Powder Coatings and Crystalline Donors and / or Acceptors

Abstract

The present invention relates to a powder coating composition comprising a crosslinkable composition and a catalyst system, the crosslinkable composition being formed by a crosslinkable donor component A and a crosslinkable acceptor component B crosslinkable by true Michael addition (RMA), at least a portion of which is (semi-)crystalline and comprises a polyurethane backbone formed by reacting a polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), with a compound (i), more preferably a diol; and a compound (iia) comprising at least one, preferably one, isocyanate reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic CH donor group in an activated methylene or methine, with a compound (iib) comprising at least one, preferably (1) isocyanate reactive group, preferably a hydroxyl, and at least one functional group having at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B.

Description

[Technical field]

[0001] The present invention relates to a powder coating composition crosslinkable by Real Michael Addition (RMA) comprising a semi-(crystalline) polyurethane donor or acceptor component, a method for preparing the powder coating composition, a method for coating an article using said powder coating composition, the coated article and the semi-(crystalline) polyurethane donor or acceptor component. [Background technology]

[0002] Powder coatings are finely divided, free-flowing solid materials that dry at room temperature and have gained popularity over liquid coatings in recent years. Powder coatings are generally cured at elevated temperatures, between 120°C and 200°C, more typically between 140°C and 180°C. High temperatures are necessary to provide sufficient flow of the binder to allow film formation and achieve good coating surface appearance, as well as high reactivity for crosslinking reactions. At lower curing temperatures, reaction kinetics that do not allow for short curing times may be encountered when demanding full mechanical and resistance property development. On the other hand, in systems where high reactivity of the components can be created, the coating may have poor appearance due to the relatively high viscosity of such systems at such low temperatures, which may further increase rapidly as the curing reaction proceeds, and the time-integrated fluidity of such systems may be too low to achieve sufficient leveling (see, for example, Progress in Organic Coatings, Vol. 72, pp. 26-33 (2011)). Flow and appearance may be limited, especially when thinner films are targeted. Furthermore, very high reactivity can lead to problems due to premature reaction when compounding the powder coating in the extruder, limiting storage stability; lowering the Tg of the powder coating improves flow but is detrimental to storage stability.

[0003] Crystalline components can aid the flow of powder coating systems if they melt and plasticize the coating under curing conditions, thereby reducing the melt viscosity. It is important that they can do so without adversely affecting the chemical resistance or mechanical properties of the resulting network. It is preferable for such components to be able to exist in a crystalline state in the powder coating before curing, avoiding the adverse effects on storage stability by already resulting in excessive plasticization at this stage. It is also preferable that this crystalline state is not too coarse and can be easily achieved after melt mixing of the formulation in the extruder. Furthermore, melting is preferably completed at the intended low curing temperature.

[0004] Patent application WO 2019 / 145472 describes a powder coating composition that can provide a coating on a substrate, such as a heat-sensitive substrate such as medium density fiberboard (MDF), wood, plastics and certain metal alloys, and can be cured at low temperatures with high cure rates and acceptably short cure times. The coating composition is curable by RMA using a catalyst system that initiates the RMA reaction.

[0005] CN112457751 and CN112457752 describe low-temperature RMA curable compositions containing a donor, an acceptor, and a (semi-)crystalline component as a vinyl ether polyurethane resin or a (semi-)crystalline polyester methacrylate component.

[0006] However, the crystalline vinyl ethers act as plasticizers that do not become part of the polymer RMA network, thus reducing the crosslink density and chemical resistance. The polyester methacrylates described do not easily crystallize from the entire formulation, thus reducing the Tg of the powder coating already before application.

[0007] Thus, there remains a need for low temperature cure RMA crosslinkable powder coating compositions that have good storage stability and provide good mechanical, adhesive, chemical resistance and flow properties upon cure. Summary of the Invention

[0008] The present invention addresses one or more of the above problems by providing a powder coating composition as claimed in claim 1.

[0009] Thus, a first aspect of the present invention is a powder coating composition comprising a crosslinkable composition and a catalyst system, wherein the crosslinkable composition is formed by a crosslinkable donor component A and a crosslinkable acceptor component B which are crosslinkable by a true Michael Addition (RMA) reaction via the catalyst system, and the catalyst system is capable of catalysing the RMA crosslinking reaction at a curing temperature of less than 140°C, preferably less than 120°C, even more preferably less than 110°C or less than 100°C, preferably at least 70°C, preferably at least 80, 90 or 100°C, The crosslinkable composition comprises a) a crosslinkable donor component A having at least two acidic CH donor groups in the activated methylene or methine; and b) a crosslinkable acceptor component B having at least two activated unsaturated acceptor groups C=C which reacts with component A by true Michael addition (RMA) to form a crosslinked network; Including, at least the crosslinkable donor component A and / or the crosslinkable acceptor component B are (semi)crystalline, a polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and a compound (iia) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic CH donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; or Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B The present invention relates to a powder coating composition comprising a polyurethane backbone formed by reacting

[0010] The second embodiment is (semi)crystalline, a polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and a compound (iia) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic CH donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; or Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B The present invention relates to a crosslinkable donor component A and / or a crosslinkable acceptor component B comprising a polyurethane backbone formed by reacting with

[0011] A third aspect is a method of powder coating a substrate, comprising the steps of: a. applying a layer comprising a powder coating composition according to the first aspect to a substrate surface, the substrate being preferably a temperature sensitive substrate, preferably a temperature sensitive metal substrate such as MDF, wood, plastic, composite or alloy; b. heating, preferably using infrared heating, to a curing temperature Tcur of 75-160°C, preferably 80-150°C, more preferably 80-140, 130 or even 120°C, 110°C, 100°C, wherein the melt viscosity at the curing temperature Tcur is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas; c. curing at Tcur for a cure time preferably less than 40, 30, 20, 15, 10, or even 5 minutes; The present invention relates to a method comprising the steps of:

[0012] A fourth third aspect relates to a powder coated article having the powder coating composition according to the first aspect, preferably having a temperature sensitive substrate, preferably selected from the group of MDF, wood, plastic, composites or metal alloys, preferably having a crosslink density XLD of at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / ml (as determined by DMTA), preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / ml.

[0013] Detailed Description of the Invention The inventors have surprisingly found that powder coating compositions according to the invention comprising a donor A and / or an acceptor B having a polyurethane backbone which is (semi-)crystalline and prepared with an isocyanate which is substantially HDI and a compound having at least two isocyanate-reactive groups which are preferably diols, recrystallize well after extrusion compounding to give powder paints with good Tg and storage stability, leading to final coatings with good mechanical resistance, improved adhesion and mechanical properties as well as improved flowability, and the crystalline component has a melting temperature in the paint which is compatible with the low curing temperatures.

[0014] In the context of the present invention, the term "(semi)crystalline compound" is a compound that has a melting temperature Tm above which the compound is liquid. In the context of the present invention, the "melting temperature" of a (semi)crystalline compound is the temperature at which the compound melts completely when present in a composition comprising at least a crosslinkable system and a catalyst system as described in the present invention, unless otherwise specified in the following description as the melting temperature of the compound itself. The melting temperatures reported herein are determined from differential scanning calorimetry (DSC) using a heating rate of 10°C / min.

[0015] In the context of the present invention, the term "(meth)acrylate" is meant to encompass both acrylate and methacrylate components. [Brief description of the drawings]

[0016] [Figure 1] 1H NMR spectrum of cyclohexyl vinyl ether. [Diagram 2] 1H NMR spectrum of the kinetic test mixture before curing. [Diagram 3] 1H NMR spectrum of the kinetic test mixture after curing at 110 °C for 30 min. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] crosslinking component In the present invention, the crosslinkable composition comprises a) a crosslinkable donor component A having at least two acidic CH donor groups in the activated methylene or methine; and b) a crosslinkable acceptor component B, which has at least two activated unsaturated acceptor groups C=C and reacts with component A by true Michael addition (RMA) to form a crosslinked network; Including, at least a part of the crosslinkable donor component A and / or the crosslinkable acceptor component B is (semi)crystalline, a polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and a compound (iia) which comprises at least one, preferably one, functional group having at least one isocyanate-reactive group, preferably a hydroxyl, and at least one acidic CH donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; or Compounds (iib) which contain at least one, preferably one functional group having at least one isocyanate-reactive group, preferably hydroxyl, and at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B The polyurethane backbone is formed by reacting

[0018] Surprisingly, it has been found that (semi-)crystalline donor A and / or acceptor B provide powder coating compositions having a urethane backbone from selected diols and hexamethylene diisocyanate (HDI) with targeted molecular weight, have suitable melting temperatures, recrystallize after extrusion, have reduced melt viscosity compared to amorphous donor / acceptor systems, and provide coatings with better adhesion and flexibility compared to amorphous donor / acceptor systems.

[0019] Preferably, compound (i) is selected to provide a melting temperature below the intended curing temperature for component A or B. In a preferred embodiment, the (semi-)crystalline donor A and / or acceptor B component has a melting temperature below 140°C, preferably below 120°C, 110°C, 105°C or even below 100°C.

[0020] In another embodiment, the (semi-)crystalline donor and / or acceptor components have a melting temperature of the compound itself, i.e. when not present in the coating composition, below 145° C., 130° C., preferably below 120° C., 110° C., or even below 100° C., for example between 80 and 130° C., preferably between 80 and 120° C. The melting temperature of the (semi-)crystalline donor and / or acceptor itself can be slightly higher than the melting temperature when formulated in the paint and thus when present in the coating composition.

