An important development in the urethane coating area is the use of polyisocyanates, in combination with hydroxylated acrylic resins, to provide room‐temperature‐curing coatings. These new formulations, according to Klein and Elms [Journal of Paint Technology, 43, November (1971) p. 68], demonstrate lightfastness, good outdoor durability and solvent resistance when the acrylic resin is coreacted with an aliphatic polyisocyanate. The acrylic resins are copolymers which contain either the hydroxypropyl or hydroxybutyl ester of acrylic or methacrylic acid as one component. Hydroxypropyl acrylate acetoacetate extends the potlife of this two‐component coating. The authors describe work in which glass transition temperature is used as a means for selecting the correct hydroxylated acrylic resins for use in the system. If the glass transition temperature is between 22 and 54°C, a flexible coating with good impact resistance results, but the system requires baking. At a glass transition temperature of 54° and a hydroxyl value of 26, a composition results which dries rapidly at ambient temperatures and which provides good hardness and mar resistance. The coreactant in this instance is an aliphatic diisocyanate composition based on hexamethylene diisocyanate.
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