The curing temperatures of various curing agents are different, and the heat resistance of cured products is also very different. In general, a cured product having excellent heat resistance can be obtained using a curing agent having a high curing temperature. For addition polymerization type curing agents, the curing temperature and heat resistance increase in the following order: aliphatic polyamines
The heat resistance of the catalytic polyaddition curing agent is generally at the aromatic polyamine level. The anion polymerization type (tertiary amine and imidazole compound) and cationic polymerization type (BF3 complex) have substantially the same heat resistance. This is mainly because although the initial reaction mechanism is different, the ether bond network is formed in the end. structure.
The reaction is a chemical reaction, which is greatly influenced by the curing temperature. The temperature increases, the reaction speed increases, and the gelation time becomes shorter. The logarithm of the gel time decreases in a straight line with the increase of the curing temperature, but the curing temperature is too high and often causes curing. The performance of the material is degraded, so there is an upper limit of the curing temperature; it is necessary to select a temperature that makes the curing speed and the properties of the cured material a compromise, as an appropriate curing temperature.
The curing agent can be divided into four categories according to the curing temperature: the curing temperature of the low temperature curing agent is lower than room temperature; the curing temperature of the room temperature curing agent is room temperature to 50°C; the curing temperature of the medium temperature agent is 50 to 100°C; and the curing temperature of the high temperature curing agent is 100°C or higher . There are few kinds of curing agents that belong to low-temperature curing type, such as polysterol type and polyisocyanate type; T-31 modified amines and YH-82 modified amines developed and put into operation in China can all be cured below 0°C. There are many types of room-temperature curing type: aliphatic polyamines, alicyclic polyamines, low-molecular polyamides, and modified aromatic amines. There are alicyclic polyamines, tertiary amines, carbazoles, boron trifluoride complexes, and the like which are moderate temperature curing types. Examples of high-temperature curing agents include aromatic polyamines, acid anhydrides, resole resins, amino resins, dicyandiamide, and hydrazide.
For the high-temperature curing system, the curing temperature is generally divided into two stages. The low-temperature curing is performed before the gel. After reaching a gel state or slightly higher than the gel state, the high-temperature heating is used for post-cure. The previous stage cures to pre-cure.
Epoxy resins must react with the curing agent to produce a three-dimensional structure that is of practical value. Therefore, the structure and quality of curing agent will directly affect the application effect of epoxy resin. The research and development of curing agents in foreign countries is far more active than epoxy resins. Compared with epoxy resin varieties, 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 or opening up a new use of epoxy. It can be seen that the development of new curing agents is far more important than the development of new epoxy resins.
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