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Leaving your mark. Ink-Jet technology

6/08/2012

Today, there are various product marking methods available, and it is important to identify the most suitable technology for every particular need.


Ink-Jet printing has become very popular over the past 5 years, and it is the recommended marking system for several industrial sectors and has been confirmed as the most efficient and cost-effective solution for overprinting data and coding changes, as well as for personalized applications, including also graphic elements.


Industrial Ink-Jet printers are the simplest marking system: they can increase productivity through automation, provide feedback and information on the products moving along the lines, communicating with the PLC and the other devices on your plant. Given that the coding changes carried out on the products by the PLC are instantaneous, thanks to this technology costly errors may be avoided. Errors like forgetting to modify the product stamp. What is more, this technology allows you to print only what you want on every single product, on the contrary to the common continuous string printing.


Therefore, thanks to this system it is possible to print various kinds of information, for example barcodes, batch numbers, expiry and production dates, etc., directly onto the products being processed, thus guaranteeing the most suitable solutions for product codification and tracking. Ink-Jet printing allows for the indelible coding of any kind of product, and may be applied to any type of material (glass, plastic, cardboard, etc.) without altering the product appearance. Over the past few years particular attention has been paid to the Ink-Jet system, especially as far as batch management and material tracking is concerned (conforming to the European Parliament CE Regulation no. 178/2002).


There are different Ink-Jet systems and they can be grouped into three main technologies: "continuous (CIJ)", "high resolution" and "drop-on-demand".


The first ever well-known ink-jet printing process is the "continuous" system, where the ink is pumped without interruptions through a nozzle and jetted onto the surface to be printed. In actual fact, despite its name, the resulting flow of ink is not really continuous. Due to a physical phenomenon tied to the instability of the fluids in movement, the jetted ink inevitably tends to break down into droplets, of basically random sizes.


This process has been perfected over time, thus becoming "high resolution" and involving the use of a Piezo-electric crystal which vibrates at the right frequency in proximity to the nozzle. This breaks up the ink flow at regular intervals, in order to obtain more homogenous drops. The ink drops are then loaded electrostatically by two facing electrodes, so as to be aimed by applying a magnetic field.


The "drop-on-demand" process, can guarantee both better control on the positioning of the drops, as well as less waste.
This principle is adopted to obtain the final aim: the nozzle from which the ink is delivered represents the terminal element of a micro-camera that is constantly fed by the main reservoir.

Behind the micro camera is the Piezo-electric element which, when charged with current, deforms, alternatively assuming a concave and convex form. In the first case, the movement causes a rise in the pressure in the micro-camera that forces the ink towards the nozzle; in the second case, it creates a depression allowing the new ink to flow, thanks to a capillary action from the cartridge to the printhead.

However, the use of a Piezo-electric crystal is not the only way to obtain "drop-on-demand" printing. By chance, during some laboratory tests, an engineer working for Canon discovered this different method by accidentally touching a needle full of ink with a soldering iron. The sudden heating of the needle caused the liquid to squirt out of the syringe, therefore "thermal ink-jet" technology derived from this lucky accident; it is an alternative to the Piezo-electric technology, and in October 1977 Canon deposited the relative patent.


Therefore, when adopting the "thermal inkjet" method the Piezo-electric element is replaced by a heating element, which, when charged with electricity causes the sudden evaporation of the contact ink and the consequent formation of a bubble that strongly increases the pressure inside the micro-camera, pushing the ink towards the nozzle, and therefore onto the support to be printed.

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