactive donor moiety and an acceptor moiety that react upon curing to form a crosslinked network in the coating. Components (i) and (ii) can be present on separate molecules, or on one molecule, referred to as a hybrid (i) / (ii) component, or a combination thereof.

[0081] Preferably, components (i) and (ii) are separate molecules, each independently in the form of a polymer, oligomer, dimer, or monomer. For coating applications, at least one of components (i) or (ii) is preferably an oligomer or polymer. Note that an activated methylene group CH contains two CH acidic groups. Even though the reaction of the second CH acidic group is more difficult after the reaction of the first CH acidic group, the functionality of such an activated methylene group counts as two, for example, in reaction with a methacrylate compared to an acrylate. Reactive components (i) and (ii) can also be combined into a single (i) / (ii) hybrid molecule. In this embodiment of powder coating composition AB, both CH and C=C reactive groups are present in a single (i) / (ii) molecule.

[0082] Preferably, component (i) is a polymer, preferably a polyester, polyurethane, acrylic, epoxy or polycarbonate, having as functional groups component (i) and optionally one or more components from component B, or catalyst system C. Mixtures or hybrids of these polymer types are also possible. Suitably, component (i) is a polymer selected from the group of acrylic polymers, polyester polymers, polyesteramide polymers, polyester-urethane polymers.

[0083] Malonate or acetoacetate is the preferred donor type in component (i). In consideration of high reactivity and durability in the most preferred embodiment of the crosslinkable composition, component (i) is a malonate C-H containing compound. It is preferred that the majority of activated C-H groups in powder coating composition AB 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 C-H groups in powder coating composition AB are malonate-derived.

[0084] Oligomeric and / or polymeric malonate group-containing components, such as polyesters, polyurethanes, polyacrylates, epoxy resins, polyamides and polyvinyl resins or hybrids thereof, containing malonate-type groups in the backbone, pendant or both, are preferred.

[0085] The total amount of donor C-H and acceptor C=C groups per gram of binder solids, regardless of their distribution among the various crosslinkable components, is preferably 0.05 to 6 meq / gram, more typically 0.10 to 4 meq / gram, even more preferably 0.25 to 3 meq / gram, and most preferably 0.5 to 2 meq / gram. Preferably, the stoichiometry between components (i) and (ii) is selected so 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, and most preferably greater than 0.4, and in the case of acrylate functional groups, preferably greater than 0.5, and most preferably greater than 0.75, with the ratio being preferably less than 10, preferably less than 5, and more preferably less than 3, 2, or 1.5.

[0086] Malonate-group-containing polyesters are preferably obtained by transesterification of methyl or ethyl diesters of malonic acid with polyfunctional alcohols, which may be polymeric or oligomeric, but may also be incorporated by Michael addition 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. Polymer component (i) can also be prepared by known methods, for example, by radical polymerization of ethylenically unsaturated monomers, including (meth)acrylates, functionalized with activated CH acid (donor) groups, preferably acetoacetate or malonate groups, particularly 2-(methacryloyloxy)ethyl acetoacetate or malonate-containing moieties. 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 as GPC polystyrene equivalent) of less than 20,000, preferably less than 10,000, and most preferably less than 6,000.

[0087] Suitable crosslinkable acceptor components (ii) can generally be ethylenically unsaturated components whose carbon-carbon double bond is activated by an electron-withdrawing group, such as a carbonyl group at the α-position. Representative examples of such components are disclosed in U.S. Pat. No. 2,759,913 (column 6, line 35 to column 7, line 45), German Patent No. 835,809 (column 3, lines 16 to 41), U.S. Pat. No. 4,871,822 (column 2, line 14 to column 4, line 14), U.S. Pat. No. 4,602,061 (column 3, lines 14 to 20 to column 4, line 14), U.S. Pat. No. 4,408,018 (column 2, lines 19 to 68), and U.S. Pat. No. 4,217,396 (column 1, line 60 to column 2, line 64).

[0088] Acrylates, methacrylates, itaconates, fumarates, and maleates are preferred. Itaconates, fumarates, and maleates can be incorporated into the backbone of polyesters or polyester-urethanes. Preferred examples of resins containing activated unsaturated groups include polyesters, polycarbonates, polyurethanes, polyamides, acrylics, and epoxy resins (or hybrids thereof), polyethers, and / or alkyd resins. These include, for example, urethane (meth)acrylates obtained by reacting polyisocyanates with hydroxyl-containing (meth)acrylic esters, such as hydroxyalkyl esters of (meth)acrylic acid or components prepared by esterifying polyhydroxy components with less than a stoichiometric amount of (meth)acrylic acid; polyether (meth)acrylates obtained by esterifying hydroxyl-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. Polyesters end-capped with glycidyl methacrylate are also preferred. The acceptor component can contain multiple types of acceptor functional groups.

