Thermal Ink Jet:
Most consumer ink jet printers (Hewlett-Packard, Canon) work by having a print cartridge with a series of tiny electrically heated chambers constructed by photolithography. To produce an image, the printer runs a pulse of current through the heating elements. A steam explosion in the chamber forms a bubble, which propels a droplet of ink onto the paper (hence Canon's tradename for its inkjets, Bubblejet). The ink's surface tension as well as the condensing and thus contraction of the vapour-bubble, pulls another charge of ink into the chamber through a narrow channel attached to an ink reservoir.
The ink used is usually water-based, pigment-based or dye-based but the print head is produced usually at less cost than other ink jet technologies.
Piezoelectric Ink Jet:
All Epson printers and most commercial and industrial ink jet printers use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the crystal changes shape or size, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. This is essentially the same mechanism as the thermal inkjet but generates the pressure pulse using a different physical principle. Piezoelectric ink jet allows a wider variety of inks than thermal or continuous ink jet but is more expensive.
InkJet with Piezoelectric is very fast and cost effective, when the Piezo crystal has an applied voltage, the crystal will shake the ink stream causing it to break off in very small, fine droplets as the ink leaves the oriface plate hole. This droplet of ink can then be either charged or not charged depending on if the droplet of ink is to be printed or not.
If the droplet is to be printed onto the paper, the ink droplet is not charged. However, if the droplet is not required to be printed to the paper, it is charged with a positive bias, this way the ink droplet is then attracted to the negatively biased charge plate, the ink will hit the plate then be vacuumed away by a ink recycle system.
The emerging Ink jet material deposition market uses ink jet technologies, typically piezoelectric ink jet, to deposit materials on substrates.
Continuous Ink Jet:
The continuous ink jet method is used commercially for marking and coding of products and packages. The first patent on the idea is from 1867, by William Thomson. The first commercial model was introduced in 1951 by Siemens. In continuous ink jet technology, a high-pressure pump directs liquid ink from a reservoir through a Gunbody and a microscopic nozzle, creating a continuous stream of ink droplets. A piezoelectric crystal effects an acoustic wave as it vibrates within the gunbody and causes the stream of liquid to break into droplets at regular intervals - 64000 to 165000 drops per second may be achieved. The ink droplets are subjected to an electrostatic field created by a charging electrode as they form. The field is varied according to the degree of drop deflection desired. This results in a controlled, variable electrostatic charge on each droplet. Charged droplets are separated by one or more uncharged "guard droplets" to minimize electrostatic repulsion between neighboring droplets.
The charged droplets pass through an electrostatic field and are directed (deflected) to the receptor material (substrate) to be printed by electrostatic deflection plates, or are allowed to continue on undeflected to a collection gutter for re-use. The more highly charged droplets are deflected to a greater degree.
Continuous ink jet is one of the oldest ink jet technologies in use and is fairly mature. One of its advantages is the very high velocity (~50 m/s) of the ink droplets, which allows the ink drops to be thrown a long distance to the target. Another advantage is freedom from nozzle clogging as the jet is always in use. Volatile solvents (ketones and alcohols) can therefore be used, giving the ability of the ink to "bite" into the substrate and dry quickly. The fluid handling systems can be quite complex. Droplets are generated at ~ 64 to 165 kHz; only a few percent of the droplets are used to print; the rest are recycled.