For the term epoxy resin curing agent, many people may not be familiar with it. But the processed products are now widely used in our daily life. Its classified products are mainly used in potting of electronic and electrical components, epoxy floor midsole coatings, epoxy mortar, adhesives, etc. Next, Kangyu New Materials will explain some common specifications of curing agents.
Epoxy resin curing agent
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 (tertiary amine and imidazolium antiquities) and cationic polymerized (BF3 complex) is basically the same. This is mainly because although the initial reaction mechanism is different, they eventually form a network of ether bonds. structure.
The curing reaction is a chemical reaction. It 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 increase of the curing temperature. However, if the curing temperature is too high, the performance of the cured product is often reduced, so there is an upper limit for the curing temperature; a temperature that compromises the curing speed and the performance 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 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 in recent years 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.
Structure and characteristics of epoxy resin curing agent
As mentioned above, the curing temperature of the epoxy resin curing agent is strongly related to the heat resistance of the cured product. Similarly, in the same type of curing agent, although they have the same functional group, due to different chemical structures, their properties and cured product characteristics are also different. Therefore, a comprehensive understanding of the properties and characteristics of polyamine curing agents with the same functional group and different chemical structures is very important for the selection of epoxy resin curing agents.
In terms of hue, the alicyclic group is light and basically transparent, while the aliphatic and aromatic groups have a considerable degree of coloration. Viscosity is also very different, alicyclics are only a few Pa·s, while polyamides are very viscous, up to several Pa·s, and aromatic amines are mostly solid. The length of the pot life is exactly the opposite of the curability, the aliphatic reactivity is high, and the alicyclic, amide, and aromatic are sequentially reduced.