Film formation mechanism of two component waterborne polyurethane coatings

Two component (2K) waterborne polyurethane coatings are a new technology which has been demonstrated in a number of heavy duty applications. They exhibit performance properties equivalent to 2K solvent-borne polyurethanes, with the advantage of reduced volatile organic compounds (VOCs). Although the use of these systems has been demonstrated successfully, the details of their film formation mechanism have not been established. The objective of this work was to propose and confirm the film formation mechanism of these systems. A dynamic series of interrelated events which occur during the process was identified using a number of analytical techniques to study two isocyanate/hydroxyl functional dispersion systems. The mechanism is presented in terms of an ''event timeline'' that chronicles the critical events which occur prior to and after application of the coating. Film property development after application also was evaluated and these results were analyzed in terms of the proposed film formation mechanism.