Abstract

Room temperature cure, rapid setting epoxy primer have long been aspired in automotive re-finish sector. The
cure process is generally slower, relative to that of the room temperature curing polyurethane system. To
overcome the problem of long drying/sanding time, Epoxy based systems are blended with Polyacrylate
functional resins, which react based on the Aza-Michael addition mechanism. However, these system shows,
very short potlife cause of rapid reactivity of the Amino hydrogen with Acrylates in presence of strong base
catalyst, which is needed to complete the cure. Carboxylic acid blockers are popularly used with tertiary amines
that control the in-can reactivity imparting longer potlife. However, the deblocking is not efficient at room
temperature. Use of Carbonic acid as blocker, by the way of using Ammonium Bi-carbonate (ABC) as source
for the same is being claimed in literature2. Tetrabutyl Ammonium Hydroxide (TBAH) and Di-aza-Bicylco
Undec-1-ene (DBU) are good catalysts and blocking the catalysts with Di-methyl Carbonate (DMC), and
subsequently with ABC, would result in temporary blockage of catalyst activity, thereby allowing potlife.
However, the carbonic acid/Carbonates degrade into the atmosphere on exposure to air as the content are
applied, it thereby, releases the catalyst which cures the Epoxy-Amine-Acrylate system. By varying dosage of
catalyst and tertiary amine and by use of high molecular weight (HMW) epoxies with low reactive
polyamidoamines and Polyacrylates the above catalyst system results in good application properties yet with
acceptable coating performance durability.