Powder coating composition blend

Abstract

A powder coating composition blend comprising a cross-linkable composition and a catalyst system, wherein the cross-linkable composition is formed from a cross-linkable donor component A and a cross-linkable acceptor component B which are cross-linkable by a true Michael addition (RMA) reaction by means of the catalyst system, wherein the catalyst system is a separate catalyst system comprising a macroscopically physically separated catalyst precursor composition (P) and a catalyst activator composition (C); or wherein the cross-linkable donor component A and the cross-linkable acceptor component B are macroscopically physically separated.

Description

Technical Field

[0001] This invention relates to a powder coating composition blend comprising a crosslinkable composition that can be crosslinked by true Michael addition (RMA) and a catalyst system for catalyzing RMA, a method for coating an article using the powder coating composition blend, and the coated article. Background Technology

[0002] Powder coatings are solid materials that dry at room temperature, are finely pulverized, and flow freely, and have become more popular than liquid coatings in recent years. Powder coatings are typically cured at high temperatures of 120–200 °C, more typically 140–180 °C. High temperatures are required to provide sufficient binder flow to allow film formation and achieve a good coating surface appearance, and also to achieve the high reactivity of the crosslinking reaction. At low curing temperatures, reaction kinetics may not allow for short curing times when sufficient mechanical and electrical properties are required; on the other hand, for systems where high reactivity of the components may occur, the coating may have a poor appearance due to the relatively high viscosity at such low temperatures, and this increases further rapidly with the progress of the curing reaction. The time-integral flowability of such systems is too low to achieve sufficient leveling (see, for example, Progress in Organic Coatings, 72, lines 26–33 (2011)). The appearance may be limited, especially when the target is a thin film. Furthermore, when formulating powder coatings in an extruder, very high reactivity can cause problems due to premature reaction. In addition, highly reactive formulations may have limited storage stability.

[0003] Many powder coating compositions provide coatings with a high gloss after curing. There is a growing demand for powder coatings and resins that provide high-quality coatings exhibiting reduced gloss. Furthermore, it is advantageous if this type of coating can be applied to heat-sensitive substrates such as medium-density fiberboard (MDF), wood, plastics, and certain metal alloys.

[0004] Patent application WO 2019 / 145472 describes a powder coating composition that provides a glossy coating on heat-sensitive substrates such as medium-density fiberboard (MDF), wood, plastics, and certain metal alloys. It is capable of curing at low temperatures with high curing rates and acceptable short curing times, allowing for a sufficiently long open curing time to permit flow and coalescence, resulting in a good film with a favorable coating appearance. The coating composition can be cured via RMA using a catalyst system that promotes the RMA reaction.

[0005] Powder coating compositions based on this system may still react prematurely after prolonged storage. Therefore, there is a need for a powder coating composition with good performance that can cure at a high curing rate at low temperatures, provide a matte coating, and ensure a long shelf life during storage.

[0006] Invention Summary

[0007] The present invention addresses one or more of the above-mentioned problems by providing a powder coating composition blend as described in claim 1.

[0008] Therefore, a first aspect of the present invention relates to a powder coating composition blend comprising a crosslinkable composition and a catalyst system, wherein the crosslinkable composition is formed from a crosslinkable donor component A and a crosslinkable acceptor component B, the crosslinkable donor component A and the crosslinkable acceptor component B being crosslinkable via a true Michael addition (RMA) reaction using the catalyst system, and the catalyst system being capable of catalyzing the RMA crosslinking reaction at a curing temperature below 200°C, preferably below 175°C, more preferably below 150°C, 140, 130 or even 120°C, and preferably at least 70°C, preferably at least 80, 90 or 100°C.

[0009] The crosslinkable composition comprises:

[0010] a) A crosslinkable donor component A, having at least two acidic CH donor groups in the activated methylene or methine group, and

[0011] b) A crosslinkable receptor component B having at least two activated unsaturated receptor groups C=C, which reacts with component A via true Michael addition (RMA) to form a crosslinked network; and

[0012] The catalyst system described herein is a separated catalyst system, comprising a macroscopically physically separated catalyst precursor composition (P) and catalyst activator composition (C); wherein:

[0013] The catalyst precursor composition (P) comprises catalyst precursor P1; and

[0014] The catalyst activator composition (C) comprises catalyst activator C1; or

[0015] The crosslinkable donor component A and the crosslinkable acceptor component B are macroscopically physically separated; and the catalyst system is:

[0016] A potential catalyst system comprising catalyst precursor P1 and catalyst activator C1; or

[0017] Non-potential catalyst systems containing strong bases;

[0018] The catalyst precursor P1 is a weak base, and its pKa in protonated form is more than 2 units lower than that of the activated CH group in donor component A, preferably more than 3 units, more preferably more than 4 units, and even more preferably at least 5 units lower. The catalyst activator C1 can react with P1 at the curing temperature to produce a strong base (C1P1) that can catalyze the Michael addition reaction between component A and component B.

[0019] In a second aspect, the present invention relates to a method for powder coating a substrate, comprising:

[0020] A layer comprising a blend of powder coating compositions of the first aspect is applied to a substrate surface, wherein the substrate is preferably a thermosensitive substrate, preferably MDF, wood, plastic, composite material, or thermosensitive metal substrate, such as an alloy; and

[0021] Infrared heating is preferred, with a curing temperature T of 75-200°C, more preferably 80-180°C, and even more preferably 80-160, 150, 140, 130, or even 120°C. cur Among them, at the curing temperature T cur The melt viscosity is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas; and

[0022] In T cur For the next curing step, a curing time of less than 40, 30, 20, 15, 10, or even 5 minutes is preferred.

[0023] In a third aspect, the present invention relates to articles coated with powder using a blend of powder coating compositions having the first aspect, wherein the articles preferably have a temperature-sensitive substrate preferably selected from MDF, wood, plastic or metal alloy, and wherein the crosslinking density XLD is preferably at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / ml (determined by dynamic mechanical thermal analysis (DMTA), and preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / ml. Invention Details

[0025] The inventors have surprisingly discovered that the powder coating composition blend in which the catalyst system or crosslinkable components of the present invention are macroscopically physically separated provides a coating composition that can be cured at low temperatures with a high curing rate, has a long shelf life, and provides a coating with a matte appearance.

[0026] According to the present invention, the term "macrophysically separated" refers to a powder blend in which reactive compounds are substantially unable to undergo chemical reactions below the curing temperature. This is because not all reactive components in a powder coating composition blend are melt-mixed (also known as extruded) together. In the present invention, the crosslinkable components are macrophysically separated, or the catalyst system is macrophysically separated.

[0027] When the crosslinkable components are macroscopically physically separated, this means that the crosslinkable donor component A is not melt-mixed with the crosslinkable acceptor component B. When the separated catalyst system is macroscopically physically separated, this means that the catalyst precursor composition (P) is not melt-mixed with the catalyst activator composition (C).

[0028] The inventors have discovered that when component A and component B, or (P) and (C) are macroscopically physically separated, powder blends that can be cured to form powder coatings of good quality with a matte or glossy appearance can be provided. Furthermore, since component A and component B, or (P) and (C) are macroscopically physically separated, the likelihood of a reaction occurring during storage is much lower, resulting in a longer shelf life.

[0029] In addition, powder coating composition blends are also suitable for coating compositions that can be cured at low temperatures with relatively high curing rates, acceptable short curing times, and good crosslinking with a good coating appearance.

[0030] The powder coating composition blends of the present invention can be cured at a curing temperature T of 75-200°C, preferably 80-180°C, more preferably 100-160°C, 150°C, 140°C, 130°C, or even 120°C. cur The curing process is preferably carried out 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, according to ASTM D4287 using a Brookfield CAP 2000 cone-plate rheometer with spindle #5, and at the beginning of the reaction or on a blend of powder coating compositions without catalyst activity.

[0031] The low curing temperature allows the powder coating composition blends to be used for powder coating of temperature-sensitive substrates, preferably MDF, wood, plastics, composites, or temperature-sensitive metal substrates, such as alloys. Therefore, the present invention also particularly relates to articles coated with the powder coating composition blends of the present invention. It has been found that good coating properties, with a good crosslinking density (XLD) and resulting good coating performance, can be obtained. Brief description of the attached diagram

[0033] The various aspects of the invention will now be described in more detail. Therefore, reference is made to the following figures.

[0034] Figure 1 Isothermal DSC plots of powder coating composition PW1 cured at 120°C are described after fresh preparation and storage at 35°C for 5 days.

[0035] Figure 2 Isothermal DSC plots of a 50 / 50 blend of powder coating composition PWC3A+PWC3B1 cured at 120°C are described after fresh preparation and after storage at 35°C for 30 days.

[0036] Figure 3 DSC temperature scans of the 20 / 1 blend of PWC5A and PWC5B are described between 10 and 230 °C after fresh preparation and after storage at 35 °C for 30 days.

[0037] Figure 4 Isothermal DSC plots of PW6 and PW8 at 100℃ are described.

[0038] Figure 5 DSC temperature scans of PW6 and PW8 are described between -30 and 230 °C.

[0039] Description of the implementation plan

[0040] Powder coating composition blends

[0041] In one embodiment, the powder coating composition blend is prepared by the following steps:

[0042] Components A and / or B in the crosslinkable composition are melt-mixed with a catalyst precursor composition (P) and an optional retarder T to obtain a precursor extruder;

[0043] Components A and / or B in the crosslinkable composition are melt-mixed with the catalyst activator composition (C) and optional retarder T to obtain the activator extrusion;

[0044] The precursor extrudate and activator extrudate are cured and granulated to obtain a precursor powder composition and an activator powder composition.

[0045] The precursor and activator powder composition are dry-blended to obtain the powder coating composition blend.

[0046] In this embodiment, the separated catalyst compositions (P) and (C) are not melt-mixed (melt mixing is also known as extrusion). The precursor extruder may contain one or both of RMA crosslinkable components A and B. If the precursor extruder contains only component A, the activator extruder contains at least component B, and vice versa.

[0047] In another embodiment, the powder coating composition blend is prepared by the following steps:

[0048] Crosslinkable component A is melt-mixed to obtain a donor extrusion and / or crosslinkable component B is melt-mixed to obtain an acceptor extrusion, thereby melt-mixing crosslinkable components A and / or B with a potential or non-potential catalyst system.

