Basically, epoxy resin systems consist of two components, namely the resin and the curing agent (hardener), that react with each other to form a hard, inert material which is used in several applications to glue, seal, laminate or encapsulate other materials. Uncured resins are viscous solids or liquids which are usually long-chain polymers. These are often the bi-product of the condensation of Epichlorohydrin and Bisphenol-A, a general-purpose resin that demonstrates excellent resistance to alkaline, acid and other solvents.
On the other hand, curing agents (sometimes referred to as hardeners, accelerators, activators, catalysts or setting agents) can be roughly classified into the following groups: amines, mercaptans, sulfones, cycloaliphatics, and polyamides. This plays a major role in determining the properties of the final cured epoxy, including the drying time, pot life, and penetration and wetting ability. These various compounds are chosen according to the type of application, but basically once the curing agent reacts with the resin, it will form a very hard epoxy material.
The most diverse group of curing agents used to catalyze epoxy systems are amines and amine derivatives. These are also the earliest catalysts used with epoxy resins with its performance labeled as “unmatched” – a fully polymerized epoxy resin system exhibits a wide range of mechanical and thermal properties that will fit a variety of applications. Some examples of amine compounds include aliphatic polyamines, polyaminoamides, ketamine, alicyclic diamine, aromatic diamines and several others.
When it comes to automotive, construction and various industrial applications and products, mercaptans are among the curing agents that are more commonly utilized. These have exceptionally rapid cure speed and hardness development properties that are perfect for DIY enthusiasts. Some types of mercaptans may offer cure speed of as fast as a minute to half an hour. These will also bond effectively on metal, concrete, glass, wood and other materials. Mercaptans may also be used to accelerate other catalysts such as amines and polyamides.
This agents are used for high performance applications because these offer outstanding chemical and thermal resistance properties that may reach up to 150 degrees Celsius. These are usually solid at room temperature and will require some increased temperature before application. These are widely used as adhesives and coatings for several applications such as in aerospace works, electronic encapsulation, potting, PCB laminates and more.
These ring structured aliphatics are basically ammonia with a single or more hydrogen atoms replaced by organic groups. These curing agents generally provide better resistance to water and moisture, weatherability and chemical resistance. These are designed for applications that require good electrical insulation performance, high-temperature resistance and UV resistance. Basically, these are commonly used for outdoor solvent-based coatings.
These are basically ammonia with a hydrogen atom replaced by an oxygen or carbon and organic group, which can also be considered as modified polyfunctional aliphatic amines. The reaction of polyamides with epoxy resins are also similar to amines but the ratio of the resin and the curing agent is less critical because polyamides are large polymers. Properties of the end material may either be semi-flexible to hard. These agents cure at room temperature, and may rapidly lose structural strength and insulation value with fluctuations in temperature, thus it is highly advised to be used for applications under 65 degree Celsius.
When using epoxy for certain applications, one must always keep in mind safety and, thus, handle the product with utmost care, especially the curing agents as these may be more irritating and sensitizing than the resin component itself. Most catalysts are active irritant for the eyes, skin and respiratory system. Some agents, such as amines, may even cause severe burns and other skin problems such as dermatitis. Thus, not only should one observe standard care procedures but should also wear necessary and appropriate personal protective equipment when dealing with epoxy resin systems.