The performance properties that can ultimately be obtained from an epoxy resin system depend primarily on the nature of the curing agent. For many applications where epoxy systems are expected to cure at normal ambient temperature, amine-based curatives are primarily used. Primary and secondary aliphatic, aromatic and cycloaliphatic polyamines, and their derivatives, will react with and cure epoxy resins. Amine-cured epoxy systems are used for general industrial and some architectural (indoor) applications as well as floor coatings and monolithic floor toppings. Each type of polyamine lends different performance properties, assuming the same epoxy resin is used. For the purpose of this article we will focus on the common cycloaliphatic diamines used for ambient curing, two-component epoxy coatings.
Epoxy curing agents based on cycloaliphatic diamines are typically used for coating applications that require low color, good color stability, long open time and good resistance to amine blush (or carbamation). Other desirable properties include high hardness values, good mechanical properties and resistance to chemicals such as alkalis and dilute acid solutions. An undesirable phenomenon that can occur with an epoxy coating cured using a cycloaliphatic diamine-based curing agent is amine blush. Amine blush can occur under a variety of cure conditions, but becomes more likely as the ambient temperature decreases and/or as the relative humidity increases. It should be noted that aliphatic diamines tend to have a higher blushing tendency than cycloaliphatics. Aromatic diamines have the least tendency toward blushing, however they are usually dark in color and many are toxic.