Influence of Structural Properties on Non-Impact Printability of Nanostructured Silica–Polymer Coatings

Abstract

The ink jet printing properties of papers coated with two different types of aggregated silica were compared. The structure of the nanoporous aggregates has been investigated with different techniques such as BET and CTAB surface area, Hg porometry and light scattering. The aggregates were thereafter mixed with polyvinylalcohol (PVA). The affinity of the PVA for the silica surface has been studied through adsorption isotherms at pH 5 and 9. It appears that the affinity is much more important at pH 5. PVA– silica slurries were prepared at pH 5 and coated on a non-coated common copier paper and finally printed. Swelling experiments and transmission electron microscopy have been performed on the coatings in order to have additional information on its structure. Black and white image analysis of typographic characters printed on the coatings show that smoothness of contours, gray level, contrast, definition, surface area of the typographic characters depend mostly on the structural properties of the silica, but also on its compatibility with the binder. The combination of both effects determines how important the remaining free porous volume accessible to ink fluids will be, and ultimately how the printing properties, such as shade and pixel resolution, will be. When pores are too large, they become filled with polymer and the silica aggregates lose their absorbency capacity.