The curing temperature of various curing agents including epoxy curing agent is different, and the heat resistance of curing products is also very different. Generally speaking, the curing agent with high curing temperature can be used to obtain the cured product with excellent heat resistance. For addition polymerized curing agents, the curing temperature and heat resistance are increased in the following order: aliphatic polyamines & lt; alicyclic polyamines & lt; aromatic polyamines ≈ phenolic & lt; anhydrides.
The heat resistance of the curing agent is at the level of aromatic polyamine. The heat resistance of anionic polymerization type (tertiary amine and imidazole compounds) and cationic polymerization type (BF3 complex) are basically the same, which is mainly due to the different initial reaction mechanism, but eventually form the ether bond network structure.
The curing reaction belongs to the chemical reaction, which is greatly influenced by the curing temperature, the temperature is increased, the reaction speed is accelerated, the gel time is shorter, the gelation time decreases linearly with the increase of curing temperature, but the curing temperature is too high, which often degrades the curing property, so there is the upper limit of curing temperature. As a suitable curing temperature.
According to the curing temperature, the curing agents can be divided into four categories: the curing temperature of low temperature curing agent is below room temperature; the curing temperature of room temperature curing agent is between room temperature and 50 ℃; the curing temperature of medium temperature curing agent is between 50 ℃ and 100 ℃; the curing temperature of high temperature curing agent is above 100 ℃. There are few kinds of curing agents belonging to low-temperature curing type, such as polyisocyanate type and polyrylcohol type. T-31 modified amines and yh-82 modified amines developed and put into production in China can be cured below 0 ℃. There are many kinds of room temperature curing: aliphatic polyamines, alicyclic polyamines, low molecular polyamides and modified aromatic amines. Some aliphatic polyamines, tertiary amines, mimidazoles and boron trifluoride complexes belong to the medium temperature curing type. The high temperature curing agents include aromatic polyamines, anhydrides, phenolic resins, amino resins, dicyandiamide and hydrazide.
For high temperature curing system, the curing temperature is generally divided into two stages. The gel is solidified at low temperature before reaching the gel state or slightly higher than the gel state. Then the post-cure is solidified at high temperature and solidified as pre curing (pre-cure).
The curing agent of epoxy resin must react with curing agent to form three-dimensional structure. Therefore, the structure and quality of curing agent will directly affect the application effect of epoxy resin. In foreign countries, the research and development of curing agent is far more active than that of epoxy resin. Compared with the variety of epoxy resin, the curing agent has more varieties and strong confidentiality. Every time a new curing agent is developed, one aspect of the problem can be solved, which is equivalent to developing a new epoxy resin or opening up a new application of epoxy resin. It can be seen that the development of new curing agent is far more important than the development of new epoxy resin.
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