What criteria should be considered when selecting an amine or polyamide hardener ?
For polyadditive linkingof epoxide resins the hardenersused generally have hydrogen atoms bonded to notrogen. This prerequisite is satisfied by both polyamines and polyamides. The use of amines is particularly recommended for ambient curing. These result in coatings with outstanding hardness and hig chemical resistance. The most frequently used are aliphatic di- and triamines with primary amino groups leading to dense crosslinking.
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 polyamine.
Any reidual sensitivity to moisture or unpleasant odour can be avoided by the use of harderners obtained by adduct formation of polyamines with polycarboxylic acids. Such polyamide resins ( more precisely polyamidoamines ) impart epoxide resins with good flexibility. The curing reactions, however, proceed more slowly than with polyamines; adherence to stoichiomwtric mixtures is not quite so important.
Polyamide 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 polyamides in which film formation takes place unaffected by the presence of water.