阅读说明：本技术 粉末涂料组合物 (Powder coating composition ) 是由 R·H·G·布林克威斯 R·沃森 M·博斯马 P·J·M·D·埃尔弗林克 A·J·W·布塞尔 于 2019-01-25 设计创作，主要内容包括：本发明涉及适用于低温粉末涂料交联的粉末涂料组合物,所述粉末涂料组合物通常在固化温度75-140℃,可用于粉末涂覆热敏基材,如MDF、木材、塑料或热敏金属合金。所述粉末涂料组合物包含可交联组分A,其具有活化亚甲基或次甲基中的至少2个酸性C-H供体基团；可交联组分B,其具有至少2个活化不饱和受体基团C＝C,在催化剂体系C的作用下,通过Real Michael Addition与组分A反应,所述催化剂体系C优选为潜伏催化剂体系。本发明还涉及制造此类粉末涂料组合物的方法,涉及使用所述粉末涂料组合物涂覆制品的方法以及所得的涂覆制品。本发明还涉及用于粉末涂料的特定聚合物,以及特定催化剂体系在此类粉末涂料组合物中的用途。(The present invention relates to powder coating compositions suitable for the crosslinking of low temperature powder coatings, which are generally useful for powder coating heat sensitive substrates such as MDF, wood, plastics or heat sensitive metal alloys at curing temperatures of 75 to 140 ℃. The powder coating composition comprises a crosslinkable component a having at least 2 acidic C-H donor groups of activated methylene or methine groups; crosslinkable component B, which has at least 2 activated unsaturated acceptor groups C ═ C, is reacted with component a by Real Michael Addition under the action of catalyst system C, which is preferably a latent catalyst system. The invention also relates to a process for making such powder coating compositions, to a process for coating an article using said powder coating composition and to the resulting coated article. The invention also relates to specific polymers for powder coatings, and to the use of specific catalyst systems in such powder coating compositions.)

1. A powder coating composition comprising one or more crosslinkable components and a catalyst, characterized in that the one or more crosslinkable components are crosslinkable by a Real Michael Addition (RMA) reaction, the powder coating composition comprising:

a. a crosslinkable component A having at least 2 acidic C-H donor groups in the activated methylene or methine group,

b. a crosslinkable component B having at least 2 activated unsaturated acceptor groups C ═ C, which form a crosslinked network by reaction of Real Michael Addition (RMA) with component A,

c. a latent catalyst system C comprising a strong base or strong base precursor to delay the catalytic RMA crosslinking reaction at a cure temperature of less than 200 ℃, preferably less than 175 ℃, more preferably less than 150 ℃, 140 ℃, 130 ℃, even 120 ℃, and preferably at least 70 ℃, preferably at least 80 ℃, 90 ℃ or 100 ℃,

wherein the catalyst system C is a latent catalyst system LC selected from the group consisting of:

a. a latent catalytic system LCC with chemical retardation comprising components that react at curing temperature to delay initiation of a reaction between crosslinkable components a and B, the latent catalytic system LCC comprising:

in the embodiment LCC 1:

a) a weak base C2, a weak base,

b) an activator C1 reactive with C2 or protonated C2 at cure temperature,

c) optionally further comprising an acid C3, preferably protonated C2;

in the embodiment LCC 2:

a) the weak base C2 is a Michael addition donor S2, and

b) activator C1 is a michael acceptor S1, which contains an activated unsaturated group C ═ C that can react with S2 at the curing temperature,

c) optionally further comprising an acid C3 which is the acid S3 whose corresponding base is also a Michael addition donor, preferably protonated S2,

wherein, in case S1 is an acrylate, the conjugate acid of S2 has a pKa below 8, preferably below 7, more preferably below 6, wherein pKa is defined as the value in an aqueous environment; and where S1 is a methacrylate, fumarate, itaconate or maleate, the pKa of the conjugate acid of S2 is less than 10.5, preferably less than 9, more preferably less than 8; or

A combination of embodiments LCC1 and LCC 2;

b. a latent catalyst system LCE with evaporation latency comprising a base blocked by a volatile acid or a weak base which forms a volatile acid upon protonation and which evaporates at the curing temperature, and preferably a further free volatile acid;

c. latent catalyst system LCP with physical retardation, wherein there is a catalytic system physically separated and unable to undergo chemical reaction in the powder at or below the mixing temperature and capable of undergoing chemical reaction at the curing temperature, preferably a strong base or a latent catalyst system, preferably selected from:

a) a latent catalyst system LCP1 comprising a strong base catalyst having a melting temperature below the curing temperature and above the mixing temperature, preferably above 70 ℃, 80 ℃, 90 ℃ or 100 ℃;

b) a latent catalyst system LCP2 comprising an active strong base catalyst substance encapsulated in or mixed with a material that releases a catalyst at a temperature below the curing temperature and above the mixing temperature, wherein preferably the melting temperature or glass transition temperature in the case of an amorphous material of the material is below the curing temperature and above the mixing temperature;

c) a latent catalyst system LCP3 comprising a photobase generator component which releases a base on irradiation at an appropriate wavelength; or

A combination of catalyst systems LCC, LCE and LCP.

2. The powder coating composition of claim 1, wherein in the latent catalyst system embodiment LCC1,

-the activator C1 is selected from the group consisting of epoxide, carbodiimide, oxetane, oxazoline or aziridine functional components, preferably epoxide or carbodiimide, and wherein:

the pKa of the conjugate acid of the weak base C2 is preferably more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component A, and wherein C2 is preferably a weak base nucleophilic anion selected from carboxylate, phosphonate, sulfonate, halide or phenolate anions or salts thereof, or a non-ionic nucleophile, preferably a tertiary amine, more preferably the weak base C2 is a weak base nucleophilic anion selected from carboxylate, halide or phenolate or 1, 4-diazabicyclo- [2.2.2] -octane (DABCO), and

-said latent catalyst system preferably further comprises an acid C3 having a pKa which is more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a, wherein the acid C3 is preferably protonated C2.

3. The powder coating composition of claim 1, wherein in the latent catalyst system embodiment LCC2,

the weak base S2 is preferably selected from the group consisting of phosphines, N-alkylimidazoles and fluorides, or is a weak base nucleophilic anion X "from a compound containing acidic X-H groups, wherein X is N, P, O, S or C, wherein the anion X" is a michael addition donor reactive with the activator S1, and the anion X "is characterized in that the pKa of the corresponding conjugate acid X-H is less than 8 and additionally more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a, and

-said latent catalyst system preferably further comprises an acid S3 having a pKa which is more than 1, preferably 1.5, more preferably 2 and even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a, wherein the acid S3 is preferably protonated S2.

4. A powder coating composition according to any one of claims 1-3, wherein the weak base C2 is added in the form of a salt comprising a non-acidic cation, preferably of formula Y (R')₄Wherein Y represents N or P, and wherein each R' may be the same or different alkyl, aryl or aralkyl group attached to the polymer, or wherein the cation is a protonated, very strong basic amine preferably selected from amidines, preferably 1, 8-diazabicyclo (5.4.0) undec-7-ene (DBU), or guanidines, preferably 1,1,3, 3-Tetramethylguanidine (TMG).

5. The powder coating composition according to claim 1, wherein the latent catalyst system is a latent catalyst system LCE comprising: a base blocked by a volatile acid, preferably a strong base, or a weak base which forms a volatile acid upon protonation, and wherein the latent catalyst system preferably further comprises an additional volatile acid which evaporates at the curing temperature, wherein the boiling point of the acid is below 300 ℃, preferably below 250 ℃, 225 ℃,200 ℃ or 150 ℃, and preferably above 100 ℃ or 120 ℃.

6. The powder coating composition according to any one of claims 1-5, comprising:

a. in the case of the catalyst system LCC1, the amount of activator C1 is 1 to 600 μ eq/g, preferably 10 to 400 μ eq/g, more preferably 20 to 200 μ eq/g, where μ eq/g is μ eq relative to the total weight of binder components a and B and catalyst system LCC; or in the case of the catalyst system LCC2, the amount of activator S1 is at least 1. mu. eq/g, preferably at least 10. mu. eq/g, more preferably at least 20. mu. eq/g, most preferably at least 40. mu. eq/g,

b. the amount of weak base C2 is 1-300. mu. eq/g, preferably 10-200. mu. eq/g, more preferably 20-100. mu. eq/g, relative to the total weight of binder components A and B and catalyst system LC,

c. optionally, the amount of acid C3 is 1-500. mu. eq/g, preferably 10-400. mu. eq/g, more preferably 20-300. mu. eq/g, most preferably 30-200. mu. eq/g,

d. wherein the amount of C1 or respectively S1 is:

i. higher than C3, preferably 1-300. mu. eq/g, preferably 10-200. mu. eq/g, more preferably 20-100. mu. eq/g;

preferably an amount higher than C2, and

more preferably higher than the sum of the amounts of C2 and C3.

7. The powder coating composition according to any one of claims 1 to 6,

a. wherein the weak base C2 accounts for 10-100 mol% of the sum of C2 and C3,

b. preferably the amount of acid C3 is 20-400 mol%, preferably 30-300 mol%,

c. wherein preferably the ratio of the molar amount of C1 to the total amount of C2 and C3 is at least 0.5, preferably at least 0.8, more preferably at least 1, and preferably at most 3, more preferably at most 2,

the ratio of d.c1 to C3 is preferably at least 1, preferably at least 1.5, most preferably at least 2.

8. The powder coating composition according to any one of claims 1-7 having a curing curve determined by measuring the conversion of unsaturated bonds C ═ C of component B by FTIR at a curing temperature between 80, 90, 100 and 200, 150, 135 or 120 ℃ as a function of time, wherein the ratio of the time to reach 20% conversion from 20% to 60% C ═ C is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably the time to reach 60% conversion is less than 30, 20, 10 or 5 minutes, and preferably the time to reach 20% conversion at 100 ℃ is at least 1 minute, preferably at least 2,3, 5, 8 or 12 minutes.

