LOW-TEMPERATURE CURING HIGHER-SOLIDS POLYESTER COATINGS WITH MELAMINE-FORMALDEHYDE RESIN CROSS-LINKERS

Polyester (PE)/melamine-formaldehyde (MF) coatings that cure rapidly a t low bakes (<80-degrees-C) and appreciably at ambient temperature are described. They are formulated from enhanced-reactivity MF resins hav ing very low levels of >NH and >CH2OH functional groups and from conve ntional higher-solids PE resins. Of the PE resins studied, those made from 1,4-cyclohexanedimethanol are the fastest curing. Coatings with 0 .5 parts per hundred (phr) of para-toluene sulfonic acid (p-TSA) catal yst develop hardness, solvent resistance, and impact resistance that w ould be acceptable tor many commercial applications at bakes of 60-70- degrees-C for 30 min. With 1.5 to 2 phr of catalyst, ambient temperatu re curing PE/MF coatings for certain applications appear feasible. The rate of apparent cure was correlated with the rate of disappearance o f -OCH3 groups observed by FTIR.