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The operating principle of high quality white ink printer H850P :
Electrically conductive ink is supplied under pressure to a nozzle assembly. The nozzle face-plate has an orifice (hole) and an ink stream is formed as the ink is forced out through this small orifice. As it passes through the nozzle, the stream is pulsed or modulated by a piezo crystal located on the back side of the nozzle. This modulation breaks up the stream into a continuous series of drops that are all equally spaced, and of equal size 70µ-microns diameter.
Details：
http://www.hi-pack-coding.com/