The entire curing process of unsaturated polyester resin includes three stages:
Gel-from viscous resin to loss of fluidity to produce semi-solid and elastic gel;
Qualitative-from gel to having a certain hardness and fixed shape, the cured product can be removed from the mold without deformation;
Maturation-It has stable chemical and physical properties and achieves 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 is short. Generally, it can be completed within a few hours from gel to setting. In addition, when the unsaturated polyester is cured, no extra small molecules escape from the system, and the structure is relatively compact. Therefore, the unsaturated polyester resin has the best room temperature contact molding process performance compared with other thermosetting resins.