[0089] The most preferred activated unsaturated group-containing acceptor component (ii) is an unsaturated acryloyl-, methacryloyl-, and fumarate-functional component. Preferably, the number-average functionality of activated C=C groups per molecule is 2 to 20, more preferably 2 to 10, and most preferably 3 to 6. The equivalent weight (EQW: average molecular weight per reactive functional group) is 100 to 5,000, more preferably 200 to 2,000, and the number-average molecular weight Mn is preferably 200 to 10,000, more preferably 300 to 5,000, most preferably 400 to 3,500 g / mol, and even more preferably 1,000 to 3,000 g / mol.

[0090] Considering use in powder systems, and the need for powder stability, the Tg of the acceptor component (ii) is preferably greater than 25, 30, 35, more preferably at least 40, 45, and most preferably at least 50°C or even at least 60°C. Tg is defined as the value measured by DSC, midpoint, at a heating rate of 10°C / min. As will be appreciated by those skilled in the art, if one of the components has a Tg substantially higher than 50°C, the Tg of the other formulation components may be lower.

[0091] Suitable acceptor components (ii) are urethane (meth)acrylates prepared by reacting hydroxy- and (meth)acrylate-functional compounds with isocyanates to form urethane linkages, the isocyanates preferably being at least in part diisocyanates or triisocyanates, preferably isophorone diisocyanate (IPDI). While the urethane linkages themselves introduce rigidity, preferably high Tg isocyanates are used, such as cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic isocyanates. The amount of such isocyanates used is preferably selected so that the Tg of the (meth)acrylate-functional polymer is greater than 40°C, preferably greater than 45 or 50°C.

[0092] Powder coating composition AB is preferably designed so that after curing it has 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, most preferably at least 0.08 mmol / cc, and typically less than 3, 2, 1 or 0.7 mmol / cc.

[0093] Powder coating composition AB should remain a free-flowing powder at ambient conditions and therefore preferably have a Tg of greater than 25°C, preferably greater than 30°C, more preferably greater than 35, 40, 50°C as midpoint determined by DSC at a heating rate of 10°C / min.

[0094] As noted above, the preferred component (i) is a malonate-functional component. However, the incorporation of malonate moieties tends to lower the Tg, and providing a powder coating composition AB based on malonate as the primary component (i) with a sufficiently high Tg has been a challenge.

[0095] With a view to achieving a high Tg, the powder coating composition AB preferably comprises a crosslinkable composition, the crosslinkable donor component (i) and / or the crosslinkable acceptor component B (which may be in the form of a hybrid component A / B) of which contain amide, urea or urethane bonds and / or whereby the crosslinkable composition comprises a high Tg monomer (preferably an alicyclic or aromatic monomer), or in the case of polyesters, one or more monomers selected from the group consisting of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, pentaspiroglycol, hydrogenated bisphenol (i) and tetra-methyl-cyclobutanediol.

[0096] Furthermore, with a view to achieving a high Tg, the powder coating composition AB comprises a component (ii) or hybrid component (i) / (ii) 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 end-capped with an isocyanate or epoxy functional activated unsaturated group.

[0097] The polymer characteristics Mn, Mw, and Mw / Mn are selected taking into consideration the desired powder stability on the one hand, the desired low melt viscosity on the other hand, and the expected coating properties. A high Mn is preferred to minimize the Tg-depressing effect of end groups, but on the other hand, melt viscosity is very closely related to Mw, and low viscosity is desirable, so a low Mw is preferred. Therefore, a low Mw / Mn is preferred.

[0098] With a view to achieving a high Tg, the RMA crosslinkable polymer preferably contains an amide bond, a urea bond or a urethane bond and / or contains a high Tg monomer (preferably an alicyclic or aromatic monomer), or in the case of polyesters, a monomer selected from the group of 1,4-dimethylolcyclohexane (CHDM), TCD diol, isosorbide, pentaspiroglycol or hydrogenated bisphenol A and tetramethylcyclobutanediol.

[0099] When the RMA crosslinkable polymer is an (i) / (ii) hybrid polymer, it is further preferred that the polymer also contains one or more component (ii) groups selected from the group consisting of acrylate or methacrylate, fumarate, maleate, and itaconate, preferably (meth)acrylate or fumarate. Furthermore, when used as a crystalline material, the RMA crosslinkable polymer preferably has a crystallinity (measured by DSC at a heating rate of 10°C / min) with a melting temperature between 40°C and 130°C, preferably at least 50 or even 70°C, preferably below 150, 130, 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 blend.

[0100] In a preferred embodiment, the RMA crosslinkable polymer comprises a polyester, polyesteramide, polyester-urethane, or urethane-acrylate containing urea, urethane, or amide linkages derived from a cycloaliphatic or aromatic isocyanate, preferably a cycloaliphatic isocyanate, the polymer having a Tg of at least 40°C (preferably at least 45 or 50°C) and at most 120°C, a number average molecular weight Mn of 450 to 10,000, preferably 1,000 to 3,500 gr / mol, and a maximum Mw of preferably 20,000, 10,000, or 6,000 gr / mol, the polymer comprising RMA crosslinkable component (i) or (ii), or both. The polymer can be obtained, for example, by reacting a precursor polymer containing the RMA crosslinkable group with an amount of a cycloaliphatic or aromatic isocyanate to increase the Tg. The amount of such isocyanate added or the amount of urea / urethane linkages formed is selected so as to raise the Tg by at least 40°C, preferably by at least 45 or 50°C.

