Print mottling: Solid-liquid adhesion related to optical appearance

Print mottling has been widely studied over the years and several reasons for uneven print have been pointed out. Factors affecting mottling are, e.g., heterogeneity of the coating layer, uneven absorption of the ink, ink properties and printing conditions such as machine settings. In this study, the focus was put on the adhesion between the coated base paper and model liquids representing ink components, and its influence on both color and gloss mottling. Furthermore, the aim was to thoroughly characterize the surface structure of the coated papers and to use these features and the optical properties to re-evaluate the physico-chemical meaning of mottling. The surface adhesion energy of the coated papers was determined with static contact angle (CA) measurements, and the topographical analysis was done with atomic force microscopy (AFM). The print quality was inspected using a diffractive optical-element-based glossmeter (DOG) for gloss mottling and an imaging spectrometer for color mottling measurements. By plotting the solid-liquid work of adhesion against color and gloss deviation of prints, it was observed that the samples with lower work of adhesion, between liquid and substrate, produce both color and gloss mottling. The samples appeared to be sensitive only to dispersive model liquids (referring to ink oils). The surface topography had a significant effect on wetting of the studied samples. (c) 2007 Elsevier B.V. All rights reserved.