Epoxy resins are organic polymers containing two or more epoxy groups in their molecules. Except for a few, their relative molecular weight is not high. The molecular structure of epoxy resin is characterized by the active epoxy groups in the molecular chain, which can be located at the end of the chain, in the middle, or a circular structure. Due to the active epoxy groups in the molecular structure, they can cross-link with many kinds of curing agents to form insoluble and insoluble polymers with a three-way network structure.
Properties and properties of epoxy resin
1. Various forms. A variety of resins, curing agents, and modifier systems can be adapted to almost any type of application, ranging from extremely low viscosity to high melting point solids.
2. Easy to cure. With various curing agents, the epoxy resin system can be cured in the temperature range of 0 ~ 180℃.
3. Strong adhesion. The existence of polar hydroxyl and ether bond inherent in the molecular chain of epoxy resin makes it have high adhesion to various substances. Epoxy resins have low shrinkage and low internal stress during curing, which also contributes to higher adhesion strength.
4. Low contractility. The reaction of the epoxy resin with the curing agent is carried out by direct addition reaction or ring-opening polymerization of the epoxy group in the resin molecules without water or other volatile by-products being released. They exhibit very low shrinkage (less than 2%) during curing compared with unsaturated polyester and phenolic resins.
5. Mechanical properties. The cured epoxy resin system has excellent mechanical properties.
6. Electrical properties. The cured epoxy resin system is an excellent insulating material with high dielectric properties, surface leakage resistance, and arc resistance.
7. Chemical stability. Generally, the cured epoxy resin system has excellent resistance to alkali, acid, and solvent. Like other properties of cured epoxy systems, chemical stability depends on the resin and curing agent chosen. Proper selection of epoxy resin and curing agent can make it have special chemical stability.
8. Dimensional stability. The combination of these properties gives the epoxy resin system outstanding dimensional stability and durability.
9. Mold resistance. The cured epoxy system is resistant to most molds and can be used under harsh tropical conditions.
The inherent disadvantages of epoxy resin are its poor impact damage resistance, brittle toughness, and low heat resistance (less than 170℃).