[0101] Preferably, the RMA crosslinkable polymer is a polyester or polyester-urethane comprising malonate as the main component (i) and containing a number average malonate functionality of 1 to 25, more preferably 1.5 to 15, even more preferably 2 to 15, and most preferably 2.5 to 10 malonate groups per molecule, and having a GPC weight average molecular weight of 500 to 20000, preferably 1000 to 10000, and most preferably 2000 to 6000 gr / mol, prepared by reacting a hydroxy and malonate functional polymer with an isocyanate to form a urethane bond.

[0102] Furthermore, the polymer can be an amorphous or crystalline polymer or a mixture thereof. 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 at most 130, 120, 110, or 100°C. The DSC Tg of such a component in a completely amorphous state is preferably below 40°C, more preferably below 30, 20, or even 10°C.

[0103] Non-RMA reactive component (iii) and further components The powder coating composition AB may further comprise a non-RMA reactive component (iii). Component (iii) may be a crystalline compound CC, such as any type of crystalline component typically used in powder coating resins. An example is a crystalline or semi-crystalline polyester resin.

[0104] A further example is a polyurethane made by reacting a polyurethane compound, preferably hexamethylene diisocyanate, with an isocyanate-reactive group, the polyurethane preferably having an Mn greater than 500, greater than 750, greater than 1000, and less than 5000, less than 4000, less than 3000. The isocyanate-reactive group may be a diol, preferably selected from the group consisting of diethylene glycol, triethylene glycol, 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol, thiodiethanol, dithiodiethanol, bis(hydroxyethyl)methylamine, tetraethylene glycol, di(1,3-propanediol), di(1,4-butanediol), preferably diethylene glycol or 3-methylpentanediol.

[0105] The non-RMA reactive component (iii) can also be an additive known in the prior art. If the additive is crystalline, these compounds can be considered as crystalline compounds CC according to the present invention. Although not claiming to be a complete list, additives that can be used include leveling agents, anti-crater additives, texturizing agents, degassing agents, antioxidants, UV absorbers, (tribo) charge control substances, anti-blocking additives (e.g., waxes for improving storage stability), flow agents, flame retardants, IR absorbers, and additives for improving surface properties (e.g., hardness, abrasion resistance, scratch resistance, chemical resistance, recoatability, adhesion, surface tension, and substrate wetting).

[0106] The powder coating composition may also contain pigments and / or fillers. These components are not considered non-RMA reactive components (iii) because they may not be taken into account when calculating the amount of crystalline component present in coating composition AB or when calculating the maximum plasticizing effect of melting crystalline component CC. This is because pigments and fillers form separate phases and do not mix with other components upon melting.

[0107] Substrates and Coatings The present invention provides a. applying a layer of powder coating composition AB to a substrate surface; and b. heating, optionally and preferably using infrared heating, to a curing temperature Tcur of 75 to 150°C, preferably 80 to 150°C, more preferably 80 to 140, 130 or 120°C; c. Curing at Tcur for a cure time of preferably less than 40, 30, 20, 15, 10 or even 5 minutes; The present invention also relates to a method for powder coating a substrate, comprising:

[0108] In this method, the cure at T is preferably characterized by a cure profile determined by measuring the conversion of the unsaturated C=C bonds of component (ii) as a function of time by FTIR, preferably such that the time to reach 60% conversion is less than 30, 20 or 10 minutes, the ratio of the time to go from 20% to 60% C=C conversion to the time to reach 20% conversion is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, and the powder coating composition at T has a melt viscosity at the cure temperature of preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even less than 5 Pas. The melt viscosity is measured at the very start of the reaction or without C2 of the catalyst system.

[0109] In a preferred embodiment of the method, the curing temperature is between 75 and 140°C, preferably between 80 and 120°C, and the catalyst system C is a latent catalyst system as described above, which allows the powder coating of temperature-sensitive substrates, preferably MDF, wood, plastic or temperature-sensitive metal substrates such as alloys.

[0110] Due to the dead matte effect of the two-component powder coating composition AB, the article can have a gloss level of less than 20 GU at an angle of 60°.

[0111] Thus, the present invention also relates to an article coated with the powder coating composition of the present invention, preferably having a temperature-sensitive substrate such as MDF, wood, plastic or metal alloy, and preferably having a crosslink density XLD (as measured by DMTA) of at least 0.01 (preferably at least 0.02, 0.04, 0.07 or even 0.1) mmol / cc, preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / cc.

[0112] The invention is illustrated by the following examples.

