| abstract |
The present invention provides a process for the preparation of a carboxyl functional polyuretdione resin for the use in powder coating compositions comprising the steps a) reacting at least one isocyanate (NCO) functional uretdione with at least one alcohol in a ratio of free NCO groups to hydroxyl groups in a range of 0.5 :1 to 0.5 : 3, preferably 0.5 :1 to 0.5 : 2, and, b) reacting the resulted hydroxyl functional polyuretdione with di-and/or polyfunctional acid(s) and/or their anhydride(s), wherein the resulted carboxyl functional polyuretdione resin having a carboxyl value in the range of 20 to 300 mg KOH/g, particularly 50 to 250 mg KOH/g, the carboxyl value defined according to DIN EN ISO 2114. The process according to the invention provides a carboxyl functional polyuretdione resin for the use in powder coating compositions, particularly for the use as hardener (crosslinker, curing agent) providing a higher crosslinking densitiy and provide desired technological properties, in particular, thin films and high flexibility in combination with an excellent weather resistance of the coating layers. |