SURFACE ENRICHMENT BEHAVIOR OF HIGHLY MET HYLATED MELAMINE-FORMALDEHYDE RESIN IN POLYESTER FILMS CURED BY MELAMINE-FORMALDEHYDE RESIN

Surface structure of polyester film cured by melamine-formaldehyde res in (MF) was investigated by X-ray photoelectron spectroscopy. We found that paints containing polyester resin having low hydroxyl values, hi ghly methylated MF and strong acid catalyst neutralized by volatile am ines gave film surface having higher nitrogen concentration, which mea nt higher MF concentration. A mechanism for MF enrichment in the surfa ce was proposed as the following. In the paints containing volatile am ines, as amines vaporized easily near the surface in the curing period , acidity near the surface increased with decreasing amine concentrati on. High acidity near the surface accelerated self-condensation reacti on of highly methylated MF having high reaction rate under existence o f strong acid catalyst. MF diffused from the bulk of the film to the s urface because MF concentration near the surface decreased, and then M F condensates are concentrated in the surface.