[0049] The donor and / or acceptor extrudates are cured and granulated to obtain donor powder compositions and / or acceptor powder compositions.

[0050] With components A and B already melt-mixed, the donor powder composition and the acceptor powder composition are dry-blended; or with only components A or B already melt-mixed, the donor powder composition or the acceptor powder composition is dry-blended with crosslinkable components B or A in the form of grindable solids, respectively, to obtain the powder coating composition blend.

[0051] In one specific embodiment, the powder coating composition blend comprises a catalyst activator composition (C), which includes:

[0052] When the catalyst activator C1 is a liquid, the catalyst activator exists on the support;

[0053] In another specific embodiment, the powder coating composition blend comprises a catalyst precursor composition (P), said catalyst precursor composition (P) comprising:

[0054] When the catalyst precursor P1 is liquid, the catalyst precursor exists on the support;

[0055] The carrier is a porous material capable of absorbing liquids, such as a silica carrier. Preferably, the particle size of the carrier (defined as D) v 50 The value is 5-200μm, more preferably 10-150μm, even more preferably 10-100μm or 15-50μm.

[0056] In such an embodiment, the powder coating composition blend can be prepared by the following steps:

[0057] Components A and B in the crosslinkable composition are melt-mixed with the catalyst precursor composition (P) and optional retarder T to obtain a precursor extruder;

[0058] The precursor extrudate is cured and granulated to obtain a precursor powder composition;

[0059] The precursor powder composition is dry-blended with a catalyst activator present on a support to obtain the powder coating composition blend; or

[0060] Components A and B in the crosslinkable composition are melt-mixed with the catalyst activator composition (C) and optional retarder T to obtain the activator extrudate;

[0061] The activator extrudate is cured and granulated to obtain an activator powder composition;

[0062] The activator powder composition is dry-blended with a catalyst precursor present on a support to obtain the powder coating composition blend.

[0063] According to the invention, for melt blending (also known as extrusion), standard processes commonly used for manufacturing powder resins can be used. Thus, typically, after the extrudate is formed in an extruder, it is immediately cured by forcibly spreading the extrudate onto a cooling belt, as is well known to those skilled in the art. The cured extrudate can be in the form of a cured sheet as it travels along the cooling belt. At the end of the belt, the sheet is then granulated, and therefore preferably crushed into smaller pieces by a crusher to form a powder composition. At this point, there is no significant shape control over the particles, but a statistically maximum size is preferred. The particles can then be transferred to a classifying micronizer, where they are further ground. The powder composition is then blended to form a powder coating composition blend. Cured sheets derived from precursor and activator extrudates or donor and acceptor extrudates can also be granulated, ultimately micronized, and blended together. Since in one embodiment catalyst precursor P1 and catalyst activator D1, or in another embodiment donor component A and acceptor component B, are not extruded together, they are macroscopically physically separated in the powder coating composition blend.

[0064] When a powder coating composition blend with macroscopically physically separated reactants (i.e., precursor P1 and activator C1 or donor component A and acceptor component B) is used as a powder coating, a powder layer will form on the base material, which will still have macroscopically physically separated complementary reactants at the start of melting. The progress of the curing reaction will depend on the diffusion of these complementary reactants together from this initial condition, and the diffusion length and time required for this process will depend on the dimensional details of the original powder blend and the diffusion coefficient. When considering the formation of random stacks during application, the size of this compositional control at the initial condition depends on the particle size and volume ratio of the individual particle blend components. When the particles used for blending are small, the diffusion length and diffusion time required for good overall crosslinking properties will be shorter; excessively large particles may result in too large a distance to be overcome during the curing step. Therefore, the particle size of the powder composition used for blending (defined as D) v50 The maximum size is preferably 200 μm, more preferably 150 μm, more preferably not exceeding 100 μm, and most preferably less than 50 μm.

[0065] D v 50 It is a particle size measured in micrometers, where 50% of the samples are smaller and 50% are larger. This value is also known as the mass median diameter (MMD) or the median of the volume distribution.

[0066] The mass ratio of different powder compositions in the powder coating composition blend can also play a role. In cases of strong asymmetry in the ratio, the effective diffusion length will be longer because most components are less likely to come into direct contact with complementary particles in the original particle stack. Therefore, the mass ratio (wt% / wt%) of the precursor powder composition and activator powder composition or donor powder composition and acceptor powder composition used for dry blending is preferably between 20 and 0.05, more preferably between 10 and 0.1, even more preferably between 5 and 0.2, or between 2 and 0.5. Generally, higher asymmetry can be tolerated if smaller particles are involved.

[0067] When one of the components used in the dry blending is a catalyst precursor or activator present on the support, the amount of this component is preferably 1-30 wt%, more preferably 3-20 wt%, and more preferably 4-15 wt%, based on the total powder composition blend.

[0068] The powder coating composition blend may further comprise additives, such as those selected from: pigments, dyes, dispersants, degassing agents, leveling additives, matting additives, flame retardant additives, additives for improving film-forming properties, optical appearance of the coating, and additives for improving mechanical properties, adhesion, or stability, such as color and UV stability. These additives may be melt-blended with one or more components of the powder coating composition blend.

[0069] Separated catalyst system

[0070] In a preferred embodiment, the catalyst system is a separate catalyst system comprising a catalyst precursor composition (P) and a catalyst activator composition (C), wherein the catalyst precursor composition (P) comprises a catalyst precursor P1, which is a weak base whose pKa in its protonated form is greater than 2 points, preferably greater than 3 points, more preferably greater than 4 points, and even more preferably at least 5 points lower than the pKa of the activated CH donor group in the activated methylene or methine of the crosslinkable donor component A; the catalyst activator composition (C) comprises a catalyst activator C1 that can react with P1 at a curing temperature to produce a strong base (C1P1) capable of initiating a Michael addition reaction between A and B. The catalyst precursor composition (P) and the catalyst activator component (C) are macroscopically physically separated.

[0071] Most preferably, the catalyst precursor composition (P) further comprises a crosslinkable donor composition A and / or a crosslinkable acceptor composition (B), and the catalyst activator composition (C) further comprises a crosslinkable donor composition A and / or a crosslinkable acceptor composition (B). Preferably, the donor composition (A) and the acceptor composition (B) are present in a separate catalyst system in such a way that they are melt-mixed together with the catalyst precursor P1 or the catalyst activator C1. Surprisingly, it has been found that when the catalyst precursor P1 or the catalyst activator C1 is extruded together with the crosslinkable donor composition A and / or the crosslinkable acceptor composition (B), the composition provides a powder coating with lower gloss and better MEK resistance compared to a powder coating made from a blend of powder compositions (where the catalyst precursor P1 or the catalyst activator C1 is added as a separate compound to a blend of the donor composition (A), the acceptor composition (B), and the complementary component of the catalyst system (catalyst precursor P1 or catalyst activator C1)).

[0072] In one embodiment, the catalyst system comprises: a catalyst activator composition (C) containing an activator C1, wherein the activator C1 is preferably selected from epoxides, carbodiimides, oxadienes, oxazolines, or aziridine functional components, preferably epoxides or carbodiimides; and a catalyst precursor composition (P) containing a catalyst precursor P1, wherein the catalyst precursor P1 is preferably a weak base nucleophilic anion or nonionic nucleophile selected from carboxylate, phosphonate, sulfonate, halide, or phenolic anion, preferably a tertiary amine or phosphine, more preferably a weak base nucleophilic anion selected from carboxylate, halide, or phenolic anion, or 1,4-diazabicyclo-[2.2.2]-octane (DABCO) or N-alkylimidazole, most preferably carboxylate.

[0073] In another embodiment, the separated catalyst system comprises a catalyst precursor composition P in which the catalyst precursor P1 is a Michael addition donor and a catalyst activator composition C in which the activator C1 is a Michael acceptor comprising an activated unsaturated C=C group that can react with P1. In such an embodiment, when C1 is an acrylate, the pKa of the conjugate acid of P1 is less than 8, preferably less than 7, more preferably less than 6, wherein pKa is defined as a value in an aqueous environment, and when C1 is a methacrylate, fumarate, itaconic acid, or maleate, the pKa of the conjugate acid of P1 is less than 10.5, preferably less than 9, more preferably less than 8. The Michael acceptor activator C1 may be of the same type as defined in component B, or may have different (more reactive) properties.

[0074] In this embodiment, the catalyst precursor composition (P) comprises a catalyst precursor P1, which is preferably a weak base selected from phosphine, N-alkylimidazolium, and fluorides, or a weak base nucleophilic anion X from an acidic compound containing an XH group. - Where X is N, P, O, S, or C, and the anion X - It is a Michael addition donor that can react with activator C1.

[0075] The most preferred catalyst activator C1 contains an epoxy group. Suitable choices of epoxides as preferred activator C1 are alicyclic epoxides, epoxidized oils, and glycidyl epoxides. Suitable components C1 are described, for example, in column 3, lines 21-56 of US4749728, including C10-18 alkylene oxides and oligomers and / or polymers having epoxide functional groups (including multiple epoxy functional groups). Particularly suitable monoepoxides include tert-butyl glycidyl ether, phenyl glycidyl ether, glycidyl acetate, glycidyl esters of tert-carbonates, glycidyl methacrylate (GMA), and glycidyl benzoate. Useful multifunctional epoxides include bisphenol A diglycidyl ether and higher homologues of such BPA epoxy resins, glycidyl ethers of hydrogenated BPA, such as Eponex 1510 (Hexion), ST-4000D (Kukdo), aliphatic ethylene oxides such as epoxidized soybean oil, diglycidyl adipic acid, 1,4-diglycidyl butyl ether, glycidyl ethers of phenolic resins, glycidyl esters of diacids such as Araldite PT910 and PT912 (Huntsman), TGIC, and other commercial epoxy resins. Bisphenol A diglycidyl ether and its solid high molecular weight homologues are preferred epoxides. Also useful are acrylic (co)polymers with epoxide functional groups derived from glycidyl methacrylate. In a preferred embodiment, the epoxy component is an oligomer or polymer component with a Mn of at least 400 (750, 1000, 1500). Other epoxide compounds include 2-methyl-1,2-hexene oxide, 2-phenyl-1,2-propene oxide (α-methylstyrene oxide), 2-phenoxymethyl-1,2-propene oxide, epoxidized unsaturated oils or fatty esters, and 1-phenylpropene oxide. Useful and preferred epoxides are glycidyl esters of carboxylic acids, which may be mounted on carboxylic acid-functionalized polymers, or preferably on highly branched hydrophobic carboxylic acids such as Cardura E10P (Versatic). TM The preferred crosslinking agents are typical epoxy components: triglycidyl isocyanurate (TGIC), Araldite PT910 and PT912, and phenolic glycidyl ethers or acrylic (co)polymers of glycidyl methacrylate that are solid at ambient temperature.

