Лако-красочные материалы — производство

Stoichiometric ratios can be calculated similarly for hardeners. In principle, each active hydrogen will react with one epoxy group. Thus a low-molecular-weight aliphatic poly­amine such as diethylene triamine (DETA) has a molecular weight of 103 and five active hydrogens. The hydrogen equivalent is thus 20.6. The stoichiometrically correct ratio with an epoxy resin of EEW 200 would thus be 100 parts resin to 10.3 parts of DETA. In practice there is always a percentage of homopolymerization, especially at the temperature of reaction, and smaller amounts of DETA will still cause a complete cure, at the expense of increasing brittleness.

In general, suppliers of proprietary hardeners do not furnish detailed chemical descriptions. Instead, they supply data on recommended mix ratios, and from this the formulator can calculate the correct quantities. With catalysts, stoichiometry is not criti­cal, in theory. In practice, however, the quantity used will affect both the rate of cure and the cured properties. Thus with catalysts, in practice, the mix ratio is sometimes more critical than is the case with hardeners.