CROSS-LINKED COATINGS BY CO-REACTION OF ISOCYANATE METHOXYMETHYL MELAMINE SYSTEMS

Two-components methoxymethyl melamine/isocyanate and three-components methoxymethyl melamine/isocyanate/polyol coating systems were studied. Methoxymethyl melamine was shown to react with isocyanate groups thro ugh the carbocation formed by splitting within the methoxymethyl group . In three-components systems, methoxymethyl melamine/polyol and metho xymethyl melamine/isocyanate reactions appear to occur, but not isocya nate/polyol reactions. This was ascribed to the release from the metho xymethyl melamine/polyol reaction of methanol which reacts more rapidl y than the polyol with the isocyanate group. A blocked isocyanate was then used whereby the methoxymethyl melamine reacts at an earlier stag e and urethane formation is delayed. Introducing the blocked isocyanat e, however, required significant increases in cure temperature for the isocyanate/polyol reaction, narrowing the cure temperature window of the system. (C) 1995 John Wiley & Sons, Inc.