Adhesion properties of phosphate- and siloxane-containing polyurethane dispersions to steel: An analysis of the metal-coating interface
Polyurethane dispersions containing phosphate and siloxane groups in the main chain were investigated as possible self-assembling metal coatings. Improved adhesion of the polymer to the metal was observed because of the formation of an insoluble metal phosphate layer at the metal-coating interface. The neutralizing amine of the dispersions affected the formation of this metal phosphate, and the metal phosphate formation was dependent on the curing temperature and boiling point of the amine used for neutralization. A crosscut comparative study of adhesion proved that the phosphate-containing coatings had better adhesion because of the formation of ionic bonds at the metal-coating interface. A solid-state adhesion prediction method based on thermodynamic considerations was used. The results of the solid-state adhesion method correlated well with that obtained from the crosscut adhesion test method. © 2003 Wiley Periodicals, Inc.