9. The powder coating composition according to any one of claims 1-8, wherein:

a. crosslinkable component A comprises at least 2 acidic C-H donor groups in an activated methylene or methine group of the structure Z1(-C (-H) (-R) -) Z2, wherein R is hydrogen, a hydrocarbon, oligomer or polymer group, Z1 and Z2 are identical or different electron withdrawing groups, preferably selected from the group consisting of keto, ester, cyano or aryl, and preferably comprises an activated C-H derivative having the structure of formula 1:

wherein R is hydrogen or optionally substituted alkyl or aryl, Y and Y 'are the same or different substituents, preferably alkyl, aralkyl, aryl or alkoxy, or wherein in formula 1, -C (═ 0) -Y and/or-C (═ 0) -Y' are substituted with CN or aryl, no more than one aryl, or wherein Y or Y 'may be NRR' (R and R 'are H or optionally substituted alkyl) but preferably are not both, wherein R, Y or Y' are optionally attached to the oligomer or copolymer;

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 number of C-H acid groups in the crosslinkable component A,

b. component B comprises at least 2 activated unsaturated RMA acceptor groups, preferably derived from an acryloyl, methacryloyl, itaconate, maleate or fumarate functional group,

wherein preferably at least one and more preferably both of components A or B are polymeric, and

wherein preferably the composition comprises a total amount of donor groups C-H and acceptor groups C ═ C, from 0.05 to 6meq/g of binder solids, and preferably the ratio of acceptor groups C ═ C to donor groups C-H is greater than 0.1 and less than 10.

10. A powder coating composition according to any one of claims 1 to 9, wherein at least one of the crosslinkable components a or B or the mixed a/B is a polymer, preferably selected from acrylic, polyester, polyesteramide, polyesterurethane polymers, said polymer:

a) a number average molecular weight Mn, determined by GPC, of at least 450g/mol, preferably at least 1000, more preferably at least 1500, most preferably at least 2000g/mol,

b) a weight average molecular weight Mw, determined by GPC, of at most 20000g/mol, preferably at most 15000, more preferably at most 10000, most preferably at most 7500g/mol,

c) the molecular weight distribution Mw/Mn is preferably less than 4, more preferably less than 3,

d) C-H or C ═ C equivalent EQW is at least 150, 250, 350, 450 or 550g/mol, preferably at most 2500, 2000, 1500, 1250 or 1000g/mol, the reactive group C-H or C ═ C has a number average functionality of from 1 to 25, more preferably from 1.5 to 15, even more preferably from 2 to 15, most preferably from 2.5 to 10C-H groups/molecule,

e) preferably a melt viscosity of less than 60 pas, more preferably less than 40, 30, 20, 10 or even 5 pas at a temperature of 100-140 c,

f) preferably containing amide, urea or urethane linkages and/or containing high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from the group consisting of 1, 4-dimethylolcyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetramethyl-cyclobutanediol,

g) tg as the midpoint value determined by DSC at a heating rate of 10 ℃/min is above 25 ℃, preferably above 35 ℃, more preferably above 40, 50 or even 60 ℃, or is a crystalline polymer having a melting temperature of 40-150 ℃, preferably 130 ℃, preferably at least 50 or even 70 ℃, and preferably below 120 ℃ (determined by DSC at a heating rate of 10 ℃/min).

11. The powder coating composition according to any one of claims 1-10, comprising one or more components a or B or components of catalyst system C or separate different plasticizers in the powder in a (semi-) crystalline state and having a melting temperature of 40-130 ℃, preferably 50-120 ℃, more preferably 60-110 ℃, more preferably 60-100 ℃.

12. The powder coating composition according to any one of claims 1-11, wherein component B is a polyester (meth) acrylate, a polyester urethane (meth) acrylate, an epoxy (meth) acrylate or a urethane (meth) acrylate, or is a polyester comprising fumarate, maleate or itaconate units, preferably fumarates, or is a polyester terminated with isocyanate or epoxy functional activated unsaturated groups.

13. A process for preparing a powder coating composition according to any one of claims 1 to 12, comprising the steps of:

a. providing component a, component B, catalyst system C, and optional additives;

b. preferably at a temperature T below 140 deg.C, more preferably below 120, 100, 90 or even below 80 deg.C_MixingExtruding the components;

c. cooling, optionally including an annealing step, to crystallize the crystallizable component;

d. shaping the extruded mixture into pellets before, during or after cooling;

e. optionally, adding other additives;

f. grinding the particles into a powder.

14. A method of powder coating a substrate comprising:

a. providing a powder comprising the powder coating composition of any one of claims 1 to 12 or obtained according to the process of claim 13,

b. applying a layer of said powder onto the surface of a substrate, wherein the substrate is preferably a heat-sensitive substrate, preferably an MDF, wood, plastic or heat-sensitive metal substrate, such as an alloy, and

c. heating to a curing temperature T of 75-200 ℃, preferably 80-180 ℃, more preferably 80-160, 150, 140, 130 or even 120 ℃_CuringPreferably, infrared heating is also used,

d. wherein at a curing temperature T_CuringPreferably a melt viscosity of less than 60 pas, more preferably less than 40, 30, 20, 10 or even 5 pas,

e. at T_CuringThe sub-cure is preferably less than 40, 30, 20, 15, 10 or even 5 minutes cure time.

15. Article coated with a powder comprising the coating composition according to any one of claims 1-12 or the powder coating composition obtained according to the process of claim 13, preferably with a heat sensitive substrate selected from MDF, wood, plastic or metal alloy, and wherein the cross-linking density XLD is preferably at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1mmol/ml (determined by DMTA), and preferably below 3, 2, 1.5, 1 or even 0.7 mmol/ml.

16. Use of a catalyst system C as claimed in any one of claims 1-12 for the preparation of RMA crosslinkable powder coating compositions for catalyzing a crosslinking reaction in RMA crosslinkable powder coating compositions at a curing temperature below 200 ℃, preferably below 180 ℃, more preferably below 160, 140 or even 120 ℃.

17. An RMA crosslinkable polymer, preferably selected from the group consisting of acrylic, polyester-amide and polyester-urethane polymers, comprising:

a. one or more components a comprising at least 2 acidic C-H donor groups in an activated methylene or methine group of the structure Z1(-C (-H) (-R) -) Z2, wherein R is hydrogen, a hydrocarbon, oligomer or polymer group, Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from ketone, ester, cyano or aryl, preferably activated C-H derivatives having the structure of formula 1:

wherein R is hydrogen or optionally substituted alkyl or aryl, Y and Y ' are the same or different substituents, preferably alkyl, aralkyl, aryl or alkoxy, or wherein in formula 1, -C (═ 0) -Y and/or-C (═ 0) -Y ' are substituted with CN or aryl, no more than one aryl, or wherein Y or Y ' may be-NRR ' (R and R ' are H or optionally substituted alkyl) but preferably not both; said component a is preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, most preferably a malonate that provides at least 50%, preferably 60%, 70% or even 80% of the total number of C-H acid groups in crosslinkable component a, wherein R, Y or Y' provides attachment to the polymer;

b. optionally one or more components B comprising at least 2 activated unsaturated RMA acceptor groups, preferably acryloyl, methacryloyl, itaconate, maleate or fumarate functional groups, forming an A/B conjunct polymer, and

c. optionally one or more components of catalytic system C,

wherein the polymer:

h. a number average molecular weight Mn, determined by GPC, of at least 450g/mol, preferably at least 1000, more preferably at least 1500, most preferably at least 2000g/mol,

i. a weight average molecular weight Mw, determined by GPC, of at most 20000g/mol, preferably at most 15000, more preferably at most 10000, most preferably at most 7500g/mol,

j. the molecular weight distribution Mw/Mn is preferably less than 4, more preferably less than 3,

k.C-H equivalent EQW is at least 150, 250, 350, 450 or 550g/mol, preferably at most 2500, 2000, 1500, 1250 or 1000g/mol, the number average functionality of the reactive groups C-H is from 1 to 25, more preferably from 1.5 to 15, even more preferably from 2 to 15, most preferably from 2.5 to 10C-H groups/molecule,

preferably, the melt viscosity at a temperature of 100-140 ℃ is less than 60 pas, more preferably less than 40, 30, 20, 10 or even 5 pas,

preferably comprising amide, urea or urethane linkages and/or comprising high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from 1, 4-dimethylolcyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetramethyl-cyclobutanediol,

n. a Tg higher than 25 ℃, preferably higher than 35 ℃, more preferably higher than 40, 50 or even 60 ℃ as determined by DSC with a heating rate of 10 ℃/min, or a crystalline polymer having a melting temperature of 40-150 ℃, preferably 130 ℃, preferably at least 50 or even 70 ℃ and preferably lower than 150, 130 or even lower than 120 ℃ (as determined by DSC with a heating rate of 10 ℃/min).

18. A polymer comprising weak base groups C2 and optionally acid groups C3, wherein the weak base groups C2 are preferably formed by partial or complete neutralization of the acid groups C3 on the polymer, wherein C2 and C3 are preferably carboxylate and carboxylic acid groups, wherein the polymer is preferably selected from acrylic, polyester-amide and polyester-urethane polymers, wherein the polymer optionally comprises C-H donor groups, C ═ C acceptor groups or both, wherein the polymer preferably has:

a. the acid number in non-neutralized form is at least 3, more preferably 5, 7, 10, 15 or even 20mg KOH/g, and preferably less than 100, 80, 70, 60mg KOH/g,

b. a quaternary ammonium or phosphonium cation or a phosphonium cation,

mn of at least 500, preferably at least 1000 or even 2000, and Mw of not more than 20000, preferably not more than 10000 or 6000,

d. in the presence of a C-H donor and/or C ═ C acceptor group; a reactive C-H donor or C ═ C acceptor EQW of at least 150, preferably at least 250, 350 or even 450g/mol and not more than 2000, preferably not more than 1500, 1200 or 1000g/mol,

e. in the absence of C-H donor and C ═ C acceptor groups, the acid number in the non-neutralized form is at least 10, more preferably 15, 20mg KOH/g, and preferably less than 100, 80, 70, 60mg KOH/g.

19. Use of a polymer as defined in claim 18 as a latent base catalyst component and/or use of a RMA crosslinkable polymer as defined in claim 17 in RMA crosslinkable powder coatings.

Technical Field

The present invention relates to powder coating compositions curable at low curing temperatures, to a process for preparing such powder coating compositions, to a process for coating an article using said powder coating compositions and to the resulting coated article. The invention also relates to specific polymers and catalyst systems for powder coating compositions.

