1997 Volume 83 Issue 11 Pages 725-730
Surface structure of polyester film cured by melamine-formaldehyde resin (MF) was investigated by X-ray photoelectron spectroscopy. We found that paints containing polyester resin having low hydroxyl values, highly methylated MF and strong acid catalyst neutralized by volatile amines gave film surface having higher nitrogen concentration, which meant higher MF concentration. A mechanism for MF enrichment in the surface was proposed as the following. In the paints containing volatile amines, as amines vaporized easily near the surface in the curing period, acidity near the surface increased with decreasing amine concentration. High acidity near the surface accelerated self-condensation reaction of highly methylated MF having high reaction rate under existence of strong acid catalyst. MF diffused from the bulk of the film to the surface because MF concentration near the surface decreased, and then MF condensates are concentrated in the surface.
