Manuel Scolari – EUROSYN
Radical photoinitiators are molecules characterized by their ability to absorb energy at a specific wavelength.
Their purpose is to generate free radicals, which initiate the polymerization reaction, leading to the hardening of the formulation. The photoinitiators most commonly used in industry absorb at wavelengths in the ultraviolet spectrum, and those who use these systems often employ specific lamps as an energy source. Depending on their reaction mechanism, photoinitiators are divided into two families: type 1 photoinitiators and type 2 photoinitiators.
The main difference is that type 1 photoinitiators do not require any synergist (co-initiator) compared to type 2 photoinitiators.
Type 1 photoinitiators include α-aminoketones, α-hydroxyketones, and phosphine oxides such as TPO, TPO-L, and BAPO. Type 2 photoinitiators include benzophenone and its derivatives such as MBZ, PBZ, OMBB, and thioxanthones (DETX and ITX), where the most commonly used synergists are amines such as EHA and EDB, which act as hydrogen donors, allowing the formulation to polymerize. In recent years, many of these molecules have been reclassified as more hazardous, not only because of their intrinsic danger, but also because of the by-products they generate.
In Norrish reactions, 100% yield is never achieved, and the main sources of concern are unreacted photoinitiators and by-products of parasitic reactions which, having the ability to migrate, can come into contact with the human body. In recent years, a series of safer products have been developed and designed to reduce the migratory capacity of byproducts, including polymeric benzophenones, such as Jrcure 1515, and polymeric thioxanthones, such as Jrcure 1508 and the polymeric α-aminoketone Jrcure 1521.
Polymeric amines, such as Jrcure A151, and acrylate amines, such as Jrcure P-102, have also been developed.
Migration can be reduced in two ways: the first consists in functionalizing the photoinitiators or the amines, making them reactive towards radicals and becoming part of the polymer network, thus reducing their ability to migrate. Another widely used method consists in increasing the molecular weight by making the photoinitiator or amine a polymer. The volume of these molecules is significantly higher than that of conventional ones, causing the byproducts to remain within the network. Among the most developed products in terms of desired properties are polymeric photoinitiators arranged in linear, grafted, or hyper-branched chains.
Amines and polymeric photoinitiators are ideal for applications where regulations are more stringent, such as food packaging, where exposure limits are measured in ppb (parts per billion).
Being much larger molecules, they have a slightly slower reaction speed than conventional systems but can be modified to work even in low-energy systems, ensuring greater safety and sustainability.
Jiurichem is the trademark of Tianjin JiuRi Chemical Co., Ltd., a Chinese company based in Tianjin, specializing in the production and sale of photoinitiators, resins, monomers, and other materials for photopolymerization and UV curing applications.
Jiurichem products are distributed in Italy by Eurosyn.