Background

Powder coatings are dry, finely divided, free flowing solid materials at room temperature and in recent years have gained promise over liquid coatings. The powder coatings are typically cured at elevated temperatures of 120-200 deg.C, more typically 140-180 deg.C. High temperatures are required to provide sufficient binder flow to allow film formation and to obtain good coating surface appearance, while achieving high reactivity of the crosslinking reaction. At low curing temperatures, when sufficient mechanical strength and resistance are required, reaction kinetics may be encountered that do not allow short curing times; on the other hand, for systems which may give rise to high reactivity of the components, the viscosity increases further rapidly as the curing reaction proceeds, due to the relatively high viscosity of such systems at this lower temperature: the time-integrated flow of such systems is too low to achieve sufficient leveling, resulting in a coating that may have a poor appearance (see, e.g., progress Organic Coatings, pages 72, 26-33 (2011)). Especially for thinner films, the appearance may be limited. Furthermore, when formulating powder coatings in an extruder, the extremely high reactivity may cause problems due to premature reaction.

Due to this temperature limitation, powder coatings are not readily used to coat heat sensitive substrates such as Medium Density Fiberboard (MDF), wood, plastics and certain metal alloys. Research and development efforts to reduce curing temperatures are ongoing, with an emphasis on green technology and corresponding pressures to reduce energy costs and to enable coating of heat-sensitive substrates. Powder coatings that cure at low temperatures are advantageous when applied to large metal parts because such parts heat slowly.

Recently, a great deal of effort has been directed to finding powder coatings that cure at lower temperatures. Thus, the term "lower" temperature in the field of powder coatings generally means a temperature significantly above room temperature but below 160 ℃, preferably below 150 ℃, more preferably below 140 ℃, even more preferably below 130 ℃ or even below 120 ℃. It has generally been found that when low curing temperatures are used, typically less than 150 c, especially less than or equal to 140 c, it is difficult to obtain sufficiently high reactivity within an acceptable curing time window to obtain the film crosslink density required for the properties to achieve suitable chemical resistance, mechanical properties (such as impact resistance, flexibility, surface hardness and weatherability), while also obtaining good flow and coating appearance.

Indeed in systems that cure at very low temperatures of 120-130 ℃. These tend to be epoxy-curable (e.g., triglycidyl isocyanurate (TGIC)) polyester systems. Typically, such systems have poor appearance and are used only to produce textured coatings.

Appearance can be improved by allowing the use of lower Tg powders (requiring refrigeration) or designing powder coatings with crystalline components that melt between Tg and the curing temperature, however, both approaches introduce complications.

Another method to allow low temperature curing of powder coatings is to use UV initiated free radical curing for crosslinking. This provides the opportunity to incorporate low temperature curing, yet have a good appearance within a limited curing time window; however, this method still has the following disadvantages: the need for radiation curing settings, non-uniform irradiation of complex shaped substrates, potential problems of limited penetration depth in pigmented systems, and relatively high costs associated with binders and photoinitiators.

The general problem with the described crosslinkable low temperature curable compositions of the prior art is that the cure speed is low or, if the cure speed is high, the resulting coating has a poor appearance and may introduce complications during extrusion formulation, or the components used are expensive or less desirable from an environmental point of view. In combination with all the requirements, there is a need for a system that essentially has the appropriate level of reactivity required, where the cure kinetics can be tightly controlled to allow good appearance and sufficient resistance to chemical and mechanical build-up within the challenging combination of cure time, cure temperature and film thickness.

Thus, there remains a need for a powder coating composition that can be cured at high cure speeds at low temperatures to achieve acceptably short cure times, but with a sufficiently long open time to allow flow and coalescence and to achieve good film formation with good coating appearance. In this context, "open time" refers to the time at the curing temperature before the reaction has progressed to increase the viscosity to such an extent that further flow of the paint becomes insignificant.

Summary of The Invention

The present invention solves one or more of these problems by providing a powder coating composition comprising one or more crosslinkable components and a catalyst, characterized in that the one or more crosslinkable components are crosslinkable by a Real Michael Addition (RMA) reaction, the powder coating composition comprising:

a. a crosslinkable component A having at least 2 acidic C-H donor groups in the activated methylene or methine group,

b. a crosslinkable component B having at least 2 activated unsaturated acceptor groups C ═ C, which form a crosslinked network by reaction with component A via Real Michael Addition (RMA),

c. a latent catalyst system C comprising a strong base or strong base precursor to delay the catalytic RMA crosslinking reaction at a cure temperature of less than 200 ℃, preferably less than 175 ℃, more preferably less than 150 ℃, 140, 130 or even 120 ℃, and preferably at least 70 ℃, preferably at least 80, 90 or 100 ℃,

wherein catalyst system C is a latent catalyst system LC selected from:

a. a latent catalytic system LCC with chemical delay comprising components that react at curing temperature to delay initiation of a reaction between crosslinkable components a and B, the latent catalytic system LCC comprising:

in the embodiment LCC 1:

a) a weak base C2, a weak base,

b) an activator C1 reactive with C2 or protonated C2 at cure temperature,

c) optionally further comprising an acid C3, preferably protonated C2;

wherein in the case of embodiment LCC 2:

a) the weak base C2 is a Michael addition donor S2, and

b) activator C1 is a michael acceptor S1, which contains an activated unsaturated group C ═ C that can react with S2 at the curing temperature,

c) optionally further comprising an acid C3 which is the acid S3 whose corresponding base is also a Michael addition donor, preferably protonated S2,

wherein the pKa of the conjugate acid of S2, where pKa is defined as the value in an aqueous environment, is less than 8, preferably less than 7, more preferably less than 6, in the case where S1 is an acrylate, and

where S1 is a methacrylate, fumarate, itaconate or maleate, the pKa of the conjugate acid of S2 is less than 10.5, preferably less than 9, more preferably less than 8;

alternatively, a combination of embodiment LCC1 and LCC 2;

b. a latent catalyst system LCE with evaporation delay comprising a base blocked by a volatile acid or a weak base which forms a volatile acid upon protonation and which evaporates at the curing temperature, and preferably additionally a free volatile acid;

c. latent catalyst system LCP with physical retardation, wherein a catalytic system, preferably a strong base or a latent catalyst system, is present, which is physically separated and does not undergo a chemical reaction in the powder at or below the mixing temperature and does undergo a chemical reaction at the curing temperature, preferably selected from:

a) a latent catalyst system LCP1, comprising a strong base catalyst with a melting temperature below the curing temperature and above the mixing temperature, preferably above 70, 80, 90 or 100 ℃; or

b) A latent catalyst system LCP2 comprising an active strong base catalyst material encapsulated in or mixed with a material that releases the catalyst at a temperature below the curing temperature and above the mixing temperature, wherein preferably the melting temperature or glass transition temperature (in the case of amorphous materials) of the material is below the curing temperature and above the mixing temperature;

c) a latent catalyst system LCP3 comprising a photobase generator component which releases a base on irradiation at an appropriate wavelength;

or a combination of catalyst systems LCC, LCE and LCP.

The inventors have found that RMA powder coating compositions are well suited for powder coatings that can be cured at relatively high cure speeds, acceptably short cure times, but still have a sufficiently long open time to allow film formation and achieve good crosslinking and good coating appearance using any of the described latent base catalyst systems at low temperatures, as detailed below.

In another aspect, the invention relates to a process for preparing the powder coating composition of the invention and to a process for powder coating a substrate. In the method, the curing temperature T_CuringIs chosen between 75-200 c, preferably between 80-180 c and more preferably between 80-160, 150, 140, 130 or even 120 c and preferably also infrared heating is used. Preferably, the curing is characterized by a curing curve (which is determined by FTIR measuring the conversion of unsaturated bonds C ═ C of component B as a function of time), wherein the ratio of the time from 20% to 60% C ═ C conversion to the time to reach 20% conversion is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably the time to reach 60% conversion is less than 30, 20, 10 or 5 minutes, and preferably the time to reach 20% conversion is at least 1 minute, preferably at least 2,3, 5, 8 or 12 minutes, upon curing at 100 ℃. Preferably the melt viscosity at said solidification temperature is less than 60Pa · s, more preferably less than 40, 30, 20, 10 or even 5Pa · s. Melt viscosity can be measured, for example, with a Brookfield CAP 2000 cone plate rheometer according to ASTM D4287 using a #5 spindle, and should be measured at the very beginning of the reaction or on a powder coating composition without catalyst activity.

The powder coating composition has the particular advantage that it can be used at low curing temperatures, and therefore the method for powder coating a substrate, preferably a heat-sensitive substrate, preferably uses curing temperatures between 75-140 ℃, preferably between 80 ℃ and 130 ℃ or 120 ℃, most preferably 100-. This makes it possible to use the method for powder coating heat-sensitive substrates, preferably MDF, wood, plastics or heat-sensitive metal substrates such as alloys. The invention therefore also relates in particular to articles coated with the powder coating composition of the invention. It was found that good coating properties can be obtained, with good crosslink density XLD and resulting good coating properties.

In another aspect, the present invention relates to the use of the latent catalyst system described herein in the preparation of RMA crosslinkable powder coating compositions for catalyzing a crosslinking reaction in RMA crosslinkable powder coating compositions at a curing temperature below 200 ℃, preferably below 180 ℃, more preferably below 160, 140 or even 120 ℃ and above 75, 80, 90 or 100 ℃.

