This refers to a process of initiating polymerisation with electromagnetic radiation in the ultraviolet range. It is used to harden plastics such as adhesives and paint finishes. Known as “photoinitiation,” the electromagnetic radiation excites a radical starter, so that it dissociates and creates a free radical.
This free radical attacks an unsaturated compound, the monomer, thus creating another radical which, in turn, can attack another monomer. Depending on which substituents are on the carbon atoms, a three-dimensional network can form, causing the paint or plastic to harden. The ultraviolet radiation can be emitted from a variety of different sources. UV lamps are frequently used for this purpose. Special plasmas emit UV radiation with higher intensity, which hardens the paint more quickly. This can be used to expedite painting processes and accelerate production. If a UV lamp is replaced with plasma, the previously used UV paint can still be used, since both UV sources cause hardening using the same mechanism.