[0113] Test Method Acid value A freshly prepared solvent blend of 1:1 xylene:ethanol is prepared. A certain amount of resin is accurately weighed into a 250 ml Erlenmeyer flask. 50-60 ml of 1:1 xylene:ethanol is then added. The solution is gently heated until the resin is completely dissolved, but is not allowed to boil. The solution is then cooled to room temperature and titrated potentiometrically with 0.1 M potassium hydroxide until after the equivalence point.

[0114] OH value The OHV was determined by manual titration of prepared blank and sample flasks. The indicator solution was made by dissolving 0.80 g of thymol blue and 0.25 g of cresol red in 1 L of methanol. Ten drops of the indicator solution were added to the flask, which was then titrated with a standardized 0.5 N methanolic potassium hydroxide solution. The color changed from yellow to gray and then to blue, and the endpoint was reached when the blue coloration was maintained for 10 seconds. The hydroxyl value was then calculated as follows: Hydroxy value = (BS) × N × 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 = sample weight (base resin) AV = Acid value of base resin Net hydroxy value is defined as follows: Net OHV = (BS) x N x 56.1 / M

[0115] Amine Value 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. 50-60 ml of 3:1 xylene:ethanol is then added. The solution is gently heated until the resin is completely dissolved, but is not allowed to boil. The solution is then cooled to room temperature and titrated potentiometrically with 0.1 M hydrochloric acid until after the equivalence point.

[0116] GPC molecular weight The molar mass distributions of the polymers were determined by gel permeation chromatography (GPC) on a Perkin-Elmer HPLC Series 200 instrument using a refractive index (RI) detector and a PLgel column, THF as eluent, and calibration with polystyrene standards. Experimental molecular weights are expressed in terms of polystyrene equivalents.

[0117] DSC Tg The glass transition temperatures of the coating components are the midpoint Tg determined from differential scanning calorimetry (DSC) using a heating rate of 10 °C / min. The glass transition temperatures of the individual components are determined by DSC in a program in which the sample is heated and cooled between -30 and 150 °C / min, starting from -30 °C. For amorphous materials, the midpoint Tg of the first and second heating steps is reported. For (semi)crystalline materials, the midpoint Tg of the first cooling step is reported.

[0118] Dry film thickness (DFT) Dry film thickness (DFT) was measured using a Positector 6000 Coating Thickness Gauge.

[0119] Gloss at (60°) The gloss of the coating is measured using a Zehntner ZGM 1130 gloss meter.

[0120] Abbreviation [Table 1a]

[0121] [Table 1b]

[0122] Preparation of materials Preparation of malonate donor resin A 5-liter round-bottom reactor equipped with a four-way valve, metal anchor stirrer, Pt-100, a packed column with an overhead thermometer, a condenser, a distillate collection vessel, a thermocouple, and a N2 inlet was charged with 1300 g of isosorbide (80%), 950 g of NPG, and 1983 g of TPA. The reactor temperature was gently increased to approximately 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 with continued stirring under nitrogen until the reaction mixture became clear and the acid number was below 2 mg KOH / g. At the end of the reaction, a vacuum was applied to complete the reaction. The temperature was then reduced to 120°C, and 660 g of diethyl malonate was added. The reactor temperature was then increased to 190°C and maintained until no more ethanol was formed. A vacuum was again applied to complete the reaction. After the transesterification was complete, the hydroxyl number of the polyester was measured: the final OHV was 27 mg KOH / g, the GPC Mn was 1763, and the Mw was 5038. The Tg determined in the first cooling step and the second heating step are 59°C and 63°C, respectively.

[0123] Preparation of urethane acrylate acceptor resin A urethane acrylate based on IPDI, hydroxypropyl acrylate, and glycerol is prepared with the addition of a suitable polymerization inhibitor, as described, for example, in EP 0585742. A 5-liter reactor equipped with a thermometer, stirrer, injection funnel, and gas bubbling inlet is charged with 1020 parts IPDI, 1.30 parts dibutyltin dilaurate, and 4.00 parts hydroquinone. Next, 585 parts hydroxypropyl acrylate is charged, while avoiding the temperature from rising above 50°C. Once the addition is complete, 154 parts glycerin are added. After 15 minutes, after the exothermic reaction has subsided, the reaction product is cast onto a metal tray. The resulting urethane acrylate is characterized by a GPC Mn of 744 and a Mw of 1467, a residual isocyanate content of less than 0.1%, and a theoretical unsaturation EQW of 394 g / mol. The Tg determined in the first cooling step and the second heating step are 46° C. and 51° C., respectively.

[0124] Preparation of crystalline urethane acrylate resin CUA-1 Similarly, 504.6 g of HDI, 0.1 g of DBTL, and 5 g of BHT were charged into a 2-liter round-bottom reactor and heated to 50°C under dry air. A mixture of 232.2 g of hydroxyethyl acylate and 236.3 g of 3-methyl-1,5-pentanediol was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120°C. The resulting (semi-)crystalline urethane acrylate CUA-1 had maximum and final DSC melting temperatures of 95°C and 102°C, respectively. The theoretical values ​​were Mn = 973 and unsaturation EQW = 487 g / mol. The Tg, determined during the first cooling step, was -20°C.

