Solid uretdione groups containing polyurethane powder coatings compositions curable at low temperature

摘要

A polyurethane powder coating composition includes uretdione-containing powder coating hardener(s) based on aliphatic, (cyclo)aliphatic or cycloaliphatic polyisocyanates and hydroxyl-containing compounds, having a m.pt. of 40-130[deg]C, a free cyanate content of less than 5 wt.%, and a uretdione of 6-18 wt.%; hydroxyl-containing polymer(s) having a m.pt. of 40-130[deg]C, and a hydroxyl number of 20-200 mg potassium hydroxide/g; and catalyst(s). A polyurethane powder coating composition comprises: (A) uretdione (UD)-containing powder coating hardener(s) based on aliphatic, (cyclo)aliphatic or cycloaliphatic polyisocyanates and hydroxyl (OH)-containing compounds, having a m.pt. of 40-130[deg]C, a free cyanate (NCO) content of less than 5 wt.%, and a UD of 6-18 wt.%; (B) OH-containing polymer(s) having a m.pt. of 40-130[deg]C, and an OH number of 20-200 mg potassium hydroxide (KOH)/g; and (C) catalyst(s) of formula [R1>R2>R3>R4>]=[R5>]. R->R4>alkyl, aryl, aralkyl, heteroaryl or alkoxyalkyl radicals, each with other radicals R1>-R4>, to form cyclic, bicyclic or tricyclic systems, possible bridging atoms including not only C but also heteroatoms, having 1-18C and each radical R1>-R4> may further contain alcohol(s), amino, ester, keto, thio, urethane, urea or allophanate groups, double bonds, triple bonds or halo; R5>OH or F. (A) and (B) are present in a ratio such that for each OH group of (B) there is 0.3-1 uretdione group of (A), and the fraction of (C) is 0.001-3 wt.%. An independent claim is also included for a process for preparing a polyurethane powder coating composition, by combining the above specified components (A-C) at =130, preferably =120[deg]C.