Polyurethane powder coating compositions containing uretdione groups
and curing at low temperatures are provided, along with processes for preparing
such compositions, and their use as powder coatings, wherein the compositions generally
contain: A) a uretdione-containing powder coating hardener derived from aliphatic,
(cyclo)aliphatic, cycloaliphatic or aromatic polyisocyanates and hydroxyl-containing
compounds, and having a melting point from 40 to 130 C., a free NCO content
of less than 5% by weight, and a uretdione content of 6-18% by weight; B) a hydroxyl-containing
polymer having a melting point from 40 to 130 C., and an OH number between
20 and 200 mg KOH/gram, and C) a catalyst of the formula [NR1R2R3R4]+[R5]-;,
in which R1-R4 simultaneously, or independently of one another,
are alkyl, aryl, aralkyl, heteroaryl or alkoxyalkyl radicals, and each R1-R4
is aromatic, linear or branched, unbridged or bridged with other radicals, R1-R4.