[0125] Preparation of crystalline urethane acrylate resin CUA-2 504.6 g of HDI, 0.1 g of DBTL, and 5 g of BHT were charged into a 2-liter round-bottom reactor and heated to 50°C under dry air. A mixture of 288.3 g of hydroxybutyl acylate and 212.2 g of diethylene glycol was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120°C. The resulting (semi-)crystalline urethane acrylate CUA-2 had maximum and final DSC melting temperatures of 106°C and 115°C, respectively. The theoretical values ​​of Mn = 1005 and unsaturation EQW = 506 g / mol. The Tg determined during the first cooling step was -7.5°C.

[0126] Preparation of Carboxylate-Terminated Retarder Resin A 5-liter round-bottom reactor equipped with a four-way valve, metal anchor stirrer, Pt-100, a packed column with an upper thermometer, a condenser, a distillate collection vessel, a thermocouple, and a nitrogen inlet was charged with 1180 g of NPG and 2000 g of IPA. The reactor temperature was increased to 230 °C, and polymerization was allowed to proceed with continuous stirring under nitrogen until the reaction mixture became clear. The resulting final product had an AV of 48 mg KOH / g. The Tg values ​​determined during the first cooling and second heating stages were 52 °C and 55 °C, respectively.

[0127] Preparation of catalyst precursor To prepare the catalyst precursor, carboxylate-terminated polyester resin (48% AV) was melted and mixed with an aqueous solution of tetraethylammonium bicarbonate (TEAHCO3) (41%) using a Leistritz ZSE 18 twin-screw extruder. The extruder was equipped with a barrel containing nine successive heating zones configured to maintain the following temperature profile from inlet to outlet: 30-50-80-120-120-120-120-100-100°C. Solid polyester resin was added at a rate of 2 kg / h through the first zone, and liquid TEAHCO3 was injected at 0.60 kg / h through the second zone. Mixing occurred between zones 4 and 7, with the shaft set to rotate at 200 rpm. Volatiles and water evolved from the acid-base neutralization were removed using vacuum in zone 7. After exiting the die, the extruded strand was 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 of 42°C and 48°C, determined in the first cooling step and in the second heating step, respectively.

[0128] Preparation of glycidyl methacrylate AMSD-GMA acrylic-based activator 189 g of α-methylstyrene dimer (AMSD) was charged into a 2-liter round-bottom reactor and heated to 140°C. 641 g of methyl methacrylate, 284 g of glycidyl methacrylate, and 19.5 g of Trigonox® 121 were mixed in a separate flask and then added dropwise to the reactor to initiate the reaction. The addition was completed in 6 hours, and the process temperature was maintained at 140-145°C. The reaction was then allowed to proceed for another hour at 140°C. Finally, an additional 1.9 g of Trigonox® 121 was added to the reactor over 30 minutes. Finally, residual monomer was removed by distillation under vacuum. The resulting AMSD-GMA had a theoretical Mn of 1114 and an epoxy EQW of 557. The Tg values ​​determined during the first cooling and second heating stages were 43°C and 46°C, respectively.

[0129] Preparation of Powder Coating Compositions and Powder Coating Component Compositions To prepare the powder coating composition (PW1) or powder coating components (PWC2-10), 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. After extrusion, the extrudate was ground using a Kemutec laboratory classifier micronizer. The classifier was set at 5.5 rpm, the rotor was set at 7 rpm, and the feed was set at 5.2 rpm. The extruder speed was 250 rpm, and the four extruder barrel zone temperatures were set at 25, 60, 100, and 100°C. The ground extrudate was sieved to less than 100 μm using a Russell Finex 100-micron mesh Demi Finex laboratory vibrating sieve. The formulation compositions (in parts by weight) of PW1, PWC2-PWC3, PWC4-PWC7 and PWC8-PWC10 are shown in Tables 1, 2, 4 and 6, respectively.

[0130] result PW1 is a comparative powder coating example in which all compounds listed in Table 1 were extruded together. The amount of crystalline component (e.g., CUA-1) was 18.7 wt %, which corresponds to a maximum plasticization of 16.5°C.

[0131] [Table 1c]

[0132] PWC2A, PWC2B, PWC3A, and PWC3B are powder coating components having the compositions shown in Table 2. These were prepared to produce comparative powder coating blends PW2 and PW3, which did not use a crystalline component in the formulation. To prepare PW2, catalyst precursor component PWC2A and activator component PWC2B were combined in a 50 / 50 ratio. To prepare PW3, catalyst precursor component PWC3A and activator component PWC3B were combined in a 52 / 48 ratio.

[0133] Comparative powder coating compositions PW1-PW3 were sprayed onto aluminum Q panels and cured at 120°C for 30 minutes. Dry film thickness, 60° gloss level, calculated Tg store and Tg flow are summarized in Table 3.

