JURY
News Details
14
2023
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06
Photocuring Technology Series — Photoinitiator 1
A photoinitiator is a class of reactive chemical species that, upon absorbing light energy, generates active radicals or ions capable of initiating the polymerization of corresponding monomers and resins, thereby yielding functional materials. The energy of light varies with wavelength: generally, longer wavelengths correspond to lower energy, while shorter wavelengths correspond to higher energy (Figure 1). The light sources required for photopolymerization typically fall within the ultraviolet and visible regions, with ultraviolet light—ranging from 200 to 400 nm—being predominant.
Figure 1: Distribution of Light at Different Wavelengths
There are many types of photoinitiators, which can be classified in various ways depending on the criteria used, as shown in Figure 2.
Figure 2 Classification of Photoinitiators
Among the many photoinitiators currently available, those with high market maturity and substantial market share are predominantly radical‑type photoinitiators. Based on their mechanisms for generating radicals, they can be further classified into cleavage‑type radical photoinitiators and hydrogen‑abstraction‑type radical photoinitiators. Figure 3 illustrates the radical‑generation processes of these two types of radical photoinitiators.
Figure 3. The process by which a free-radical photoinitiator generates free radicals.
Taking the conventional photoinitiator JRCure 1173 as an example, Figure 4 illustrates the process by which it undergoes photolysis to generate free radicals and initiate the polymerization of monomers/resins. Benzaldehyde and acetone are by‑products and constitute the primary sources of odor observed in 1173 after photocuring.
Figure 4. The cleavage of JRCure 1173 and the initiation of photopolymerization.
As one of the key components in photopolymerization formulations, photoinitiators exert a wide range of influences on the performance of photopolymerized products; Figure 5 lists several common factors.
Figure 5: Effect of Photoinitiators on Photocuring
Different photoinitiators exhibit distinct properties, and in practical applications, relying on a single photoinitiator often fails to achieve the desired performance. Consequently, identifying a photoinitiator formulation that suits a particular system typically requires extensive experimentation and hands-on experience.
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