Polycarbodiimides as Crosslinkers for Coatings

摘要

Crosslinking is widely practiced in nearly all coatings industries with the main purpose to improve the performance of the coating. These improvements include wear abrasion and chemical resistances and toughnes. The improved performance originates from the formation of a continuous three-dimensional (3D} network, which may be formed by the crosslinker alone, or by reaction of the crosslinker with the bindef'.An important crossIinking system for aqueous resins are the water-dispersible oligomeric polyisocyanates. In general, the use of such polyisocyanate cross-linkers is not based on a reaction with functional groups in the coatings, but they form an interpenetrating polymer network upon reaction with water Their main drawbacks are their sensibility to moisture and limited pot life. Aziridines are another type of crosslinker, but their use is decreasing because of concerns about their toxicity and handling. Polycarbodiimides are less used as crosslinkers in coatings based on aqueous resins, but the situation is changing since there are new types available which are very advantageous: stable water-based polycarbodiimides and the newest developed VOC-free types. They are extremely easy to use and exhibit a much longer useful pot life than isocyanates could achieve.