[0076] Suitable examples of catalyst precursor P1 are weakly basic nucleophilic anions selected from the following: carboxylate, phosphonate, sulfonate, halide or phenolate anions or their salts, or nonionic nucleophiles, preferably tertiary amines or phosphine. More preferably, the weak base P1 is a weakly basic nucleophilic anion selected from carboxylate, halide or phenolate, most preferably a carboxylate, or it is 1,4-diazabicyclo[2.2.2]octane (DABCO) or N-alkylimidazole. Catalyst precursor P1 can react with catalyst activator C1 (preferably an epoxy component) to produce a strongly basic anionic adduct that can initiate the reaction of crosslinkable components A and B.

[0077] Another suitable example of catalyst precursor P1 is a weak base nucleophilic anion selected from the following: a weak base anion X- from an acidic compound containing an XH group, wherein X is N, P, O, S or C, wherein the anion X- is a Michael addition donor that can react with the Michael acceptor activator C1, wherein the anion X- is characterized in that the pKa of the corresponding conjugate acid XH is less than 8, preferably less than 7, more preferably less than 6, wherein pKa is defined as a value in an aqueous environment, and in the case that C1 is methacrylate, fumarate, itaconic acid or maleate, the pKa of the conjugate acid of P1 is less than 10.5, preferably less than 9, more preferably less than 8.

[0078] The catalyst precursor P1, being a weak base, is preferably reacted with the catalyst activator C1 at a temperature below 150°C, preferably 140, 130, 120, and more preferably at least 70, 80, or 90°C on the timescale of the curing process. The reaction rate of the weak base P1 with the activator C1 at the curing temperature is low enough to provide a useful open time, and high enough to allow sufficient curing within the desired time window.

[0079] When the catalyst precursor P1 is an anion, it is preferably added in the form of a salt comprising a non-acidic cation. Non-acidic means it does not have hydrogen competing with the crosslinkable donor component A for the base, thus not inhibiting the crosslinking reaction at the intended curing temperature. Preferably, the cation is substantially non-reactive to any component of the crosslinkable composition. The cation can be, for example, an alkali metal, quaternary ammonium, or phosphonium, or a protonated "superbase" that is non-reactive to any component A, B, or C of the crosslinkable composition. Suitable superbases are known in the art.

[0080] 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 of the general formula Y(R')4, wherein Y represents N or P, and wherein each R' can be the same or different alkyl, aryl, or aralkyl groups that can be attached to the polymer, or wherein the cation is a protonated, very strong basic amine, preferably selected from 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 or substantially do not interfere with the RMA crosslinking chemistry. Most preferably, R' is an alkyl group having 1-12, most preferably 1-4 carbon atoms.

[0081] Optionally, in some preferred embodiments, the separated catalyst system further comprises a retarder T, which is an acid with a pKa 2 points lower, preferably 3 points, more preferably 4 points, and most preferably 5 points lower than the pKa of the activated CH in the crosslinkable donor component A, and which, upon deprotonation, produces a weak base that can serve as a precursor to P1, and can react with the activator C1 to produce a strong base capable of catalyzing the Michael addition reaction between A and B. The retarder T is preferably the protonation precursor P1. The retarder T can be part of a catalyst precursor composition or a catalyst activator composition. It can also be part of both a catalyst precursor composition and a catalyst activator composition. Preferably, the retarder T and the protonation precursor P1 have boiling points 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. Using the retarder T can have a beneficial effect in delaying the crosslinking reaction to allow greater interdiffusion of the components during curing, before flow restriction becomes significant.

[0082] In one specific embodiment, catalyst activator C1 is an acrylate acceptor group, and components P1 and T are X - The XH component, preferably a carboxylate / carboxylic acid compound, has a pKa (acid form) of less than 8, more preferably less than 7, 6, or even 5.5. Examples of useful XH components for powder coating compositions containing acrylate acceptors include cyclic 1,3-diones, such as 1,3-cyclohexanedione (pKa 5.26) and dimethyl ketone (5,5-dimethyl-1,3-cyclohexanedione, pKa 5.15), ethyl trifluoroacetoacetate (7.6), and isopropyl malonate (4.97). XH components with a boiling point of at least 175°C, more preferably at least 200°C, are preferred.

[0083] In another embodiment, the catalyst activator C1 is a methacrylate, fumarate, maleate, or itaconic acid acceptor group, preferably a methacrylate, itaconic acid, or fumarate group, and components P1 and T are acids with a pKa of less than 10.5, more preferably less than 9.5, 8, or even less than 7. - / XH component.

[0084] The pKa values ​​mentioned in this patent application are aqueous pKa values ​​under ambient conditions (21°C). They can be readily found in the literature and, if desired, can be determined in aqueous solutions using procedures known to those skilled in the art.

[0085] In order to provide a beneficial delay in the crosslinking reaction under curing conditions, the reaction of the retarder T and its deprotonated form P1 with the activator C1 should proceed at an appropriate rate.

[0086] A preferred separated catalyst system comprises an epoxy component as catalyst activator C1, a weakly basic nucleophilic anionic group as catalyst precursor P1 (which reacts with the epoxide group of C1 to form a strongly basic adduct C1), and most preferably, a retarder T. In a suitable separated catalyst system, P1 is a carboxylate, C1 is an epoxide, carbodiimide, oxadiene, or oxazoline, more preferably an epoxide or carbodiimide, and T is a carboxylic acid. Alternatively, P1 is DABCO, C1 is the epoxy component, and T is a carboxylic acid.

[0087] To avoid being bound by theory, it is assumed that the nucleophilic anion P1 reacts with the activator epoxide C1 to produce a strong base, but this strong base is immediately protonated by the retarder T to produce a salt (functionally similar to P1) that does not directly and strongly catalyze the crosslinking reaction. The reaction process occurs until the retarder T is essentially completely depleted, which provides an open time during which no significant amount of the strong base is available to significantly catalyze the reaction of the crosslinkable components A and B. When the retarder T is depleted, the strong base will form and persist to effectively catalyze the rapid RMA crosslinking reaction.

[0088] The features and advantages of the present invention will be understood when referring to the following exemplary reaction process.

[0089]

[0090] Specifically, for the cases where carboxylates, epoxides, and carboxylic acids are P1, C1, and T substances, they can be plotted as follows: **Replace image**

[0091]

[0092] In some cases, the detailed mechanism of the reaction between activator C1 and precursor P1 may be unknown or a subject of debate, and a reaction mechanism involving the protonated form of P1 actually involved in the reaction may be proposed. The net effect of such a reaction sequence may resemble the sequence described based on its progression through the deprotonated form of P1. Systems in which the reaction may be considered to proceed along the protonated P1 pathway are included in this invention. In this case, after the depletion of the repressor T, C1 will react with the protonated P1 generated by the acid-base equilibrium with Michael donor A, and the reaction will activate crosslinking because this acid-base equilibrium is pulled to the deprotonated Michael donor side.

[0093] If the activator will react via the protonated form of P1H, the reaction mechanism will be explained by the following mechanism:

[0094]

[0095] In one embodiment, the retardant T is a protonated anionic group P1, preferably a carboxylic acid T or a carboxylate P1, which can be formed, for example, by partially neutralizing an acid-functionalized component, preferably a polymer containing an acid group as the retardant T, to partially convert it into an anionic group on P1. The partial neutralization is preferably carried out by a cationic hydroxide or carbonate (bicarbonate) ion, preferably a tetraalkylammonium or tetraalkylphosphonium ion. In another embodiment, the polymer-bound component P1 can be prepared by hydrolyzing the ester groups in a polyester using the aforementioned hydroxide ions.

[0096] Preferably, the boiling points of the conjugate acids of components T and P1 are higher than the expected curing temperature of the powder coating composition blend to prevent poorly controlled evaporation of these catalyst system components during curing conditions. Formic acid and acetic acid are less preferred retarders T because they may evaporate during curing. Preferably, the boiling points of the conjugate acids of retarders T and P1 are above 120°C.

[0097] Although less preferred, at least one of the components P1, C1, or T in the separated catalyst system can be a group on a crosslinkable component A or B, or both. In this case, it must be ensured that P1 and C1 are macroscopically physically separated in the powder coating composition blend. One or more, but not all, of the groups P1, C1, and T can be on a crosslinkable RMA component A or B, or both. In a convenient embodiment, both P1 and T are on crosslinkable RMA components A and / or B, and P1 is preferably formed by neutralizing an acid-functionalized polymer containing acid groups of T with a base moiety containing a cation as described above to convert the acid group moiety on T into an anionic group on P1. Another embodiment will have a component P1 formed by the hydrolysis of a polyester (e.g., the polyester of component A) and existing in the form of a polymeric substance.

[0098] In the case of a separate catalyst system, the powder coating composition blend preferably comprises:

[0099] a. Activator C1, in an amount of 1-600 μeq / g, preferably 10-400, more preferably 20-200 μeq / g, wherein μeq / g is relative to the total weight of binder component A, component B, and the separated catalyst system.

[0100] b. A precursor of the weak base P1, in an amount of 1-300 μeq / g, preferably 10-200, more preferably 20-100 μeq / g, relative to the total weight of binder component A, component B, and the separated catalyst system.

[0101] c. An optional retardant T, in an amount of 1-500, preferably 10-400, more preferably 20-300 μeq / g, and most preferably 30-200 μeq / g.

[0102] d. The preferred equivalent of C1 is:

[0103] i. An equivalent higher than T, preferably 1-300 μeq / g, more preferably 10-200, and even more preferably 20-100 μeq / g.

[0104] ii. Preferably, the equivalent is higher than P1, and

[0105] iii. Preferably, the sum of the equivalents of P1 and T is higher.