[0021] In a preferred embodiment, the compound (i) comprising at least two isocyanate reactive groups is a diol, the diol being or having a linking chain between the hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-SS-CH2-, the linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between the hydroxyl groups; having a linking chain between the hydroxyl groups containing -CH(CH3)- or -CH(CH2CH3)- units, preferably at a central position, whereby the linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between the hydroxyl groups; The hydroxyl groups are primary hydroxyl groups and the diol is not aromatic and is not alicyclic.

[0022] In yet another embodiment, the compound (i) comprising at least two isocyanate reactive groups is a diol, preferably selected from the group consisting of diethylene glycol, triethylene glycol, 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol, thiodiethanol, dithiodiethanol, bis(hydroxyethyl)methylamine, tetraethylene glycol, di(1,3-propanediol), di(1,4-butanediol).

[0023] In one embodiment, the number average molecular weight of the (semi)crystalline donor A and / or acceptor B is 300-4000 g / mol, preferably 500-3000, more preferably 1000-2000 g / mol.

[0024] In yet another embodiment, the ratio of isocyanate reactive groups of compound (i) and compound (iia) or (iib) to isocyanate groups is preferably greater than 1, more preferably the molar ratio of isocyanate reactive groups to isocyanate groups is from 1.0 to 1.5, more preferably from 1.01 to 1.2.

[0025] In another preferred embodiment, a (semi-crystalline) acceptor component B is used and compound (iib) is a hydroxyl-functional (meth)acrylate, preferably selected from the group consisting of hydroxybutyl (meth)acrylate and hydroxyethyl (meth)acrylate or mixtures thereof, or compound (iib) has hydroxyl and maleate, fumarate or itaconate functional groups.

[0026] It should be understood that the C=C in vinyl ethers is not an activated unsaturated acceptor group according to the present invention, therefore, compound (iib) comprising at least one functional group having at least one activated unsaturated acceptor group C=C is not a vinyl ether group.

[0027] In yet another preferred embodiment, a (semi-crystalline) donor component A is used, and compound (iia) is a hydroxyl-functional acetoacetate, as in the transesterification product of a diol with an alkyl acetoacetate, or a mono-hydroxyl-functional component resulting from the partial transesterification of a diol with a dialkyl malonate. When using a transesterification product of a diol with a dialkyl malonate, some bis-hydroxyl malonate components can be formed from the double reaction of the malonate, which can be incorporated into the diol compound (i).

[0028] Also disclosed are (semi)crystalline donor A and / or acceptor B components which do not use compound (i) to prepare the urethane backbone.

[0029] In another embodiment, the powder coating composition comprises: a. The crosslinking component A comprises at least two acidic CH donor groups in activated methylene or methine of the structure Z1(-C(-H)(-R)-)Z2, where R is hydrogen, hydrocarbon, oligomer or polymer, and Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from keto, ester or cyano or aryl groups, preferably represented by the formula 1 [ka] formula 1 wherein R is hydrogen or optionally substituted alkyl or aryl, Y and Y' are the same or different substituents, preferably alkyl, aralkyl or aryl, or alkoxy, or in formula 1 -C(=O)-Y and / or -C(=O)-Y' are substituted with CN or aryl, not more than one aryl, or Y or Y' may be NRR' (R and R' are H or optionally substituted alkyl), but preferably not both, R, Y or Y' optionally providing a connection to an oligomer or polymer, said 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 of CH acid groups in the crosslinkable component A, b. component B contains at least two activated unsaturated RMA acceptor groups, preferably derived from acryloyl, methacryloyl, itaconate, maleate or fumarate functional groups; At least one of the donor component A and / or the acceptor component B is a (semi)crystalline component having a polyurethane skeleton as described above, Preferably, the composition comprises a total amount of donor groups CH and acceptor groups C═C per gram of binder solids of from 0.05 to 6 meq / gr binder solids, and preferably the ratio of acceptor groups C═C to donor groups CH is greater than 0.1 and less than 10.

[0030] In yet another embodiment, the amount of crystalline polyurethane component in the formulation is from 2 to 95% by weight, preferably from 2 to 70% by weight, more preferably from 3 to 50% by weight, and most preferably from 6 to 35% by weight, based on the total amount of crosslinkable components A and B.

[0031] In yet another embodiment, the (semi-)crystalline crosslinkable components A and B are a polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and a compound (iia) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic CH donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; and Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B A (semi)crystalline hybrid A / B component formed by reacting

[0032] True Michael Addition (RMA) crosslinkable coating compositions comprising crosslinkable components A and B have been generally described for use in solvent borne systems in EP 2556108, EP 0808860 or EP 1593727, the specific descriptions of which are deemed to be incorporated herein.

[0033] Components A and B each contain an RMA reactive donor and acceptor moiety that reacts upon curing to form a crosslinked network in the coating. Components A and B can be on separate molecules, but can also be on one molecule, referred to as a hybrid A / B component or combinations thereof.

[0034] Preferably, components A and B are separate molecules, each independently in the form of a polymer, oligomer, dimer or monomer. For coating applications, at least one of components A or B is preferably an oligomer or polymer. Note that the activated methylene group CH2 contains two CH acid groups. Even if after the reaction of the first CH acid group, the reaction of the second CH acid group is more difficult, the functionality of such an activated methylene group counts as 2, for example, in reaction with methacrylates, compared to acrylates. Reactive components A and B can also be combined into one A / B hybrid molecule. In this embodiment of the powder coating composition, both CH and C=C reactive groups are present in one AB molecule.

[0035] Preferably, component A is a polymer, preferably a polyester, polyurethane, acrylic, epoxy or polycarbonate, having as functional groups component A and optionally one or more components B, or components from catalyst system C. Mixtures or hybrids of these polymer types are also possible. Suitably, component A is a polymer selected from the group of acrylic, polyester, polyesteramide, polyester-urethane polymers.

[0036] Malonate or acetoacetate are the preferred donor types in component A. In view of the high reactivity and durability in the most preferred embodiment of the crosslinkable composition, component A is a malonate CH-containing compound. In the powder coating composition, it is preferred that the majority of the activated CH groups are malonate-derived, i.e., more than 50%, preferably more than 60%, more preferably more than 70%, and most preferably more than 80% of all activated CH groups in the powder coating composition are malonate-derived.

[0037] Oligomeric and / or polymeric malonate group-containing components are preferred, such as polyesters, polyurethanes, polyacrylates, epoxy resins, polyamides and polyvinyl resins or hybrids thereof that contain malonate-type groups in the backbone, pendant or both.

[0038] The total amount of donor groups CH and acceptor groups C=C per gram of binder solids, regardless of how they are distributed over the various crosslinkable components, is preferably between 0.05 and 6 meq / gr, more typically between 0.10 and 4 meq / gr, even more preferably between 0.25 and 3 meq / gr of binder solids, most preferably between 0.5 and 2 meq / gr. Preferably, the stoichiometry between components A and B is chosen such that the ratio of reactive C=C groups to reactive CH groups is greater than 0.1, preferably greater than 0.2, more preferably greater than 0.3, most preferably greater than 0.4, and in the case of acrylate functional groups B, preferably greater than 0.5, most preferably greater than 0.75, the ratio being preferably less than 10, preferably less than 5, more preferably less than 3, 2 or 1.5.

[0039] Malonate group-containing polyesters are preferably obtainable by transesterification of methyl or ethyl diesters of malonic acid with polyfunctional alcohols which may be of polymeric or oligomeric nature, but which may also be incorporated by Michael addition reaction with other components. Particularly preferred malonate group-containing components for use in the present invention are malonate group-containing oligomeric or polymeric esters, ethers, urethanes and epoxy esters as well as hybrids thereof, such as polyester-urethanes containing 1 to 50, more preferably 2 to 10, malonate groups per molecule. The polymer component A can also be prepared in known manner, for example by radical polymerization of ethylenically unsaturated monomers containing activated CH acid (donor) groups, preferably acetoacetate or malonate groups, such as (meth)acrylates, functionalized with moieties containing 2-(methacryloyloxy)ethyl acetoacetate or -malonate. In practice, polyesters, polyamides and polyurethanes (and hybrids thereof) are preferred. It is also preferred that such malonate group-containing components have a number average molecular weight (Mn) in the range of about 100 to about 10,000, preferably 500 to 5,000, and most preferably 1,000 to 4,000, and an Mw (expressed in GPC polystyrene equivalent) of less than 20,000, preferably less than 10,000, and most preferably less than 6,000.

[0040] Suitable crosslinking component B can generally be an ethylenically unsaturated component whose carbon-carbon double bond is activated by an electron-withdrawing group, for example, a carbonyl group at the α position.Representative examples of such components are disclosed in US Pat. No. 2,759,913 (column 6, line 35 to column 7, line 45), DE-PS No. 835,809 (column 3, line 16 to line 41), US Pat. No. 4,871,822 (column 2, line 14 to column 4, line 14), US Pat. No. 4,602,061 (column 3, line 14, line 20 to column 4, line 14), US Pat. No. 4,408,018 (column 2, line 19 to line 68) and US Pat. No. 4,217,396 (column 1, line 60 to column 2, line 64).

