Jet array driven flow on the nozzle plate of an inkjet printhead in deposition of molten nylon materials

During research into an inkjet-integrated manufacturing process, jetting of molten caprolactam was investigated using a piezoelectric drop-on-demand printhead. Due to the start-up purging step and the surface energy differences, a wetting melt layer on the printhead's nozzle plate was formed. With appropriate parameters, a stable jet array was made. However, contamination on the nozzle plate disturbed the jet stability resulting in jet trajectory errors and even jet failures. Particles were used to characterise the melt flow field on the nozzle plate during jetting when multiple nozzles were actuated. Particle tracking velocimetry revealed that movement of the particles followed a specific pattern when the jet array was developed. Flow pattern driven by an actuating nozzle influenced those of adjacent nozzles. The movement of particles towards and from the actuating nozzles was observed at the same time and position with velocities up to 2 mm/s. This showed that a complex flow system was generated on the nozzle plate during jetting with multiple nozzles which influenced the reliability of the inkjet printhead.