In another aspect, the present invention relates to a RMA crosslinkable polymer and the use of said RMA crosslinkable polymer in RMA crosslinkable powder coatings. The RMA crosslinkable polymer is an RMA crosslinkable donor polymer. The RMA crosslinkable polymer is preferably selected from the group consisting of acrylic, polyester-amide and polyester-urethane polymers comprising:

a. one or more components a comprising at least 2 acidic C-H donor groups in an activated methylene or methine group of structure Z1(-C (-H) (-R) -) Z2, wherein R is hydrogen, a hydrocarbon, an oligomer or a polymer group, wherein Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from a ketone group, an ester group or a cyano group or an aryl group, preferably an activated C-H derivative having the structure of formula 1 below:

wherein R is hydrogen or optionally substituted alkyl or aryl, Y and Y ' are the same or different substituents, preferably alkyl, aralkyl, aryl or alkoxy, or wherein in formula 1, -C (═ 0) -Y and/or-C (═ 0) -Y ' are substituted with CN or aryl, no more than one aryl, or wherein Y or Y ' may be-NRR ' (R and R ' are H or optionally substituted alkyl) but preferably not both; said component a is preferably a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate group, most preferably a malonate, which provides at least 50%, preferably 60, 70 or even 80% of the total number of C-H acid groups in the crosslinkable component a, wherein R, Y or Y' provides the linkage to the polymer;

b. optionally one or more components B comprising at least 2 activated unsaturated RMA acceptor groups, preferably an acryloyl, methacryloyl, itaconate, citraconate, crotonate, cinnamate, maleate or fumarate functional group forming an A/B hybrid polymer, and

c. optionally one or more components of catalytic system C,

wherein the polymer:

a. a number average molecular weight Mn, determined by GPC, of at least 450g/mol, preferably at least 1000, more preferably at least 1500, most preferably at least 2000g/mol,

b. a weight average molecular weight Mw, determined by GPC, of at most 20000g/mol, preferably at most 15000, more preferably at most 10000, most preferably at most 7500g/mol,

c. the molecular weight distribution Mw/Mn is preferably less than 4, more preferably less than 3,

d.C-H equivalent EQW is at least 150, 250, 350, 450 or 550g/mol, preferably at most 2500, 2000, 1500, 1250 or 1000g/mol, the number average functionality of the reactive groups C-H is from 1 to 25C-H groups per molecule, more preferably from 1.5 to 15, even more preferably from 2 to 15, most preferably from 2.5 to 10,

e. the melt viscosity at a temperature of 100-140 ℃ is preferably less than 60 pas, more preferably less than 40, 30, 20, 10 or even 5 pas,

f. preferably containing amide, urea or urethane linkages and/or containing high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from the group consisting of 1, 4-dimethylolcyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetramethyl-cyclobutanediol,

g. tg higher than 25 ℃, preferably higher than 35 ℃, more preferably higher than 40, 50 or even 60 ℃ as determined by DSC with a heating rate of 10 ℃/min, or a crystalline polymer having a melting temperature of 40-150 ℃, preferably 130 ℃, preferably at least 50 or even 70 ℃, and preferably lower than 150, 130 or even lower than 120 ℃ (as determined by DSC with a heating rate of 10 ℃/min).

Detailed Description

The inventors have found that RMA powder coating compositions of the present invention can be cured at relatively low temperatures at high cure speeds compared to conventional powder coating compositions. The latent base catalyst system provides open time and good leveling at low temperatures. A latent catalyst system is a catalyst system that delays the initial stage of cure at the cure temperature. The delay is controlled by the choice of the components of the catalytic system and the particular of the crosslinkable components A and B relative to the RMAThe combination is selected to provide a preferred cure profile as described below. The RMA crosslinking reaction between components a and B requires the presence of a base, which is generally defined herein as a "strong base". The strong base is capable of being at T_CuringBase to catalyze RMA. In the present invention, as will be explained in more detail below, this strong base is generated by the latent catalyst system C. The latent catalytic system C may be a chemical retarding system LCC (LCC1 and/or LCC2), an evaporative retarding system LCE or a physical retarding system LCP or a combination of at least two of the foregoing systems.

In a preferred embodiment, the powder coating composition has a chemically retarded catalyst system LCC. Suitable catalyst systems LCC1 include:

in the embodiment LCC 1:

a) a weak base C2, a weak base,

b) an activator C1 reactive with C2 or protonated C2 at cure temperature,

c) optionally further comprising an acid C3, preferably protonated C2.

The chemical retardation is obtained by the time required for the weak base C2 to chemically react with the activators C1 or S1, and preferably an acid C3 is included to further increase the retardation.

In a preferred embodiment, the powder coating composition comprises a chemically retarded catalyst system embodiment LCC1, wherein:

-the activator C1 is selected from epoxide, carbodiimide, oxetane, oxazoline or aziridine functional components, preferably epoxide or carbodiimide, and wherein:

the pKa of the conjugate acid of the weak base C2 is preferably more than 1 unit, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component A, and wherein C2 is preferably a weak base nucleophilic anion selected from carboxylate, phosphonate, sulfonate, halide or phenolate anions or salts thereof, or a non-ionic nucleophile, preferably a tertiary amine, more preferably the weak base C2 is a weak base nucleophilic anion selected from carboxylate, halide or phenolate or 1, 4-diazabicyclo- [2.2.2] -octane (DABCO), and

the latent catalyst system preferably further comprises an acid C3 having a pKa which is more than 1, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a, wherein the acid C3 is preferably protonated C2.

In an alternative embodiment, the powder coating composition comprises a chemically retarded catalyst system embodiment LCC2 comprising:

a) the weak base C2 is a Michael addition donor S2, and

b) activator C1 is a michael acceptor S1, which contains an activated unsaturated group C ═ C that can react with S2 at the curing temperature,

c) optionally further comprising an acid C3 which is the acid S3 whose corresponding base is also a Michael addition donor, preferably protonated S2,

wherein the conjugate acid of S2 has a pKa below 8, preferably below 7, more preferably below 6, where pKa is defined as the value in an aqueous environment, in case S1 is an acrylate; and

where S1 is a methacrylate, fumarate, itaconate or maleate, the pKa of the conjugate acid of S2 is less than 10.5, preferably less than 9, more preferably less than 8.

Combinations of embodiments LCC1 and LCC2 are also possible. The powder coating composition preferably comprises a latent catalyst system embodiment LCC2, wherein:

the weak base S2 is preferably selected from phosphines, N-alkylimidazoles and fluorides, or is a weak base nucleophilic anion X from an acidic X-H group containing compound^-Wherein X is N, P, O, S or C, wherein the anion X^-Is a Michael addition donor reactive with activator S1, and anion X^-Is characterized in that the corresponding conjugate acid X-H has a pKa of less than 8 and is additionally more than 1, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component A, and

-said latent catalyst system preferably further comprises an acid S3 having a pKa which is more than 1, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a, wherein the acid S3 is preferably protonated S2.

For component S3 or its deprotonated variant S2, in the embodiment LCC2 which provides suitable kinetic characteristics, it is important that the reaction of these components with michael addition acceptor groups can be carried out at a suitable rate to avoid too fast a reaction and to enable delayed curing under the thermal conditions associated with powder coatings. Finding a suitable reactivity window requires selection of S3 XH (or S2X)^-) Suitable combinations of components and acceptor functionality for use in powder coating compositions.

WO2014/16680 describes RMA crosslinkable compositions using as catalyst C a combination of an acid X-H and an anion X-of the acid, wherein the anion X^-Is also a Michael addition donor reactive with component B. Use in powders is mentioned, but this document focuses on solvent-borne compositions curable at room temperature (22 ℃ according to the examples) and does not describe powder coating compositions curable at elevated temperatures (i.e. at temperatures above room or ambient temperature). For such solvent-borne room temperature curable compositions, the combination of acrylate acceptor groups with component X-H is reported to use X-H/X^-Components such as succinimide, 1,2, 4-triazole and benzotriazole act as catalysts. However, this combination was found to be unsuitable for powder coating compositions curable at high temperatures, since X is^-The anions are too reactive with acrylates so they do not provide the desired amount of retardation.

It has been found that for powder coating compositions comprising acrylate acceptor groups, a catalyst system LCC2 may be used, wherein component S1 is an acrylate acceptor group and components S2 and S3 are X with an acid pKa below 8 and more preferably below 7, 6 or even 5.5^-a/X-H component. Examples of useful X-H components that can be used in the acrylate acceptor-containing powder coating compositions include cyclic 1, 3-diketones such as 1, 3-cyclohexanedione (pKa 5.26) and dimethylketone (5, 5-dimethyl-1, 3-cyclohexanedione, pKa5.15), ethyl trifluoroacetoacetate (7.6), cycloisopropyl malonate (4.97). Preferably, an X-H component is used having a boiling point of at least 175 deg.C, more preferably at least 200 deg.C.

It has further been found that the compositions comprise methacrylates, fumarates, maleates or itaconatesPowder coating compositions of acceptor groups, catalyst system LCC2 may be used, wherein component S1 is an acceptor group as listed above, preferably a methacrylate, itaconate or fumarate group, and components S2 and S3 are X with an acid pKa of less than 10.5 and more preferably less than 9.5, 8 or even less than 7^-a/X-H component.

The pKa values mentioned are the aqueous pKa values at ambient conditions (21 ℃). They can be easily found in the literature and, if desired, can be determined in aqueous solution by methods known to the person skilled in the art. The pKa values of the relevant components are tabulated below.

Succinimides	9.5	Isatine	10.3
				Ethanesulfonylimine	9.3	Uracils	9.9
Phthalimides	8.3	4-Nitro-2-methylimidazole	9.6
				5, 5-dimethylhydantoin	10.2	Phenol and its preparation	10.0
1,2, 4-triazoles	10.2	Acetoacetic acid ethyl ester	10.7
				1,2, 3-triazoles	9.4	Ethyl cyanoacetate	9.0
Benzotriazole compounds	8.2	Acetylacetone	9.0
				Benzenesulfonamides	10.1	1, 3-cyclohexanediones	5.3
Nitromethane	10.2	Saccharin	2.0
				Nitroethane	8.6	Barbituric acid	4.0
2-nitropropane	7.7	Malonic acid diethyl ester	13.0

Suitable components C1 are described in column 3, lines 21-56 of US4749728 and include C2-18 alkylene oxides and oligomers and/or polymers having epoxide functional groups comprising a plurality of epoxide functional groups.particularly suitable alkylene oxides include 1, 2-epoxyhexane, tert-butyl glycidyl ether, phenyl glycidyl ether, glycidyl acetate, glycidyl ester of tert-carbonate, glycidyl methacrylate and glycidyl benzoate.A particularly suitable polyfunctional epoxide includes bisphenol A diglycidyl ether, and higher homologs of this class of BPA epoxy resins, diglycidyl adipate, 1, 4-diglycidyl butyl ether, glycidyl ethers of novolac resins, glycidyl esters of diacids (such as Araldite PT910 and PT912, TGIC et al, commercial diglycidyl ethers of bisphenol A and their solid higher molecular epoxides are epoxy groups, preferably epoxy esters of propylene oxide, 2-glycidyl esters, preferably epoxy esters derived from 2, 2-epoxypropane, 2-epoxypropane or glycidyl methacrylate, more preferably from the group consisting of 2-2 glycidyl esters of acrylic acid, 2-glycidyl esters of bisphenol A diglycidyl ethers and their higher molecular epoxides are preferably branched glycidyl esters, such as glycidyl esters of bisphenol A diglycidyl ethers, 2-glycidyl esters of bisphenol A, preferably glycidyl esters of bisphenol A, 2-epoxypropane-1-2-epoxypropane, 2-epoxypropane-epoxyesters, and polymers such as highly branched polymers, 2-epoxypropane-epoxyesters, 2-epoxypropane, preferably epoxypropane-epoxypropane, 2-epoxypropane, 2-epoxypropane, 2-epoxypropane, acrylic acid, 2-epoxypropane, phenol-epoxypropane, phenol-^TMGlycidyl ester of Acid 10). Most preferred are the typical powder cross-linker epoxy components: triglycidyl isocyanurate (TGIC), Araldite PT910 and PT912, and phenolic glycidyl ethers which are solid in nature at ambient temperature.

