Application of photoinitiator in UV curing

As the main light absorbing substance, photoinitiator is the key component of photopolymerization system. The more the absorption peaks of photoinitiator overlap with the main emission bands of UV LED light source, the higher the intensity of the effective radiation of photoinitiator.

Photoinitiator is mainly used in UV curing technology in radiation curing industry, which has a great influence on the specific curing rate of UV system and plays an important role in the photocuring system. Photoinitiators can be divided into two categories according to the active intermediates produced after absorbing light energy, among which the free radical photoinitiators are the most widely used. According to the type of absorbed radiation, it can be divided into ultraviolet initiator and visible initiator.

In the whole photopolymerization system, photoinitiator occupies a small proportion, but it is an important component. Its absorption wavelength, molar extinction coefficient and photoreactivity have obvious effects on photoinitiation performance. In addition, photoinitiator has great influence on curing speed, yellowing tendency and cost of the system. After absorbing light energy, photoinitiator molecules generate active species mainly in the excitation triplet state through related chemical reactions, which leads to the polymerization of the system, thus forming a crosslinked network structure.

The more the absorption peak of photoinitiator and the main emission band of light source overlap, the higher the intensity of the effective radiation of photoinitiator, the better the effect of improving the curing rate of ink. UV-LED wave crest is narrow and radiation energy is concentrated in the narrow UV spectrum, so UV-curing can only concentrate in a narrow range of the UV spectrum. At present, the wavelength of UV-LED curing light source mainly includes 365nm, 375nm, 385nm, 395nm and 405nm, and the emission band width of each wavelength light source is about 10nm. However, most photoinitiators on the market have strong absorption in the range of 300-370nm, but poor light absorption performance in the range of more than 370nm, which leads to the problem that the emission spectrum of light source in uV-LED curing system does not match the absorption spectrum of traditional photoinitiators, which will eventually affect the initiation efficiency of photoinitiators.

In addition, due to the low power of UVLED lamps, especially shortwave UV-LED lamps, the intensity of output light and low luminous efficiency reduce the sensitivity of photoinitiator to it and affect the quantum efficiency of photoinitiator luminous chemical reaction.