Development and characterization of silicon micromachined nozzle units forcontinuous ink jet printers

The design of a silicon micromachined nozzle unit to be used in continuous ink jet printers is suggested and characterized. A truncated pyramid shaped nozzle geometry was obtained by anisotropic etching and p-n junction etch stop processing of <100> silicon wafers. The pyramid shaped nozzle, with th e exit on the front side of the silicon die, has a square orifice, which co nnects to the center of a 10 mm x 0.7 mm x 30 mum (L x W x D) channel situa ted on the backside of the die. The channel was sealed by an anodically bon ded glass lid, which provided in- and outlet via drilled holes. The flow th rough option, given by the connection of the in- and outlet to each end of the channel, facilitates cleaning at the end of the manufacturing process a s well as de-clogging of the nozzle during operation. The stimulation of th e jet, to attain constant droplet size and distance between droplets, was a chieved with the aid of a piezoelectric element that was glued to the glass lid on the backside of the nozzle unit, The piezoelectric element was posi tioned adjacent to the orifice of the nozzle to secure a good acoustic coup ling to the jet. A jet emerged from a nozzle (10 mum x 10 mum orifice) with a velocity of 50 m/s at a flow rate of 0.22 ml/min when a pressure of 10 b ar was used to force the ink through the nozzle unit. The droplet flight st ability was characterized by an in-house developed optical measurement syst em. The results showed that the nozzle unit generated droplets with high dr oplet flight stability (less than 15 degrees standard deviation in droplet period width measured at 7 mm from the orifice) in a large stimulation freq uency region around the desired frequency of 1 MHz.