When using ink-jet printing devices, an entire print job can be printed with static data as it would be on a conventional piece of printing equipment or the application can be printed with variable data in which every piece in a single print run is unique. The types of ink-jet technologies are continuous jet and drop-on-demand, which are described below.

Continuous jet is a technology in which a printing device ejects drops of ink that are produced constantly during the printing process and are applied to the substrate with precision in order to create the image. A pump sends the ink drops through a nozzle of the printing head at the rate of over a million per second, which can produce an image of nearly the same quality as a continuous tone image (photograph). There are three types of continuous ink-jet technologies: charged drops for printing, uncharged drops for printing, and electronic deflection.

Charged Drops for Printing

Drops of ink are given a charge and are deflected to the substrate to produce the image. The ink drops that are uncharged are recycled through the system to be reused.

Uncharged Drops for Printing

This type of technology also applies a charge to the ink drops except that the uncharged drops are used for the actual printing and the charged drops are recycled.

Electronic Deflection

This type of technology applies a charge to all of the ink drops and the application of the drops is determined by deflection, which is controlled electronically.

Drop-on-demand is a type of ink-jet technology in which the ink drops are formed and then applied as a response to a digital signal. As the name indicates, drop-on-demand systems expel ink only when there is a demand for the ink. There are three types of drop-on-demand ink-jet printing systems: piezoelectric liquid, thermal liquid/bubble jet, and solid ink-jet.

Piezoelectric Liquid

A piezoelectric crystal is given an electric charge, which produces a pressure pulse in the imaging head. This produces the emission of an ink droplet onto the substrate. The ink droplet is applied very accurately, resulting in excellent quality. A printer equipped with this technology contains print heads with ink reservoirs that are refillable, which differs from most other drop-on-demand printers that have disposable print heads.

Thermal Liquid/Bubble Jet

Heat produced from an electrical resistor vaporizes the moisture in the ink, which causes an ink bubble to form. The expanding bubble creates pressure inside the ink nozzle and propels the ink to the paper. The ink bubble then contracts, which lowers the pressure causing more ink to be drawn into the printing head. The entire process occurs very rapidly in the printing device. In fact, the process is repeated thousands of times per second, producing extremely high quality results.

Solid Ink-Jet

A solid ink-jet printer is also known as a phase change ink-jet printer. The ink begins as a solid and is heated to convert it to a liquid state. The ink is propelled as drops onto the substrate from the impulses of a piezoelectric crystal. Once the ink droplets reach the substrate, another phase change occurs as the ink is cooled and returns to a solid form instantly. The print quality is excellent and the printers are capable of applying ink on almost any type of paper and transparency substrates.