In the photocurable system, including UV glue, UV coating, UV ink, etc., chemical changes occur after receiving or absorbing external energy, and decompose into free radicals or cations, thus triggering the polymerization reaction.
Photoinitiators are substances that can produce free radicals and further initiate polymerization by illumination.After some monomers are illuminated, they absorb photons and form an excited state M* : M+ HV →M*;
After homolysis of the activated molecule, the free radical M*→R·+R ‘· is generated, and then the monomer polymerization is initiated to form the polymer.
Radiation curing technology is a new Energy Saving and Environmental protection technology, which is irradiated by ultraviolet light (UV), electron beam (EB), infrared light, visible light, laser, chemical fluorescence, etc., and fully meets the “5E” characteristics: Efficient, Enabling, Economical, Energy Saving, and Environmental Friendly. Therefore, it is known as “Green Technology”.
Photoinitiator is one of the important components of photocurable adhesives, which plays a decisive role in curing rate.
When the photoinitiator is irradiated by ultraviolet light, it absorbs the energy of the light and splits into two active free radicals, which initiates the chain polymerization of the photosensitive resin and the active diluent, making the adhesive cross-linked and solidified. The photoinitiator has the characteristics of fast, environmental protection and energy saving.
The initiator molecules can absorb light in the ultraviolet region (250~400 nm) or visible region (400~800 nm). After absorbing light energy directly or indirectly, the initiator molecules transition from the ground state to the excited singlet state, and then to the excited triplet state through intersystem transition.
After the singlet or triplet state is excited through monomolecular or bimolecular chemical reaction, the active fragments that can initiate monomer polymerization can be free radicals, cations, anions, etc.
According to different initiation mechanism, photoinitiators can be divided into free radical polymerization photoinitiator and cationic photoinitiator, among which the free radical polymerization photoinitiator is the most widely used.
Post time: Apr-08-2021