New inkjet technologies allow digital printing systems to be used in industrial print environments that were, until recently, largely the exclusive domain of screen or pad printing. Ensuring that an implementation of digital print systems is successful, a multitude of influencing parameters need to be uncovered and analyzed. This article will already point out some of the complexity and the considerations for finding the right print solution, by merely touching on a few technical aspects on how to decide on substrate treatment, inks and printhead selection.

Industrial screen printing environments have existed for decades. Pre-press workflows and print processes have been optimized throughout that time. Similarly, the traditional inks have been optimized to become perfectly adapted for their application requirements. From decorative or functional printing onto papers and cardboards, textiles, plastics, metals and flat and hollow glass or wood, the application range has become widely spread. Existing analogue production systems have since long been adjusted, improved and standardized to the point of satisfactory levels.

Meanwhile, inkjet printing has also evolved over the years, from the graphical large format printing market to a viable alternative printing solution in many of the aforementioned applications. Newer printhead technologies, new chemistries, inks and substrates made it possible for inkjet to become an economic replacement as a flexible, short-run alternative for traditional systems, even including industrial environments.

Crucial elements influencing print quality

We are all aware of the fact that there is a multitude of factors influencing the print quality in a printing process. But how can we correlate all single elements between screen and digital printing processes? What influence does a substrate pre-treatment have? Or a change of inkset? And what impact does the choice of printhead have on the functionality of a dedicated print system?

In order to implement digital technology into an existing screen printing production environment and fulfill all its requirements, a lot of questions need to be answered first.

What is the difference between print technologies?

There are many digital printing technologies available, which allow printing smaller production runs, variable data, doing quick job turnarounds and offering great technical features. But the key factor in industrial deposition or decorative printing is to select the right printing system for a dedicated application. One of the most crucial elements is to define the right printhead technology.

In screen printing, the influencing factors that define the print quality and functionality of a printed ink layer, are the selected mesh, the squeegee, the stencil and the ink, just to name a few. Each of these factors has its proper parameters, which will change the print quality. The hardness, the pressure, the angle and the speed of the squeegee, for example, will define how the ink is pushed through the stencil and the mesh onto the substrate. The analogies of these elements with Inkjet Piezo Technology are for example fire frequency, Volt levels and pulse shapes or in short: “waveform design” which will define droplet formation.

Can I choose the ink manufacturer I want?

Inks make incredible things possible, therefore they are an enabler but also a limiting factor, especially in inkjet.

In screen printing, there are numerous ways to alter viscosity, adhesion, drying and robustness of the ink by adding thinners and additives to make an ink perform better in the mesh and stencil, whereas for inkjet these tools area not available. Changing inkjet ink formulations by adding thinners or additives will have enormous impact on droplet formation and on print quality.

Screen printing inks are formulated with very high viscosity (can range between 20.000 to 50.000 cPs). These viscosities allow a big window of tolerance for late stage ink modifications on the print floor. Inkjet ink formulations need to be a lot thinner to be jettable (firing viscosities can range between 5 – 12 cPs depending on head type) and cannot be altered. The challenge of reaching the right performance of inkjet inks during printing, lies already in the initial formulation phase of the ink.

I have a print head and an ink, what about material pre-treatment?

To promote adhesion of inks to the material surfaces, a wide range of pre-treatment solutions can be selected depending on the material you are printing on. Solutions for material surface pre-treatment can either be physical or chemical treatments or the application of printable or spray-able primers and coatings.

Inkjet inks do not have “a lot of body”, so to speak, because they do not contain a lot of resin. The result is a less robust variant to the traditional ink solutions. It is therefore often necessary to use additional top-coats to promote the robustness of the ink. Applying protective layers onto the ink can either be done by using an additional piezo printhead or by spray gun or even by traditional coating techniques.

The needed solutions are mostly not available off the shelf and need to be developed specific to the process involved. Formulating new jettable primers and top-coats means inviting development partners that understand the characteristics and limitations of new technologies.

So how can I find a good digital solution for my screen printing process?

Digital printing technologies are increasingly replacing parts of production volumes from analogue printing processes. Thanks to the higher productivity of inkjet printing systems, it is becoming the preferred production process for many industrial applications. However, there are still a lot of industrial screen printing applications that have not yet shifted to digital alternatives because of the challenges in ink and printing system design.

Instead of going through a time consuming thin path of raw materials screening to formulate the best possible inkjet ink, an easier approach could be to go through a printhead technology screening and find out which technologies can be used with the existing screen printing ink formulations. Some inkjet print technologies are specifically designed for higher viscous liquids. This way, the ink characteristics are not influenced that much, and the advantages of a digital print solution may still be accomplished.

Finding answers and connecting the dots

Looking at the few above mentioned questions, it becomes clear that there are many parameters that need to be reviewed when wanting to convert from analogue processes to digital inkjet alternatives. Besides the obvious differences between print processes, more detailed and hidden specifications, limitations and possibilities need to be uncovered and addressed. And often, these are not that obvious.

In order to get access to specific know-how about suited inkjet solutions that match the intended printing process and production environment, and to the get answers on the many more questions about conversion of systems, it often proves more economical and quicker to connect with experts that have been involved in previous research and development cycles.

Independent expert cooperation LMNS was formed specifically to assist with product and business development questions as described above. LMNS, an ESMA technology partner and pan-European expertise network, specializes in finding the right technology, suppliers and solutions for the printing industry and connects the dots before one dot is printed.

_{This article was written by Jochen Christiaens, LMNS associate expert. Jochen has over 15 years experience in inkjet product development and support in chemistry development, color management and with defining dedicated inkjet print systems. He closely works with his network of printhead manufacturers, system integrators, software developers, institutes, strategic consultants and ink manufacturers. With international customers in Asia, USA and Europe, Jochen has led development projects and steered multi-level commercial and technical teams. Current projects include developments of inkjet printable glues and masking liquids for architectural glass decoration, single pass industrial and large format printing.}

_{More information about Jochen can be found at: www.inkjet-consulting.de}