Curing temperature and heat resistance of curing agent
The curing temperature of various curing agents varies, and the heat resistance of cured products varies greatly. Generally speaking, curing agents with high curing temperature can be used to obtain cured materials with good heat resistance. For addition polymeric curing agents, curing temperature and heat resistance are increased in the following order:
Aliphatic polyamines < alicyclic polyamines < aromatic polyamines < phenolic < anhydride
The heat resistance of catalytic additive curing agent is generally at the level of aromatic polyamines. Anionic polymerization (tertiary amines and imidazolium compounds) and cationic polymerization (BF3 complexes) have basically the same heat resistance, which is mainly due to the formation of ether bonded network structures, although the initial reaction mechanism is different.
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, and the gelation time value generally decreases linearly with the increase of curing temperature. However, the curing temperature is too high, which often leads to the decrease of the curing properties, so there is an upper limit of the curing temperature. It is necessary to choose a suitable curing temperature to compromise the curing speed with the curing properties. According to curing temperature, curing agents can be divided into four categories: low temperature curing agent curing temperature below room temperature; room temperature curing agent curing temperature between room temperature and 50 C; medium temperature curing agent 50-100 C; high temperature curing agent curing temperature above 100 C. There are few kinds of curing agents which belong to low temperature curing type, such as polyisocyanate type and poly-ryl alcohol type. T-31 modified amine and YH-82 modified amine developed and put into production in China can be cured below 0 C. There are many kinds of room temperature curing: aliphatic polyamines, alicyclic polyamines, low molecular weight polyamides and modified aromatic amines. Some alicyclic polyamines, tertiary amines, orbital azoles and boron trifluoride complexes belong to the moderate temperature curing type. Aromatic polyamines, anhydrides, phenolic resins, amino resins, dicyandiamides and hydrazides are high temperature curing agents.
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).