DISTRIBUTION OF MELAMINE IN MELAMINE POLYESTER COATINGS - FT-IR SPECTROSCOPIC STUDIES

Studies of polyester/melamine films using ATR FT-IR spectroscopy indicate that the melamine distribution across the films is uniform unless the hydroxyl content is low and the cure temperatures are relatively high. With polyester resins having an OH number as low as 6, curing at 250-degrees-C with 30 w/w% melamine gives rise to melamine enrichment at the film-air interface. Enrichment is believed to result from melamine self-condensation near the interface. Although the distribution is a complex function and depends upon the amount of acid catalyst, the hydroxyl number of polyester, the film thickness and the reaction rate difference between the film-air and film-substrate interfaces, the primary factor leading to self-condensation is the loss of amine at the sur-face. Apparently, these factors play a key role in melamine self-condensation near the film-air interface and may control such properties as the crosslink density and the modification of properties such as flexibility and stain resistance.