[0106] However, in the case where the activator C1 is a Michael acceptor containing an activated unsaturated group C=C that can react with P1, there is no relevant upper limit on concentration, because in this case C1 can also be component B.

[0107] A separated catalyst system can also operate with a lower amount of C1 than P1. However, this is less preferred because it leaves unreacted P1. The disadvantages are limited when the amount of C1 (especially epoxides) is higher than P1, as it can react with P1 and T or other nucleophilic residues but remains basic after the reaction, or it can remain in the network without much problem. However, considering the cost of C1 other than the epoxide component, excess C1 may be disadvantageous.

[0108] Furthermore, preferably, in the powder coating composition blend:

[0109] a. The precursor P1 accounts for 10-100% of the sum of P1 and T.

[0110] b. The amount of the antagonist T is preferably 20-400 equivalents of the amount of P1, preferably 30-300 equivalents.

[0111] c. Preferably, the ratio of the equivalent of C1 to the sum of the equivalents of P1 and T is at least 0.5, preferably at least 0.8, more preferably at least 1, and preferably at most 3, more preferably at most 2.

[0112] The equivalence ratio of C1 to T is preferably at least 1, preferably at least 1.5, and most preferably at least 2.

[0113] 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 a catalyst precursor group P1 and optionally an acid group T, wherein the P1 group is preferably formed by partially or completely neutralizing the acid group T on the polymer, wherein P1 and T are preferably carboxylate and carboxylate groups, wherein said polymer is preferably selected from acrylic, polyester, polyester-amide, and polyester-urethane polymers, wherein said polymer optionally comprises a CH donor group, a C=C acceptor group, or both, wherein said polymer preferably has:

[0114] a) The acid value of the non-neutralized form is at least 3, more preferably 5, 7, 10, 15 or even 20 mg KOH / g, and preferably less than 100, 80, 70, 60 mg KOH / g.

[0115] b) Quaternary ammonium or phosphonium cations, preferably tetrabutylammonium or ethylammonium cations.

[0116] c) Mn is at least 500, preferably at least 1000 or even 2000, and Mw does not exceed 20000, preferably not exceeding 10000 or 6000.

[0117] d) In the presence of a CH donor and / or a C=C acceptor group, the reactive CH donor or C=C acceptor equivalent is 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.

[0118] A powder coating composition blend based on separated crosslinkable components

[0119] In one embodiment of the invention, crosslinkable components A and B are macroscopically physically separated. In this case, the catalyst system is a latent catalyst system (LCS) comprising catalyst precursor P1 and catalyst activator C1, or a non-latent catalyst system comprising a strong base (i.e., already capable of activating the RMA crosslinking reaction). The RMA reaction will only occur at the curing temperature, at which point components A and B become chemically contactable with each other and the catalyst system catalyzes the RMA reaction.

[0120] The potential catalyst system comprises the components C1, P1 and optional T as described above.

[0121] The non-potential catalyst system comprises a strong base with sufficiently high basicity, said basicity being sufficient to deprotonate the Michael donor group to initiate RMA crosslinking with the present donor and acceptor. The strong base can include many active catalysts described in the literature, typically salts of basic anions (e.g., hydroxide, carbonate) and non-acidic cations (alkali or alkaline earth metals, quaternary ammonium or phosphonium ions), strongly basic amines such as amidines and guanidines (e.g., DBU, DBN, TBD, or TMG), and other strong bases known to those skilled in the art.

[0122] Crosslinkable component A and component B

[0123] The powder coating composition blend further comprises a crosslinkable composition, the crosslinkable composition comprising:

[0124] a) A crosslinkable donor component A, which has at least two acidic CH donor groups in the activated methylene or methine group, and

[0125] b) A crosslinkable receptor component B having at least two activated unsaturated receptor groups C=C, which react with component A via true Michael addition (RMA) to form a crosslinked network.

[0126] Preferably, the crosslinkable component A contains at least two acidic CH donor groups in the activated methylene or methine of structure Z1(-C(-H)(-R)-)Z2, wherein R is hydrogen, hydrocarbon, oligomer, or polymer, and wherein Z1 and Z2 are the same or different electron-withdrawing groups, preferably selected from ketone, ester, cyano, or aryl groups, and preferably includes activated CH derivatives having the structure of Formula 1:

[0127]

[0128] Wherein R is hydrogen or an optionally substituted alkyl or aryl group, Y and Y' are the same or different substituents, preferably alkyl, aralkyl, aryl or alkoxy, or wherein in Formula 1, -C(=O)-Y and / or -C(=O)-Y' is replaced by CN or aryl, not more than one aryl group, or wherein Y or Y' may be NRR' (R and R' are H or optionally substituted alkyl groups), but preferably not both, wherein R, Y or Y' optionally provides a link to the oligomer or polymer, wherein component A is preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, preferably providing at least 50%, preferably 60%, 70% or even 80% of the total amount of CH acidic groups in crosslinkable component A.

[0129] Component B contains at least two activated unsaturated RMA acceptor groups, preferably derived from acryloyl, methacryloyl, itaconic acid, maleate, or fumarate functional groups.

[0130] Preferably, at least one of component A or B, more preferably both, is a polymer.

[0131] Preferably, the crosslinkable composition comprises 0.05-6 meq / g binder solids of donor groups CH and acceptor groups C=C, and preferably the ratio of acceptor groups C=C to donor groups CH is greater than 0.1 and less than 10.

[0132] True Michael addition (RMA) crosslinkable coating compositions containing crosslinkable component A and component B are generally described for use in solvent-based systems in EP2556108, EP0808860 or EP1593727, with a detailed description of crosslinkable component A and component B provided therein.

[0133] Components A and B each contain an RMA reactive donor and acceptor moieties, which react upon curing to form a crosslinked network in the coating. Components A and B can exist on individual molecules, or on a single molecule (referred to as a hybrid A / B component), or in combination thereof. They cannot be hybrid A / B components if the crosslinkable components A and B are macroscopically physically separated.

[0134] Preferably, components A and B are separate molecules, each independently existing as a polymer, oligomer, dimer, or monomer. For coating applications, at least one of components A or B is preferably an oligomer or polymer. Notably, the activated methylene CH2 contains two CH acid groups. Even after the reaction of the first CH acid group, the reaction of the second CH acid group is more difficult, for example, with methacrylates, where the activated methylene has a functionality of 2 compared to acrylates. Reactive components A and B can also be combined into an A / B blend molecule. In this embodiment of the powder coating composition blend, both CH and C=C reactive groups are present in a single AB molecule.

[0135] Preferably, component A is a polymer having component A as a functional group and optionally one or more components B or components from the catalytic system C, preferably polyester, polyurethane, acrylic, epoxy, or polycarbonate. Furthermore, mixtures or hybrids of these polymer types are also possible. Suitably, component A is a polymer selected from acrylic, polyester, polyesteramide, and polyester-urethane polymers.

[0136] Malonate or acetoacetate is a preferred donor type in component A. Considering the high reactivity and durability in the most preferred embodiment of the crosslinkable composition, component A is a compound containing malonate (CH). Preferably, in the powder coating composition blend, the majority of the activated CH groups originate from malonate, i.e., more than 50%, preferably more than 60%, more preferably more than 70%, and most preferably more than 80% of all activated CH groups in the powder coating composition blend originate from malonate.

[0137] Preferred components are those containing oligomeric and / or polymeric malonic acid ester groups, such as polyester, polyurethane, polyacrylate, epoxy resin, polyamide and polyethylene resin, or mixtures thereof containing malonic acid ester type groups in the main chain, side chain or both.

[0138] The total amount of donor CH groups and acceptor C=C groups per gram of binder solids, regardless of their distribution on various crosslinkable components, is preferably 0.05-6 meq / g, more typically 0.10-4 meq / g, even more preferably 0.25-3 meq / g, and most preferably 0.5-2 meq / g binder solids. Preferably, the stoichiometry between component A and component B is chosen such that the ratio of reactive C=C groups to reactive CH groups is greater than 0.1, preferably greater than 0.2, more preferably greater than 0.3, and most preferably greater than 0.4, and in the case of acrylate functional group B, preferably greater than 0.5, most preferably greater than 0.75, and this ratio is preferably less than 10, preferably 5, more preferably less than 3, 2, or 1.5.

[0139] Polyesters containing malonic acid groups can preferably be obtained by transesterification of methyl or ethyl malonic acid with a polyfunctional alcohol, which may be polymeric or oligomeric, but can also be introduced through Michael addition reactions with other components. Particularly preferred components containing malonic acid groups for use in this invention are oligomeric or polymeric esters, ethers, urethanes, and epoxy esters and mixtures thereof containing malonic acid groups, such as polyester-urethanes containing 1-50, more preferably 2-10 malonic acid groups per molecule. Polymer component A can also be prepared in known ways, for example by free radical polymerization of olefinically unsaturated monomers (including monomers such as (meth)acrylates), with partial functionalization containing activated CH acid (donor) groups (preferably acetoacetate or malonic acid groups, particularly 2-(methacryloyloxy)ethylacetoacetate or malonic acid). In practice, polyesters, polyamides, and polyurethanes (and mixtures thereof) are preferred. It is also preferred that the number average molecular weight (Mn) of the component containing malonic acid ester groups is about 100-10000, preferably 500-5000, most preferably 1000-4000, and Mw is less than 20000, preferably less than 10000, most preferably less than 6000 (expressed in GPC polystyrene equivalent).

[0140] Suitable crosslinkable component B can typically be an olefinic unsaturated component in which the 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 US2759913 (column 6, line 35 to column 7, line 45), DE-PS-835809 (column 3, lines 16-41), US4871822 (column 2, lines 14 to column 4, line 14), US4602061 (column 3, lines 14-20 to column 4, line 14), US4408018 (column 2, lines 19-68), and US4217396 (column 1, line 60 to column 2, line 64).

