Principles of IJP

Inkjet (or ink jet) printers operate by propelling tiny droplets of liquid ink onto paper to form characters. Inkjets are the most common type of computer printer for businesses due to their low cost, high quality of output, capability of printing in vivid color, and ease of use. In the computer market, inkjet printers predominate. They are usually inexpensive, quiet, reasonably fast, and many models -- such as those offered by Dartronics -- can produce high quality output. Like most modern technologies, the present-day inkjet has built on the progress made by many earlier versions, and today use one of three main technologies: thermal, piezoelectric, and continuous.

Thermal Ink Jet

Most consumer ink jet printers 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. The ink's surface tension pulls another charge of ink into the chamber through a narrow channel attached to an ink reservoir.
Thermal ink jet technology is used almost exclusively in the consumer ink jet market. 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

Most commercial and industrial ink jet printers use a piezoelectric crystal in each nozzle instead of a heating element. When current is applied, the crystal changes shape or size, forcing a droplet of ink from the nozzle. Piezoelectric ink jets allow a wider variety of inks than thermal or continuous ink jet, but are more expensive.
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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 microscopic nozzle, creating a continuous stream of ink droplets. A piezoelectric crystal causes the stream of liquid to break into droplets at regular intervals. 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 are then directed (deflected) to the receptor material to be printed by electrostatic deflection plates, or are allowed to continue on undeflected to a collection gutter for reuse. 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 a very high velocity 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 (because 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.

Feat of electronics - Ink Jet Printer

To print a character on the product, individual drops of ink are electronically controlled to the correct positions.

 

  • Ink is pressured by a ink supply pump and flows from the ink bottle to the nozzle.
  • The nozzle uses ultrasonic vibration to break a pressurized ink stream into small droplets as it leaves the nozzle.
  • The drops are ejected from the nozzle at high speed. They pass through the charge electrode tunnel / and then on between the deflection electrode.
  • Here the drops are deflected, by an amount which depends on the charge they were given by the charge electrode.
  • After the drops leave the region of the deflection electrode they continue to travel in their new direction until they pass out of the printhead and to the substrate.
  • Drops that aren't required for printing are caught by the gutter and subsequently recycled back to the ink bottle.