One component heat-curable powder coating composition

A one component heat curable powder coating composition comprising:

• (i) a polyester resin containing reactive unsaturations, the polyester resin having a weight per the reactive unsaturations (WPU) as determined using 1H-NMR which is higher than 250 and lower than 1500 g/mole,
• (ii) a thermal initiation system comprising (a) a transition metal catalyst and (b) a peroxide, wherein
• (a) the transition metal catalyst is selected from the group consisting of transition metal salts, transition metal complexes and mixtures thereof, wherein the transition metal is Mn, Fe, Co or Cu, and wherein
• (b) the peroxide is selected from the group consisting of peroxyesters, monoperoxycarbonates and mixtures thereof, and wherein the peroxide is represented by formula (1):
• wherein
• R1, R2 and R3 each independently stand for an alkyl, and wherein X stands for R4 or for OR4, wherein R4 stands for an alkyl, an aryl or for an oligomer or polymer, and wherein
• the amount of peroxide is at least 10 mmol peroxide/Kg resin containing reactive unsaturations and co-crosslinker, and
• (iii) a co-crosslinker having a weight per unsaturation (WPU) as determined using 1H-NMR higher than 150 and lower than 870 g/mole, said crosslinker being chosen from the group consisting of vinylethers, vinyletherurethanes, vinylesters, vinylamides, itaconates, enamines and mixtures thereof, wherein
• all of the reactive unsaturations of the polyester resin are carbon-carbon double bonds connected directly to an electron withdrawing group and are reactive towards radicals generated by the peroxide, and wherein
• the thermal initiation system is present in an amount such that when the powder coating composition is applied to a substrate and cured at a temperature of 130° C. for 20 minutes, the resulting coating resists at least 70 acetone double rubs (ADR), wherein each ADR is a back and forward movement over a surface of the coating having a thickness of approximately 60 μm using a cotton cloth drenched in acetone covering a hammer head having a weight of 980 grams and a contact surface area with the coating of 2 cm2.