Resin adduct, melamine-polyester

The acid-crosslinkable prepolymers are polyester-alkyd, urea-formaldehyde, or melamine-formaldehyde resin adducts combined with a "blocked" acid catalyst that becomes "unblocked" at the dryer temperatures f7, 11, 12). e. g., a melamine-polyester resin adduct with "blocked" -toluenesulphonic acid catalyst (12). These acid-crosslinkable prepolymers are stable on the press distribution system but are converted to tiiree-dimensional polymer networks by heating to 275-325° F. 

Amino Resins. Formaldehyde-modified amino resins (i.e., melamine, benzogua-namine, and urea resins) are the most important resins for the heat curing of hydroxyfunctional polyester resins. These resins are readily available with a low molecular mass (very good polyester compatibility, but less reactive) or in precondensed form (limited compatibility, but very reactive). In order to prevent premature reaction in the wet paint, the amino resins are blocked by etherification with, for example, methanol or butanol. Sulfonic acids (e.g., p-toluenesulfonic acid, dodecyl-benzenesulfonic acid) have proved suitable for accelerating the deblocking of amino resins during heat curing. These acids must also be used in blocked form (ammonium salts, thermolabile adducts). 

---