Powder coating composition

An RMA crosslinkable polymer preferably chosen from the group of acrylic, polyester, polyester-amide and polyester-urethane polymers, comprising

• a. One or more components A comprising at least 2 acidic C—H donor groups in activated methylene or methine in a structure Z1(-C(—H)(—R)—)Z2 wherein R is hydrogen, a hydrocarbon, an oligomer or a polymer, and wherein Z1 and Z2 are the same or different electron-withdrawing groups, preferably chosen from keto, ester or cyano or aryl groups, preferably an activated C—H derivative having a structure according to formula 1:
• wherein R is hydrogen or an optionally substituted alkyl or aryl and Y and Y′ are identical or different substituent groups, preferably alkyl, aralkyl or aryl , or alkoxy or wherein in formula 1 the —C(═O)—Y and/or —C(═O)—Y′ is replaced by CN or aryl, no more than one aryl, or wherein Y or Y′ can be NRR′ (R and R′ are H or optionally substituted alkyl)but preferably not both, said component A preferably being a malonate, acetoacetate, malonamide, acetoacetamide or cyanoacetate groups and most preferably malonate providing at least 50, preferably 60, 70 or even 80% of the total of C—H acidic groups in crosslinkable component A, wherein R, Y or Y′ provide connection to the polymer,
• b. Optionally one or more components B comprising at least 2 activated unsaturated RMA acceptor groups preferably acryloyl, methacryloyl, itaconates, maleate or fumarate functional groups forming an AB hybrid polymer, and
• c. Optionally one or more components of catalytic system C,
• wherein the polymer
• h. has a number average molecular weight Mn, as determined with GPC, of at least 450 gr/mole, preferably at least 1000, more preferably at least 1500 and most preferably at least 2000 gr/mole,
• i. has a weight average molecular weight Mw, as determined with GPC, of at most 20000 gr/mole, preferably at most 15000, more preferably at most 10000 and most preferably at most 7500 gr/mole,
• j. preferably has a molecular weight distribution Mw/Mn below 4, more preferably below 3,
• k. has an equivalent weight EQW in C—H of at least 150, 250, 350, 450 or 550 gr/mole and preferably at most 2500, 2000, 1500,1250 or 1000 gr/mole and a number average functionality of reactive groups C—H between 1-25, more preferably 1.5-15 even more preferably 2-15, most preferably 2.5-10 C—H groups per molecule,
• l. preferably has a melt viscosity at a temperature in the range between 100 and 140° C. less than 60 Pas, more preferably less than 40, 30, 20, 10 or even 5 Pas
• m. preferably comprises amide, urea or urethane bonds and/or comprises high Tg monomers, preferably cycloaliphatic or aromatic monomers, in particular polyester monomers chosen from the group of 1,4-dimethylol cyclohexane (CHDM), tricyclodecanedimethanol (TCD diol), isosorbide, penta-spiroglycol or hydrogenated bisphenol A and tetramethyl-cyclobutanediol,
• n. has a Tg above 25° C., preferably above 35° C., more preferably above 40, 50 or even 60° C. as determined by DSC at a heating rate of 10° C./min or is a crystalline polymer with a melting temperature between 40° C. and 150, preferably 130° C., preferably at least 50 or even 70° C. and preferably lower than 150, 130 or even lower than 120° C. (as determined by DSC at a heating rate of 10° C./min).

A polymer comprising a weak base groups C2 and optionally acid groups C3, wherein weak base groups C2 are preferably formed by partially or fully neutralizing acid groups C3 on the polymer, wherein C2 and C3 are preferably carboxylate and carboxylic acid groups, wherein the polymer is preferably chosen from the group of acrylic, polyester, 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. an acid value in non-neutralized form of at least 3, more preferably 5, 7, 10, 15 or even 20 mg KOH/g, and preferably less than 100, 80, 70, 60 mg KOH/g,
• b. a quaternary ammonium or phosphonium cation,
• c. an Mn at least 500, preferably at least 1000 or even 2000, and Mw no more than 20,000, preferably no more than 10,000 or 6000,
• d. in case C—H donor and/or C═C acceptor groups are present;
• a reactive C—H donor or C═C acceptor EQW of at least 150, preferably at least 250, 350 or even 450 g/mol and no more than 2000, preferably no more than 1500, 1200 or 1000 g/mol,
• e. in case no C—H donor and C═C acceptor groups are present an acid value in non-neutralized form of at least 10, more preferably 15, 20 mg KOH/g, and preferably less than 100, 80, 70, 60 mg KOH/g.