Stability of Lines with Zero Receding Contact Angle Produced by Inkjet Printing at Small Drop Volume.

We present an experimental study of the maximum and minimum bounding drop spacing for a parallel-sided liquid line produced by inkjet printing with drop volumes of 1.5 and 8.5 pL, on substrates with advancing contact angles of 46 and 54°, and zero receding contact angle. The results are used to validate models of the limiting bounds for the formation of stable parallel-sided lines as a function of drop spacing and transverse printing speed. The model for the maximum drop spacing bound (minimum line width) shows a good agreement with our results, but, when used to predict the stable line width, there is an influence of printing speed not captured by the model. This is probably because of a coupling between printed drop volume and ejection velocity outside the scope of the model. The minimum drop spacing bound (maximum stable line width) is limited by a bulging instability, and our results agree with the existing model, except for printing with the largest drop volumes at low temperature. It is shown that under these conditions, there is a different mechanism for bulging that occurs after printing over a period of minutes, if the liquid bead is present on the surface for a significant period of time before drying. Our results suggest that this mechanism is possibly triggered by imperfections on the substrate.