| abstract |
A polyurethane powder enamel free of volatile cleavage products comprising an adduct of the uretidinedione dimer of isophorone diisocyanate with a diol, wherein the adduct has the formula <IMAGE> +TR <IMAGE> wherein R= <IMAGE> X=NCO or <IMAGE> R''=a divalent aliphatic, cycloaliphatic, aromatic or araliphatic hydrocarbon radical or a diol, n>1, and R'=a monoalcohol radical or primary or secondary monoamine radical with 1-30 C-atoms, wherein the NCO/OH ratio of the dimer to the diol is from 1:0.5 to 1:0.9, the dimer/diol molar ratio is from 2:1 to 6:5, the average molecular weight is between 550 and 4300, and the melting point is >/=70 DEG C. and </=130 DEG C., and wherein the uretidinedione groups present in the adduct are cleavable with heat into >/=98% -NCO groups, and a polyol having an OH functionality >/=3.4 to </=7, an average molecular weight of 2000 to 5000, an OH number between 30 and 100 mg KOH/g, a viscosity of <100,000 mpa.s at 160 DEG C., and a melting point >/=70 DEG C. and </=120 DEG C., and wherein the mole ratio of the adduct to the polyol is chosen so that the ratio of NCO groups in the adduct to OH groups in the polyol is from 0.8:1 to 1.2:1. |