For several years now, inkjet printing has been an integral part of the international print market. It boasts a number of advantages in comparison to the more traditional printing processes – especially for UV users.
The main difference between inkjet printing and other printing processes is that there is no printing form required for transferring the image to the material. The image is printed directly and contact-free onto the substrate. This is done using what is known as a “Computer-to-Print” process. Inkjet printing distinguishes between an image format in just one flow (single-pass systems) and an image format in several flows (multi-pass systems). With the single-pass system, the quality of the print is restricted by the resolution of the print heads, whereas the multi-pass system achieves greater print quality, however at the expense of productivity. In terms of technology, the inkjet process boasts the most compact tools for transferring information as a printed image to the substrate.
There are two different options when it comes to applying ink, which in turn also offer further possibilities. For the continuous inkjet process, a continuous flow of small ink drops is created. Depending on the image to be printed, they may also be electrically charged to some extent. Any drops not required are diverted and collected; the drops required continue on to the substrate. With the drop-on-demand process, an ink drop is only created once it is required for the image. There are two different options here: Either the ink drop is created by heating or locally evaporating a liquid in the nozzle chamber (thermal inkjet), or the drops are formed through the deformation of what is known as a piezoelectric crystal. This is attached to the nozzle chamber and is deformed by the electrical voltage. The drops are formed from the resulting excess pressure, catapulted out of the nozzle chamber and onto the substrate (piezo inkjet). With the development of this type of colour application, the advantages of UV technology have also been made accessible to the inkjet printing market. In contrast to thermal inkjet systems, piezo inkjet systems facilitate higher frequencies and a greater variety of colour formulations.
It is mainly low-viscosity (liquid) inks that are used for inkjet printing. Depending on the print head, this means a variety of layer thicknesses can be used when applying the ink, resulting in very high quality prints. The use of UV inks for inkjet printing also has a number of further advantages which contribute towards increased output and process safety. Through the development of coordinated UV ink systems and suitable print heads, a superb result can be achieved with regard to ink resistance, resistance to fading, as well as chemical and mechanical stability, without any additional coating or lamination. UV inks are 100 percent solid formulations. They do not contain any solvents and therefore cannot dry out. There are no unpleasant odours or health risks posed by the inks, and legally stipulated limit values are met. There is also less maintenance and cleaning work required at the printing press as UV inks are only cured when in contact with UV light.
Almost all materials can be used for inkjet printing. As it is a non-contact printing technique, even 3D materials, complete with angles and curves, can be printed directly. Under certain circumstances, pretreatment of the substrate is required to avoid any “running” of the inks and guarantee sufficient adhesion of the inks on the surface. UV technology makes it possible to print across a wide substrate spectrum. The split-second curing of the ink means products can be processed immediately afterwards. UV systems also boast high process reliability and limited print quantities can be produced economically.
The first application areas for inkjet printing were coding and marking (e.g. the printing of best before dates on food packaging) in continuous inkjet printing and using solvent-based inks. In the meantime, the scope of application has increased considerably, also in the area of UV, thanks to improved inks and technology, and can match the standard of quality met by analogue printing techniques. There is no analogue printing plate required for inkjet printing, thus making it possible to print various information on a substrate without any major complication. This is particularly effective when parts need to be personalised or consecutively numbered. Inkjet is recommended for small print runs and/or content that changes at short intervals, e.g. for mailings, signage or in commercial printing and limited print quantities. Examples here include posters, placards, banners and signs, maps, bar codes, numbering, best before dates, direct mail and business papers.
With high-quality, non-contact printing on the most varied of materials, completely new application fields have opened up for industrial printing (direct printing on industrial products). The integration of print heads has made inline printing of the necessary content or graphics directly onto the end product possible, saving both time and resources. And, industrial inkjet printing is not just restricted to the graphic design of a product. Increasing improvements in head technology and precision machinery have since made it possible to print defined, extremely thin or delicate, functional layers in the semiconductor industry. There is also a trend for 3D printers, which can inexpensively produce single editions of any 3D products using inkjet technology. With regard to UV finishing, hybrid solutions comprising standard and LED UV technology are opening up new possibilities for special haptic effects on printed products. By combining LED UV units for what is known as “pinning”, the pre-curing of inks during the printing process and a standard UV system for end of press drying, optimum results are achieved. Thus opening up another niche for special print finishes.