[0141] Preferred resins include acrylates, methacrylates, itaconic acid esters, fumarates, and maleates. Itaconic acid esters, fumarates, and maleates can be incorporated into the backbone of polyesters or polyester-urethane esters. Preferred examples of resins include, for example, polyesters, polycarbonates, polyurethanes, polyamides, acrylics and epoxy resins (or mixtures thereof), polyethers, and / or alkyd resins containing activated unsaturated groups. These include, for example, urethane (meth)acrylates obtained by reacting polyisocyanates with hydroxyl-containing (meth)acrylates (e.g., hydroxyalkyl esters of (meth)acrylate), or components prepared by esterification of a polyhydroxy component with less than a stoichiometric amount of (meth)acrylate, polyether (meth)acrylates obtained by esterification of a hydroxyl-containing polyether with (meth)acrylate, multifunctional (meth)acrylates obtained by reacting hydroxyalkyl (meth)acrylates with polycarboxylic acids and / or polyamino resins, poly(meth)acrylates obtained by reacting (meth)acrylate with epoxy resins, and polyalkyl maleate esters obtained by reacting monoalkyl maleate with epoxy resins and / or hydroxyl-functional oligomers or polymers. Similarly, polyesters capped with glycidyl methacrylate are preferred examples. The acceptor component can contain various types of acceptor functional groups.

[0142] The most preferred component B, containing activated unsaturated groups, is a component functionalized with unsaturated acryloyl, methacryloyl, and fumarate groups. Preferably, the number-average functionality per molecule of activated C=C groups is 2-20, more preferably 2-10, and most preferably 3-6. The equivalent weight (EQW: average molecular weight per reactive functional group) is 100-5000, more preferably 200-2000, and the number-average molecular weight Mn is preferably 200-10000, more preferably 300-5000, most preferably 400-3500 g / mol, and even more preferably 1000-3000 g / mol.

[0143] Given its use in powder systems, and due to the requirement for powder stability, component B preferably has a Tg higher than 25, 30, or 35, more preferably at least 40 or 45, and most preferably at least 50°C or even at least 60°C. Tg is defined as measured using DSC at the midpoint of the heating at a heating rate of 10°C / min. As those skilled in the art will understand, if the Tg of one component is significantly higher than 50°C, the Tg of the other formulation components may be lower.

[0144] Suitable component B is a urethane (meth)acrylate, prepared by reacting a hydroxyl and (meth)acrylate-functionalized compound with an isocyanate to form a urethane bond, wherein the isocyanate is preferably at least partially a diisocyanate or triisocyanate, preferably isophorone diisocyanate (IPDI). The urethane bond itself introduces stiffness, but it is preferable to use a high Tg isocyanate, such as an alicyclic or aromatic isocyanate, preferably an alicyclic one. The amount of such isocyanate is preferably selected such that the Tg of the (meth)acrylate-functionalized polymer is increased to above 40°C, preferably above 45°C or 50°C.

[0145] The preferred design of the powder coating composition blend is such that the crosslinking density (using DMTA) after curing can be measured 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.

[0146] The powder coating composition blend should remain a free-flowing powder under ambient conditions, therefore, Tg is preferably above 25°C, more preferably above 30°C, and more preferably above 35, 40, or 50°C, as the midpoint value determined by DSC at a heating rate of 10°C / min.

[0147] As mentioned above, the preferred component A is a malonate-functionalized component. However, the introduction of the malonate moiety tends to lower the Tg, and providing a powder coating composition blend with a sufficiently high Tg based on malonate as the main component A has always been a challenge.

[0148] To obtain a high Tg, the powder coating composition blend preferably includes a crosslinkable donor component A and / or a crosslinkable acceptor component B (which may be in the form of a hybrid component A / B) comprising amide, urea, or urethane bonds, and / or the crosslinkable composition contains a high Tg monomer, preferably an alicyclic or aromatic monomer, or, in the case of a polyester, one or more monomers selected from 1,4-dimethylolcyclohexane (CHDM), tricyclodecanediethanol (TCD diol), isosorbide, pentaspirol, hydrogenated bisphenol A, and tetramethylcyclobutanediol.

[0149] In addition, in order to obtain a high Tg, the powder coating composition blend includes component B or hybrid component A / B which is polyester (meth)acrylate, polyester urethane (meth)acrylate, epoxy (meth)acrylate or urethane (meth)acrylate, or a polyester containing fumarate, maleate or itaconic acid (preferably fumarate) units, or a polyester end-capped with an activated unsaturated group with isocyanate or epoxy functionality.

[0150] Most preferably, the powder coating composition blend comprises an RMA-crosslinkable composition having characteristics suitable for use in RMA-crosslinkable powder coating composition blends. In particular, to obtain good flowability and leveling properties, as well as good chemical and mechanical resistance, it is found that at least one of the crosslinkable components A or B, or a mixture of A / B, is preferably a polymer in the powder coating composition blend, preferably selected from acrylics, polyesters, polyesteramides, and polyester-urethane polymers, wherein the polymer:

[0151] a) The number-average molecular weight Mn, as determined by GPC, is at least 450 g / mol, preferably at least 1000, more preferably at least 1500, and most preferably at least 2000 g / mol.

[0152] b) The weight-average molecular weight (Mw) determined by GPC is 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.

[0153] c) The polydispersity Mw / Mn is preferably less than 4, more preferably less than 3, and significantly greater than 1.

[0154] d) The equivalent weight (EQW) in CH or C=C is at least 150, 250, 350, 450, or 550 g / mol, and preferably at most 2500, 2000, 1500, 1250, or 1000 g / mol, and the number-average functionality of the reactive group CH or C=C is 1-25 per molecule, more preferably 1.5-15, even more preferably 2-15, and most preferably 2.5-10 CH groups.

[0155] e) The melt viscosity at a temperature of 100-140°C is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas.

[0156] f) Preferably, polyester monomers contain amide, urea, or urethane bonds and / or contain high Tg monomers, preferably alicyclic or aromatic monomers, particularly polyester monomers selected from 1,4-dimethylolcyclohexane (CHDM), tricyclodecanediethanol (TCD diol), isosorbide, pentaspirol, or hydrogenated bisphenol A and tetramethylcyclobutanediol.

[0157] g) A Tg of 25°C or higher, preferably 35°C or higher, more preferably 40, 50 or even 60°C or higher, as the midpoint value determined by DSC at a heating rate of 10°C / min, or a crystalline polymer with a melting temperature of 40-150°C, preferably 130°C, preferably at least 50 or even 70°C and preferably below 150, 130 or even 120°C (determined by DSC at a heating rate of 10°C / min).

[0158] The selection of the polymer characteristics Mn, Mw, and Mw / Mn takes into account the required powder stability, the desired low melt viscosity, and the envisioned coating performance. High Mn is preferred to minimize the Tg reduction effect of the end groups, while low Mw is preferred because melt viscosity is highly correlated with Mw and low viscosity is required; therefore, a low Mw / Mn ratio is preferred.

[0159] To obtain high Tg, the crosslinkable polymer of RMA preferably includes amide, urea or urethane bonds and / or contains high Tg monomers, preferably alicyclic or aromatic monomers, or in the case of polyesters, contains monomers selected from 1,4-dimethylolcyclohexane (CHDM), TCD diol, isosorbide, pentaspirol or hydrogenated bisphenol A and tetramethylcyclobutanediol.

[0160] When the RMA-crosslinkable polymer is an A / B hybrid polymer, it is further preferred that the polymer also contains one or more component B groups selected from: acrylate or methacrylate, fumarate, maleate, and itaconic acid ester, preferably (meth)acrylate or fumarate. Furthermore, if intended for use as a crystalline material, the RMA-crosslinkable polymer preferably has a crystallinity with a melting temperature of 40-130°C, preferably at least 50 or even 70°C, and preferably below 150, 130, or even 120°C (determined by DSC at a heating rate of 10°C / min). Note that this is the melting temperature of the (pure) polymer itself, not the melting temperature of the polymer in the blend.

[0161] In a preferred embodiment, the RMA-crosslinkable polymer comprises a polyester, polyesteramide, polyester-urethane, or urethane-acrylate containing urea, urethane, or amide bonds derived from alicyclic or aromatic isocyanates, preferably alicyclic isocyanates, wherein the polymer has a Tg of at least 40°C, preferably at least 45 or 50°C and at most 120°C, and a number-average molecular weight Mn of 450–10000, preferably 1000–3500 g / mol, preferably a maximum Mw of 20000, 10000, or 6000 g / mol, and the polymer provides an RMA-crosslinkable component A or B, or both. The polymer can be obtained, for example, by reacting a precursor polymer containing the RMA-crosslinkable group with a certain amount of alicyclic or aromatic isocyanate to increase the Tg. The amount of such isocyanate added or the amount of urea / urethane bond formed is selected such that the Tg is increased to at least 40°C, preferably at least 45 or 50°C.

[0162] Preferably, the crosslinkable polymer of RMA is a polyester or polyester-urethane containing malonic acid ester as the main component A and 1-25, more preferably 1.5-15, even more preferably 2-15, and most preferably 2.5-10 malonic acid ester groups per molecule with a number-average malonic acid ester functionality, having a GPC weight-average molecular weight of 500-20000, preferably 1000-10000, and most preferably 2000-6000 g / mol, and is prepared by reacting a polymer with hydroxyl and malonic acid ester functionalities with isocyanate to form urethane bonds.

[0163] Furthermore, the polymer can be an amorphous or (semi-)crystalline polymer or a mixture thereof. Semi-crystalline refers to a partially crystalline and partially amorphous state. The degree of (semi-)crystallinity is defined by the DSC melting endothermic temperature, and the target crystallinity is defined as a DSC peak melting temperature Tm of at least 40°C, preferably at least 50°C, more preferably at least 60°C, and 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.

[0164] Substrate and coating

[0165] The present invention also relates to a method for powder coating a substrate, comprising:

[0166] a. Providing a blend of the powder coating composition of the present invention.

[0167] b. Apply a layer of powder to the surface of the substrate, and

[0168] c. Heating to a curing temperature T between 75-200°C, preferably 80-180°C, more preferably 80-160, 150, 140, 130, or even 120°C. curOptionally and preferably, infrared heating is used, and

[0169] d. In T cur For the next curing step, a curing time of less than 40, 30, 20, 15, 10, or even 5 minutes is preferred.

[0170] In the method described, at T cur The curing characteristics are preferably defined by a curing curve determined by FTIR measurement of the conversion rate of unsaturated C=C bonds in component B as a function of time, wherein the ratio of the time for the C=C conversion from 20% to 60% to the time for reaching 20% ​​conversion is less than 1, preferably less than 0.8, 0.6, 0.4, or 0.3, and preferably less than 30, 20, or 10 minutes for reaching 60% conversion, and at T cur The melt viscosity of the powder coating composition at the curing temperature is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas. The melt viscosity is measured at the beginning of the reaction or in the absence of a catalytic system in C2.