[0041] Preferred are acrylates, methacrylates, itaconates, fumarates and maleates. Itaconates, fumarates and maleates can be incorporated into the backbone of polyesters or polyester-urethanes. Preferred exemplary resins include polyesters, polycarbonates, polyurethanes, polyamides, acrylics and epoxy resins (or their hybrids), polyethers and / or alkyd resins that contain activated unsaturated groups. These include, for example, urethane (meth)acrylates obtained by reacting polyisocyanates with hydroxyl group-containing (meth)acrylic acid esters, such as hydroxyalkyl esters of (meth)acrylic acid, or components prepared by esterification of poly-hydroxyl components with substoichiometric amounts of (meth)acrylic acid; polyether (meth)acrylates obtained by esterification of hydroxyl group-containing polyethers with (meth)acrylic acid; multifunctional (meth)acrylates obtained by reacting hydroxyalkyl (meth)acrylates with polycarboxylic acids and / or polyamino resins; poly(meth)acrylates obtained by reacting (meth)acrylic acid with epoxy resins, and polyalkylmaleates obtained by reacting monoalkylmaleate esters with epoxy resins and / or hydroxy-functional oligomers or polymers. Also, polyesters end-capped with glycidyl methacrylate are preferred examples. The acceptor component can contain multiple types of acceptor functional groups.

[0042] The most preferred activated unsaturated group-containing components B are unsaturated acryloyl, methacryloyl and fumarate functional components. Preferably, the number average functionality of activated C=C groups per molecule is 2-20, more preferably 2-10, most preferably 3-6. The equivalent weight (EQW: average molecular weight per reactive functional group) is 100-5000, more preferably 200-2000, and the number average molecular weight is preferably Mn200-10000, more preferably 300-5000, most preferably 400-3500 g / mol, even more preferably 1000-3000 g / mol.

[0043] Considering use in powder systems, the Tg of component B is preferably greater than 25, 30, 35, more preferably at least 40, 45, most preferably at least 50°C, or even at least 60°C, due to the need for powder stability. Tg is defined as measured by DSC, midpoint, heating rate of 10°C / min. If one of the components has a Tg substantially higher than 50°C, the Tg of the other formulation components may be lower, as will be understood by those skilled in the art.

[0044] Suitable component B is a urethane (meth)acrylate prepared by reacting hydroxy- and (meth)acrylate functional compounds with isocyanates to form urethane bonds, the isocyanates being preferably at least partially di- or tri-isocyanates, preferably isophorone diisocyanate (IPDI). The urethane bonds introduce rigidity by themselves, but preferably high Tg isocyanates are used, such as cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic. The amount of such isocyanates used is preferably selected so that the (meth)acrylate functional polymer Tg is raised above 40°C, preferably above 45 or 50°C.

[0045] Powder coating compositions are preferably designed such that after curing they have a crosslink density (using DMTA) that can be determined to be at least 0.025 mmol / cc, more preferably at least 0.05 mmol / cc, and most preferably at least 0.08 mmol / cc, and typically less than 3, 2, 1 or 0.7 mmol / cc.

[0046] The powder coating composition should remain a free flowing powder at ambient conditions and therefore preferably have a Tg greater than 25°C, preferably greater than 30°C, more preferably greater than 35, 40, 50°C as a mean value as determined by DSC at a heating rate of 10°C / min.

[0047] As noted above, the preferred component A is a malonate-functional component. However, the incorporation of malonate moieties tends to lower the Tg, and providing a powder coating composition based on malonate as the primary component A with a sufficiently high Tg has been a challenge.

[0048] With a view to achieving a high Tg, the powder coating composition preferably comprises a crosslinkable composition, in which the crosslinkable donor component A and / or the crosslinkable acceptor component B, which may be in the form of a hybrid component A / B, comprise an amide, urea or urethane bond and / or thereby a high Tg monomer, preferably an alicyclic or aromatic monomer, or in the case of polyesters, one or more monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetra-methyl-cyclobutanediol.

[0049] Furthermore, with a view to achieving a high Tg, the powder coating composition comprises component B or hybrid component A / B which is a polyester (meth)acrylate, polyester urethane (meth)acrylate, epoxy (meth)acrylate or urethane (meth)acrylate, or is a polyester containing fumarate, maleate or itaconate units, preferably fumarate, or is a polyester endcapped with isocyanate or epoxy functional activated unsaturated groups.

[0050] In yet another embodiment, the crosslinkable component A or B or the hybrid A / B is a polymer, preferably selected from the group of acrylic, polyester, polyesteramide, polyester-urethane polymers, said polymer being have a number average molecular weight Mn, measured by GPC, of ​​at least 450 gr / mol, preferably at least 1000, more preferably at least 1500 and most preferably at least 2000 gr / mol, have a weight average molecular weight Mw, measured by GPC, of ​​at most 20 000 gr / mol, preferably at most 15 000, more preferably at most 10 000 and most preferably at most 7500 gr / mol, has a polydispersity Mw / Mn preferably less than 4, more preferably less than 3, an equivalent weight EQW in CH or C=C of at least 150, 250, 350, 450 or 550 gr / mol, preferably at most 2500, 2000, 1500, 1250 or 1000 gr / mol, and a number-average functionality of reactive groups CH or C=C of 1 to 25, more preferably 1.5 to 15, even more preferably 2 to 15 and most preferably 2.5 to 10 CH groups per molecule, preferably has a melt viscosity of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas at a temperature in the range of 100 to 140°C, preferably comprising amide, urea or urethane bonds and / or comprising high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), tricyclodecane dimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol, and / or have a mean Tg, determined by DSC at a heating rate of 10° C. / min, of greater than 25° C., preferably greater than 35° C., more preferably greater than 40, 50 or even 60° C.

[0051] The polymer properties Mn, Mw and Mw / Mn are selected taking into account the desired powder stability on the one hand, the desired low melt viscosity on the other hand, as well as the envisaged coating properties. A high Mn is preferred to minimize the Tg-decreasing effect of end groups, and a low Mw is preferred on the other hand, since the melt viscosity is very much related to Mw and low viscosity is desirable. Thus, a low Mw / Mn is preferred.

[0052] With a view to achieving a high Tg, the RMA crosslinkable polymers preferably contain amide, urea or urethane bonds and / or contain high Tg monomers, preferably cycloaliphatic or aromatic monomers, or in the case of polyesters, monomers selected from the group of 1,4-dimethylolcyclohexane (CHDM), TCD diol, isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol.

[0053] When the RMA crosslinkable polymer is an A / B hybrid polymer, it is further preferred that the polymer also comprises one or more component B groups selected from the group of acrylate or methacrylate, fumarate, maleate and itaconate, preferably (meth)acrylate or fumarate.

[0054] In a preferred embodiment, an RMA crosslinkable polymer comprising polyesters, polyesteramides, polyester-urethanes or urethane-acrylates comprising urea, urethane or amide bonds derived from cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic isocyanates, has a Tg of at least 40°C, preferably at least 45 or 50°C, maximum 120°C and a number average molecular weight Mn of 450 to 10000, preferably 1000 to 3500 gr / mol, preferably a maximum Mn of 20000, 10000 or 6000 gr / mol, the polymer being provided with RMA crosslinkable components A or B or both. The polymer can be obtained, for example, by reacting a precursor polymer comprising said RMA crosslinkable groups with an amount of cycloaliphatic or aromatic isocyanates to increase the Tg. The amount of such isocyanates added or urea / urethane bonds formed is selected such that the Tg is increased to at least 40°C, preferably at least 45 or 50°C.

[0055] Preferably, the RMA crosslinkable polymer is a polyester or polyester-urethane comprising malonate as main component A, containing a number average malonate functionality of 1-25, more preferably 1.5-15, even more preferably 2-15 and most preferably 2.5-10 malonate groups per molecule, having a GPC weight average molecular weight of 500-20000, preferably 1000-10000, most preferably 2000-6000 gr / mol, and prepared by reacting a hydroxy- and malonate-functional polymer with an isocyanate to form a urethane bond.

[0056] Catalyst system A preferred catalyst system comprises a precursor P, an activator C, and optionally a retarder T, the precursor P is a weak base whose protonated form has a pKa greater than 2 units, preferably greater than 3 units, more preferably greater than 4 units, and even more preferably at least 5 units lower than the pKa of the activated CH group in the donor component A; and the activator C is capable of reacting with P at the curing temperature to produce a strong base (CP) capable of catalyzing the Michael addition reaction between A and B; The retarder T is an acid that has a pKa that is more than 2 points, more preferably more than 3 points, and even more preferably more than 4 or 5 points lower than the pKa of the activated CH in A, and that upon deprotonation produces a weak base that can react with the activator C to produce a strong base that can catalyze the Michael addition reaction between the crosslinkable compositions A and B.

[0057] In one embodiment, the activator C is selected from the group of epoxide, carbodiimide, oxetane, oxazoline or aziridine functional components, preferably epoxides or carbodiimides, the catalyst precursor P is a weakly basic nucleophilic anion selected from the group of carboxylate, phosphonate, sulfonate, halogenide or phenolate anions or a non-ionic nucleophile, preferably a tertiary amine or a phosphine, more preferably a weakly basic nucleophilic anion selected from the group of carboxylate, halogenide or phenolate anions or 1,4-diazabicyclo-[2.2.2]-octane (DABCO) or N-alkylimidazoles, most preferably a carboxylate; and / or A retarder T which is preferably a protonated precursor P.

[0058] In another embodiment, the activator C is a Michael acceptor containing an activated unsaturated group C=C reactive with P, preferably an acrylate, methacrylate, fumarate, itaconate or maleate, and the catalyst precursor P is a weak base selected from the group of phosphines, N-alkylimidazoles and fluorides, or a weak base nucleophilic anion X, which is a Michael addition donor reactive with the activator C from an acidic XH group-containing compound, where X is N, P, O, S or C. - and / or a retarder T which is preferably a protonated precursor P1.

