A viscous and flowable unsaturated polyester resin that undergoes free radical copolymerization in the presence of initiator adhesive. The process of generating a stable body structure is called the curing of unsaturated polyester.
The reaction mechanism is basically the same as that of the aforementioned free radical copolymerization reaction, which occurs in the free radical copolymerization reaction between linear polyester resin molecules and crosslinking agent molecules. The copolymerization between polyester macromolecules with multiple double bonds (i.e. having multiple functional groups) and the double bonds of crosslinking agent styrene will ultimately result in the formation of a bulky structure.
Stages of solidification
The entire curing process of unsaturated polyester resin includes three stages:
Gel - elastic gel from viscous flow resin to semi solid panel glue without flow;
The cured material can be removed from the mold without deformation; Stereotyping - from gel to a certain hardness and fixed shape.
Achieve a high degree of curing for panel adhesive. Maturation - possessing stable chemical and physical properties.
It can be divided into three stages, the curing process of all active linear oligomers. However, due to different reaction mechanisms and conditions, the characteristics exhibited by the three stages are also different. The curing of unsaturated polyester resin is free radical copolymerization of panel glue, so it has the nature of chain reaction, which means that in the three stages, the time interval is relatively short. Generally, gel can be completed within a few hours after setting. In addition, when the unsaturated polyester is cured, there is no excess small molecules escaping from the system, and the structure is relatively tight. Therefore, compared with other thermosetting resins, the unsaturated polyester resin has the best process performance of panel glue contact molding at room temperature.
Initiator
Generally, it is an organic peroxide compound. The characteristics of various organic peroxide compounds are the same as initiators used for curing unsaturated polyester resins and free radical polymerization. It is usually expressed by the content of reactive oxygen species, critical temperature, and half-life of the laminated adhesive.
Active oxygen content
The content of reactive oxygen species is an indicator of the purity of organic peroxides. In fact, the content of reactive oxygen species is also known as the effective oxygen content. For authentic peroxides. Due to the instability of organic peroxides in the storage of laminated boards, they are usually mixed with inert diluents such as dibutyl phthalate to facilitate storage and transportation.
critical temperature
This can be reflected in the exothermic effect of solidification. The critical temperature is a process indicator applied during the curing of unsaturated polyester resin. The minimum temperature required for the thermal decomposition of peroxides to form free radicals is called the critical temperature. Splicing glue usually triggers a reaction above the critical temperature.