[0171] In a preferred embodiment of the method, the curing temperature is 75-140°C, preferably 80-120°C, and the catalyst system C is a latent catalyst system as described above, which allows powder coating of a temperature-sensitive substrate, preferably MDF, wood, plastic, or a temperature-sensitive metal substrate, such as an alloy.

[0172] Therefore, the present invention also relates to articles 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 wherein preferably, the crosslinking density XLD of the coating is at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / cc (determined by DMTA) and preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / cc.

[0173] The present invention will be illustrated by the following examples.

[0174] Test methods

[0175] acid value

[0176] A freshly prepared 1:1 xylene:ethanol solvent mixture was prepared. A measured amount of resin was accurately weighed into a 250 ml Erlenmeyer flask. Then, 50–60 ml of the 1:1 xylene:ethanol mixture was added. The solution was gently heated until the resin was completely dissolved, ensuring that the solution did not boil. The solution was then cooled to room temperature and potentiometrically titrated with 0.1 M potassium hydroxide until the equivalence point was reached.

[0177] OH value

[0178] The OH value (OHV) is defined as the number of mg of KOH equivalent to the amount of acetic acid esterified after the hydroxyacetylation reaction of 1 g of sample. OHV is determined by manually titrating blank and sample flasks. An acetylation solution is prepared by weighing 15 g (accuracy 0.001) of acetic anhydride diluted with analytical grade pyridine in a 250 mL Erlenmeyer flask. 20 mL of the acetylation mixture is added to a flask containing the precisely weighed sample. The acetylation solution containing the sample is placed in a 100 °C incubator and refluxed for 1 hour. After cooling and adding water to hydrolyze unreacted acetic anhydride, the solution containing the sample is ready for titration. The blank solution is prepared using the same procedure, except that no sample is added. An indicator solution is prepared by dissolving 0.80 g of thyme blue and 0.25 g of cresol red in 1 L of methanol. 10 drops of the indicator solution are added to the flask, and then titrated with a standard 0.5 N methanol-potassium hydroxide solution. The endpoint is reached when the color changes from yellow to gray and then to blue, remaining blue for 10 seconds. The hydroxyl value is then calculated using the following formula:

[0179] Hydroxyl value = (BS) x N x 56.1 / M + AV

[0180] in:

[0181] B = the number of milliliters (ml) of KOH used for blank titration

[0182] S = number of milliliters of KOH used for sample titration

[0183] N = equivalent to potassium hydroxide solution

[0184] M = Sample weight (base resin)

[0185] AV = Acid value of the base resin

[0186] The net hydroxyl value is defined as: Net OHV = (BS) x N x 56.1 / M

[0187] Amine value

[0188] Prepare a freshly prepared 3:1 xylene:ethanol-propanol solvent mixture. Accurately weigh a certain amount of resin into a 250 ml Erlenmeyer flask. Then add 50-60 ml of the 3:1 xylene:ethanol mixture. Gently heat the solution until the resin is completely dissolved, ensuring the solution does not boil. Then cool the solution to room temperature and perform potentiometric titration with 0.1 M hydrochloric acid until the equivalence point is reached.

[0189] GPC molecular weight

[0190] The molar mass distribution of the polymer was determined by gel permeation chromatography (GPC) on a Perkin-Elmer HPLC Series 200 instrument, using a refractive index (RI) detector and a PLgel column, with THF as eluent and calibration using polystyrene standards. The molecular weights are expressed as polystyrene equivalents.

[0191] DSC Tg

[0192] The glass transition temperatures of the resins and coatings reported in this article were determined by differential scanning calorimetry (DSC) using a heating rate of 10 °C / min, specifically the midpoint Tg.

[0193] Thin film thickness (DFT)

[0194] Film thickness (DFT) was measured using a Posector 6000 coating thickness gauge.

[0195] Gloss (60°)

[0196] The gloss of the coating was measured using a Zehntner ZGM 1130 gloss meter.

[0197] Solvent resistance

[0198] The solvent resistance of the cured film was measured by wiping it back and forth with a small cotton ball saturated with methyl ethyl ketone (MEK). The resistance was determined by the number of wiping cycles (50 times) or by using a rating system as described below (0-5 times, best to worst).

[0199] 0. No obvious changes. Do not scratch with fingernails.

[0200] 1. Slightly reduced gloss

[0201] 2. The gloss has decreased.

[0202] 3. The coating has a very dull finish and can be scratched with a fingernail.

[0203] 4. The coating is matte and quite soft.

[0204] 5. Coating cracking

[0205] Chemical storage stability

[0206] The chemical stability of powder coating compositions can be determined by measuring the kinetic curves of the compositions using differential scanning calorimetry (DSC). In this method, we measure the exothermic reaction of the powder coating composition at a relevant temperature as a function of time in an isothermal scan. The sample is heated to the curing temperature of interest at a rate of 60 °C / min, and the heat generated from this moment is measured as a function of time. An exothermic peak is typically observed after a certain induction time. The onset time (in minutes) of this exothermic reaction is recorded as ts. We can determine ts when the powder coating composition is freshly prepared (i.e., tsf) and after storage at 35 °C for a certain time (i.e., tss). Alternatively, for powder coating compositions with a short or no induction time at the temperature of interest, we can measure the exothermic reaction in a temperature scan between 10–230 °C. Using this method, the onset of the exothermic reaction is observed at a specific temperature, and it can be re-plotted to determine the onset time because the heating rate is constant at 10 °C / min. The storage stability factor (SSF) can be determined by dividing the difference between tsf and tss by the storage time (t).

[0207] SSF(DSC)=(tsf–tss) / t

[0208] This factor indicates the degree of premature reaction of the powder coating composition during storage. The SSF value of the powder coating composition is preferably close to 0 min / day, and preferably less than 0.1 min / day.

[0209] Particle size measurement

[0210] Particle size was measured using static light scattering (SLS) with a Malvern Mastersizer 3000 equipped with an Aero S powder dispersion unit. The feed rate and dispersion rate of the powder in the optical chamber were set to 35%, and the pressure was not exceeding 2 bar. Volumetric particle size distribution was determined according to the Fraunhofer diffraction method. Each value given is the average of five measurements of Dx(50).

[0211] abbreviation

[0212] Table 1: Explanation of abbreviations used in the embodiments

[0213] NPG Neopentyl glycol IPA isophthalic acid TPA terephthalic acid IPDI Isophorone diisocyanate TGIC Triglycidyl isocyanurate <![CDATA[TEAHCO3]]> Tetraethylammonium bicarbonate Methyl ethyl ketone MEK AV acid value OHV Hydroxyl value Acid value Wt% weight percentage Mn Number average molecular weight Mw weight average molecular weight Tg Glass transition temperature EQW Equivalent weight

[0214]

[0215] Material preparation

[0216] Preparation of malonate donor resins

[0217] Add 1300 g of isosorbide (80%), 950 g of NPG, and 1983 TPA to a 5-liter round-bottom reactor equipped with a 4-necked cap, a metal anchor stirrer, Pt-100, a packed column with a top thermometer, a condenser, a distillate collection vessel, a thermocouple, and an N2 inlet. Slowly raise the reactor temperature to approximately 100°C and add 4.5 g of... KR46B catalyst. The reaction temperature was gradually increased to 230°C, and polymerization was carried out with continuous stirring under nitrogen until the reaction mixture was clear and the acid value was below 2 mg KOH / g. In the final part of the reaction, a vacuum was applied to drive the reaction to completion. The temperature was lowered 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 applied again to drive the reaction to completion. After the transesterification reaction was completed, the hydroxyl value of the polyester was measured. The final OHV was 27 mg KOH / g, GPC Mn was 1763, Mw was 5038, and Tg(DSC) was 63°C.

[0218] Preparation of urethane acrylate acceptor resins

[0219] As described in, for example, EP0585742, a urethane-acrylate based on IPDI, hydroxypropyl acrylate, and glycerol was prepared by adding a suitable polymerization inhibitor. In a 5-liter reactor equipped with a thermometer, stirrer, feed funnel, and bubble inlet, 1020 parts of IPDI, 1.30 parts of dibutyltin dilaurate, and 4.00 parts of hydroquinone were added. Then, 585 parts of hydroxypropyl acrylate were added, taking care to prevent the temperature from rising above 50°C. Once the addition was complete, 154 parts of glycerol were added. The reaction product was cast onto a metal tray 15 minutes after the exothermic reaction subsided. The resulting urethane-acrylate was characterized by a GPC Mn of 744, a Mw of 1467, a Tg (DSC) of 51°C, a residual isocyanate content of <0.1%, and a theoretical degree of unsaturation (EQW) of 392.

[0220] Preparation of epoxy-acrylate acceptor resin

[0221] 640 g of bisphenol A epoxy resin (Mn approximately 1075), 3.20 g of 4-methoxyphenol (MEHQ), 3.20 g of β-ionol, and 4.73 g of ethyltriphenylphosphine bromide were placed in a 3-liter reaction vessel and heated to 135 °C with stirring. In a separate flask, 81.50 g of acrylic acid was mixed with 0.08 g of MEHQ and 0.03 g of phenothiazine, and then added to the reaction vessel over 30 minutes. The reaction was allowed to proceed at 130 °C for another 5 hours until completion (AV = 0). The final product had a GPC Mn of 1399, a Mw of 4956, a Tg (DSC) of 39 °C, and a theoretical degree of unsaturation EQW of 637.

[0222] Preparation of carboxylic acid ester end-capping repressant resin

[0223] 1180 g of NPG and 2000 g of IPA were added to a 5-liter round-bottom reactor equipped with a 4-neck cap, a metal anchor stirrer, Pt-100, a packed column with a top thermometer, a condenser, a distillate collection vessel, a thermocouple, and an N2 inlet. The reactor temperature was raised to 230 °C, and polymerization was carried out under continuous stirring under nitrogen until the reaction mixture became clear. The final product obtained had an AV of 48 mg KOH / g and a Tg (DSC) of 55 °C.