[0059] The most preferred catalyst activators C1 contain epoxy groups. Suitable choices of epoxides as preferred activators C1 are cycloaliphatic epoxides, epoxidized oils and glycidyl-type epoxides. Suitable components C1 include C10-18 alkylene oxides and oligomers and / or polymers with epoxide functionality, including multiple epoxy functionality, as described, for example, in US Pat. No. 4,749,728, column 3, lines 21-56. Particularly suitable monoepoxides include tert-butyl glycidyl ether, phenyl glycidyl ether, glycidyl acetate, glycidyl esters of versatic esters, glycidyl methacrylate (GMA) and glycidyl benzoate. Useful multifunctional epoxides include bisphenol A diglycidyl ether and higher homologs of such BPA epoxy resins, glycidyl ethers of hydrogenated BPA such as Eponex 1510 (Hexion), ST-4000D (Kukdo), aliphatic oxiranes such as 13ystem13zed soybean oil, diglycidyl adipate, 1,4-diglycidyl butyl ether, glycidyl ethers of novolac resins, glycidyl esters of diacids such as Araldite PT910 and PT912 (Huntsman), TGIC and other commercially available epoxy resins. Bisphenol A diglycidyl ether and its solid high molecular weight homologs are preferred epoxides. Acrylic (co)polymers with epoxide functionality derived from glycidyl methacrylate are also useful. In a preferred embodiment, the epoxy component is an oligomeric or polymeric component with an Mn of at least 400 (750, 1000, 1500). Other epoxide compounds include 2-methyl-1,2-hexene oxide, 2-phenyl-1,2-propene oxide (α-methylstyrene oxide), 2-phenoxymethyl-1,2-propene oxide, epoxidized unsaturated oils or fatty esters, and 1-phenylpropene oxide.Useful and preferred epoxides are the glycidyl esters of carboxylic acids, which may be present on a carboxylic acid functional polymer or, preferably, on a highly branched hydrophobic carboxylic acid such as Cardura E10P (glycidyl ester of Versatic™ Acid 10). Most preferred are the typical powder crosslinker epoxy components: triglycidyl isocyanurate (TGIC), Araldite PT910 and PT912, and phenolic glycidyl ethers that are naturally solid at ambient temperature, or acrylic (co)polymers of glycidyl methacrylate.

[0060] Suitable examples of catalyst precursor P1 are weakly basic nucleophilic anions or non-ionic nucleophiles selected from the group of carboxylate, phosphonate, sulfonate, halogenide or phenolate anions or their salts, preferably tertiary amines or phosphines. More preferably, weak base P1 is a weakly basic nucleophilic anion selected from the group of carboxylate, halogenide or phenolate salts, most preferably carboxylate salts, or is 1,4-diazabicyclo[2.2.2]octane (DABCO) or N-alkylimidazole. Catalyst precursor P1 can react with catalyst activator C1, preferably epoxy, to produce a strongly basic anionic adduct that can initiate the reaction of crosslinkable components A and B.

[0061] Another suitable example of catalyst precursor P1 is a weakly basic nucleophilic anion selected from the group of anions X-, which are weakly basic anions X- from acidic XH group-containing compounds, where X is N, P, O, S or C, that are Michael addition donors capable of reacting with Michael acceptor activators C1, characterized by a pKa of the corresponding conjugate acid XH of less than 8, preferably less than 7, more preferably less than 6, where pKa is defined as the value in an aqueous environment, and when C1 is methacrylate, fumarate, itaconate or maleate, P1 has a pKa of the conjugate acid of less than 10.5, preferably less than 9, more preferably less than 8.

[0062] The catalyst precursor, which is a weak base P1, preferably reacts with the catalyst activator C1 at a temperature on the time scale of the curing process of less than 150° C., preferably 140, 130, 120, preferably at least 70, preferably at least 80 or 90° C. 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 in the intended time window.

[0063] When the catalyst precursor P1 is an anion, it is preferred to add it as a salt containing a non-acidic cation. By non-acidic, it is meant that it does not have hydrogens that compete with the crosslinkable donor component A for base, and therefore does not inhibit the crosslinking reaction at the intended curing temperature. Preferably, the cation is substantially non-reactive with any component in the crosslinkable composition. The cation can be, for example, an alkali metal, a quaternary ammonium or a phosphonium, but can also be a protonated "superbase" that does not react with any of the components A, B or C in the crosslinkable composition. Suitable superbases are known in the art.

[0064] Preferably, the catalyst precursor P is a non-acidic cation, preferably of the formula Y(R') 4 where Y represents N or P, and each R' may be the same or different alkyl, aryl or aralkyl group that may be linked to the polymer, or the cation is a protonated very strong basic amine, which is preferably selected from the group of amidines, preferably 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) or guanidine, preferably 1,1,3,3-tetramethylguanidine (TMG). R' can be substituted with substituents that do not interfere or do not substantially interfere with the RMA crosslinking chemistry, as known to those skilled in the art. Most preferably, R' is an alkyl having 1 to 12, most preferably 1 to 4 carbon atoms.

[0065] Optionally, in some preferred embodiments, the catalyst system further comprises a retarder T, which is an acid having a pKa 2, preferably 3, more preferably 4, most preferably 5 points lower than the pKa of the activated CH in the crosslinkable donor component A, which upon deprotonation produces a weak base that can act as a P1 precursor, and which can react with the activator C1 to produce a strong base that can catalyze the Michael addition reaction between A and B. The retarder T is preferably the protonated precursor P1. The retarder T can be part of the catalyst precursor composition or the catalyst activator composition. It may be part of both the catalyst precursor composition and the catalyst activator composition. Preferably, the retarder T and the protonated precursor P1 have a boiling point of at least 120°C, preferably 130°C, 150, 175, 200 or even 250°C. Preferably, the retarder T is a carboxylic acid. The use of the retarder T can have a beneficial effect in delaying the crosslinking reaction to allow more interdiffusion of the components during curing before mobility limitations become significant.

[0066] In one specific embodiment, the catalyst activator C1 is an acrylate acceptor group and the components P1 and T are X having a pKa (in acid form) of less than 8, more preferably less than 7, 6 or even 5.5. - / XH component, preferably carboxylate / carboxylic acid compound. Examples of useful XH components for acrylate acceptor-containing powder coating compositions include cyclic 1,3-diones such as 1,3-cyclohexanedione (pKa 5.26) and dimedone (5,5-dimethyl-1,3-cyclohexanedione, pKa 5.15), ethyl trifluoroacetoacetate (7.6), Meldrum's acid (4.97). Preferably, XH components are used that have a boiling point of at least 175°C, more preferably at least 200°C.

[0067] In another embodiment, the catalyst activator C1 is a methacrylate, fumarate, maleate or itaconate acceptor group, preferably a methacrylate, itaconate or fumarate group, and the components P1 and T are X having an acid pKa of less than 10.5, more preferably less than 9.5, 8 or even less than 7. - / XH component.

[0068] The pKa values ​​referred to in this patent application are aqueous pKa values ​​at ambient conditions (21° C.). They can be readily found in the literature and, if necessary, can be determined in aqueous solution by procedures known to those skilled in the art.

[0069] The reaction of retarder T and its deprotonated version P1 with activator C1 should occur at an appropriate rate so as to provide a useful delay of the crosslinking reaction under the curing conditions.

[0070] A preferred catalyst system includes an epoxy as catalyst activator C1, a weakly basic nucleophilic anion group as catalyst precursor P1 that reacts with the epoxide group of C1 to form a strongly basic adduct C1, and most preferably also includes a retarder T. In a suitable catalyst system, P1 is a carboxylate salt, C1 is an epoxide, carbodiimide, oxetane or oxazoline, more preferably an epoxide or carbodiimide, and T is a carboxylic acid. Alternatively, P1 is DABCO, C1 is an epoxy, and T is a carboxylic acid.

[0071] Without wishing to be bound by theory, it is believed that the nucleophilic anion P1 reacts with the activator epoxide C1 to produce a strong base which is immediately protonated by the retarder T to produce a salt (functionally similar to P1) that does not directly and strongly catalyze the crosslinking reaction. The reaction scheme is carried out until the retarder T is substantially completely depleted, which provides an open time since during that time there is no significant amount of strong base to significantly catalyze the reaction of the crosslinkable components A and B. Once the retarder T is depleted, a strong base is formed which remains to effectively catalyze the rapid RMA crosslinking reaction.

[0072] The features and advantages of the present invention will be understood with reference to the following illustrative reaction schemes. [ka]

[0073] Specifically, for carboxylates, epoxides and carboxylic acids as the P1, C1 and T species, this can be depicted as: [ka]

[0074] In some cases, the detailed mechanism of the reaction of activator C1 with precursor P1 may not be known or is under debate, and a reaction mechanism may be suggested that involves the protonated form of P1 actually participating in the reaction. The net effect of such a reaction sequence may be similar to the sequence described based on its progression through the deprotonated form of P1. Systems are included in the present invention where the reaction may be argued to proceed along the protonated P1 pathway. In this case, after the retarder T is depleted, C1 reacts with the protonated P1 generated from the acid-base equilibrium with Michael donor species A, which activates crosslinking due to this acid-base equilibrium being drawn to the deprotonated Michael donor side.

[0075] The reaction scheme when the activator reacts via the protonated form of P1H may be shown by the following scheme: [ka]

[0076] In one embodiment, the retarders T are protonated anionic groups P1, preferably carboxylic acids T and carboxylates P1, which can be formed, for example, by partial neutralization of an acid functional component, preferably a polymer containing an acid group as retarder T, to partially convert it to an anionic group on P1, the partial neutralization being preferably carried out with a hydroxide cation or a (bi)carbonate, preferably a tetraalkylammonium or tetraalkylphosphonium cation. In another embodiment, the polymer-bound component P1 can be made by hydrolyzing the ester groups in the polyester with the aforementioned hydroxides.

