Electrostatic inkjet

There are very few commercial implementations of electrostatic inkjet, though these are increasing. Electrostatic inkjet (of which the most widely known is Tonejet by TTP) is characterized by drops being drawn from an orifice under the influence of an electrostatic field. This field, acting between an electrode and the orifice, attracts free charges within the ink (sometimes described as a liquid toner) to its surface in such a way that a drop is produced when the electrostatic pull exceeds the surface tension of the ink (Fig. 4). As this technique relies on the attraction of free charges, the ink is required to be conductive. 

The advantages of an electrostatic inkjet are that it allows you to print a more concentrated fluid than the formulation that actually passes through the print head, and that the achievable resolution is not a function of the nozzle diameter so that potentially higher resolutions than piezo inkjet are possible. Additionally, very small drops can be formed while still using pigments, as the size of the drop... 

There are currently four main types of inkjet inks phase-change, solvent-based, water-based, and UV curable. Other types exist, but are less prevalent, such as oil-based and hquid toner (for electrostatic inkjet technology). Hybrid versions of the four main types also exist (e.g., water-based inks containing some amount of solvent). The various inkjet ink types will be discussed briefly in this chapter, and will be followed by detailed description in separate chapters (solvent-based, water-based, and UV cmable inks). 

Figure A A Inkjet printing ejection mechanisms (a) Thermal inkjet printing (Reprintedfrom Bcdlarinet at, 2004, with permission from Elsevier), (h) piezoelectric inkjet printing (Fuller et al., 2002) (c) electrostatic inkjet printing (Lin and Bai, 2004) (d) acoustic inkjet printing (Parashkov et al., 2005).

When a paper display is needed or when textual information is to be printed, as in a report, it is common to use a digital printer such as a laser jet or inkjet printer. These devices are inexpensive and provide 600 to 2400 dots per inch, more than adequate for most applications. The laser jet devices use an electrostatic transfer of black toner material to paper to form the desired image, which is then fused to the paper by passage over a heater. Color versions are available but are more expensive because they require three toner cartridges, one for each of the primary colors. The inkjet printers use movable solid-state heads with many fine holes through which small droplets of ink are ejected by selective localized heating behind the orifices. The ink is drawn by capillary action from a reservoir chamber and, by use of three primary colors, full-color images can be printed at up to 2400 dots per inch. 

Noncontact methods of printing are electrostatic, ink jet, and laser etching. Electrostatic printing applies dry ink to areas by a difference in electrical potential. Inkjet printing is a direct adaptation of the ink jet printer used to print on paper. Laser etching printing reqviires that a laser beam be aimed via a series of computer-controlled mirrors. The... 

The transfer process of ink jet printing is one of removing a drop of liquid ink from the bulk and giving it a velocity of sufficient precision and magnitude to place it on a substrate in close proximity to but not touching the printhead. There are three broad techniques continuous, electrostatic, and drop on demand. Continuous inkjet printing, because of its intrinsic high drop rate, has tended to find more applications... 

A second type of inkjet with an electrostatic actuator has been fabricated in the Sandia SUMMiT V process [3], [4]. In this design, the ink fills in the gap in the electrostatic actuator, increasing the dielectric constant and thus the pressure that is generated. Since the ink is exposed to the drive voltages, a high-frequency RF drive signal is used to avoid problems with electrolysis of the ink. A schematic cross section of the drop ejector is shown in Figure 6.13 [5]. 

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