XPS STUDY OF THE INFLUENCE OF A FLOW AID AND OF TWO CROSSLINKING AGENTS IN THE SURFACE COMPOSITION OF POLYESTER BASED COATINGS

摘要

Great differences have been found in the surfaces composition by XPS analysis of a series of model coatings. Crosslinking and flow aid agent have a strong influence in determining the composition of the very first layers of a coating. The analysis of the first set of samples, the one including the flow aid agent into the formulations, showed a lower amount of nitrogen than expected. This is due to the segregation of the flow aid agent which forms a layer of ca. 1nm at the surface. This segregation is not influenced by the crosslinking agent included in the formulation. HMMM and TIC do not influence each other when the flow aid is present, however, when the flow aid agent is excluded from the formulation, the presence of the HMMM is necessary to promote the migration of the TIC to the surface. The TIC does need that another agent migrates to the surface to move into the first layers of a coatings. According to previous work, the coatings cured only with TIC are expected to yield a poorer intercoat adhesion than the coatings cured with HMMM. For this reason, if the intercoat adhesion is one of the most important properties required to the coating, the replacement of the HMMM with the TIC is not suggested. In the same way, the coatings formulated without a flow aid agent are expected to yield a poorer adhesion than the same coatings formulated including the flow aid agent. As it was shown, the exclusion of a flow aid agent from the formulations has negative aspects, so it is convenient to include this agent. A new set of samples, with the same formulations as the samples analysed, but with different flow aid agent concentrations, will be prepared and analysed. This will be done trying to optimize the concentration of flow aid agent to include in a formulation in order to maximize the intercoat adhesion properties of the coatings without decreasing the spreading of the coatings over a metal substrate. Future work will involve the use ToF-SIMS in order to understand in which form the crosslinking agents segregate in the coatings surface.