Suitable examples of weak bases C2 in embodiment LCC1 are weak base nucleophilic anions selected from carboxylate, phosphonate, sulfonate, halide or phenolate anions or salts thereof, or non-ionic nucleophiles, preferably tertiary amines, and for the catalyst system LCC of embodiment 1C2 is preferably a weak base nucleophilic anion selected from carboxylate, halide or phenolate, most preferably a carboxylate salt, or it is 1, 4-diazabicyclo- [2.2.2] -octane (DABCO). Component C2 is capable of reacting with the group C1 (preferably epoxy) to give strongly basic anionic adducts which can in principle initiate the reaction of the crosslinkable components. Alternatively, it may react through its conjugate acid form to produce a non-acidic adduct. Preferably, the weak base group C2 is not substantially basic to the acidic C-H groups of crosslinkable component a, but is reactive with epoxides under low temperature crosslinking conditions (e.g., half value is typically less than 30, preferably 15 minutes at the intended curing temperature).

Another suitable example of a weak base C2 is selected from the weak base anions X^-The weak base nucleophilic anion of (a), the weak base anion X^-From compounds containing acidic X-H groups, in which X is N, P, O, S or C, in which the anion X^-Is a michael addition donor reactive with activator C1 and the anion X-is characterized in that the pKa of the corresponding conjugate acid X-H is more than 1, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a. In the embodiment LCC2, these C2 components are designated as S2, reacting with the C ═ C acceptor group S1, but in the embodiment LCC1, it is also possible as nucleophile C2 in the reaction with activator component C1, for example with epoxy groups, which according to embodiments LCC1 and LCC2 can provide 2 reaction pathways.

On the time scale of the curing window, the group C2 is preferably reacted with the group C1 at a temperature of less than 150 ℃, preferably 140, 130, 120, preferably at least 70, preferably at least 80 or 90 ℃. The reaction rate of the group C2 with the group C1 at the curing temperature is sufficiently low to provide a useful open time, and sufficiently high to allow for adequate curing within the desired time window.

If anionic, the weak base C2 is preferably added as a salt comprising a non-acidic cation. Non-acidic means that there is no hydrogen competing with component a for base and therefore does not inhibit the crosslinking reaction at the intended curing temperature. The cation is preferably substantially non-reactive with any of the components in the crosslinkable composition. The cation may be, for example, an alkali metal, quaternary ammonium or phosphonium, but may also be a protonated "superbase" that is not reactive with any component A, B or C in the crosslinking composition. Suitable superbases are known in the art.

Preferably, the salt comprises an alkali or alkaline earth metal cation, in particular a lithium, sodium or potassium cation, or preferably of the formula Y (R')₄Wherein Y represents N or P, and wherein each R' may be the same or different alkyl, aryl or aralkyl groups which may be attached to the polymer, or wherein the cation is a protonated, very strong basic amine preferably selected from amidines, preferably 1, 8-diazabicyclo (5.4.0) undec-7-ene (DBU), or guanidines, preferably 1,1,3, 3-Tetramethylguanidine (TMG). As known to those skilled in the art, R' may be substituted with substituents that do not interfere or substantially interfere with RMA crosslinking chemistry. R' is most preferably an alkyl group having 1 to 12, most preferably 1 to 4 carbon atoms.

EP0651023 describes a catalyst system for RMA crosslinkable solvent-borne compositions comprising a catalyst C comprising a quaternary ammonium or phosphonium salt of Cl, Br, I, a salicylate, a polycarboxylate, a nitrate, a sulfonate, a sulfate, a sulfite, a phosphate or an acid phosphate anion in combination with an epoxy compound.

Most preferably, the powder coating composition comprises a catalyst system LCC further comprising an acid C3 having a pKa which is more than 1 unit, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component a, wherein the acid C3 is preferably protonated C2. Preferably, the conjugate acid of acids C3 and C2 has a boiling point of at least 120 ℃, preferably 130 ℃, 150, 175, 200 or even 250 ℃. Preferably, C3 is a carboxylic acid.

A preferred catalyst system is catalyst system LCC1, which contains an epoxy group C1, a weak base nucleophilic anionic group C2, which reacts with the epoxy group C1 to form a strongly basic anionic adduct C1/2, most preferably also including an acid group C3. In a suitable catalyst system LCC1, C2 is a carboxylate and C1 is an epoxide, carbodiimide, oxetane or oxazoline, more preferably an epoxide or carbodiimide, or C2 is DABCO and C1 is an epoxy.

Without wishing to be bound by theory, it is believed that the nucleophilic anion C2 reacts with the activator epoxide C1 to form a strong base, but the strong base is protonated by the acid C3 to form a salt (similar in function to C2) that does not directly catalyze the crosslinking reaction strongly. This reaction scheme proceeds until the acid C3 is substantially completely consumed, which provides open time because a large amount of strong base is not present during this time to significantly catalyze the reaction of the crosslinkable components. When the acid C3 is exhausted, a strong base will be formed and remain to effectively catalyze the rapid RMA crosslinking reaction. Alternatively, the cycle may also proceed similarly when the activation reaction with C1 occurs with protonated C2 species (C2 is protonated due to acid-base equilibrium with component a); again, this protocol will result in the consumption of excess acid C3 and provide the deprotonated a species as the cycle proceeds further.

The features and advantages of the present invention will be appreciated with reference to the following exemplary reaction schemes.

C2^-+C1→C1C2^-(Strong base)

C1C2^-+ C3H → C1C2H (non-acidic) + C3^-(weak base)

C3^-+C1→C1C3^-(Strong base)

After the acidic substance C3H is consumed

Especially for the case of carboxylates, epoxides and carboxylic acids as C2, C1 and C3 species, it can be plotted as:

if the activator will react through the protonated form of C2, the reaction scheme will be illustrated by the next scheme:

the open time can be adjusted by the amount of acid (C3) and by the choice of the amount and reactivity of the reactants C1 and C2. Epoxide C1 must be available to initiate the reaction and preferably the molar amount of epoxide is greater than the molar amount of acid C3.

In one embodiment, the acid groups C3 are protonated anionic groups C2, preferably carboxylic acids C3 and carboxylic acid salts C2, which may be formed, for example, by partial neutralization of acid-functional components, preferably polymers comprising acid groups C3, to partially convert to anionic groups C2, wherein partial neutralization is preferably carried out by cationic hydroxides, preferably tetraalkylammonium hydroxides or tetraalkylphosphonium hydroxides. In another embodiment, polymer-bound component C2 can be prepared by hydrolyzing the ester groups in the polyester with the above-described hydroxide.

Ethyl triphenyl phosphonium Acid Acetate is known as a catalyst for crosslinking epoxy functional polymers as described in "ETPPAAc Solutions Ethyl triphenyl phosphonium Acid Acetate", 20.04.2007, pages 1-2, XP 055319211. It is not known to use this compound as components C2 and C3 in RMA crosslinkable powder coating compositions. Furthermore, it is preferred that the conjugated acids of components C3 and C2 have boiling points above the expected curing temperature of the powder coating composition to prevent evaporation of these catalyst system components under curing conditions from being well controlled. Formic acid and acetic acid are less preferred acids C3 because they may evaporate during the curing process. Preferably, for the LCC type systems, the conjugated acids of components C3 and C2 have a boiling point above 120 ℃.

The catalyst system LCC1 is preferably a catalyst composition comprising the individual components C1, C2 and optionally C3. This is most convenient for mixing with the particular combination of donor and acceptor polymers selected. Alternatively, at least one of C1, C2, or C3 of catalyst system LCC1 is a group on crosslinkable component a or B, or both. In that case, if one or more but not all of the groups C1, C2, and C3 are on crosslinkable component a or B or both, the remaining components are added separately. In this case, typically and preferably, both C2 and C3 are on the polymer and C1 is added separately, or C1 and C3 are on the polymer and C2 is added separately. The advantage is that the reaction parameters can be flexibly optimized by simply adjusting the catalyst composition. In one convenient embodiment, both C2 and C3 are on crosslinkable polymer components a and/or B, and C2 is preferably formed by neutralizing an acid-functional polymer comprising acid groups C3 with a cation-containing base moiety to convert the acid groups C3 moieties to anionic groups C2 as described above. Another embodiment would have component C2 formed by hydrolysis of a polyester, such as the polyester of component a, and be present as a polymeric material.

In another embodiment, the powder coating composition comprises a latent catalytic system LCC2 wherein the weak base C2 is selected from the group consisting of phosphines, N-alkylimidazoles, fluorides and weak base anions X from compounds containing acidic X-H groups^-Wherein X is N, P, O, S or C, wherein the anion X-is a Michael addition donor reactive with activator S1, and the anion X-is characterized in that the pKa of the corresponding conjugate acid X-H is more than 1, preferably 1.5, more preferably 2, even more preferably at least 3 units lower than the pKa of the acidic C-H group of the main component A. In this embodiment, the reaction of the weak base C2 with an unsaturated group having Michael acceptor character (S1, which may be equal to B, but may also be another Michael addition acceptor species) triggers the generation of a more catalytically active, strongly basic species to accelerate the reaction between components A and B.

