The photocuring reaction system usually consists of monomers, oligomers and initiators.

1. monomer

Monomer, also called active diluent, has low viscosity. Similar to solvent, it can dilute and dissolve low polymers and photoinitiators, but unlike solvent, its chemical structure contains active functional groups that can undergo photo-curing reaction.

2. Oligomer

Oligomers are photosensitive resins with relatively small molecular weights ranging from hundreds to thousands, which also contain the same active functional groups as monomers, and can participate in the photocuring reaction. Oligomers often have high viscosity because of their certain molecular weight, and the properties of cured materials are usually provided by them. There are two main types of oligomers, namely acrylate resin and epoxy resin.

If there are only monomers and oligomers in the system, it is generally very stable, and it is difficult to carry out photo-curing reaction (except electron beam curing). The photo-curing reaction also needs the initiation of photoinitiator.

3. Photoinitiators

Photoinitiators are light-sensitive chemicals, which can generate active species, such as free radicals or cationic active species, after receiving appropriate light, and trigger the curing of monomers and oligomers. Usually, the liquid photosensitive resin system is very stable in the dark, and it can be stably stored for six months to one year or even longer, but it will undergo a rapid curing reaction once exposed to light. Because the average functionality of the liquid photosensitive resin system is usually greater than 1, a crosslinked polymer network system is formed after curing, and the liquid photosensitive resin becomes a solid crosslinked polymer network.