Chemico-physical Properties of Nano- Sized Ceramic Inks for Ink-jet Printing

This work is aimed at developing suitable nano-sized ceramic inks (nano-inks) for the ink-jet printing four-colour process. Nano-inks of different pigment composition were prepared with various solid loadings, and their chemico-physical properties, relevant for the ink-jet application, were measured. Moreover, penetration kinetics of the inks through different unfired ceramic tile bodies was experimentally appraised. Results show that pigment particle sizes are in the 10-90 nm range, and that all the nano-inks are stable for long time (i.e. more than one year) due to both their high values of ζ-potential and the steric effect of the dispersing medium. This high stability avoids problems of nozzle clogging which might arise from particle sedimentation. Most of nano-inks have a Newtonian behaviour with relatively low viscosities (< 50 mpa s) even if, according to pigment composition, more concentrated nano-inks may have an excessive viscosity for ink-jet applications. Surface tension requirements for ink-jet printing (i.e. 35÷45 mN/m) are fulfilled by the tested nano-inks, although the values vary significantly with pigment loading. The electrical conductivity is, generally, in the 1-100 μS/cm range and is influenced by pigment composition (e.g. inks containing metallic particles exceed 1 S/cm). The penetration kinetics is mostly affected by pigment loading and composition, while it does not significantly depend on microstructure and composition of the two ceramic substrates considered. In conclusion, most of nano-inks investigated show satisfactory chemico-physical properties for ink-jet applications, as proved by preliminary tests. Those which are out of typical ranges can be enhanced by modifying the composition and/or the operating parameters.