Fixed array printhead for higher viscosity inks

US 2012/0069104 A1
EP 2 436 520 A1
Liquid discharge head and recording device using same
Kyocera Corporation

Here Kyocera wishes to improve image quality when using higher viscosity inks, such as UV curable. These inks have a higher viscosity than aqueous inks – 8 cP is mentioned, and therefore the actuators must be driven to generate higher pressures to form drops at the same velocity. Unfortunately, at the higher pressures satellite drops are formed and image quality deteriorates.

Mar12a  Mar12b

The solution is to introduce a restriction in the descending passage leading to the nozzle. Here a section through the printhead is shown. Ink flows from manifold 5 into actuator chamber 10 via connecting passageway 6. The actuator consists of two piezo layers 21a and 21b, both around 20 microns thick. In between the piezo layers is a common electrode 34, and on the top the individual electrode 35. A stack of Fe-Ni plates 4, each separately etched, defines the ink chamber and channels. The plates are fixed together using a thermosetting resin with a curing temperature of 100-150C. The reason for the relatively low temperature curing is to reduce the chances of stresses being set up between the different materials on cooling.

<a href=”http://inkjetpatents.com/blog/wp-content/uploads/2012/03/Mar12b1.gif”><img class=”size-full wp-image-75 alignright” title=”Mar12b” src=”http://inkjetpatents.com/blog/wp-content/uploads/2012/03/Mar12b1.gif” alt=”” width=”297″ height=”218″ /></a>Drops are fired using a bi-polar waveform. To begin with the piezo actuator rises, increasing the chamber volume. The drive waveform is then reversed driving the actuator down and reducing the chamber volume. The pulse width between these two events is set to the acoustic length between the manifold 5 and the nozzle 8. This allows the positive reflected pressure wave from the expansion phase to be added to the drive phase so that a stronger overall pressure wave is generated. This is the well-known “fill before fire” technique. Drops generated are 5-7 pl.

Returning to the objective of these patent applications, that is to reduce the satellite drops being generated, the solution is to introduce a restriction in the descender. This increases the damping and hence pressure oscillation at the nozzle. The feature is defined by plate 28, where the descender diameter is reduced from Sd1 to Sd3 with a height Ld3. The distance Ld2 is also important. Ratios of Ld3/Ld0 of 10-15% and Ld2/Ld0 of 20-40% were effective at eliminating satellite drops during tests.

Mike Willis

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