[0134] [Table 2]

[0135] [Table 3]

[0136] Powder coating blend PW4 according to the present invention was prepared by blending powder coating precursor component PWC4A with powder coating activator component PWC4B in a 50 / 50 ratio. Crystalline urethane acrylate CUA-1 acceptor resin was incorporated into both PWC4A and PWC4B. The amount of CUA-1 was 18.7 wt%, corresponding to a maximum plasticization of 16.5°C. The overall composition of this powder coating blend according to the present invention is identical to that of comparative powder coating PW1 in terms of the relative amounts of donor / acceptor, catalyst precursor concentration, and activator concentration. The blend according to the present invention was sprayed onto aluminum Q panels and cured at 120°C for 30 minutes. Compared to the comparative unblended powder coating PW1, coating blend PW4 according to the present invention achieved a much lower gloss level (<20 GU) and had a smoother finish.

[0137] Furthermore, inventive coating blend PW4 has the same donor / acceptor ratio, catalyst precursor concentration, and activator concentration as comparative coating blend PW2, except that a crystalline urethane-acrylate (CUA-1) is used in the formulation of PW4. Comparing the gloss levels of PW4 and PW2 demonstrates that the addition of a crystalline component can further reduce the gloss level of the blend coating composition from 22 GU to 9 GU at a 60° angle. Figure 1 shows DSC isothermal analysis at 120°C for both powder coating blends PW4 and PW2. As can be seen from the DSC plot, PW4 has a faster cure rate than PW2, as the set of cure events initiated earlier and the cure exotherm was completed more quickly. It is believed that the crystalline component in PW4 (e.g., CUA-1) lowered the Tg of the coating (e.g., maximum plasticization of 16.5°C), thereby lowering the melt viscosity of the powder coating. This facilitates the diffusion of molecules, which may be the reason for the enhanced reactivity of coating blend PW4.

[0138] PW5-PW7 are powder coating blends according to the present invention. Similarly, PW5-PW7 were prepared by blending powder coating precursor component PWC5A, PWC6A, or PWC7A with the corresponding powder coating activator component PWC4B, PWC5B, or PWC6B in a 50 / 50 ratio. Crystalline urethane acrylate CUA-1 acceptor resin was incorporated into both components A and B. The amount of CUA-1 was 27.4 wt%, 9.6 wt%, and 4.8 wt% for PW5, PW6, and PW7, respectively, corresponding to maximum plasticization temperatures of 23.9°C, 8.6°C, and 3.6°C. Blends PW5-PW7 according to the present invention were sprayed onto aluminum Q panels and cured at 120°C for 30 minutes. Again, very low gloss levels (<20 GU) and smooth finishes were achieved for all examples. The compositions and application results of PW4 to PW7 are summarized in Tables 4 and 5, respectively.

[0139] [Table 4]

[0140] [Table 5]

[0141] PW8 and PW9 are powder coating blends according to the present invention in which an alternative epoxy compound is used as an activator. The AMSD-GMA acrylic has a lower molecular weight compared to Almatex™ PD-3402. Similarly, PW8 and PW9 were prepared by blending powder coating precursor component PWC8A or PWC9A with the corresponding powder coating activator component PWC8B or PWC9B in ratios of 47 / 53 and 52 / 48, respectively. Crystalline urethane acrylate CUA-1 acceptor resin was incorporated into both components A and B. The amount of CUA-1 was 16.5 wt% and 20.5 wt% for PW8 and PW9, respectively, corresponding to maximum plasticization at 14.3°C and 18.0°C. Blends PW8 and PW9 according to the present invention were sprayed onto aluminum Q panels and cured at 120°C for 30 minutes. Again, very low gloss levels (<20 GU) and a smooth finish were achieved. Coating blend PW9 according to the invention has the same donor / acceptor ratio, catalyst precursor concentration, and activator concentration as comparative coating blend PW3, except that a crystalline urethane-acrylate (CUA-1) is used in the formulation of PW9. Comparing the gloss levels of PW9 and PW3 demonstrates that the addition of a crystalline component can further reduce the gloss level of the blend coating composition from 28 GU to 10 GU at a 60° angle.

[0142] PW10 is a coating blend according to the present invention in which an alternative crystalline urethane-acrylate, CUA-2, is used in the formulation. CUA-2 has higher maximum and final DSC melting temperatures than CUA-1. PW10 was prepared by blending powder coating precursor component PWC10A with the corresponding powder coating activator component PWC10B in a 49 / 51 ratio. The crystalline urethane acrylate CUA-2 acceptor resin was incorporated into both components A and B. The amount of CUA-2 was 18.8 wt%, corresponding to a maximum plasticization of 13.9°C. Blend PW10 according to the present invention was sprayed onto aluminum Q panels and cured at 120°C for 30 minutes. Again, a very low gloss level (<20 GU) and a smooth finish were achieved. The compositions and application results of PW8 through PW10 are summarized in Tables 6 and 7, respectively.

