Low temperature heat-curable powder coating composition comprising a crystalline polyester resin, an amorphous resin and a peroxide

The invention relates to heat-curable powder coating composition comprising: i) at least one crystalline polyester resin present in an amount of at least 7.5 wt%; and ii) at least one amorphous polyester resin present in an amount of at most 92.5 wt%; and iii) at least one peroxide present in an amount of at least 0.65 parts of peroxide in hundred parts of i)+ ii) (pph), wherein the at least one crystalline polyester resin has 2-butenedioic acid ethylenic unsaturations and/or the at least one amorphous polyester resin has 2-butenedioic acid ethylenic unsaturations; wherein if the at least one amorphous polyester resin has 2-butenedioic acid ethylenic unsaturations, then the theoretical weight per ethylenic unsaturation (WPU) of the at least one amorphous polyester resin is at most 850 g/mol; wherein the wt% is based on the total amount of i)+ ii); wherein the peroxide is chosen from the group of peresters and monopercarbonates according to formula RC(=O)OOR (I) and peranhydrides of formula RC(=O)OOC(=O)R (II) and any combination of peroxides according to formula (I) and formula (II) thereof. The compositions of the invention may be cured to an acceptable degree at low temperature of for example at most 130°C for at most 20 minutes, said compositions may be ground, sieved and extrudable and said compositions can upon heat cure form powder coatings that may also exhibit enhanced flexibility. The compositions of the invention upon heat curing may also provide powder coatings that exhibit good adhesion. In addition, the compositions of the invention can suitably be used on heat- and/or non heat-sensitive, even if the composition is highly pigmented.