Effect of a binary solvent on film formation in ink-jet printing

The effect of a binary solvent with high and low boiling points on the film formation in ink-jet printing of a polymer solution was studied experimentally. The principal reason that the binary solvent prevents the formation of a ring-stain is that the low boiling solvent evaporates quickly, resulting in an increase in the solution viscosity at the pinning of the contact line. The experimental results revealed that this increase in viscosity is caused by Marangoni convection due to the concentration profile of the solvents on the free surface. Based on this finding, experiments with a single-solvent droplet showed that ring-stain formation can be suppressed by increasing the initial solute concentration. With the binary solvent, it becomes possible to impact fluids of even higher viscosity on the surface by increasing the evaporation of the low boiling solvent. Furthermore, the atmospheric temperature and the gap between the nozzle and the surface affect the viscosity at impact at which the ring stain is eliminated.