Bench Talk

(Source: Mumemories - stock.adobe.com)

The industrial printing industry has rapidly converted from traditional analog printing techniques like offset lithography and roto-gravure to digital inkjet printing techniques such as continuous inkjet (CIJ) or drop-on-demand (DOD). In this blog, we examine how the proliferation of inkjet technology is revolutionizing industrial printing by improving efficiency and minimizing waste while achieving new levels of print quality.

Industrial inkjet printing refers to the use of inkjet technology to print or deposit materials onto various surfaces—a process similar to your standard home or office inkjet printer. Industrial inkjet printers are not just limited to printing or marking; they can also apply coatings, deposit precise amounts of functional materials, and even build micro or macro structures.

Inkjet technology ejects patterns of tiny drops onto various materials without physically making contact with the surface of the object. These patterns of dots are comprised of different colored inks, which, when combined, can create photo-quality images, as seen in Figure 1.

Figure 1: New inkjet technologies are enabling industrial printers to produce photo-quality images with rich detail and crisp colors. (Source: DmyTo/Stock.adobe.com)

At first glance, this technique may appear fairly simple, but the design of these systems is incredibly complex. The systems are designed to achieve image resolutions up to 1440 dots per inch (DPI). The ejected dots are smaller than the diameter of a human hair, with a diameter of 50 to 60 microns, requiring the systems to be built for extreme precision. The two primary inkjet technologies currently leading across the printing world are thermal bubble and piezoelectric.

Thermal bubble inkjet technology (TIJ) operates by utilizing resistors, which generate vapor bubbles within an ink-filled chamber. These bubbles, created by the heating elements, expel ink droplets through nozzles onto the printing surface, forming text, images, or graphics. The system typically consists of multiple ink chambers or channels, each connected to a tiny nozzle. Once the printing command is received, the printer sends electrical pulses to specific resistors based on the desired pattern or image. The resistors that receive the electrical pulse rapidly heat up, causing the ink to vaporize and form small bubbles. The collapsing bubble creates a pressure wave that propels a tiny droplet of ink out of the nozzle and onto the printing surface.

The second technique is based on piezoelectric technology, which uses the reverse piezoelectric effect to produce ink drops, wherein piezoelectric material deforms under the influence of an electric field (Figure 2). This deformation is used to push ink out of a chamber, either by forcing a diaphragm down that forms part of the ink chamber, or by deformation of the ink chamber walls when these are made of piezoelectric material. Ejection of an ink drop also refills the ink chamber from the ink reservoir.

Unlike thermal bubble inkjet technology, which uses a current to heat a resistor, piezoelectric inkjet printing uses voltage to create an electric field in the piezoelectric material. The piezo is deformed, resulting in mechanical movement that pushes the ink particle out.

Figure 2: A piezoelectric inkjet printer’s control system applies a voltage to the piezoelectric material, creating a change in shape or size of the material, and forcing a tiny droplet of ink out of the nozzle. (Source: Mouser Electronics)

With these printing technologies at hand, there are two primary classifications of industrial inkjet printing systems and their associated printheads: continuous inkjet (CIJ) and drop-on-demand (DOD), each with variations between them.

An efficient and dependable printing technique, CIJ printing operates by expelling electrically charged ink droplets from a printhead nozzle and propelling them through an electric field. CIJ printers utilize piezoelectric technology to break up the continuous inkjet stream into individual drops, which then fly through a charge tunnel where they are individually charged. After the drops are individually charged, they pass through a static electric field where they are deflected depending on their individual charge. Drops without charge are deflected into the gutter for reuse, while the charged drops land on the substrate depending on their charge and amount of deflection.

CIJ had traditionally been preferred over other inkjet technologies because it can use inks based on volatile solvents that dry quickly and improve adhesion on numerous substrates. However, the technology has several drawbacks, including moderately low print resolution, high maintenance requirements, and environmental risks because of its use of large volumes of volatile solvent-based fluids. Furthermore, the requirement that the printed fluid be electrically chargeable restricts the technique's applicability.

Unlike CIJ printing, DOD only ejects ink drops from the printhead when and where it is required and exactly the amount of ink required to create the image (Figure 3). The quality of DOD printheads is unmatched, as they can achieve resolutions of 1440DPI, as well as gradients and greyscale effects at resolutions up to 1200DPI.

Figure 3: CIJ printing operates by expelling electrically charged ink droplets from a printhead nozzle, propelling ink droplets through an electric field, and recycling non-electrically charged ink droplets back into the ink supply in the printhead. DOD inkjet printing only ejects the exact amount of ink droplets from the printhead when and where it is required to create the image (Source: Mouser Electronics)

Regardless of the digital technology that is being used, these systems need adequate and equally complex power analog components to drive the dynamic or capacitive loads demanded by these printers. Apex Microtechnology offers power operational amplifiers specifically designed to drive CIJ and DOD inkjet printheads, meeting power requirements and boasting excellent waveform fidelity independent of the varying load capacitance for superior print quality.

The Industrial Inkjet Printing blog was first published on apexanalog.com and was reposted here with permission.