Characteristics and applications of dicyandiamide curing agents
Characteristics of Dicyandiamide Curing Agent
Dicyandiamide curing agents are among the earliest types of heat-cured latent curing agents. They are solid at room temperature and are insoluble in epoxy resins. They are dispersed in epoxy resins in a dust-like form and, upon heating, gradually dissolve and rapidly react to cure when the temperature approaches the melting point.
Dicyandiamide appears as a gray-white crystalline powder with a melting point around 209°C. It is partially soluble in water, alcohol, toluene, and dimethylformamide but insoluble in xylene.
Applications of Dicyandiamide Curing Agent
When dicyandiamide is dispersed as a fine powder into epoxy resins, the storage life can exceed 6 months. It remains stable, does not separate, and does not cure prematurely. The curing reaction temperature typically ranges from 160–180°C, with a curing reaction time of 20–60 minutes. For bisphenol A epoxy resin with a viscosity of 190, the theoretical amount of dicyandiamide curing agent (calculated based on active hydrogen content) is 11.1 parts, but the actual usage is often within the range of 4–10 parts (based on 100 parts by weight of epoxy resin).
Accelerators for Dicyandiamide Curing Agent
A major drawback of dicyandiamide is its high curing temperature. To lower the curing temperature, increase the curing rate, and improve compatibility with epoxy resins, dicyandiamide is generally used in combination with various accelerators. Since the use of accelerators can reduce the pot life and affect the storage stability, it is important to select suitable accelerators based on the processing requirements.
Common accelerators for dicyandiamide are weakly basic organic compounds, including imidazoles, organic ureas, modified acrylic amines, and hydrazines.
Properties of Dicyandiamide Cured Epoxy Resins
Dicyandiamide-cured epoxy resins exhibit excellent bonding properties and high Tg temperatures, and they do not discolor. However, the water resistance of dicyandiamide-cured resins is relatively poor. In practical applications, performance testing and adjustment of dicyandiamide usage may be considered to optimize the resin properties.
Main Uses of Dicyandiamide
Dicyandiamide-cured epoxy resins are used in applications such as electrostatic powder coatings, carbon fiber prepregs, heat-cured printing inks, polyimide films, and single-component adhesives.