Resin compositions for thermosetting powder coating compositions

A resin composition comprising at least:

• (a) an organophosphorous compound;
• and
• (b) a branched amorphous carboxylic acid functional polyester, said polyester having a Tg of at least 40° C. as measured by Differential Scanning calorimetry at a heating rate of 5° C./min, wherein said polyester comprises polycondensed residues derived from at least the following monomers:
• bi) 8 to 40% mol of 2,2-dimethyl-1,3-propanediol;
• bii) 3 to 21% mol of a C3 to C5 aliphatic diol AD1 not including 2,2-dimethyl-1,3-propanediol, wherein the C3 to C5 aliphatic diol AD1 is a saturated diol having only hydrogen carbon bonds, carbon carbon single bonds and two hydroxyl groups which are each attached to a carbon atom;
• biii) 1 to 10% mol of a C6 to C50 aliphatic or cycloaliphatic diol AD2;
• biv) 0.5 to 10% mol of an at least trifunctional monomer;
• bv) 10 to 55% mol of terephthalic acid;
• wherein
• the % mol is based on the polyester, and wherein
• the molar ratio of AD1 to AD2 (=mol AD1/mol AD2) in the polyester is at least equal or higher to 1 and at most equal to 10, and wherein
• the polyester has:
• an acid value (AV) as measured titrimetrically according to the ISO 2114-2000, between 14 and 120 mg KOH/g polyester, and
• a hydroxyl value (OHV) as measured titrimetrically according to the ISO 4629-1978, less than 13 mg KOH/g polyester, and
• a viscosity measured at 160° C. using as a cone and plate rheometer the Brookfield CAP 2000+, with spindle CAP-S-05 at 21 rpm (shear rate 70 s-1) of at most 150 Pa·s.