Influence of silica and alumina oxide on coating structure and print quality of ink-jet papers.

Advances in ink-jet printing have resulted in a new generation of ink-jet printers, which can print faster, at wider widths, producing four-color images close to photographic quality. Ink-jet printing papers must respond to these changes through quick ink absorption, minimizing ink bleeding and wicking, while retaining favorable ink optical density. Amorphous and precipitated silica and silica gels, prepared by the acidification of a solution of sodium silicate, are commonly used in premium matte coated ink-jet papers. Aqueous coatings for paper or paperboard applications use traditional coating pigments such as clay, calcium carbonate, and titanium dioxide. However, for matte coated ink-jet papers, precipitated and gelled silica are used for their unique morphological properties. The structure of these pigments provides an internal and packing porosity that enables the rapid diffusion of liquid inks into the coating layer. The rapid uptake of the ink immobilizes the anionic dyes at the surface of the coating. This accumulation of dye at the surface allows high optical print densities to be achieved. The particle size of precipitated and gelled silica is typically in the 3–16 mm range. Particles of this size significantly reduce gloss, which limits their use in glossy ink-jet media. Thus, they are primarily used in matte grades. This study compared coatings of non-porous fumed silica, aluminum oxide, and precipitated silica in ink-jet media. We used a blade coat process on a cylindrical lab coater (CLC) rather than the cast coat process. We focused on the contribution of pigment chemistry, functionality, and particle size on coating structure, and coating influences on ink-jet print quality. The pigments used are commercially available and, because of this work, currently being used commercially. [ABSTRACT FROM AUTHOR]