A photopolymer is a polymer which is cured by exposure to light, often in the ultraviolet spectrum. These polymers are useful in dentistry for fillings and in rapid prototyping in the stereolithography and 3D printing processes. Its also used as a relief plate for flexographic printing, mainly used in flexible packaging, plastics, paper, labels and corrugated boxes. Some commercial brands worldwide include DuPont Cyrel, BASF Nyloflex, Elaslon and McDermid. Basic material is soft and light sensitive, then is applied a selective exposure to UV lamps, then it is developed and then cured. Process: (1) exposing imagewise a photopolymerizable element to actinic radiation emitting a wavelength in the range of 365 nm, (2) removing the unexposed or unpolymerized areas of the plate with solvent and (3) drying the resulting plate. The photopolymerized element can then be detackified by exposing the element to U.V. radiation emitting a wavelength in the range of 254 nm. To ensure final plate hardening and photopolymerization, the printing element can be further post-exposed to radiation emitting at wavelengths in the range of 365 nm. Current platemaking processes utilize various sources of radiation for developing relief images and maximizing plate hardening. For example, actinic radiation from a variety of sources can be used, including commercial ultraviolet fluorescent tubes, medium, high, and low pressure mercury vapor lamps, argon glow lamps, photographic flood lamps, pulsed xenon lamps, carbon arc lamps, etc. Called photopolymeric flexographic relief printing plates in the flexographic printing plate industry because maximum consistent print quality will be obtained using plates with reduced shrinkage.
