Investigation of methylolation reaction parameters to reduce free formaldehyde content in methylated melamine formaldehyde resin

In oven cured paint systems, melamine formaldehyde resin is used as the crosslinker of hydroxyl group-containing resins such as acrylic, polyester, alkyd. It is synthesized by modification with alcohols in order to increase the compatibility in organic systems. Methanol modified, methylated, melamine formaldehyde resin was produced in this study. Methylol groups are formed by the addition of formaldehyde to amine groups in melamine molecule. The reaction called methylolation reaction is the first step of production process. Melamine formaldehyde resin is formed by self-condensation reaction between methylol groups which are formed by methylolation. Although self-condensation is desired at a ratio, it is desired to modify some part of methylol groups by alcohol in resin synthesis. The resin is purified to the desired level by removing unreacted raw materials and the byproducts from the product mixture by distillation. The final mixture contains free formaldehyde from both unreacted formaldehyde and formaldehyde released from self-condensation reactions even if some amount of formaldehyde is removed by distillation. The raw material ratios and reaction conditions affect the amount of free formaldehyde during resin production. In the study, the effect of formaldehyde source, method of formalin preparation, formaldehyde/melamine molar ratio, initial formaldehyde concentration, methylolation, reaction pH, temperature and time was investigated on the amount of free formaldehyde. Key Words: melamine, formaldehyde, methanol, methylolation, self condensation