[0077] The boiling points of the conjugate acids of components T and P1 are preferably above the anticipated curing temperature of the powder coating composition to prevent uncontrolled evaporation of these catalyst system components during the curing conditions. Formic acid and acetic acid are less preferred retarders T because they can evaporate during curing. Preferably, the conjugate acids of retarders T and P1 have boiling points above 120°C.

[0078] Less preferably, at least one of the components P1, C1 or T of the catalyst system can be a group of one or both of the crosslinking components A or B. In that case, it must be ensured that P1 and C1 are macrophysically present in the powder coating composition. One or more, but not all, of the groups P1, C1 and T can be on the RMA crosslinking components A or B or both. In an advantageous embodiment, P1 and T are both on the RMA crosslinking components A and / or B, and P1 is preferably formed by partially neutralizing an acid functional polymer containing acid groups of T with a base containing a cation as described above to partially convert the acid groups on T to anionic groups on P1. Another embodiment has component P1 formed by hydrolysis of a polyester, e.g., a polyester of component A, and present as a polymeric species.

[0079] In yet another embodiment, the catalyst system comprises: an activator C in an amount of 1 to 600 μeq / gr, preferably 10 to 400, more preferably 20 to 200 μeq / gr, relative to the total weight of the binder components A and B and the catalyst system; a precursor P in an amount of 1 to 300 μeq / gr, preferably 10 to 200, more preferably 20 to 100 μeq / gr, based on the total weight of the binder components A and B and the catalyst system; optionally a retarder T in an amount of 1 to 500, preferably 10 to 400, more preferably 20 to 300 μeq / gr, most preferably 30 to 200 μeq / gr, based on the total weight of the binder components A and B and the catalyst system, Preferably, the equivalent of C1 is i. if present, preferably in an amount of 1 to 300 μeq / gr, preferably 10 to 200, more preferably 20 to 100 μeq / gr, greater than the amount of T; ii. preferably in an amount greater than that of P1; iii. More preferably, it is greater than the sum of the amounts of P1 and T.

[0080] However, if activator C1 is a Michael acceptor containing an activated unsaturated group C=C reactive with P1, then there is no reasonable upper limit to the concentration since C1 can also be component B in this case.

[0081] It is also possible for the catalyst system to function with an amount of C1 less than that of P1. However, this is less preferred as it leaves P1 unreacted. If the amount of C1, especially the epoxide, is greater than the amount of P1, it may react with P1 and T or other nucleophilic residues, but it may still remain basic or remain in the network after the reaction, which is not a big problem, so the drawbacks are limited. Nevertheless, an excess of C1 can be a disadvantage in terms of the cost of C1 other than the epoxy.

[0082] In yet another embodiment, the catalyst system comprises a precursor P and a retarder T and an activator C, The weak base P represents 10-100 equivalent percent of the sum of P and T, Preferably, the amount of retarder T is 20-400 equivalent % of the amount of P, preferably 30-300 equivalent %; preferably, the ratio of the equivalents of C to the sum of the amounts of P and T is at least 0.5, preferably at least 0.8, more preferably at least 1, preferably at most 3, more preferably at most 2, The ratio of C to T is preferably at least 1, preferably at least 1.5, most preferably at least 2.

[0083] In a preferred embodiment, the powder coating composition also comprises a precursor P and / or a retarder T, the precursor P and / or the retarder T being (semi-)crystalline and preferably having a polyurethane backbone prepared by reacting HDI with a compound (i) having at least two isocyanate-reactive groups, preferably a diol, the diol (i) being or having a linking chain between the hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-SS-CH2-, the linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between the hydroxyl groups; having a linking chain between the -CH(CH3)- units or -CH(CH2CH3)- containing hydroxyl groups, preferably at a central position, whereby the linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between the hydroxyl groups; The hydroxyl groups are primary hydroxyl groups and the diol is not aromatic and is not alicyclic.

[0084] Preferably, the (semi-)crystalline precursor P and / or retarder T and the (semi-)crystalline donor component A and / or acceptor component B each have a polyurethane backbone prepared by reacting HDI with the same compound (i).

[0085] (Semi)crystalline donor component A and acceptor component B In a second aspect, the present invention relates to a (semi-)crystalline a polyisocyanate, which is essentially hexamethylene diisocyanate (HDI), with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and a compound (iia) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic CH donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; or Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C=C, forming a (semi-)crystalline acceptor component B The present invention relates to a crosslinkable donor component A and / or a crosslinkable acceptor component B comprising a polyurethane backbone formed by reacting with

[0086] The embodiments and preferences described above for the (semi-)crystalline donor component A and / or the acceptor component B in the first aspect of the invention also apply to the second aspect of the invention.

[0087] Substrates and Coatings The present invention also provides a method of powder coating a substrate, comprising the steps of: a. providing a powder coating composition according to the present invention; b. applying a layer of powder to a substrate surface; c. heating, preferably using infrared heating, to a curing temperature Tcur of 75°C to 140°C, preferably 80°C to 130, 120, 110°C or even 100°C; d. Curing at Tcur for a cure time preferably less than 40, 30, 20, 15, 10 or even 5 minutes. The present invention relates to a method comprising the steps of:

[0088] The powder coating composition at Tcur preferably has a melt viscosity at the curing temperature of less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas. The melt viscosity is measured at the very start of the reaction or without C2 of the catalyst system.

[0089] In a preferred embodiment of the method, the curing temperature is between 75°C and 140°C, preferably between 80°C and 120°C, and the catalyst system C is a latent catalyst system as described above that allows the powder coating of temperature-sensitive substrates, preferably MDF, wood, plastics, composites, or temperature-sensitive metal substrates such as alloys.

[0090] The present invention therefore also relates to an article, preferably having a temperature sensitive substrate like MDF, wood, plastic or metal alloy, coated with the powder coating composition of the present invention, preferably wherein the crosslink density XLD of the coating is at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1 mmol / cc (determined by DMTA), and preferably less than 3, 2, 1.5, 1 or even 0.7 mmol / cc.

[0091] The powder coating composition may further comprise additives such as additives selected from the group of pigments, dyes, dispersants, degassing aids, leveling additives, matting additives, flame retardant additives, additives for improving film forming properties, additives for the optical appearance of the coating, additives for improving mechanical properties, adhesion, or additives for stability properties such as color and UV stability. These additives may be melt mixed with one or more of the components of the powder coating composition.

[0092] Powder paints can also be designed to produce matte coatings using similar means as conventional powder coating systems, relying on additives or by deliberate heterogeneous crosslinking using either powder blend systems or systems based on blends of polymers of different reactivity.

[0093] Standard powder coating processes can be used, which typically involve solidifying the extrudate immediately after it leaves the extruder by forcing it to spread over a cooling band. The extruded paint can take the form of a solidified sheet as it travels along the cooling band. At the end of the band, the sheet is then broken into small pieces, preferably via a peg breaker, into granules. At this point, no significant shape control is applied to the granules, although a statistical maximum size is preferred. The paint granules are then transferred to a classifying microniser, which breaks down the paint to a very precise particle size distribution. The product then becomes the finished powder coating paint.

[0094] The invention is illustrated by the following non-limiting examples.

[0095] example OH value The OHV was determined by manual titration of prepared blank and sample flasks. The indicator solution is composed by dissolving 0.80 g of thymol blue and 0.25 g of cresol red in 1 L of methanol. Ten drops of indicator solution are added to the flask and then titrated with a standardized 0.5 N methanolic potassium hydroxide solution. The end point is reached when the color changes from yellow to gray to blue and a blue coloration occurs that is maintained for 10 seconds. The hydroxyl value is then calculated according to the following: Hydroxy value = (BS) x N x 56.1 / M + AV During the ceremony, B = ml of KOH used for blank titration S = ml of KOH used in sample titration N = normality of potassium hydroxide solution M = weight of sample (base resin) AV = Acid value of base resin Net hydroxy value is defined as follows: Net OHV = (BS) x N x 56.1 / M

[0096] Amine Number A freshly prepared solvent blend of 3:1 xylene:ethanol propanol is prepared. A quantity of resin is accurately weighed into a 250 ml Erlenmeyer flask. 50-60 ml of 3:1 xylene:ethanol is then added. The solution is gently heated until the resin is completely dissolved, being careful not to allow the solution to boil. The solution is then cooled to room temperature and titrated potentiometrically with 0.1 M hydrochloric acid until after the equivalence point.

[0097] GPC molecular weight The molar mass distribution of the polymers was determined by gel permeation chromatography (GPC) on a Perkin-Elmer HPLC series 200 instrument using a refractive index (RI) detector and a Plgel column, using THF as the eluent and calibration with polystyrene standards. Experimental molecular weights are expressed as polystyrene equivalents.

[0098] DSC Tg Resin and coating glass transition temperatures reported herein are those of the midpoint Tg determined from differential scanning calorimetry (DSC) using a heating rate of 10° C. / min.

[0099] Rheological properties of materials The flow and curing properties of the powder coatings were characterized using an Anton-Paar stress-controlled MCR302 rheometer fitted with an electric heating device and corresponding heating / cooling hood (ETD400 P and H). The experiments were carried out in a 25 mm parallel plate configuration with disposable parts. The sample material was applied at a starting temperature of 80 °C for a few minutes, followed by a gap of 0.5 to 0.6 mm between the plates. The powder coatings were then cooled at normal force levels below 15 N for approximately 47 K min. -1 Heating was started at a rate of 0.05 to 120°C, where the samples were left at isothermal conditions for 45 minutes, long enough to achieve complete crosslinking of the samples, if appropriate. Complex viscosity was determined under small strain oscillatory shear conditions with an amplitude of 2% at a frequency of 1 Hz.