[0143] [Table 6]

[0144] [Table 7]

Claims

1. A two-component powder coating composition AB comprising a coating component A and a coating component B, said powder coating composition AB comprising: a crosslinkable composition formed by a crosslinkable donor component (i) and a crosslinkable acceptor component (ii) that are crosslinkable by a true Michael addition (RMA) reaction, the donor component (i) has at least two activated methylene or methine acidic C—H donor groups; and The acceptor component (ii) has at least two activated unsaturated acceptor groups C═C that react with the donor component (i) via a true Michael addition (RMA) reaction via a catalytic system; a crosslinkable composition; The catalyst system, which comprises a catalyst precursor (P) and a catalyst activator (C), The coating material component A contains the catalyst precursor (P), The coating material component B contains the catalyst activator (C). They are separated as follows: the catalyst precursor (P) is a weak base having a pKa of its protonated form more than 2 units lower than the pKa of the activating C—H group in donor component (i), and the catalyst activator (C) is capable of reacting with (P) at a curing temperature, T, to produce a strong base (CP); A catalyst system; Optionally, a non-RMA reactive component (iii) different from the donor component (i), the acceptor component (ii), the catalyst precursor (P), and the catalyst activator (C); Including, said coating composition AB comprises a crystalline component CC, which is present in an amount of 1 to 50 wt. %, preferably 2 to 40 wt. %, more preferably 4 to 30 wt. %, based on the total weight of said catalyst system, said crosslinkable composition, and, if present, said non-RMA reactive component (iii); whereby at least a portion of the donor component (i) and / or the acceptor component (ii) and / or the non-RMA reactive component (iii) is the crystalline component CC; and Both coating components A and B comprise the donor component (i) and the acceptor component (ii); Two-component powder coating composition AB.

2. Tg of 2 to 50°C, preferably 3 to 40°C, more preferably 4 to 30°C ｓｔｏｒｅ -Tg ｆｌｏｗ 2. The two-component powder coating composition AB according to claim 1, characterized by a maximum plasticizing effect due to the melting of the crystalline component CC, calculated as: Tg ｓｔｏｒｅ and Tg ｆｌｏｗ teeth, [Equation 1] is calculated as During the ceremony, i represents each individual component of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii), not including the crystalline component CC; j represents each individual component of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii), including the crystalline component CC; Tgi and Tgj represent the glass transition temperatures Tg, in Kelvin, of the individual components of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii), as midpoints determined by differential scanning calorimetry (DSC) at a cooling rate of 10°C / min; wi or wj is the weight fraction w of the individual component based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii); Two-component powder coating composition AB.

3. 3. The two-component powder composition AB of claim 1 or 2, wherein the catalyst system further comprises a catalyst retarder material T that is an acid having a pKa more than 2 points lower than the pKa of the activating C—H of the donor component (i) and that, upon deprotonation, produces a weak base that can react with the catalyst activator C to produce a strong base that can catalyze the RMA reaction between components (i) and (ii).

4. 4. The two-component powder composition AB according to any one of claims 1 to 3, wherein precursor (P) is present in an amount of 20 to 400 meq / g, preferably 30 to 250 meq / g, more preferably 60 to 130 meq / g, based on the total weight of said catalyst system, said crosslinkable composition and, if present, said non-RMA reactive component (iii).

5. 5. The two-component powder composition AB according to any one of claims 1 to 4, wherein the activator (C) is present in an amount of 60 to 1200 meq / g, preferably 90 to 750, even more preferably 180 to 390 meq / g, based on the total weight of the catalyst system, the crosslinkable composition and, if present, the non-RMA reactive component (iii).

6. 6. The two-component powder composition AB according to any one of claims 1 to 5, wherein the retarder (T) is present in an amount of 10 to 800, 15 to 500, 30 to 260 meq / g based on the total weight of the catalyst system, the crosslinkable composition, and, if present, the non-RMA reactive component (iii).

7. 7. The two-component powder composition AB according to any one of claims 1 to 6, wherein said crystalline component CC has a melting temperature of less than 140°C, preferably less than 120°C, even more preferably less than 110°C, or even less than 100°C.

8. The two-component powder composition AB according to any one of claims 1 to 7, wherein the crystalline component CC is present in both coating components A and B in an amount such that the difference in weight fraction of the crystalline component CC relative to the weight of coating component A and coating component B is less than 5 wt.%.

9. 9. The two-component powder composition AB according to any one of claims 1 to 8, wherein said crystalline component CC is a polyurethane compound, preferably a polyurethane prepared by reacting hexamethylene diisocyanate with isocyanate-reactive groups, and preferably has an Mn of more than 500, 750, 1000 and less than 5000, 4000, 3000.

10. 10. The binary powder composition AB according to claim 9, wherein said isocyanate-reactive groups are diols preferably selected from the group consisting of diethylene glycol, triethylene glycol, 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol, thiodiethanol, dithiodiethanol, bis(hydroxyethyl)methylamine, tetraethylene glycol, di(1,3-propanediol), di(1,4-butanediol), preferably from diethylene glycol or 3-methylpentanediol.

