Photoinitiator acrylated epoxy systems

Even more important to the formulation is a photoinitiator for the UV curables or an accelerator for the EB curables. These do not necessarily have to be a separate ingredient, but they may be a molecular modification of a resin or monomer ingredient. A typical photoinitiator for a UV curable acrylic system is based on an aromatic keto compound, and for an epoxy system it is based on a diazonium or a sulfonium compound. 

Epoxy acrylates are also commonly used as oligomers in radiation-curing coatings and adhesives. However, their name often leads to confusion. In most cases, these epoxy acrylates have no free epoxy groups left but react through their unsaturation. These resins are formulated with photoinitiators to cure via uv or electron beam (EB) radiation. The reaction mechanism is generally initiated by free radicals or by cations in a cationic photoinitiated system. The uv/EB cured epoxy formulations are discussed in Chap. 14. 

Photopolymer systems are photocurable resins incorporating reactive liquid monomers, photoinitiators, chemical modihers and hhers. Typically stereolithography utilizes UV radiation, so UV-curable systems are used. Free-radical-photopolymerizable acrylate systems were originally used however, newer cationic epoxy-resin and vinyl ether systems (based on iodinium- or sulfonium-salt cationic initiators) are now being utilized. 

A number of antioxidants were examined for solubility in the monomer, effect upon the photoinitiator, UV stability, effect upon physical properties of the cured coating and their effectiveness as stabilizers. The addition of hydrogen donors, HD-2 or HD-3, or a hindered amine light stabilizer, HALS-1, improves the stability of a cured epoxy acrylate system with a minimal change in the physical properties of the resin. DSC and oxygen absorption measurements show that the secondary hindered amine, HALS-1, imparts the best stability to the resin. 

In 1987, UVEXS [145] claimed simultaneous cationic and free radical polymerization of a mixture of a cycloaliphatic epoxy resin, a hydroxy functional polyether terminated polysiloxane, an acrylate functional resin, a triarylsulfonium salt, and a free radical photoinitiator. A simultaneously cured cationically and free radically polymerized system consisting of an epoxy resin, a methacrylate monomer, an onium salt, a carbonyl type free radical photoinitiator, and tetrahydrofurfuryl alcohol accelerator was patented by Cook Paint and Varnish [146] in 1987. 

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