(Quoted from UV+EB Technology. Full article here.)
"...Polymerization is a process in which small molecules are reacted chemically to form very large molecules and molecular networks called polymers. In the coatings, ink and adhesives industries, this process also is known as curing, drying or hardening and converts liquid formulations into a hard solid film or elastomeric solid with properties designed for the application. Photopolymerization utilizes the photons (UV or visible wavelengths) emitted by a lamp source to initiate the chemical reactions by excitation of special additives called photoinitiators. Upon absorption of the UV energy..."