A New Method to Assess the Jetting Behavior of Drop-On-Demand Inkjet Fluids

Abstract

We present a new experimental method to assess the jetting performance of fluids for use in drop-on-demand (DoD) inkjet printheads. The oblique collision of two continuous liquid jets leads to the formation of a thin oval liquid sheet bounded by a thicker rim which disintegrates into ligaments and droplets. Under certain conditions the flow structure exhibits a remarkably symmetrical ‘fishbone’ pattern composed of a regular succession of longitudinal ligaments and droplets. For a series of model elastic fluids containing polystyrene (PS) in diethyl phthalate (DEP), ejected from nozzles with an internal diameter of 0.85 mm, the shape of the fishbone pattern varies strongly with polymer concentration. The same fluids were used in a Xaar piezoelectric DoD print head to characterize their jetting performance in terms of the maximum ligament length, a crucial parameter in determining the printability of the fluid. There are close similarities between the ligament collapse behaviors in both experiments. Good correlation was found between the maximum included angle of the fishbone pattern and the maximum ligament length in the jetting experiments, which suggests that a test based on oblique impinging jets may be useful in the development of fluids for inkjet printing.