In yet another embodiment, the powder coating comprises a latent catalyst system which is a latent catalyst system LCE with evaporation delay, wherein the reaction is delayed by a slow evaporation step of the acidic substance. In this embodiment, comprising 1) a base, preferably a strong base, blocked with a volatile acid, or 2) a weak base C2, which forms a volatile acid when protonated by an excess of a weakly acidic substance a, and wherein the latent catalyst system optionally further comprises a further volatile acid C3, which volatile acid is at the curing temperature T_CuringEvaporation, wherein the boiling point of the acid is below 300 ℃, preferably below 250 ℃, 225, 200 or 150 ℃ and preferably above 100 ℃ or 120 ℃. Quaternary ammonium or phosphonium salts of carboxylic acids having the above boiling points are preferred.

The powder coating composition preferably comprises:

a. in the case of the catalyst system LCC1, the amount of activator C1 is 1 to 600 μ eq/g, preferably 10 to 400 μ eq/g, more preferably 20 to 200 μ eq/g, where μ eq/g is μ eq relative to the total weight of binder components a and B and catalyst system LCC; or in the case of the catalyst system LCC2, the amount of activator S1 is at least 1 μ eq/g, preferably at least 10, more preferably at least 20, most preferably at least 40 μ eq/g;

b. the amount of weak base C2 is from 1 to 300. mu. eq/g, preferably from 10 to 200, more preferably from 20 to 100. mu. eq/g, relative to the total weight of binder components A and B and catalyst system LC;

c. optionally, the amount of acid C3 is 1-500, preferably 10-400, more preferably 20-300 μ eq/g, most preferably 30-200 μ eq/g;

d. among them, the amount of C1 or respectively S1 is preferred:

i. amounts above C3, preferably from 1 to 300. mu. eq/g, preferably from 10 to 200, more preferably from 20 to 100. mu. eq/g,

preferably an amount higher than C2, and

preferably higher than the sum of the amounts of C2 and C3.

In the case of the catalyst system LCC2, there is no relevant upper limit for the concentration for S2, since S1 may also be component B. The catalyst may also function with amounts of C1 below C2. However, it is less preferred because it may waste C2. In case the amount of C1 (especially epoxides) is higher than that of C2, the disadvantage is limited because it may react with C2 and C3 or other nucleophilic residues, but remain basic after the reaction, or it may remain in the network without much problems. However, an excess of C1 may be disadvantageous in view of the cost of C1 other than epoxy. It is noted that a combination of LCC1 and LCE embodiments is possible, in which case C2 may be higher than C1 if C2 also forms the evaporation acid and thus also promotes catalysis as an LCE-type catalyst. Furthermore, in the case where the acid C3 is a volatile acid, it provides an additional initial delay by evaporating the retarding acid C3. This is a combination of latent catalyst systems LCC and LCE. In that case, the above requirement d.i does not apply.

Furthermore, it is preferred that in the powder coating composition:

a. the weak base C2 accounts for 10-100 mol% of the sum of C2 and C3,

b. the amount of acid C3 is preferably from 20 to 400 mol%, preferably from 30 to 300 mol%,

c. wherein the ratio of the molar amount of C1 to the total amount of C2 and C3 is preferably at least 0.5, preferably at least 0.8, more preferably at least 1, and preferably at most 3, more preferably at most 2,

the ratio of d.c1 to C3 is preferably at least 1, preferably at least 1.5, most preferably at least 2.

In an alternative embodiment, the powder coating composition comprises a latent catalyst system LCP with a physical delay, wherein a catalytic system, preferably a strong base or a latent catalyst system, is present, which is physically separate and at the mixing temperature T_MixingOr below which no chemical reaction can take place in the powder and which can take place at the curing temperature, preferably selected from:

a) a latent catalyst system LCP1, comprising a catalyst with a melting point below the curing temperature and above the mixing temperature, preferably above 70, 80, 90 or 100 ℃, or

b) A latent catalyst system LCP2 comprising an active catalyst material encapsulated in or mixed with a material that releases a catalyst at a temperature below the curing temperature and above the mixing temperature, wherein preferably the melting temperature or glass transition temperature (in the case of amorphous materials) of the material is below the curing temperature and above the mixing temperature, or

c) A latent catalyst system LCP3, comprising a photobase generator component which releases a base on irradiation at an appropriate wavelength.

Note that combinations of catalyst systems LCC, LCE and LCP are possible.

EP1813630, which is incorporated herein by reference, describes encapsulated base catalysts and their process for preparing RMA crosslinkable adhesives. Capsules can be made with base catalysts using paraffin and microcrystalline waxes to provide a shell or matrix. EP6224793 discloses an encapsulated active agent comprising an active agent encapsulated in a crystallizable or thermoplastic polymer. In this context, the bagThe melting temperature or glass temperature of the glue is selected at T_MixingAnd T_CuringIn the meantime.

In an alternative embodiment LCP3, the delay of the catalyst system for the cure of powder coatings by the high temperature curable RMA may be provided by a photobase generator component (PBG) that releases base upon irradiation at the appropriate wavelength. The base generated is preferably a strong base, i.e., a strong base sufficient to catalyze the RMA reaction between a and B, or may be a weak base used as component C2 in combination with the LCC chemical delayed catalysis system. PBGs for Michael addition reaction systems are described, for example, in EP3395800, progr.org.coat. (2019)127,222-. The photoinitiator provides a high level of reactivity control similar to free radical photoinitiators; it also faces similar complications such as potential problems of uniform irradiation of complex shaped substrates, radiation penetration of pigmented coatings and specialized expensive equipment requirements. The PBGs described herein can be used if the resulting base has the pKa value and nucleophilicity required for the intended latent catalyst system. Preferably, an overbased species is generated, such as an amidine, guanidine or carbanion.

As mentioned above, powder coating compositions with RMA crosslinkable components a and B and latent catalyst system LC (preferably catalyst system LCC, most preferably catalyst system LCC1) allow a low target curing temperature compared to competitive powder systems. The low curing temperature is generally in the range of 75-150 ℃, preferably 80-130 ℃, more preferably 80-120 ℃ or 80-110 ℃, in which range the curing temperature is selected, for example in view of the temperature sensitivity of the substrate. The curing time depends on the curing temperature selected. The cure time is the time to achieve sufficient cure before cooling to room temperature, for example, by applying heat at the cure temperature in an oven. Within the specified curing temperature range, this curing time is generally between 1 or 2 and 50 minutes, preferably between 2 or 5 and 40 minutes, generally and most preferably between 5 or 10 and 30 minutes. Curing can be carried out in an oven and preferably also by heating by means of infrared radiation.

Preferably, the powder coating composition of the present invention has a kinetic curing profile, which can be determined by FTIR measuring the conversion of unsaturated bonds C ═ C of component B as a function of time, the curing temperature being selected between 80, 90, 100 and 200, 150, 135 or 120 ℃, wherein the ratio of time to reach 20% conversion of C ═ C from 20% to 60% (as determined by FTIR) is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably less than 30, 20 or 10 minutes to reach 60% conversion. Preferably, the kinetic curing curve of the powder coating is such that the time to reach 20% conversion at 100 ℃ is at least 1 minute, preferably at least 2,3, 5, 8 or 12 minutes. The cure profile is set by selecting the components of the catalytic system for the selected combination of reactants a and B and the cure temperature.

The powder coating process involves heating the substrate to a curing temperature, which involves significant energy costs. The coating process using the powder coating composition of the invention has a higher energy efficiency due to its operation at low temperatures, while allowing sufficient curing, preferably within 50, 30, 20 or even 15 minutes of curing time, and extending the open time (pre-gelation) of the applied coating film as long as possible. Preferably, the composition is characterized by a sigmoidal cure profile, initially providing maximum flow and an initial period of low reaction conversion (open time), then increasing sharply to ensure adequate final conversion within a limited cure time. A long open time maximizes fluidity prior to gelation, which is beneficial for good coating appearance. In addition to coating properties, the powder coating compositions are particularly advantageous for use in low temperature curing powders, premature crosslinking or molecular weight and viscosity increase reactions during blending and mixing of the components in the extruder being limited due to the dynamic nature of the catalyst system.

Preferably, the powder coating composition of the invention is further characterized in that:

a. crosslinkable component A comprises at least 2 acidic C-H donor groups in an activated methylene or methine group of structure Z1(-C (-H) (-R) -) Z2, wherein R is hydrogen, a hydrocarbon, oligomer or polymer group, and wherein Z1 and Z2 are the same or different electron withdrawing groups, preferably selected from a ketone group, an ester group, a cyano group or an aryl group, preferably comprising an activated C-H derivative having the structure of formula 1:

wherein R is hydrogen or optionally substituted alkyl or aryl, Y and Y 'are the same or different substituents, preferably alkyl, aralkyl, aryl or alkoxy, or wherein in formula 1, -C (═ 0) -Y and/or-C (═ 0) -Y' are substituted with CN or aryl, no more than one aryl, or wherein Y or Y 'may be-NRR' (R and R 'are H or optionally substituted alkyl) but preferably are not both, wherein R, Y or Y' optionally provide a link to the 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 number of C-H acid groups in the crosslinkable component a;

b. component B comprising at least 2 activated unsaturated RMA acceptor groups, preferably derived from an acryloyl, methacryloyl, itaconate, maleate or fumarate functional group,

wherein preferably at least one (more preferably both) of components A or B is a polymer, and

wherein preferably the composition comprises a total amount of donor groups C-H and acceptor groups C ═ C, from 0.05 to 6meq/g of binder solids, and preferably the ratio of acceptor groups C ═ C to donor groups C-H is greater than 0.1 and less than 10.

The use of RealMichael Addition (RMA) crosslinkable coating compositions comprising crosslinkable components a and B for solvent-borne systems is generally described in EP2556108, EP0808860 or EP1593727, to which specific description of the inclusion of crosslinkable components a and B is incorporated herein.

Components A and B contain RMA reactive donor and acceptor moieties, respectively, which react to form a crosslinked network in the coating upon curing. The components a and B may be present on separate molecules, but may also be present on one molecule, referred to as a mixed a/B component, or a combination thereof. Preferably, components a and B are separate molecules and are each independently in the form of a polymer, oligomer, dimer, or monomer. For coating applications, it is preferred that at least one of components a or B is preferably an oligomer or polymer. Note that activated methylene CH2 contains 2C-H acid groups. Even after the reaction of the first C-H acid group, the reaction of the second C-H acid group is more difficult, for example, for the reaction with a methacrylate, the activated methylene has a functionality of 2 compared to the acrylate. The reactive components A and B may also be combined in one A/B mixed molecule. In this embodiment of the powder coating composition, both C-H and C ═ C reactive groups are present in one a-B molecule.

