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Difference Between Continuous Inkjet Printing and On Demand Inkjet Printing

Inkjet printing is the process of depositing drops on ink in a digitally controlled manner from the print-head onto the substrate in a variety of ways. The technology was developed in the 1950s and of late, it has found many practical uses in the industrial setup as well.

In the industrial setup, there are two main types of inkjet printing. The first is continuous inkjet printing and the second is the on demand inkjet printing. The differences are explained below. In continuous inkjet printing, a pump directs the ink through one or more small nozzles. The ink droplets are ejected from the nozzles continuously at a high frequency, which in turn is varied by means of a piezoelectric crystal. Before the droplets reach the nozzle, the ink drops are made to pass through electrodes, which in turn impart a charge to them. The charged drops are then deflected by means of an electrostatic field. The drops that are not deflected are collected and circulated back. This technology has the advantage that high printing speed is possible. Further, because of the high velocity of projection, a longer distance can be maintained between the print-head and the substrate. Thus the print-head is also protected from damage. Volatile inks can be used easily and thus rapid drying of the ink ensures a quick turn-around time for the printing process. The only limitation of the technique is that high printing resolution cannot be achieved owing to the speed of the process. Further, maintenance requirements for the equipment are high and it is thought to be an environmentally unfriendly technology owing to the use of volatile inks.

In the case of drop on demand technology, the drops are ejected from the print-head only when required and the drops are spawned when a pressure pulse is created. This pressure pulse can be created in two ways. In the first method, called thermal inkjet technology, the ink is rapidly heated on a filament. The ink vaporizes and this creates a pressure pulse, leading to its ejection and the creation of fresh drops as a continuous cycle. The second method of creating a pressure pulse is by means of piezoelectric technology. A piezoelectric crystal undergoes distortion when an electric field is applied to it. This distortion is then used to create a pressure pulse, resulting in drop ejection. Of these two technologies, the piezoelectric technology is favored as it is clean. Further, since there is no heat involved, there is a larger variety of inks to choose from. The main advantage of drop on demand technology is the possibility of high printing resolution.

Whatever be the methodology involved, industrial inkjet printing finds a wide range of application, right from food processing to cardboard manufacture. It is definitely no doubt that this technology is here to stay and will only get better in the times to come.