[0224] Preparation of catalyst precursors

[0225] To prepare the catalyst precursor, a Leistritz ZSE 18 twin-screw extruder was used to melt a carboxylate-terminated polyester resin (AV 48) and mix it with an aqueous solution (41%) of tetraethylammonium bicarbonate (TEAHCO3). The extruder comprised a barrel housing nine consecutive heating zones configured to maintain the following temperature distribution from inlet to outlet: 30-50-80-120-120-120-100-100 (°C). Solid polyester resin was added through the first zone at a rate of 2 kg / h, and liquid TEAHCO3 was injected through the second zone at a rate of 0.60 kg / h. Mixing took place between zones 4 and 7, with the screw set to rotate at 200 rpm. Volatile substances and water generated by acid-base neutralization were removed in zone 7 under vacuum assistance. The extruded strands were cooled and collected immediately after exiting the die. The final product obtained had an AV of 11 mg KOH / g, an amine value of 33 KOH / g, and a Tg (DSC) of 48℃.

[0226] Preparation of comparative (semi-)crystalline vinyl ether carbamate resin CVE-1

[0227] The component was described and prepared according to the content disclosed in CN11245771. 290 g of 4-hydroxybutylvinyl ether, 0.6 g of dibutyltin dilaurate (DBTL), and 0.2 g of 2,5-di-tert-butyl-1,4-hydroquinone (BHT) were charged into a four-necked reactor equipped with a thermometer, stirrer, and distillation apparatus. The mixture was stirred under an oxygen stream and heated to 40 °C. Then, 210 g of hexamethylene-1,6-diisocyanate (HDI) was slowly added dropwise to the reactor to initiate the reaction, and the process temperature was maintained below 110 °C. After all the HDI was added, the reaction was allowed to proceed at 110 °C for 30 minutes. The maximum DSC melting temperature and the final DSC melting temperature of the obtained (semi-)crystalline vinyl ether CVE-1 were 87 °C and 107 °C, respectively. The theoretical unsaturated EQW = 200 g / mol.

[0228] The activator was loaded onto the precipitated silica carrier.

[0229] 175g ABS-D precipitated silica (particle size = 40 μm) was loaded into a 5-liter reactor equipped with a commercial vertical mixer. The mixer was turned on to reach a stable state, and then 325 g of... Resin 1510 is slowly added to the reactor. The mixture is allowed to stand and stirred until it is completely homogenized, and then discharged.

[0230] Powder coating compositions and powder coating component composition formulations

[0231] To prepare powder coating composition blends (PW1-2) or powder coating components (PWC3A and 3B, 4A and 4B, 5A, 6A, 7A, 8A and 8B, 9A and 9B), the raw materials were first premixed at 1500 rpm for 20 seconds in the premixer of a high-speed Thermoprism pilot mixer, and then extruded in a Baker Perkins (formerly APV) MP19 25:1L D twin-screw extruder. The extruder speed was 250 rpm, and the temperatures of the four extruder barrel zones were set to 15, 25, 80, and 100°C, respectively.

[0232] After extrusion, the extrudate was ground using a Kemutec laboratory classifier. The classifier was set to 5.5 rpm, the rotor to 7 rpm, and the feed to 5.2 rpm. TGIC was ground using a Retsch GRINDOMIX GM 200 grinder. The ground extrudate and TCIC were sieved to below 100 μm using a Russell Finex 100-micron Demi Finex laboratory vibrating sieve. The formulation compositions (parts by weight) of PW1-2, PWC3, PWC4, PWC5, PWC6, PWC7, PWC8, and PWC9 are given in Tables 1, 3, 8 and 10, 12, and 13, respectively.

[0233] result

[0234] PW1 and PW2 are comparative examples of powder coating compositions in which all compounds listed in Table 1 are extruded together.

[0235] Comparative powder coating compositions PW1-PW2 were sprayed onto the panel and cured at 120°C for 20 minutes. MEK resistance, dry film thickness, and 60° gloss are summarized in Table 2. Kinetic curves of the freshly prepared and aged compositions were measured by DSC using a 120°C isothermal scan to determine the storage stability factor (SSF). Figure 1As shown in Table 2 for PW1, some premature reactions occurred during storage because a pre-set exothermic reaction time began earlier. Table 2 also summarizes the SSF of two comparative examples.

[0236] Table 1: Comparison of Powder Coating Compositions PW1-PW2

[0237]

[0238] Table 2: Application and Storage Results of PW1-PW2 Powder Coating Compositions

[0239] PW1 PW2 MEK resistance (repeated wiping) >50 >50 Film thickness DFT (μm) 95 102 Gloss (60°) 93 91 Storage stability factor at 35°C, average over 5 days (min / day). 0.602 0.396

[0240] Four different powder coating composition blends of the present invention were prepared by blending powder coating component PWC3A with powder coating components PWC3B1, PWC3B2, PWCB3, or PWC3B4. The blends were sprayed onto panels and cured in a gradient oven at 120-150°C for 20 minutes. In all cases, the gloss of the coatings was significantly lower than that of comparative example PW1. Furthermore, the storage stability factor (SSF) was determined by measuring the kinetic curves of freshly prepared and aged blends using DSC with isothermal scanning at 120°C. Figure 2 An example of such a measurement is shown for the PWC3A+PWC3B1 50 / 50 blend. After storage at 35°C for 30 days, the change in curing kinetics is negligible because all SSF values ​​are close to zero (see Tables 4-7). These tables show that all coatings exhibit good MEK resistance and reduced gloss.

[0241] Table 3: Powder Coating Components Using Epoxy-Acrylic Ester as Acceptor

[0242] PWC3A = precursor composition, PWC3B = activator composition

[0243]

[0244]

[0245]

[0246] PWC4A and PWC4B were blended in different proportions to prepare powder coating composition blends of the present invention (Table 8). The blends were sprayed onto panels and cured in a gradient oven at 120-150°C for 20 minutes. In all cases, the coating gloss was significantly lower than that of comparative example PW2. The storage stability factor (SSF) was determined by measuring the kinetics of the freshly prepared and aged blends using DSC with a 120°C isothermal scan. After 30 days of storage at 35°C, the change in curing kinetics was negligible, as all SSF values ​​were close to zero (see Table 9).

[0247] Table 8: Powder Coating Component Compositions Using Carbamate-Acrylic Ester as Acceptors

[0248] PWC4A = precursor composition, PWC4B = activator composition

[0249]

[0250]

[0251] A 20 / 1 ratio of PWC5A and PWC5B (compositions shown in Table 10) was blended and applied as a powder coating composition to a panel by spraying. The blend was cured at 140°C for 15 minutes. Compared to comparative example PW2, the gloss level decreased to 43 GU at 60°C. Kinetic curves of the freshly prepared and aged blends were measured by DSC at a constant heating rate of 10°C / min using a temperature scan of 10–230°C. The re-plotted DSC curves determined the storage stability factor (SSF), such as... Figure 3 As shown in Table 11, after 30 days of storage at 35°C, the change in curing kinetics is negligible because the SSF is close to zero.

[0252] Table 10: Powder Component Compositions

[0253] PWC5A = precursor component, PWC5B = activator on the support

[0254]

[0255] Table 11: Application and storage results of powder coating blends of PW5A+PW5B blends in a 20 / 1 ratio.

[0256] Dry blend mixing ratio (wt / wt) (PWC5A / PWC5B) 20 / 1 MEK tolerance, 30 cycles (0-5, best to worst) 2 Film thickness DFT (μm) 92 Gloss (60°) 43 SSF at 35℃, 30-day average (min / day) <0.05

[0257] PWC6A and PWC7A are powder coating compositions having the compositions given in Table 12. These were prepared to prepare comparative powder coating composition blends PW6 and PW7 (which correspond to the powder disclosed in patent application CN112457751). PWC6A includes CVE-1, which is a crystalline component used as a plasticizer. PWC6A and PWC7A do not contain any activator components. PWC6 and PW7 powder coating composition blends PW6 and PW7 were prepared by blending PWC6A (average particle size 38 μm) and PWC7A (average particle size 31 μm) with milled TGIC powder (average particle size 21 μm) as an activator component in a ratio of 98:2. It should be noted here that a ratio of 94:6 was used in CN112457751. However, a lower amount of TGIC was used for comparison with the embodiments of the present invention provided herein. PW6 and PW7 were sprayed onto the aluminum Q-panel and cured at 100°C for 20 minutes.

[0258] Table 12: Comparison of Powder Coating Components PWC6A and PWC7A

[0259] Comparison of powder coating compositions (parts by weight) PWC6A PWC7A Malonate donor 415 503 Crystalline vinyl ether (CVE-1) 104 Carbamate-acrylate receptors 369 366 Catalyst precursor 102 84 Restrictor resin 37 Modaflow P6000 10 10 total 1000 1000

[0260] Table 13: Powder Coating Component Compositions PWC8A, PWC8B, PWC9A and PWC9B

[0261]

[0262] The powder coating composition blend PW8 of the present invention was prepared by blending precursor powder coating component PWC8A (average particle size 36 μm) and activator powder coating component PWC9B (average particle size 36 μm) in a 54 / 46 ratio. The overall composition of the powder coating blend is identical to the comparative powder coating blend PW6 in terms of the donor / acceptor ratio, the relative amounts of the catalyst precursor concentration and the activator concentration. The blend of the present invention was sprayed onto an aluminum Q-panel and cured at 100°C for 20 minutes. Compared to the comparative powder coating blend PW6, the coating blend PW8 of the present invention exhibited better solvent resistance and lower gloss. These application results are summarized in Table 14.

[0263] Figure 4 DSC isothermal analysis of powder coating blends PW6 and PW8 at 100°C is shown. It is clearly visible that no exothermic reaction peak was observed for PW6, indicating that little or no curing occurred at 100°C. Furthermore, DSC temperature scan analysis of the two powder coating blends (see...) Figure 5 This indicates that PW8 cures faster than PW6 because a set of curing processes begins at a lower temperature and the reaction is completed earlier.

[0264] Similarly, the powder coating composition blend PW9 of the present invention was prepared by blending precursor composition PWC9A (average particle size 34 μm) and activator composition PWC9B (average particle size 34 μm) in a 53 / 47 ratio (see Table 13). The overall composition of the powder coating blend is the same as the comparative powder coating blend PW7, considering the relative amounts of donor / acceptor ratio, catalyst precursor concentration, and activator concentration. The mixture of the present invention was sprayed onto an aluminum Q-panel and cured at 120°C for 20 minutes. Compared to the comparative powder coating blend PW7, the coating blend PW9 of the present invention exhibited better solvent resistance and lower gloss. These application results are summarized in Table 14.