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

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 the catalytic system C. Also, mixtures or hybrids of these polymer types are possible. Suitably, component a is a polymer selected from acrylic, polyester, polyesteramide, polyester-urethane polymers.

Malonate or acetoacetate esters are the preferred donor type 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 C-H containing compound. Preferably, in the powder coating composition, the majority of the activated C-H groups are derived from malonic acid esters, i.e. more than 50%, preferably more than 60%, more preferably more than 70%, most preferably more than 80% of all activated C-H groups in the powder coating composition are derived from malonic acid esters.

The advantages of the present invention are particularly evident in extremely difficult compositions having a relatively high concentration and functionality of functional groups, for example in the case where component a is a compound, in particular an oligomer or polymer, comprising an average of 2 to 30, preferably 3 to 20 and more preferably 4 to 10 activated C-H per polymer chain. Preferred are oligomeric and/or polymeric malonate group-containing components such as polyesters, polyurethanes, polyacrylates, epoxy resins, polyamides and polyvinyl resins or mixtures thereof containing malonate type groups in the main chain, in side chains or in both.

The total amount of donor groups C-H and acceptor groups C ═ C per gram of binder solids, regardless of how they are distributed over the various crosslinkable components, is preferably from 0.05 to 6meq/g, more usually from 0.10 to 4meq/g, even more preferably from 0.25 to 3meq/g of binder solids, and most preferably from 0.5 to 2 meq/g. Preferably, the stoichiometry between components a and B is chosen such that the ratio of reactive C ═ C groups to reactive C — H groups is greater than 0.1, preferably greater than 0.2, more preferably greater than 0.3, 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, and the ratio is preferably less than 10, preferably 5, more preferably less than 3, 2 or 1.5.

Malonate group-containing polyesters can preferably be obtained by transesterification of the methyl or ethyl diester of malonic acid with a polyfunctional alcohol, which can be of polymeric or oligomeric nature, but can also be introduced together with the other components by the Michael addition reaction. 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 and mixtures thereof, such as polyester-urethanes containing from 1 to 50, more preferably from 2 to 10, malonate groups per molecule. The polymer component A can also be prepared in a known manner, for example by free-radical polymerization of ethylenically unsaturated monomers, including, for example, (meth) acrylate monomers which are functionalized with moieties which contain activated C-H acid (donor) groups, preferably acetoacetate or malonate groups, in particular 2- (methacryloyloxy) acetoacetic acid ethyl ester or 2- (methacryloyloxy) malonate ethyl ester. In practice, polyesters, polyamides and polyurethanes (and mixtures thereof) are preferred. Also preferably, the malonate group-containing component has a number average molecular weight (Mn) of from about 100 to about 10000, preferably 500-5000, and most preferably 1000-4000; mw is less than 20000, preferably less than 10000, most preferably less than 6000 (expressed as GPC polystyrene equivalents).

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

Acrylates, methacrylates, itaconates, fumarates and maleates are preferred. Itaconate, fumarate and maleate esters may be incorporated into the backbone of the polyester or polyester-urethane. Preferred exemplary resins may be mentioned, such as polyesters, polycarbonates, polyurethanes, polyamides, acrylic and epoxy resins (or mixtures thereof), polyethers and/or alkyd resins containing activated unsaturated groups. These include, for example, urethane (meth) acrylates obtained by reacting polyisocyanates with hydroxyl-containing (meth) acrylates (e.g., hydroxyalkyl esters of (meth) acrylic acid) or components prepared by esterifying a polyol component with less than a stoichiometric amount of (meth) acrylic acid; polyether (meth) acrylates obtained by esterification of hydroxyl group-containing polyethers with (meth) acrylic acid; a polyfunctional (meth) acrylate obtained by reacting a hydroxyalkyl (meth) acrylate with a polycarboxylic acid and/or a polyamino resin; poly (meth) acrylates obtained by reaction of (meth) acrylic acid with epoxy resins, and polyalkyl maleates obtained by reaction of monoalkyl maleates with epoxy resins and/or hydroxy-functional oligomers or polymers. Also preferred are polyesters end-capped with glycidyl methacrylate. It is possible that the acceptor component comprises a plurality of types of acceptor functional groups.

The most preferred activated unsaturated group containing component B are unsaturated acryloyl, methacryloyl and fumarate functional components. Preferably the number average functionality per activated C ═ C group is from 2 to 20, more preferably from 2 to 10, most preferably from 3 to 6. The equivalent weight (EQW: average molecular weight per reactive functional group) is 100-.

In view of the use in powder systems, the Tg of component B is preferably higher than 25, 30, 35, more preferably at least 40, 45, most preferably at least 50 ℃ or even at least 60 ℃, due to the required powder stability. Tg is defined as the midpoint measured by DSC, and the temperature rise rate is 10 deg.C/min. As understood by those skilled in the art, if the Tg of one component is significantly higher than 50 ℃, the Tg of the other component may be lower.

Suitable components B are urethane (meth) acrylates which are prepared by reacting hydroxyl-and (meth) acrylate-functional compounds with isocyanates, preferably at least some diisocyanates or triisocyanates, preferably isophorone diisocyanate (IPDI), to form urethane bonds. The urethane linkages themselves introduce rigidity, but it is preferred to use high Tg isocyanates, such as cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic. The amount of such isocyanates is preferably selected to raise the Tg of the (meth) acrylate functional polymer above 40 ℃, preferably above 45 or 50 ℃.

The powder coating composition is preferably designed in the following way: after curing, the crosslink density (using DMTA, described below) can be determined to be at least 0.025mmol/cc, more preferably at least 0.05mmol/cc, most preferably at least 0.08mmol/cc, and typically less than 3, 2, 1, or 0.7 mmol/cc.

The powder coating composition should remain a free flowing powder at ambient conditions and therefore preferably has a Tg above 25 ℃, preferably above 30 ℃, more preferably above 35, 40, 50 ℃ as the midpoint value as determined by DSC at a heating rate of 10 ℃/min.

As mentioned above, preferred component A is a malonate functional component. However, the incorporation of malonate moieties tends to lower the Tg and it is a challenge to provide powder coating compositions based on malonates as the main component a with a sufficiently high Tg.

In view of achieving a high Tg, the powder coating composition preferably comprises a crosslinkable component a, component B or mixed components a/B containing amide, urea or urethane linkages, and/or comprises a high Tg monomer, preferably a cycloaliphatic or aromatic monomer, or in the case of polyesters one or more monomers selected from: 1, 4-dimethylolcyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A, and tetramethylcyclobutanediol.

Furthermore, in view of achieving a high Tg, the powder coating composition comprises component B or mixed components a/B being a polyester (meth) acrylate, a polyester urethane (meth) acrylate, an epoxy (meth) acrylate or a urethane (meth) acrylate, or being a polyester comprising fumarate, maleate or itaconate (preferably fumarate) units, or being a polyester end-capped with isocyanate or epoxy functional activated unsaturated groups.

The above-mentioned measures for achieving a high Tg in the crosslinkable component A or B or in the mixed A/B can advantageously be combined with the presence of a crystalline component. The components of the powder coating composition may be amorphous or crystalline. If the components in the composition are completely amorphous, the Tg of these components must be sufficiently high, but low melt viscosities at low temperatures of the combination can be difficult to achieve. It may therefore be preferred that the powder coating composition comprises one or more components, preferably crosslinkable components a or B or components of the mixed a/B or catalyst system C or different plasticizers alone, in a (semi-) crystalline state in the powder coating composition, with a melting temperature of 40-150 ℃, preferably 50-130 ℃, more preferably 60 or 70 to 120 ℃, more preferably 60-110 ℃. Preferably, one or more of the components A or B or the components of the catalyst system C are (semi-) crystalline or a mixture of amorphous and (semi-) crystalline components, but the crystalline component may also be an additive which has no additional effect in the crosslinking reaction. The crystalline component preferably has a Tg when molten at less than 50 ℃ or more preferably less than 30, 20 or even 10 ℃ and a Tm when crystallized in the coating composition within the indicated range. The crystalline component has a lower melt viscosity when molten, but does not lower the Tg when in the crystalline state. The advantage of (semi) crystalline polymers is that a higher Tg of the composition can be obtained at the solidification temperature due to plasticization upon melting, while having a lower melt viscosity at the solidification temperature. The amount of crystalline component and other Tg influencing parameters are selected to obtain the correct balance of melt viscosity at the intended curing temperature of less than 60Pa · s, more preferably less than 50, 40, 30, 20, 10 or even 5Pa · s and Tg of the powder coating preferably above 35 ℃. During the preparation, care must be taken that the crystallizable components of the powder coating used are in a crystalline state.

Most preferably, the powder coating composition comprises a RMA crosslinkable polymer according to another aspect of the present invention, which has characteristics suitable for use in RMA crosslinkable powder coating compositions. In particular in view of obtaining good flow and leveling properties as well as good chemical and mechanical resistance, it was found to be preferred that in the powder coating composition at least one of the crosslinkable components a or B or the mixed a/B is a polymer, preferably selected from acrylic, polyester, polyesteramide, polyesterurethane polymers, said polymer:

a) a number average molecular weight Mn, determined by GPC, of at least 450g/mol, preferably at least 1000, more preferably at least 1500, most preferably at least 2000g/mol,

b) a weight average molecular weight Mw, determined by GPC, of at most 20000g/mol, preferably at most 15000, more preferably at most 10000, most preferably at most 7500g/mol,

c) the molecular weight distribution Mw/Mn is preferably less than 4, more preferably less than 3, and significantly greater than 1,

d) C-H or C ═ C equivalent EQW is at least 150, 250, 350, 450 or 550g/mol, preferably at most 2500, 2000, 1500, 1250 or 1000g/mol, the reactive group C-H or C ═ C having a number average functionality of from 1 to 25, more preferably from 1.5 to 15, even more preferably from 2 to 15, most preferably from 2.5 to 10C-H groups per molecule,

e) the melt viscosity in the temperature range of 100-140 ℃ is preferably less than 60 pas, more preferably less than 40, 30, 20, 10 or even 5 pas,

f) preferably containing amide, urea or urethane linkages and/or containing high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers selected from 1, 4-dimethylolcyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol, hydrogenated bisphenol A and tetramethyl-cyclobutanediol,

g) tg as the midpoint value determined by DSC at a heating rate of 10 ℃/min is higher than 25 ℃, preferably higher than 35 ℃, more preferably higher than 40, 50 or even 60 ℃, or is a crystalline polymer having a melting temperature of 40-150 ℃, preferably 130 ℃, preferably at least 50 or even 70 ℃, and preferably lower than 150, 130 or even 120 ℃ (determined by DSC at a heating rate of 10 ℃/min).

