The entire curing process of unsaturated polyester resin includes three stages:
Gel-from viscous fluid resin to loss of fluidity to produce semi-solid elastic gel;
Qualitative-from the gel to a certain hardness and fixed shape, the cured product can be removed from the mold without deformation;
Maturation-with stable chemical and physical properties to achieve a high degree of curing.
The curing process of all active linear oligomers can be divided into three stages, but due to the different reaction mechanisms and conditions, the characteristics of the three stages are also different. The curing of unsaturated polyester resin is a free radical copolymerization reaction, so it has the nature of chain reaction, which is manifested in three stages, and its time interval has a short characteristic. Generally, it can be completed in a few hours from gel to setting. In addition, the unsaturated polyester has no excess small molecules in the system during curing, and the structure is relatively compact. Therefore, the unsaturated polyester resin has the best process performance of room temperature contact molding compared with other thermosetting resins.