Epoxy crystal formation
Under normal temperature conditions, the freezing point/melting point temperature of liquid bisphenol A epoxy resin is 45-50°C, which should be solid, but it is a supercooled liquid, which is not easy to form seeds, so it appears liquid. When the external temperature decreases, the molecular chain activity decreases, which is easy to produce seed crystals, and the epoxy resin slowly completes the phase transition, that is, the transition process from liquid to solid. Generally speaking, it is easier to crystallize in the temperature range of zero to fifteen degrees. After the crystallized resin has good transparency, free-floating crystal grains or crystal clusters will be seen, and those with poor transparency will become turbid like honey.
Cause of crystallization
The epoxy resin itself has high purity, low viscosity, and many impurities; the low temperature of the external environment and alternating cold and heat are prone to crystallization.
Solve the crystallization problem
Since crystallization will cause more trouble, it is necessary to solve the crystallization problem. The following methods are recommended:
1. Control the storage temperature of epoxy resin.
2. The crystallized epoxy resin can be restored by heating and stirring at 50-60°C.
3. Adding bisphenol F epoxy resin will effectively reduce the occurrence of crystallization and will not affect the performance. Moreover, the physical properties of bisphenol F epoxy resin are better than those of bisphenol A epoxy resin. Phenol F type epoxy resin is slightly more expensive, such as NPEF-170.
4. Use low crystalline or non-crystalline bisphenol A epoxy resin, the disadvantage is that the viscosity is slightly higher, such as: NPEL-128R, NPEL-128S.