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In the photocuring system, including UV glue, UV paint, UV ink, etc., after receiving or absorbing external energy, it undergoes chemical changes and decomposes into radicals or cations, thereby initiating polymerization.

Materials that generate free radicals by light and further initiate polymerization are collectively referred to as photoinitiators. After some monomers are illuminated, the photons are excited to form an excited state M*:M+hv→M*; the excited active molecules are homogenized to generate free radicals: M*→R·+R′·, and then the single The body is polymerized to form a polymer.

Radiation curing technology is a new energy-saving and environmental protection technology. Ultraviolet (UV) and electron beam (EB), infrared light, visible light, laser, chemical fluorescence and other radiation light curing, fully comply with the "5E" characteristics: Efficient (high efficiency), Enabling (Effective), Economical (Economic), Energy Saving (Energy Saving), and Environmental Friendly (Environmentally Friendly) are therefore known as "green technologies." Photoinitiators are one of the important components of photocurable adhesives, which play a decisive role in the cure rate. After being exposed to ultraviolet light, the photoinitiator absorbs the energy of light and splits into two active radicals, which initiates a chain polymerization of the photosensitive resin and the reactive diluent, and causes the adhesive to crosslink and solidify, which is characterized by rapid, environmentally friendly and energy-saving.

The initiator molecules have a certain light-absorbing ability in the ultraviolet region (250-400 nm) or the visible region (400-800 nm). After directly or indirectly absorbing the light energy, the initiator molecules transition from the ground state to the excited singlet state. Exciting to the triplet state; after the singlet or bimolecular chemistry of the excited singlet or triplet state, active fragments capable of initiating polymerization of the monomers are generated, which may be free radicals, cations, anions, and the like. According to the different initiation mechanism, the photoinitiator can be divided into a radical polymerization photoinitiator and a cationic photoinitiator, wherein a radical polymerization photoinitiator is most widely used.