Novel polyol dispersions with end of usable pot-life indicator

 
Decreasing VOC emissions of coatings has been a progressive effort for scientists active in the coatings industry. At equal solids content, dispersions generally afford a lower viscosity compared to solutions. Therefore, replacing solvent borne systems with waterborne dispersions is an effective strategy to reduce VOC emissions. However, dispersions often contain processing aids such as initiator and surfactants that detract from coating properties. The industry has resorted to innovative approaches to improve the performance of waterborne dispersions and facilitate this replacement without performance penalties. The biggest challenges have been in industrial coatings, which have much higher demands for performance. Performance in industrial coatings is strongly coupled to the presence of a thermoset network formed via a crosslinking mechanism. A common approach is combining a solvent borne polyol with a poly isocyanate to form a thermoset coating after application. Ideally, one wants all the hydroxyl groups to react with isocyanates after application. However, hydroxyl groups start to react with isocyanates in the pot prior to application. This reaction creates higher molecular weight species and results in an increase in solution viscosity. This way a viscosity threshold can be identified after which the paint should not be applied. Polyol dispersions can be combined with poly isocyanates to produce thermoset coatings with superior performance. Although the reaction of isocyanate with hydroxyls does happen in the pot similar to solvent borne systems, there is no clear impact on dispersion viscosity. As the result, it is not possible to identify when application should be stopped (end of usable pot-life) and to avoid applying paint that cannot provide the ultimate performance. In this contribution, we present the recent development of a novel hydroxyl functional aqueous polymer dispersion suitable for 2 pack systems with water. dispersible isocyanates. A unique attribute of this dispersion is that it provides a viscosity end of pot-life indication in the same manner as solvent based systems. Hence, this technology allows formulators to overcome one of the main hurdles in replacing 2 pack solvent borne systems with VOC compliant waterborne dispersions. This dispersion is capable of producing coatings which are suitable for high gloss top coats and direct to metal applications. The dispersion lends itself to formulation of paints with high gloss, good chemical resistance, good corrosion resistance, high hardness, adhesion, and UV durability.