It may be noted that RMA is also used for the preparation of coatings starting from liquid (non-powder) compositions. For example, WO2016166371 describes RMA crosslinkable coating compositions that use a catalyst system based on a carbon dioxide-terminated strong base catalyst, a reactive component a (e.g. a malonated polyester) and a reactive component B.

The polymer characteristics Mn, Mw and Mw/Mn are selected, on the one hand in view of the desired powder stability and, on the other hand, in view of the desired low melt viscosity, in addition to the desired coating properties. High Mn is preferred to minimize Tg reduction effect of the end groups, on the other hand, low Mw is preferred, since melt viscosity is very related to Mw, and low viscosity is desired. Therefore, low Mw/Mn is preferred.

In view of achieving a high Tg, the RMA crosslinkable polymer preferably comprises amide, urea or urethane linkages and/or comprises high Tg monomers, preferably cycloaliphatic or aromatic monomers, or in the case of polyesters, monomers selected from 1, 4-dimethylolcyclohexane (CHDM), TCD diol, isosorbide, penta-spiroglycol or hydrogenated bisphenol a and tetramethyl-cyclobutanediol.

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

In a preferred embodiment the RMA crosslinkable polymer comprises a polyester, polyesteramide, polyester-urethane or urethane-acrylate comprising urea, urethane or amide linkages derived from cycloaliphatic or aromatic isocyanates, preferably cycloaliphatic isocyanates, said polymer having a Tg of at least 40 ℃, preferably at least 45 or 50 ℃ and at most 120 ℃, a number average molecular weight Mn of 450-. The polymer may be obtained, for example, by reacting a precursor polymer comprising the RMA crosslinkable groups with an amount of a cycloaliphatic or aromatic isocyanate to increase the Tg. The amount of such isocyanate or urea/urethane linkages added or formed is selected to raise the Tg to at least 40 c, preferably at least 45 or 50 c.

Preferably, the RMA crosslinkable polymer is a polyester or polyester-urethane comprising malonate as main component A and comprising a number average malonate functionality of 1-25, more preferably 1.5-15 even more preferably 2-15, most preferably 2.5-10 malonate groups per molecule, having a GPC weight average molecular weight of 500-.

Furthermore, the polymer may be an amorphous or (semi-) crystalline polymer or a mixture thereof. Semi-crystalline refers to partially crystalline and partially amorphous. (semi) crystallinity is defined by a DSC melting endotherm and target crystallinity is defined as a DSC peak melting temperature, Tm, of at least 40 ℃, preferably at least 50 ℃, more preferably at least 60 ℃ and preferably at most 130 ℃, 120, 110 or 100 ℃. The DSC Tg of this component in a fully amorphous state is preferably below 40 ℃, more preferably below 30, 20 or even 10 ℃.

In view of improving the shelf life of the powder coating composition, it was found advantageous to use polymer-bound C2 and C3 functional groups, in particular polymers comprising carboxylic acid salts and optionally also carboxylic acid components C2 and C3. It is believed that shelf life is improved by the effect of reduced mobility and Tg. Another advantage is that polymer components with high EQW are easier to mix into the powder coating composition than low EQW components, e.g. when preparing a formulation in an extruder, and the risk of inhomogeneity is reduced.

Thus, the present invention also relates to a polymer (C3/2 polymer) comprising weak base groups C2 and optionally acid groups C3, wherein the weak base groups C2 are preferably formed by partial or complete neutralization of the acid groups C3 on the polymer, wherein C2 and C3 are preferably carboxylate and carboxylic acid groups, wherein the polymer is preferably selected from acrylic, polyester-amide and polyester-urethane polymers, wherein the polymer optionally comprises C-H donor groups, C ═ C acceptor groups or both, wherein the polymer preferably has:

a) the acid number in non-neutralized form is at least 3, more preferably 5, 7, 10, 15 or even 20mg KOH/g, and preferably less than 100, 80, 70, 60mg KOH/g,

b) quaternary ammonium or phosphonium cations, preferably tetrabutylammonium or ethylammonium cations,

c) mn of at least 500, preferably at least 1000 or even 2000, and Mw of not more than 20000, preferably not more than 10000 or 6000,

d) if a C-H donor group and/or a C ═ C acceptor group are present, the reactive C-H donor or C ═ C acceptor equivalent weight is at least 150, preferably at least 250, 350 or even 450g/mol, and not more than 2000, preferably not more than 1500, 1200 or 1000g/mol,

e) the acid number in the non-neutralized form, if no C-H donor group and C ═ C acceptor group are present, is at least 10, more preferably 15, 20mg KOH/g, and preferably less than 100, 80, 70, 60mg KOH/g.

Preferably, the donor C-H group is a malonate type functional group. The acceptor unsaturation is preferably an acrylate, methacrylate, fumarate, maleate or itaconate group. It is further preferred that the above-described C3/2 polymer has a high Tg or crystallinity by containing a high Tg monomer component and/or hard bonds as described above for RMA crosslinkable polymers.

The invention also relates to the use of RMA crosslinkable polymers in RMA crosslinkable powder coatings. The invention further relates to a process for preparing a powder coating composition comprising the steps of:

a. providing component a, component B, catalyst system C, and optional additives;

b. preferably at a temperature T below 140 deg.C, more preferably below 120, 100, 90 or even below 80 deg.C_Mixing(ii) down-extruding the components;

c. cooling;

d. shaping the extruded mixture into pellets before, during or after cooling;

e. optionally, adding other additives;

f. grinding the particles into a powder.

The optionally added coating additives are typically one or more additives selected from the group consisting of: pigments, dyes, dispersants, degassing auxiliaries, levelling additives, matting additives, flame-retardant additives, additives for improving film-forming properties, additives for the optical appearance of coatings, additives for improving mechanical properties, adhesion or additives for stability, for example colour and UV stability.

Powder coatings can also be designed for the production of matt coatings, using a similar approach to conventional powder coating systems, or by means of additives or targeted heterogeneous crosslinking by using powder mixture systems or systems based on mixtures of different reactive polymers.

Standard powder coating processing can be employed, typically involving solidification of the extrudate immediately after it exits the extruder by forced dispersion on a cooling belt. The extruded coating may be in the form of a solidified sheet as it travels along the cooling belt. The pieces are then broken into small pieces at the end of the belt, preferably into granules by a pin breaker. In this regard, although a statistically maximum size is preferred, there is no significant shape control of the particles. The coating particles are then transferred to a classifying micronizer where the coating is ground to a very precise particle size distribution. The product is the finished product powder coating. If a crystalline component is used, care must be taken to crystallize the componentAre present in the powder coating in a crystalline state. For example, this may mean selecting a T below the melting temperature Tm of the crystallizable component_MixingOr T is_MixingAbove Tm to allow the component to crystallize upon cooling.

The invention also relates to a method of powder coating a substrate comprising:

a. there is provided a powder having the powder coating composition of the invention or obtained by the above-mentioned process,

b. applying a layer of said powder onto a substrate surface, and

c. heating to a curing temperature T of 75-200 ℃, preferably 80-180 ℃, more preferably 80 ℃ to 160, 150, 140, 130 or even 120 ℃_CuringOptionally and preferably using infrared heating,

d. at T_CuringThe sub-cure is preferably less than 40, 30, 20, 15, 10 or even 5 minutes cure time.

Preferably, in the method at T_CuringThe lower cure is characterized by a cure profile which measures the conversion of the unsaturated bonds C ═ C of component B as a function of time by FTIR, wherein the ratio of the time from 20% to 60% C ═ C conversion to the time to reach 20% conversion is less than 1, preferably less than 0.8, 0.6, 0.4 or 0.3, preferably the time to reach 60% conversion is less than 30, 20, 10 minutes, and at T_CuringThe melt viscosity of the powder coating composition at the curing temperature is preferably less than 60Pa · s, more preferably less than 40, 30, 20, 10 or even 5Pa · s. The melt viscosity should be measured immediately after the start of the reaction or without the catalytic system C2.

In a preferred embodiment of the process, the curing temperature is from 75 to 140 ℃, preferably from 80 to 120 ℃, and the catalyst system C is a latent catalyst system as described above, which allows powder coating of heat-sensitive substrates, preferably MDF, wood, plastics or heat-sensitive metal substrates, such as alloys.

The invention therefore also relates to an article coated with the powder coating composition of the invention, preferably with a heat-sensitive substrate such as MDF, wood, plastic or metal alloy, and wherein the cross-link density XLD of the coating is preferably at least 0.01, preferably at least 0.02, 0.04, 0.07 or even 0.1mmol/cc (determined by DMTA), and preferably below 3, 2, 1.5, 1 or even 0.7 mmol/cc.

The present invention also relates to the use of a catalyst system C as described above for catalyzing a crosslinking reaction in RMA crosslinkable powder coating compositions at a curing temperature below 200 ℃, preferably below 180 ℃, more preferably below 160, 140 or even 120 ℃.

The present invention relates to powder coating compositions suitable for low temperature powder coating cross-linking, having a typical curing temperature of 75-140 ℃ and useful for powder coating heat sensitive substrates such as MDF, wood, plastics or heat sensitive metal alloys. The powder coating composition comprises a crosslinkable component a with at least 2 acidic C-H donor groups in the activated methylene or methine group and a crosslinkable component B with at least 2 activated unsaturated acceptor groups C ═ C, which are reacted with component a by Real Michael Addition under the action of a catalyst system C, which is preferably a latent catalyst system. The invention also relates to a process for making such powder coating compositions, to a process for coating an article using said powder coating composition and to the resulting coated article. The invention also relates to specific polymers for powder coatings, and to the use of specific catalyst systems in such powder coating compositions.