Effect of Pigments on Photocuring of Waterborne UV Ink

As a non-photosensitive component in water-based UV-curable inks, pigments compete with initiators for absorbing UV light, which largely affects the curing characteristics of systems in UV curing systems. Because the pigment can absorb a portion of the radiant energy, this will affect the absorption of light by the photoinitiator, which in turn affects the concentration of free radicals that can be generated, and as a result, the curing speed is reduced. Each color pigment has different absorption rate (light transmittance) for different wavelengths of light, the smaller the absorption rate of the pigment, the greater the transmittance, and the faster the curing speed of the coating. Carbon black has a high UV absorption capacity and is the slowest to cure. White pigments have a high degree of light reflectivity, which also hinders curing. The order of UV absorption is generally: black> purple> blue> cyan> stunning> yellow> red.

The same concentration ratio of the different pigments has different effects on the curing rate of the ink film. With the increase of the amount of pigment, the curing rate of the ink film has a different program. The amount of yellow pigment has the greatest influence on the curing rate of the ink film, followed by red pigment and green pigment. Since black has the highest absorptivity for ultraviolet light, the black ink has the lowest light transmittance, so the change in the amount thereof has no significant effect on the curing rate of the ink film. When the amount of pigment is too large, the curing rate of the surface layer of the ink film is fast, but the pigment of the surface layer absorbs a large amount of ultraviolet light, reduces the light transmittance of the ultraviolet light, and affects the solidification of the deep ink film, resulting in the surface curing of the ink film and the bottom layer Not cured, easy to produce "wrinkle skin" phenomenon.