Epoxy resins are commonly used as a matrix for materials such as adhesives, coatings and composites, and are widely used in construction, machinery, electrical and electronic, aerospace and other fields. A complete concept of epoxy resin constituents by four aspects of the composition. However, in practice, it is not necessary to have all four aspects of the components, but the resin composition must include the curing agent, which shows the importance of the curing agent.

The reason why epoxy resins are widely used is the result of the versatile co-ordination of these components. Especially the curing agent, once the epoxy resin is determined, the curing agent plays a decisive role in the processability of the epoxy resin composition and the final performance of the cured product.

Classification of epoxy curing agents

1. Classification by acid-base properties

2. Classification by reactivity and chemical structure

3. Classification by curing temperature

4. Classification by different usage

Structure and properties of curing agents

A comprehensive understanding of the properties and characteristics of polyamine curing agents with the same functional group but different chemical structures is very important for the selection of curing agents.

The main characteristics (color, ripeness, duration of use, etc.) also show a certain regularity.

Color: (good) alicyclic->aliphatic->amide->aromatic amine(bad)

Maturity: (low) alicyclic->aliphatic->aromatic->amide(high)

Application period: (Long) Aromatic->Amide->Alicyclic->Aliphatic (Short

Curability: (Fast) Aliphatic->Alicyclic->Amide->Aromatic (Slow)

Irritation: (Strong) Aliphatic->Aromatic->Alicyclic-Amide (Weak)

Gloss: (Excellent) Aromatic->Alicyclic->Polyamide->Aliphatic amide (Poor)

Flexibility: (Soft) Polyamide->Aliphatic->Alicyclic->Aromatic (Rigid)

Adhesion: (Excellent) Polyamide->alicyclic->aliphatic->aromatic (Good)

Acid resistance: (Excellent) Aromatic->Alicyclic->Aliphatic->Polyamide (Inferior)

Water Resistance: (Excellent) Polyamide->Aliphatic Amine->Aliphatic Cyclic Amine->Aromatic Amine (Good)

Development trend of curing agent

Curing agent as a core substance to play the value of epoxy resin, the nature of the cured product depends on the performance of the curing agent, so the road of research on the curing agent has far-reaching significance. From the research of curing agent to date, combined with the current situation at home and abroad, curing agent is currently facing some of the following challenges and changes.

• The development of high activity and excellent heat resistance curing agent. The use of modified polyether amine, aliphatic amine or mixed compound to prepare high activity and heat resistance curing system.
• Due to the traditional epoxy resin in the curing performance is poor, especially low toughness, brittle, greatly affecting its use, so improve the performance of epoxy resin needs to improve the toughness.
• Improve the curing environment, overcome the volatility and toxicity of amine curing agent, and promote the development of room temperature curing agent by modifying amine with physical or chemical method.
• Improve the adaptability and specialty of epoxy resin in special environments, to meet the special environments such as humid, underground low temperature environment or underwater of reservoir dam repair.
• Curing agent and curing technology matching, will be a variety of curing technology (heat curing, microwave curing, light curing) combined with the selection of the appropriate curing agent may be able to get a comprehensive performance of the curing product.
• Heating type latent curing agent has great potential, can continue to study the dicyandiamide and its modified products, organic acid hydrazide, boron - amine complex, imidazole, microcapsules and other latent curing agent.