Fabrication and Characterisation of Silicon Micromachined Nozzles for Continuous Ink Jet Printers

Abstract

A silicon micromachined nozzle for continuous ink jet printing is developed at our department. The commonly used glass nozzles in high quality applications often show large variations in frequency behaviour from unit to unit which is mainly due to mechanical resonances. The manufacturing process is rather complicated and it is difficult to achieve high droplet formation stability at a given stimulation frequency. This must be overcome by either adjusting the operating frequency in the printer or by selecting nozzles that operate well at the wanted frequency.The proposed silicon nozzle has a simple geometrical design and the fabrication process has high reproducibility which results in less variation in performance from unit to unit. The batch fabrication with several nozzles per silicon wafer will also reduce the cost per unit.In the prototype nozzle a 13 mm x 2 mm x 30 mm channel is etched in a silicon die. The orifice is etched through the die at the centre of the channel. On the nozzle front side, the silicon around the 10 micrometer x 10 micrometer orifice is removed leaving a pyramid shaped nozzle extending from the surface. The backside of the nozzle die is bonded to a glass lid.The channel is supplied with an inlet and an outlet drilled through the glass lid. The flow-through option facilitates cleaning at the end of the manufacturing process since the cleaning fluid does not have to pass the orifice. During operation the outlet is sealed.A piezo-element is attached to the silicon die close to the orifice for stimulation of the droplet formation.An 11 micrometer jet at a flow rate of 0.22 ml/min emerges at a pressure of 15 atm. compared to about 40 atm. for a typical glass nozzle. The droplet formation and flight stability is characterised with an in-house developed optical measurement system. The results show that the nozzle generates droplets with high droplet formation stability in a region around the wanted stimulation frequency of 1 MHz.