The primary components of UV inks include pigments, oligomers, monomers (reactive diluents), photoinitiators, and various additives.
The nature of the flexographic printing process dictates that the UV inks employed must not have an excessively high viscosity. Traditional flexographic inks-whether solvent-based or water-based-rely on large quantities of solvents or water for viscosity adjustment. In contrast, UV flexographic inks utilize reactive diluents to lower the system's viscosity; consequently, their overall viscosity may be higher than that of solvent-based flexographic inks. Although UV flexographic inks generally have a lower viscosity than those used for screen or offset printing, the incorporation of pigments tends to increase viscosity-particularly if the wetting, dispersion, and stabilization of the pigments are not effectively managed.
Pigments play a critical role in the rheological properties of the ink, and a certain degree of thixotropy is advantageous. Imparting appropriate thixotropic characteristics to flexographic inks helps prevent pigment flocculation and sedimentation, thereby improving printability.
