For poly additive linking of epoxide resins the hardeners used generally have hydrogen atoms bonded to nitrogen. This prerequisite is satisfied by both poly amines and poly amides. The use of amines is particularly recommended for ambient curing. These result in coatings with outstanding hardness and high chemical resistance. The most frequently used are aliphatic and triamines with primary amino groups leading to dense cross linking.
Stoichiometric addition is normally required although hardener excess of up to 15% usually allows higher reaction rates to be achieved. In order to limit the volatility of the aliphatic amines in particular, they are frequently used as adducts obtained from reactions of epoxide resin with excess poly amine.
Any residual sensitivity to moisture or unpleasant odour can be avoided by the use of hardeners obtained by adduct formation of poly amines with polycarboxylic acids. Such poly amide resins ( more precisely polyamidoamines ) impart epoxide resins with good flexibility. The curing reactions, however, proceed more slowly than with poly amines; adherence to stoichiometric mixtures is not quite so important.
Poly amide curing systems are less prone to the effect of moisture during processing than products cured with amines. In special cases there are even formulations based on poly amides in which film formation takes place unaffected by the presence of water.