Drop-on-Demand IJ Printing

Ink Jet Printing Methods

Ink Jet printing is a non impact dot matrix printing technology in which droplets of ink are jetted from a small aperture directly to a specified position on a media to create an image. There are two methods of ink jet printing with many variations within each. The first ink jet printing method discovered was continuous ink jet printing whereby a continuous ink stream is broken into droplets of uniform size and spacing and an electric charge is impressed upon the drops selectively. The charged drops when passing through an electric field are deflected into a gutter and recirculated while the uncharged drops fly directly to the media to form an image.

The second ink jet printing method is drop-on-demand ink jet printing. A drop on demand device ejects ink droplets only when they are needed to create an image on a media. This approach eliminates the complexity of drop charging and deflection hardware as well as the inherent unreliability of ink recirculation systems required for continuous ink jet technology.

DOD Methods

There are four methods of drop on demand ink jet printing; thermal, piezoelectric, electrostatic and acoustic. Most if not all of the ink jet printers on the markets today use either the thermal or piezoelectric principal. Thermal ink jet printing is a method whereby ink drops are ejected from a nozzle by the growth and collapse of a water vapor bubble on the top surface of a small heater located near the nozzle. The simple design of the thermal ink jet printhead and its semiconductor compatible fabrication process allows printheads to be built at low cost. The ability to discard the printhead after its short print life span is the primary reason for its dominance in relatively low ink usage markets such as home and office printing.

Piezoelectric methods are named after the deformation method of the piezoceramic used in the device. The four methods include squeeze, bend, push and shear. Squeeze mode ink jet can be designed with a thin tube of piezoceramic surrounding a glass nozzle. In a typical bend mode design, the piezoceramic plates are bonded to a diaphragm forming an array of bilaminar electromechanical transducers. In a push mode design as the piezoelectric rods expand, they push against the ink to eject the droplets. The shear mode design deforms the piezoelectric against ink to eject the droplets. In this case the piezo becomes an active wall in the ink chamber. Interaction between ink and piezoceramic is one of the key parameters of a shear mode printhead design.

For more information, See Progress and Trends in Ink Jet printing Technology, printed in the Journal of Imaging Science and Technology Vol. 42, Number 1
www.imaging.org/resources/leinkjet/part1.cfm