11. 11. The two-component powder composition AB according to any one of claims 1 to 10, wherein both coating components A and B have a Tg higher than 35°C, preferably higher than 40°C, and preferably lower than 60°C, more preferably lower than 55°C, the Tg being the midpoint value determined by differential scanning calorimetry (DSC) at a heating rate of 10°C / min.

12. The two-component powder coating composition AB according to any one of claims 1 to 11, wherein the weight ratio of the coating components A and B is from 0.1 to 10, preferably from 0.2 to 5, more preferably from 0.33 to 3, even more preferably from 0.5 to 2, and most preferably from 0.75 to 1.

33.

13. At least one of the crosslinkable components (i) or (ii) is a polymer preferably selected from the group of acrylic polymers, polyester polymers, polyesteramide polymers, polyesterurethane polymers, said polymers being have a number average molecular weight Mn, measured by GPC, of ​​at least 450 g / mol, preferably at least 1000, more preferably at least 1500, and most preferably at least 2000 g / mol; have a weight average molecular weight Mw, measured by GPC, of ​​at most 20,000 g / mol, preferably at most 15,000, more preferably at most 10,000, and most preferably at most 7,500 g / mol; preferably has a polydispersity Mw / Mn of 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 g / mol, and preferably at most 2500, 2000, 1500, 1250 or 1000 g / mol, and a number average functionality of reactive groups C—H 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 C—H groups per molecule, preferably has a melt viscosity at a temperature in the range of 100 to 140°C of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas; 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 consisting of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, pentaspiroglycol or hydrogenated bisphenol A and tetramethylcyclobutanediol, and / or - is a crystalline polymer with a midpoint Tg, measured by DSC at a heating rate of 10°C / min, above 25°C, preferably above 35°C, more preferably above 40, 50 or even 60°C, or a melting temperature (measured 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 and preferably below 120°C; A two-component powder coating composition AB according to any one of claims 1 to 12.

14. 14. Two-component powder coating composition AB according to any one of claims 1 to 13, wherein said activator (C) is selected from the group of epoxides, carbodiimides, oxetanes, vinyl ethers, oxazolines or aziridine functional components, preferably epoxides or carbodiimides, preferably epoxides from the group of TGIC, GMA acrylics, other glycidyl esters or phenolic glycidyl ethers.

15. 15. Two-component powder coating composition AB according to any one of claims 1 to 14, wherein said catalyst precursor (P) is a weakly basic nucleophile anion selected from the group of carboxylate, phosphonate, sulfonate, halide or phenolate anions or a non-ionic nucleophile, preferably a tertiary amine or a phosphine, more preferably a weakly basic nucleophile anion selected from the group of carboxylate, halide or phenolate anions or 1,4-diazabicyclo-[2.2.2]-octane (DABCO) or an N-alkylimidazole, most preferably a carboxylate, and wherein said retarder (T), if present, is preferably a protonated precursor (P).

16. The catalyst precursor (P) is a non-acidic cation, preferably a cation of the formula Y(R') ４ wherein Y represents N or the atom P and each R' can be the same or different alkyl, aryl or aralkyl group, optionally linked to a polymer, or said cation is a protonated superbasic amine, which is preferably selected from the group of amidines, preferably 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) or guanidines, preferably 1,1,3,3-tetramethylguanidine (TMG).

17. 17. Two-component powder coating composition AB according to any one of claims 1 to 16, comprising a total amount of donor groups C-H and acceptor groups C=C / gram binder solids of 0.05 to 6 meq / gr binder solids, preferably the ratio of acceptor groups C=C to donor groups C-H is >0.1 and <10.

18. The composition comprises: melt-mixing components (i) and / or (ii) of the crosslinkable system with said catalyst precursor (P) and optionally said retarder T to obtain component A extrudates; melt-mixing components (i) and / or (ii) of said crosslinkable system with said catalyst activator (C) and optionally said retarder T to obtain component B extrudates; solidifying and granulating the component A extrudate and component B extrudate to obtain coating component A and coating component B; dry mixing the coating component A and the coating component B to obtain the two-component powder coating composition AB; The two-component powder coating composition AB according to any one of claims 1 to 17, which is prepared by

19. 1. A method for powder coating a substrate, comprising: a) applying a layer comprising the two-component powder coating composition AB according to any one of claims 1 to 18 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 to a curing temperature T of 75-150°C; c. Curing at Tcur for a cure time preferably less than 40 minutes. A method comprising:

20. 19. An article coated with the two-component powder coating composition AB according to any one of claims 1 to 18, said article having a temperature-sensitive substrate preferably selected from the group of MDF, wood, plastic or metal alloys, and having a gloss level of less than 20 GU at an angle of 60°.

21. 21. An article coated with a two-component powder coating composition AB according to claim 20, preferably having a crosslink density XLD of at least 0.01 mmol / ml (measured by DMTA), preferably less than 3.

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