The curing temperature of each curing agent is different, and the heat resistance of the cured product is also very different. Generally speaking, using a curing agent with a high curing temperature can obtain a cured product excellent in heat resistance. For the addition polymerization type curing agent, the curing temperature and heat resistance increase in the following order: aliphatic polyamine<alicyclic polyamine<aromatic polyamine≈phenolic formaldehyde<anhydride.
The heat resistance of the catalytic addition polymerization type curing agent is generally at the level of aromatic polyamines. The heat resistance of anionic polymerized type (tertiary amine and imidazole compound) and cationic polymerized type (BF3 complex) is basically the same. This is mainly because although the initial reaction mechanism is different, they eventually form a network structure of ether bond. .
The reaction is a chemical reaction, which is greatly affected by the curing temperature. The temperature increases, the reaction speed is accelerated, and the gel time becomes shorter; the logarithm of the gel time generally decreases linearly with the curing temperature, but the curing temperature is too high, which often causes curing The physical properties are reduced, so there is an upper limit of the curing temperature; a temperature that compromises the curing speed and the properties of the cured product must be selected as the appropriate curing temperature.
According to the curing temperature, the curing agent can be divided into four categories: the curing temperature of the low-temperature curing agent is below room temperature; the curing temperature of the room temperature curing agent is room temperature ~ 50 ℃; the curing temperature of the intermediate temperature curing agent is 50 ~ 100 ℃; the curing temperature of the high temperature curing agent is above 100 ℃ . There are very few types of curing agents that belong to low-temperature curing types, such as poly-alcohol type and polyisocyanate type. T-31 modified amine and YH-82 modified amine developed and put into production in China can be cured below 0℃. There are many types of room temperature curing types: aliphatic polyamines, alicyclic polyamines; low molecular polyamides and modified aromatic amines. Some of the middle-temperature curing types include cycloaliphatic polyamines, tertiary amines, azoles, and boron trifluoride complexes. High-temperature curing agents include aromatic polyamines, acid anhydrides, resol resins, amino resins, dicyandiamide, and hydrazides.
For high-temperature curing systems, the curing temperature is generally divided into two stages. Low-temperature curing is used before gelation. After reaching a gel state or a state slightly higher than the gel state, post-cure is performed by heating at high temperature. The previous stage curing is pre-cure.
Epoxy resin must react with curing agent to produce three-dimensional three-dimensional structure to have practical value. Therefore, the structure and quality of the curing agent will directly affect the application effect of epoxy resin. The research and development of curing agents abroad are far more active than epoxy resins. Compared with the varieties of epoxy resins, there are more varieties of curing agents, and the confidentiality is very strong. Each development of a new curing agent can solve one problem, which is equivalent to developing a new epoxy resin or opening up a new use of epoxy resin. It can be seen that the development of new curing agents is far more important than the development of new epoxy resins.