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

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

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

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

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

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

[0106] Preparation of catalyst precursor P-1 To prepare the catalyst precursor, carboxylate-terminated polyester resin (AV 48) was melted and extruded with tetraethylammonium bicarbonate (TEAHCO) using a Leistritz ZSE 18 twin-screw extruder. 3 The extruder contained a barrel containing nine successive heating zones set to maintain the following temperature profile from inlet to outlet: 30-50-80-120-120-120-120-100-100 (in °C). Solid polyester resin was added at a rate of 2 kg / hr through the first zone, and liquid TEAHCO 3 was pumped through the second zone at 0.60 kg / hr. Mixing was performed between zones 4-7 with the screw set to rotate at 200 rpm. Volatiles and water evolved from the acid-base neutralization were removed using vacuum in zone 7. After leaving the die, the extruded strands were immediately cooled and collected. The resulting final product has an AV of 11 mg KOH / g, an amine number of 33 KOH / g and a Tg (DSC) of 48°C.

[0107] Preparation of (semi)crystalline components Preparation of (semi)crystalline acid retarders and the corresponding catalyst precursors CT-1&CP-1 379.3 g of DEG and 1 g of DBTL were charged into a 2 liter round bottom reactor and heated to 50°C. Then 497.9 g of HDI was added dropwise to the reactor to initiate the reaction under nitrogen protection, maintaining the process temperature below 120°C. After that, 122.8 g of succinic anhydride was charged into the reactor. The reaction is allowed to proceed at 120°C until the desired acid number is achieved. The resulting final product CT-1 has an AV of 69 mg KOH / g, a Tg(DSC) of -5°C, and maximum and end DSC melting temperatures of 115°C and 125°C, respectively.

[0108] To prepare the corresponding catalyst precursor CP-1, 1790 g of CR-1 was charged into a reactor and melted by heating to 125°C. Then, 842.5 g of tetraethylammonium hydroxide (TEAOH) aqueous solution (35%) was slowly added to the reactor and mixed with the molten crystalline acid resin under continuous stirring. The volatiles and water evolved from the acid-base neutralization were removed using vacuum. The resulting final product CP-1 has an AV of 36 mg KOH / g, an amine value of 44 mg KOH / g, a Tg(DSC) of -5°C, and maximum and end DSC melting temperatures of 110°C and 120°C, respectively.

[0109] Preparation of the (semi)crystalline acetoacetate donor resin CU-Acet according to the invention To prepare the (semi)crystalline acetoacetic resin CU-Acet, a two-step synthetic route was performed. In the first step, triethylene glycol (TEG) was transesterified with ethyl acetoacetate. Briefly, a reaction vessel was charged with 211 g of triethylene glycol and 50 g of toluene. The mixture was heated to distill off the toluene and any water that may be present in the TEG. Then, 73.0 g of ethyl acetoacetate was added to the reaction mixture along with another 50 g of toluene. At a temperature of 125 °C, distillation of the toluene / ethanol mixture was continued, occasionally refeeding toluene. After a total distillation of 3.5 h, 50 g of dry molsieves 4 Å were added and the mixture was allowed to cool slowly overnight. The molsieves were filtered and the filtrate was stripped of volatiles on a rotary evaporator to remove the last of the toluene. NMR and TLC characterization showed that the transesterification of ethyl acetoacetate was nearly complete. In the second step, the reactor was charged with 0.01 g DBTL and 29.3 g of the product obtained after transesterification. The temperature was increased to 60° C., at which point a feed of 21.2 g HDI was started. The reaction mixture was heated to 95° C. with the feeds over a period of 45 minutes. After completion of the feeds, the temperature was maintained at this temperature for an additional hour, then removed from the reactor and cooled. The resulting (semi)crystalline acetoacetate donor resin CU-Acet has maximum and end DSC melting temperatures of 73° C. and 82° C., respectively. The theoretical acetoacetate EQW is 800 g / mole.

[0110] Preparation of Comparative (Semi)Crystalline Urethane Acrylate Resin CUA-1 The process is described in patent application WO 2019 / 145472. A 5 liter reactor equipped with a thermometer, stirrer, dosing funnel and gas bubbling inlet is charged with 833 parts IPDI, 913 parts HDI, 4.20 parts DBTL and 5.00 parts BHT. 395 parts hydroxypropyl acrylate are then dosed over 60 minutes, avoiding the temperature rising above 35°C. Once the addition is complete, 896 parts 1,6-hexanediol and 5 parts BHT are added. 15 minutes after the exothermic reaction has subsided, the reaction product is cast on a metal tray. The resulting (semi)crystalline urethane acrylate CUA-1 has maximum and end DSC melting temperatures of 120°C and 140°C, respectively. Tg(DSC) of 17.7°C and theoretical unsaturation EQW of 1004 g / mol.

[0111] Preparation of the (semi)crystalline urethane acrylate resin CUA-2 according to the present invention 504.6 g HDI, 0.1 g DBTL and 5 g BHT were charged into a 2 liter round bottom reactor and heated to 50° C. under dry air. A mixture of 288.3 g hydroxybutyl acylate and 212.2 g DEG was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120° C. The resulting (semi)crystalline urethane acrylate CUA-2 has maximum and end DSC melting temperatures of 106° C. and 115° C., respectively. Theoretical values ​​Mn=1005 and unsaturation EQW=503 g / mol.

[0112] Preparation of the (semi)crystalline urethane acrylate resin CUA-3 according to the present invention Similarly, 562.7 g of HDI, 0.1 g of DBTL and 5 g of BHT were charged into a 2 liter round bottom reactor and heated to 50° C. under dry air. A mixture of 222 g of hydroxyethyl acylate and 282.4 g of 3-methyl-1,5-pentanediol was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120° C. The resulting (semi)crystalline urethane acrylate CUA-3 has maximum and end DSC melting temperatures of 95° C. and 102° C., respectively. Theoretical values ​​Mn=1067 and unsaturation EQW=558 g / mol.

[0113] Preparation of (semi)crystalline urethane acrylate resin CUA-4 Similarly, 243.3 g of HDI, 0.05 g of DBTL and 0.3 g of BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. Then, a mixture of 112.0 g of hydroxyethyl acylate and 144.8 g of triethylene glycol was added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120° C. The resulting (semi-)crystalline urethane acrylate CUA-4 has maximum and end DSC melting temperatures of 82° C. and 92° C., respectively. Theoretical values ​​Mn=1037 and unsaturation EQW=519 g / mol.

[0114] Preparation of the (semi)crystalline urethane acrylate resin CUA-5 according to the present invention Similarly, 158.8 g HDI, 0.04 g DBTL and 0.2 g BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. A mixture of 144.2 g hydroxybutyl acylate and 47.1 g DEG was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 110° C. The resulting (semi-)crystalline urethane acrylate CUA-5 has maximum and end DSC melting temperatures of 101° C. and 108° C., respectively. Theoretical values ​​Mn=700 and unsaturation EQW=350 g / mol.

[0115] Preparation of the (semi)crystalline urethane acrylate resin CUA-6 according to the present invention Similarly, 187.9 g HDI, 0.04 g DBTL and 0.2 g BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. A mixture of 68.8 g hydroxybutyl acylate and 93.3 g DEG was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 135° C. The resulting (semi-)crystalline urethane acrylate CUA-6 has maximum and end DSC melting temperatures of 119° C. and 134° C., respectively. Theoretical values ​​Mn=1468 and unsaturation EQW=734 g / mol.

[0116] Preparation of the (semi)crystalline urethane acrylate resin CUA-7 according to the present invention Similarly, 121.5 g of HDI, 0.03 g of DBTL and 0.2 g of BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. A mixture of 69.9 g of hydroxybutyl acylate and 58.7 g of thiodiethanol was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 135° C. The resulting (semi-)crystalline urethane acrylate CUA-7 has maximum and end DSC melting temperatures of 132° C. and 138° C., respectively. Theoretical values ​​Mn=1032 and unsaturation EQW=516 g / mol.

[0117] Preparation of the (semi)crystalline urethane acrylate resin CUA-8 according to the present invention Similarly, 113.3 g of HDI, 0.04 g of DBTL and 0.2 g of BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. A mixture of 71.1 g of hydroxybutyl acylate and 65.7 g of 2-hydroxyethyl disulfide was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 135° C. The resulting (semi-)crystalline urethane acrylate CUA-8 has maximum and end DSC melting temperatures of 130° C. and 140° C., respectively. Theoretical values ​​Mn=1014 and unsaturation EQW=507 g / mol.

[0118] Preparation of the (semi)crystalline urethane acrylate resin CUA-9 according to the present invention Similarly, 139.7 g HDI, 0.04 g DBTL and 0.2 g BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. A mixture of 58.1 g hydroxyethyl acylate and 52.3 g methylpropanediol was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 150° C. The resulting (semi-)crystalline urethane acrylate CUA-9 has maximum and end DSC melting temperatures of 132° C. and 142° C., respectively. Theoretical values ​​Mn=1000 and unsaturation EQW=500 g / mol.

[0119] Preparation of the (semi)crystalline urethane acrylate resin CUA-10 according to the present invention Similarly, 237.6 g of HDI, 0.05 g of DBTL and 0.3 g of BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. A mixture of 116.1 g of hydroxyethyl acylate and 146.3 g of 2-butyl-2-ethyl-1,3-propanediol was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 100° C. The resulting (semi-)crystalline urethane acrylate CUA-10 has maximum and end DSC melting temperatures of 37° C. and 63° C., respectively. Theoretical values ​​Mn=1000 and unsaturation EQW=500 g / mol.