[0265] Using pure TGIC ground into a fine powder poses a significant risk to construction workers to be exposed to fine particles of pure TGIC through inhalation or skin contact. TGIC has significant health hazards, known to be mutagenic (Hazard Statement H340), inhalation toxicity (H331), strong sensitization through skin contact (H317), and organ damage upon repeated exposure (H373). TGIC is listed as a Substance of Very High Concern (SVHC) in Europe, and for the reasons stated above, its use in powder coatings is essentially prohibited. The use of fine particles of pure TGIC in the coating application stage may be considered to pose additional health risks, except when used as a small component in the extrusion formulation of powder coating compositions.

[0266] Table 14: Application results of powder coating blends of PW6 and PW7 compared to the corresponding powder blends of PW8 and PW9 of the present invention.

[0267]

Claims

1. A powder coating composition blend comprising a crosslinkable composition and a catalyst system, wherein the crosslinkable composition is formed of a crosslinkable donor component A and a crosslinkable acceptor component B, the crosslinkable donor component A and the crosslinkable acceptor component B being crosslinkable via a true Michael addition (RMA) reaction using the catalyst system, and the catalyst system being capable of catalyzing the RMA crosslinking reaction at a curing temperature below 200°C and at least 70°C; The crosslinkable composition comprises: a) A crosslinkable donor component A, having at least two acidic CH donor groups in the activated methylene or methine group, and b) A crosslinkable receptor component B having at least two activated unsaturated receptor groups C=C, which reacts with component A via true Michael addition (RMA) to form a crosslinked network; and The catalyst system described herein is a separated catalyst system comprising a catalyst precursor composition (P) and a catalyst activator composition (C), wherein the catalyst precursor composition (P) and the catalyst activator composition (C) are not melt-mixed together but are macroscopically physically separated, and wherein: The catalyst precursor composition (P) comprises catalyst precursor P1, and The catalyst activator composition (C) comprises catalyst activator C1; The catalyst precursor P1 is a weak base, and its pKa in protonated form is more than 2 units lower than that of the activated CH group in donor component A. The catalyst activator C1 can react with P1 at the curing temperature to produce a strong base C1P1 that can catalyze the Michael addition reaction between component A and component B.

2. The powder coating composition blend according to claim 1, wherein the separated catalyst system further comprises a retarder T, said retarder T being an acid whose pKa is more than 2 points lower than that of the activated CH in component A, and which, upon deprotonation, generates a weak base capable of reacting with activator C1, thereby generating a strong base capable of catalyzing the Michael addition reaction between crosslinkable component A and component B.

3. The powder coating composition blend according to any one of claims 1-2, wherein the powder coating composition blend is prepared by the following steps: Components A and / or B in the crosslinkable composition are melt-mixed with a catalyst precursor composition (P) and an optional retarder T to obtain a precursor extruder; Components A and / or B in the crosslinkable composition are melt-mixed with the catalyst activator composition (C) and optional retarder T to obtain the activator extrusion; The precursor extrudate and activator extrudate are cured and granulated to obtain a precursor powder composition and an activator powder composition. The precursor powder composition and the activator powder composition are dry-blended to obtain a powder coating composition blend.

4. The powder coating composition blend according to claim 1 or 2, wherein the catalyst activator composition (C) comprises: When the catalyst activator C1 is a liquid, the catalyst activator C1 exists on the support; or The catalyst precursor composition (P) comprises: When the catalyst precursor is liquid, the catalyst precursor P1 exists on the support; or The particle size D of the carrier v 50 It ranges from 5 to 200 µm.

5. The powder coating composition blend according to claim 4, wherein the powder coating composition blend is prepared by the following steps: Components A and B in the crosslinkable composition are melt-mixed with the catalyst precursor composition (P) and optional retarder T to obtain a precursor extruder; The precursor extrudate is cured and granulated to obtain a precursor powder composition; The precursor powder composition is dry-blended with an activator present on a carrier to obtain the powder coating composition blend; or Components A and B in the crosslinkable composition are melt-mixed with the catalyst activator composition (C) and optional retarder T to obtain the activator extrusion; The activator extrudate is cured and granulated to obtain an activator powder composition; The activator extrudate is dry-blended with a precursor present on a carrier to obtain the powder coating composition blend.

6. The powder coating composition blend according to claim 3, wherein the precursor powder composition, activator powder composition, donor powder composition, and acceptor powder composition are defined as D v 50 The maximum particle size is 200µm.

7. The powder coating composition blend according to claim 4, wherein the mass ratio (wt%) of the precursor powder composition to the activator powder composition or the donor powder composition to the acceptor powder composition used for dry blending and obtaining the powder coating composition blend is 20-0.05; or The amount of the catalyst precursor or activator component present on the support is 1-30 wt% of the total powder composition blend.

8. The powder coating composition blend according to any one of claims 1-2, wherein in the separated catalyst system: The activator C1 is selected from epoxides, carbodiimides, oxadienes, oxazolines, or aziridine-functionalized components; and Catalyst precursor P1 is a weakly basic nucleophilic anion or nonionic nucleophile selected from carboxylate, phosphonate, sulfonate, halide, or phenolate anions, and / or The inhibitor T is a protonated precursor P1.

9. The powder coating composition blend according to claim 8, wherein the catalyst precursor P1 is selected from tertiary amines, phosphine, carboxyl groups, halides or phenolic anions, 1,4-diazabicyclo-[2.2.2]octane, or N-alkylimidazoles.

10. The powder coating composition blend according to any one of claims 1-2, wherein in the catalyst system: The activator C1 is a Michael acceptor containing an activated unsaturated group C=C that can react with the precursor P1; and The catalyst precursor P1 is a weak base selected from phosphine, N-alkylimidazolium, and fluorides, or a weak base nucleophilic anion X from an acidic compound containing an XH group. - Where X is N, P, O, S, or C, and the anion X - It is a Michael addition donor that can react with activator C1; and / or The inhibitor T is a protonated precursor P1.

11. The powder coating composition blend according to any one of claims 1-2, wherein the catalyst precursor P1 is added in the form of a salt, the salt comprising a non-acidic cation.

12. The powder coating composition blend according to claim 11, wherein the non-acidic... The positive cation is: A cation of formula Y(R')4, where Y represents N or P, and each R' is a polycation that can be linked to a polymer. The same or different alkyl, aryl or aralkyl groups on the compound, or A protonated, very strong basic amine selected from amidines or guanidines.

13. The powder coating composition blend according to any one of claims 1-2, comprising: a. Activator C1 of 1-600 μeq / g, relative to the total weight of components A and B and the separated catalyst system; b. 1-300 μeq / g of precursor P1, relative to the total weight of components A and B and the separated catalyst system; c. Optional, 1-500 μeq / g of retardant T, relative to the total weight of component A and component B and the separated catalyst system; The equivalent of C1 is: i. When present, the amount is 1-300 μeq / g higher than that of T. ii. Amount higher than P1.

14. The powder coating composition blend according to any one of claims 1-2, wherein: a. The weak base P1 represents 10-100 equivalents of the sum of P1 and T; b. The amount of inhibitor T is 20–400 equivalents of the amount of P1; c. The ratio of the equivalent of C1 to the sum of the amounts of P1 and T is at least 0.5; d. The ratio of C1 to T is at least 1.

15. The powder coating composition blend according to any one of claims 1-2, wherein: a. The crosslinkable component A contains at least two acidic CH donor groups in the activated methylene or methine of the structure Z1(-C(-H)(-R)-)Z2, wherein R is hydrogen, hydrocarbon, oligomer or polymer, and Z1 and Z2 are the same or different electron-withdrawing groups selected from ketone, ester, cyano or aryl groups; b. Component B contains at least two activated unsaturated RMA acceptor groups derived from acryloyl, methacryloyl, itaconic acid, maleate, or fumarate functional groups. At least one of component A or component B is a polymer; and The composition comprises a total amount of donor groups CH and acceptor groups C=C relative to each gram of binder solids of 0.05-6 meq / g binder solids, and the ratio of acceptor groups C=C to donor groups CH is greater than 0.1 and less than 10.

16. The powder coating composition blend according to any one of claims 1-2, wherein at least one of the crosslinkable components A or B or mixture A / B is a polymer selected from the following polymers: acrylic, polyester, polyesteramide, polyester-urethane polymer, said polymer having the following characteristics: The number-average molecular weight Mn, as determined by GPC, is at least 450 g / mol; The weight-average molecular weight Mw determined by GPC is at most 20,000 g / mol; Polydispersity Mw / Mn is less than 4; The equivalent weight (EQW) in CH or C=C is at least 150 and at most 2500, and the number-average functionality of the reactive group CH or C=C is 1-25 CH groups per molecule. The melt viscosity is less than 60 Pas at temperatures of 100-140℃; Contains amide, urea or urethane bonds and / or contains high Tg monomers; A crystalline polymer whose midpoint Tg, as determined by DSC at a heating rate of 10 °C / min, is higher than 25 °C, or whose melt temperature, as determined by DSC at a heating rate of 10 °C / min, is 40-150 °C.

17. The powder coating composition blend according to any one of claims 1-2, wherein component B is a polyester (meth)acrylate, polyester urethane (meth)acrylate, epoxy (meth)acrylate or urethane (meth)acrylate, or a polyester comprising fumarate, maleate or itaconic acid units, or a polyester end-capped with an activated unsaturated group of isocyanate or epoxy functionality.

18. A method for powder coating a substrate, comprising: a. Applying a layer comprising the powder coating composition blend of any one of claims 1-17 to a substrate surface, wherein the substrate is a temperature-sensitive substrate; and b. Use infrared heating to cure at a temperature T of 75-200℃. cur Among them, at the curing temperature T cur The melt viscosity is less than 60 Pas; and c. In T cur The curing time is less than 40 minutes.

19. An article coated with a powder having a powder coating composition blend of any one of claims 1-17, wherein the article has a temperature-sensitive substrate selected from MDF, wood, plastic or metal alloy, and wherein the crosslinking density XLD determined by DMTA is at least 0.01 and less than 3 0.7 mmol / ml.

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