Technology Description

UV-curable coatings are volatile organic compound (VOC)-, hazardous air pollutant (HAP)-, and isocyanate-free, single-component high-solid (nearly 100%) cross-linked coatings cured by brief exposure to intense UV light. The chemical reaction, or polymerization, that occurs involves two major constituents, oligomers and monomers, and is set in motion by the photoinitiators blended into the coating. Oligomers are polymers that define the coating's physical properties, with examples being urethanes, epoxies, polyester epoxies and acrylates, and polyesters. In UV-curable coating formulation, the oligomers form the backbone of the structure and the monomers "link" to the oligomers to form a network during exposure to UV light. Increasing the number of reactive groups, called multifunctional monomers, will increase the cross-linked density of the coating. In addition, these monomers are generally low viscosity and can serve as a diluent to decrease coating viscosity for application purposes, reducing or eliminating the need for reactive solvents. In the presence of UV light (and dependent on the intensity of the light), these constituents are capable of reacting at very high rates (seconds). UV-curable coatings can be applied through traditional coating techniques (brush, roll, or spray) and are rapidly cured with exposure to a UV light source of the proper intensity and frequency. A lamp system capable of generating intense bursts of UV light must be supplied in order to successfully cure the coating. The nature of the lamp system being utilized is determined largely by the shape and area of the surface being coated, while the nature of the bulbs used is determined by the photoinitiators in the coating being cured.