[0120] Preparation of the (semi)crystalline urethane acrylate resin CUA-11 according to the present invention Similarly, 121.7 g HDI, 0.05 g DBTL and 0.3 g BHT were charged into a round-bottom reactor and heated to 50° C. under dry air. Then, a mixture of 80.0 g hydroxybutyl acylate and 56.5 g N-methyldiethanolamine was added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 100° C. The resulting (semi-)crystalline urethane acrylate CUA-11 has maximum and end DSC melting temperatures of 56° C. and 67° C., respectively. Theoretical values ​​Mn=1002 and unsaturation EQW=501 g / mol.

[0121] Preparation of the (semi)crystalline urethane methacrylate resin CUMA-1 according to the present invention 504.6 g HDI, 1 g DBTL and 5 g BHT were charged into a 2 liter round bottom reactor and heated to 50° C. under dry air. A mixture of 260.3 g hydroxyethyl methacrylate and 212.2 g DEG was then added dropwise to the reactor to initiate the reaction, maintaining the process temperature below 120° C. The resulting (semi)crystalline urethane methacrylate CUMA-1 has maximum and end DSC melting temperatures of 110° C. and 115° C., respectively. Theoretical Mn=977 and unsaturated EQW=489 g / mol.

[0122] Preparation of Comparative (Semi)Crystalline Vinyl Ether Urethane Resin CVE-1 It is described in Chinese Patent Publication No. 112457751. 1g of 4-hydroxybutyl vinyl ether, 0.02g of DBTL and 0.6g of BHT were charged into a four-necked reactor equipped with a thermometer, stirrer and distillation apparatus. The mixture was stirred and heated to 40°C under the protection of nitrogen. Then 42.06g of HDI was slowly dripped into the reactor to start the reaction, and the process temperature was maintained below 110°C. After all HDI was charged, the reaction was allowed to proceed at 110°C for 30 minutes. Finally, a vacuum was applied to remove low molecular weight volatiles. The resulting (semi)crystalline vinyl ether CVE-1 has maximum and end DSC melting temperatures of 98°C and 107°C, respectively. Theoretical unsaturation EQW=200g / mol.

[0123] Preparation of Comparative (Semi)Crystalline Vinyl Ether Urethane Resin CVE-2 It is described in Chinese Patent Publication No. 112457751. 44.7g 4-hydroxybutyl vinyl ether, 8.7g DEG, 0.02g DBTL and 0.6g BHT were charged into a four-neck reactor equipped with a thermometer, stirrer and distillation apparatus. The mixture was stirred and heated to 40°C under the protection of nitrogen. Then 42.3g HDI was slowly dripped into the reactor to start the reaction, and the process temperature was maintained below 95°C. After all HDI was charged, the reaction was allowed to proceed at 95°C for 30 minutes. Finally, a vacuum was applied to remove low molecular weight volatiles. The resulting (semi)crystalline vinyl ether CVE-2 has maximum and end DSC melting temperatures of 87°C and 104°C, respectively. Theoretical unsaturation EQW=260g / mol.

[0124] Preparation of Powder Coating Compositions To prepare the powder coating compositions, the raw materials were first premixed in a high speed Thermoprism Pilot Mixer 3 premixer at 1500 rpm for 20 seconds and then extruded in a Baker Perkins (formerly APV) MP19 25:1 LD twin screw extruder. The extruder speed was 250 rpm and the four extruder barrel zone temperatures were set at 15, 25, 100 and 100°C to extrude amorphous resins, or 15, 25, 120 and 100°C to extrude (semi)crystalline resins. After extrusion, the extrudate was ground using a Retsch GRINDOMIX GM 200 knife mill. The ground extrudate was sieved to less than 100 μm using a Russel Finex 100 micron mesh Demi Finex laboratory vibrating sieve.

[0125] result Cure kinetics of vinyl ether urethanes and urethane acrylates. [Table 2]

[0126] China Patent Publication No. 112457751 states that vinyl ether urethanes are used to participate in the crosslinking reaction of powder coatings that cure via a true Michael addition (RMA) reaction. In this patent, a powder coating example was given that was prepared using a malonate donor resin, a urethane acrylate and a vinyl ether urethane. The coating was prepared using a vinyl / acrylate / CH ratio of 1.25 / 2.54 / 1. 2and 48 meq of tertiary amine catalyst concentration. Such coatings can be cured at 100°C and have been demonstrated to provide good solvent resistance. We believe that vinyl ether urethane is not suitable as an acceptor resin in the RMA reaction and cannot participate in the crosslinking reaction. Considering this issue, model studies were performed to verify the reactivity of acrylates and vinyl ethers in RMA. Diethyl malonate, butyl acrylate, cyclohexyl vinyl ether and 1,4-diazabicyclo[2.2.2]octane (DABCO) were selected as model compounds for malonate donor, acrylate acceptor, vinyl ether and tertiary amine catalyst. EPIKOTE™ 828 was selected as the activator. More specifically, 4.01 g of diethyl malonate, 8.14 g of butyl acrylate, 3.95 g of cyclohexyl vinyl ether, 0.09 g of DABCO, and 0.15 g of EPIKOTE™ 828 were mixed together in a small round bottom flask to achieve a vinyl / acrylate / C-H2 stoichiometry of 1.25 / 2.54 / 1 and a catalyst concentration of 48 meq. The mixture was heated to 110° C. 1 Samples were taken at 10 min intervals for kinetic studies using H NMR. The signal at 3.68-3.78 ppm assigned to the CH next to the ether group is used as an internal standard to compare with the vinyl CH at 6.25-6.35 ppm and the acrylate CH at 5.75-5.85 ppm. Cyclohexyl vinyl ether, integrals of the mixture before curing and after curing at 110 °C for 30 min 1 The H NMR spectra are shown in Figures 1-3, and the results are summarized in Table 2.

[0127] From this study, it is evident that the urethane acrylate was consumed, presumably via RMA, as the concentration of acrylate decreased from 3.47 mmol / g to 0.83 mmol / g after 30 minutes of curing at 110°C. In contrast, the concentration of cyclohexyl vinyl ether remained constant; therefore, cyclohexyl vinyl ether did not react and did not become part of the crosslinked network after the same cure cycle.

[0128] To further test the vinyl ether urethane as an acceptor resin in RMA powder coatings, two crystalline vinyl ether urethane resins CVE-1 and CVE-2 were prepared according to China Patent Publication No. 112457751. In comparative examples PW1-PW2, the powder coatings were mixed with 1.5:1 vinyl / CH 2 These two resins were stoichiometrically formulated as the acceptor resin to have a ratio of 100 meq of catalyst precursor, 50 meq of acid retarder and 200 meq of activator. All coatings were sprayed on aluminum and steel panels at a film thickness of 80-100 μm and cured at 120 °C for 22 min. Coating analysis and application results are summarized in Table 4. As predicted by the model tests, both PW1 and PW2 have very poor solvent resistance since the vinyl ether urethanes have not reacted with the donor resin to form a crosslinked film. This is also supported by the DSC isothermal analysis at 120 °C where only small reaction enthalpies (delta H) were obtained.

[0129] [Table 3]

[0130] In examples PW3-PW4 (comparative) and PW5-PW7 (invention), the powder coating was prepared using a 1.5:1 acrylate / CH 2 PW4 formulated to have the same amount of semi-crystalline acceptor resin as PW5, acrylate / CH 2 = 0.75), stoichiometrically to have 50 meq of catalyst precursor, 75 meq of acid retarder and 225 meq of activator, with urethane acrylate as the acceptor resin. All coatings were sprayed onto aluminum and steel panels at 80-100 μm film thickness and cured at 120 °C for 22 minutes. Coating analysis and application results are summarized in Table 6.

[0131] PW3 is a comparative paint prepared with only amorphous components. The paint has a Tg of 52°C and can be cured well after 22 minutes at 120°C, as evidenced by good solvent resistance. However, it has poor adhesion to both aluminum and steel substrates and no impact resistance. [Table 4]

[0132] PW4 is a comparative example formulated with the (semi)crystalline urethane acrylate CUA-1 as the acceptor resin. CUA-1 was prepared according to the prior art patent application WO 2019 / 145472. CUA-1 is unlikely to recrystallize in the paint after extrusion, and DSC showed very little crystals present in the paint (low delta H due to melting). This results in a rather low paint Tg of 30°C, which may cause storage instability. Furthermore, rheological analysis of PW4 at 120°C showed a higher melt viscosity compared to PW5 and PW6 (see Table 6). This is due to the relatively higher Tg of CUA-1, which results in less plasticization after complete melting. The solvent resistance of PW4 is also rather poor due to the high EQW of CUA-1.

[0133] PW5 and PW6 are powder examples formulated with the (semi)crystalline urethane acrylate CUA-2 as acceptor resin. In PW5, a 1 / 1 mix of amorphous and (semi)crystalline urethane acrylate was used. Compared to PW3, the introduction of the (semi)crystalline urethane acrylate significantly improves adhesion and impact resistance on metal substrates (see Table 5). Most of the CUA-2 is believed to have recrystallized in the paint after extrusion, and its effect on the paint Tg is much lower than that of CUA-1. As a result, much higher delta H due to melting due to the presence of crystals was measured for these two paints. CUA-2 also has the advantage over CUA-1 of providing stronger plasticization and resulting in a lower melt viscosity. Paints with lower melt viscosity have a higher flow potential and are more likely to achieve a better appearance. Good solvent resistance was achieved for both paints.

[0134] [Table 5]

[0135] [Table 6]

[0136] PW7 is an example of a powder formulated by mixing an amorphous urethane acrylate resin with the (semi)crystalline urethane acrylate CUA-3 in a 1 / 1 ratio. Compared to PW3, the introduction of the (semi)crystalline urethane acrylate significantly improves adhesion and impact resistance on metal substrates (see Table 5). Solvent resistance remains good. Most of the CUA-3 is believed to have recrystallized in the paint after extrusion, and the impact on the paint Tg is relatively low. This is evidenced by the large delta H due to melting obtained by DSC analysis. CUA-3 has the advantage of having a melting temperature below 100 °C and is therefore more suitable for preparing paints that are cured at 100-120 °C.

[0137] Several (semi)crystalline resins based on polyurethane backbones have been prepared. By using different kinds of diols, e.g. DEG, 3-methyl-1,5-pentanediol, triethylene glycol, thiodiethanol, 2-hydroxyethyl disulfide, N-methyldiethanolamine and 2-butyl-2-ethyl-1,3-propanediol, it was demonstrated that the choice of diol influences the melting temperature of the resulting (semi)crystalline resins. Also, the molecular weight of the (semi)crystalline resins influences the melting temperature. For example, CUA-2, CUA-5 and CUA-6 were all prepared using DEG, but with theoretical Mn of 1005, 700 and 1468, respectively. The resulting melting temperatures are 115, 108 and 134 °C, respectively.

Claims

1. A powder coating composition comprising a crosslinkable composition and a catalyst system, said crosslinkable composition being formed by a crosslinkable donor component A and a crosslinkable acceptor component B which are crosslinkable by a true Michael addition (RMA) reaction via said catalyst system, said catalyst system being capable of catalysing said RMA crosslinking reaction at a curing temperature below 140°C, preferably below 120°C, even more preferably below 110°C or below 100°C, preferably at least 70°C, preferably at least 80, 90 or 100°C, The crosslinkable composition comprises: a) a crosslinkable donor component A having at least two acidic C—H donor groups in activated methylene or methine; and b) a crosslinkable acceptor component B having at least two activated unsaturated acceptor groups C=C which reacts with component A by true Michael addition (RMA) to form a crosslinked network; Including, At least a part of the crosslinkable donor component A and / or the crosslinkable acceptor component B is (semi)crystalline; a polyisocyanate which is essentially hexamethylene diisocyanate (HDI) with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and or a compound (iia) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic C—H donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; or Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C═C, forming said (semi-)crystalline acceptor component B. and a polyurethane backbone formed by reacting Powder coating compositions.

2. 2. The powder coating composition according to claim 1, wherein the (semi-)crystalline donor A and / or acceptor B are in a partially crystalline state and have a melting temperature below 140°C, preferably below 120°C, below 110°C or even below 100°C.

3. The compound (i) containing at least two isocyanate reactive groups is a diol, said diol being having a linking chain between said hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-S-S-CH2-, said linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between said hydroxyl groups; or having a linking chain between said hydroxyl groups containing -CH(CH3)- or -CH(CH2CH3)- units, preferably at a central position, whereby said linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between said hydroxyl groups; the hydroxyl groups are primary hydroxyl groups, and the diol is non-aromatic and non-alicyclic; The powder coating composition of claim 1.

4. 4. The powder coating composition of claim 3, wherein the diol is selected from the group consisting of diethylene glycol, triethylene glycol, 3-methyl 1,5-pentanediol, 2-methyl 1,3-propanediol, thiodiethanol, dithiodiethanol, bis(hydroxyethyl)methylamine, tetraethylene glycol, di(1,3-propanediol), di(1,4-butanediol).

5. 2. The powder coating composition according to claim 1, wherein the (semi-)crystalline donor A and / or acceptor B have a number average molecular weight of 300-4000 g / mol, preferably 500-3000, more preferably 1000-2000 g / mol.

6. 2. The powder coating composition of claim 1, wherein the ratio of said isocyanate reactive groups of compound (i) and compound (iia) or (iib) to said isocyanate groups is preferably greater than 1, more preferably the molar ratio of said isocyanate reactive groups to isocyanate groups is from 1.0 to 1.5, more preferably from 1.01 to 1.

2.

7. 2. The powder coating composition according to claim 1, wherein the (semi-)crystalline acceptor component B is used and the compound (iib) is a hydroxyl-functional (meth)acrylate, preferably selected from the group consisting of hydroxybutyl (meth)acrylate and hydroxyethyl (meth)acrylate or mixtures thereof, or the compound (iib) has hydroxyl and maleate, fumarate or itaconate functional groups.

8. 2. The powder coating composition of claim 1, wherein a semi-(crystalline) donor component A is used and said compound (iia) is a transesterification product of a diol with an alkyl acetoacetate or a dialkyl malonate.

9. a. the crosslinkable component A contains at least two acidic C—H donor groups, preferably in activated methylene or methine in malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate; b. component B comprises at least two activated unsaturated RMA acceptor groups, preferably derived from acryloyl, methacryloyl, itaconate, maleate or fumarate functional groups; At least one of the donor component A and / or the acceptor component B is a material having a polyurethane backbone formed as described in claim 1, Preferably, the composition comprises a total amount of donor groups C—H and acceptor groups C═C per gram of binder solids of 0.05 to 6 meq / gr, and preferably the ratio of acceptor groups C═C to donor groups C—H is greater than 0.1 and less than 10; The powder coating composition of claim 1.

10. 2. The powder coating composition of claim 1, wherein the amount of the crystalline polyurethane component in the formulation is from 2 to 95% by weight, preferably from 2 to 70% by weight, more preferably from 3 to 50% by weight, and most preferably from 6 to 35% by weight, based on the total amount of crosslinkable components A and B.

11. The (semi)crystalline crosslinkable components A and B are a polyisocyanate which is essentially hexamethylene diisocyanate (HDI) with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and Compounds (iia) which contain at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic C-H donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; and Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C═C, forming said (semi-)crystalline acceptor component B.

2. The powder coating composition of claim 1, wherein the (semi-)crystalline hybrid A / B component is formed by reacting

12. said catalyst system comprising a precursor P, an activator C, and optionally a retarder T; said precursor P is a weak base whose protonated form has a pKa greater than 2 units, preferably greater than 3 units, more preferably greater than 4 units, even more preferably at least 5 units lower than the pKa of the activated C-H groups in donor component A; and said activator C is capable of reacting with P at cure temperature to produce a strong base (CP) capable of catalysing the Michael addition reaction between A and B; 2. The powder coating composition of claim 1, wherein said retarder T is an acid having a pKa more than 2 points, more preferably more than 3 points, even more preferably more than 4 or 5 points lower than the pKa of the activated C-H in A, which upon deprotonation produces a weak base capable of reacting with said activator C and a strong base capable of catalyzing the Michael addition reaction between said crosslinkable compositions A and B.

13. Said precursor P and / or retarder T are (semi)crystalline and preferably have a polyurethane backbone prepared by reacting HDI with a compound (i) having at least two isocyanate-reactive groups, preferably a diol, said diol (i) being having a linking chain between said hydroxyl groups containing an ether or thioether group, preferably -CH2-O-CH2-, -CH2-S-CH2-, -CH2-S-S-CH2-, said linking chain having a maximum length of 11 carbon atoms and / or heteroatoms between said hydroxyl groups; or having a linking chain between said hydroxyl groups containing -CH(CH3)- units or -CH(CH2CH3)-, preferably at a central position, whereby said linking chain has a chain length with an odd number of carbon atoms and / or heteroatoms less than 6 between said hydroxyl groups; 13. The powder coating composition of claim 12, wherein the hydroxyl groups are primary hydroxyl groups and the diol is non-aromatic and non-alicyclic.

14. 14. The powder coating composition according to claim 13, wherein the (semi-)crystalline precursor P and / or retarder T and the (semi-)crystalline donor component A and / or acceptor component B each have a polyurethane backbone prepared by reacting HDI with the same compound (i).

15. It is (semi)crystalline, a polyisocyanate which is essentially hexamethylene diisocyanate (HDI) with a compound (i) which contains at least two, preferably two, isocyanate-reactive groups, preferably hydroxyl, and is more preferably a diol; and or a compound (iia) which comprises at least one, preferably one, isocyanate-reactive group, preferably a hydroxyl, and at least one functional group having at least one acidic C—H donor group in an activated methylene or methine, forming a (semi-)crystalline donor component A; or Compounds (iib) which contain at least one, preferably one, isocyanate-reactive group, preferably hydroxyl, and at least one functional group carrying at least one activated unsaturated acceptor group C═C, forming a (semi-)crystalline acceptor component B. a crosslinkable donor component A and / or a crosslinkable acceptor component B comprising a polyurethane backbone formed by reacting with

16. A cross-linkable donor component A and / or a cross-linkable acceptor component B having the characteristics described in claim 1.

17. 1. A method of powder coating a substrate, comprising: a. applying a layer comprising the powder coating composition of claim 1 to a substrate surface, said substrate being preferably a temperature sensitive substrate, preferably a temperature sensitive metal substrate such as MDF, wood, plastic, composite or alloy; b. heating, preferably using infrared heating, to a curing temperature Tcur of 75-160°C, preferably 80-150°C, more preferably 80-140, 120 or even 100°C, wherein the melt viscosity at said curing temperature Tcur is preferably less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas; c. Curing at Tcur for a cure time preferably less than 40, 30, 20, 15, 10, or even 5 minutes; A method comprising:

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

Images