Interview with Dr. Vedran Durasevic

On the development of the fluids side we have seen analogue (screen, flexo, roto gravure) printing ink manufacturers as early adopters, and they have literally gone from having a single designated high-shear mixer for inkjet to a business model now focusing on the development of inkjet only. These companies have been able to transfer the know-how from their analogue business and build the digital. In the first instance, this meant transferring the raw materials from ‘analogue’ and positioning them into digital. However, since then a wide plethora of monomers, oligomers, and polymers have been synthesized to fit the requirements of, for example, quite small and narrowly distributed particle sizes and viscosities that are suitable for use in modern print heads.
In terms of the printer's development, the industry has moved away from the so-called SOHO (small office at home) printers to modern flat-bed, roll-to-roll, sheet-fed units which are used both in graphic and industrial applications.

Industrial applications are quite interesting, because there we see ceramic and silicone MEMS print head technology enabling high print qualities at high throughputs. At the moment, these print heads can easily be assembled in an array to provide the desired print width and incorporated onto an existing flexo line where they can easily print parts of the image/design/effect most likely to be changing more often than the pattern printed via flexo. Here we’re talking about QR codes, bar codes, composition, best-by dates, names, personal messages etc. However, the technology of today, both on the ink side and the machine side, is enabling the so-called ‘full digital’ solutions and there are presses out there capable of theoretically running at 300 m/min. In the future, we can expect the processes to run even faster, which will de-bottleneck for instance a fully automated filling line in which both flexo and digital are used to print the packaging.

It is no secret that digital inks per liter cost a lot more than their analogue counterparts. However, what people will often disregard is the fact that once a digital ink is delivered to the end user - either a printer or a converter - there is no altering the formula after a pouch, bottle, or container has been connected to the ink supply system. It needs to perform in a predictable and expected manner.

What’s attracting ink manufacturers is still a relatively high margin, and what’s attracting printers/converters is the ease of use. Don’t get me wrong here; the high margin is there (or a promise of it) for the ink manufacturer in case everything goes as planned. There’s a tremendous amount of behind-the-scenes work that goes towards making sure that the ink is suitable for sustainable jetting, i.e. is of the appropriate storage stability, particle size distribution, viscosity, filterability etc. There’s a lot of FMEA processes to be investigated prior to manufacturing batches of ink and shipping them all around the globe. For the end-user, the advantages of using inkjet are low initial setup costs, flexibility, web-to-print, capability of printing smaller series and doing it literally overnight. Of course, there’s also the shorter ROI period.

We are living in an era of global commerce, where goods are shipped all across the world. One of the challenges therefore that resurfaces quite often (every summer I would say) is the storage stability of inks. With printing inks we’re talking about chemically reactive systems designed to undergo curing under certain conditions (heat, moisture, UV). Therefore, there is a high concern that an ink/fluid system could be altered before reaching the end-user, spoiled and deemed unusable in a printing machine. And anyone who’s ever been working in the printing industry will tell you that the most probable culprit causing inks phase separation and gelation is the pigment dispersion.

To address this issue, we were very much like the early printing inks manufacturers adopters: able to build on our knowledge based on paints and lacquers. Over the course of time, we have developed dispersants and pigment wetting agents that support highly efficient dispersion processes and provide long-term stable dispersions suitable for the demanding requirements of inkjet applications.

Another commonly mentioned challenge is the wetting of low surface free energy substrates such as PP and PE, which comprise about 60% of the packaging substrates. Here we’re talking about substrates of around 30 mN/m, which is below the threshold that we consider printable (around 36-37 mN/m). These substrates will, therefore, need some sort of surface functionalization that will increase the surface free energy. This is usually a plasma or corona treatment; however, we also know that the effect of the treatment degrades over time, which is why it’s always best to have an in-line corona/plasma unit.

Our additives play an integral role in lowering the surface tension of the ink below the value of the free surface energy of the substrate. It’s important to say at low inclusion levels, usually even below 1%. Our additives lower both the EST and the DST of fluids and are particularly suitable for dynamic processes - such as inkjet - where surfaces are created almost constantly and the surfactant needs to have the ability of orienting towards these constant-forming surfaces. If we consider the flight path of the drop from the nozzle - spreading on a substrate and pinning - there is a window of about 100 ms in which the surface tension needs to be decreased to a point below the surface tension of the substrate. However, too low inkjet fluid DST values could cause jetting issues during hours/days of jetting as the ink could start wetting out the side walls of the nozzle which could cause dripping or flooding of the nozzle plate. So, I would say formulating a substrate wetting package that is incompatible enough with the fluid system (which will enable efficient substrate wetting) yet also compatible enough not to cause ink stability or jetting issues is quite an undertaking. Ultimately, there is no other way than preparing a number of formulations for respective ink systems and testing the jetting sustainability. There are some measurement processes that can be done prior to jetting to help a formulator, however, jetting sustainability will give the ultimate answer.

From the two topics mentioned here, I would like to say that Coating Additives has developed instrumental methods for determining the right pigment and substrate wetting additives package, that enable individualized approaches for specific pigments or fluid systems.

I’ve sat at both sides of the table. That of the formulator where I had a plethora of additives at my disposal, and that of a raw materials manufacturer. The approach to product development is the same and in both positions one confronts the same challenges. Being in line with the trends of the market, and being able to predict what the next big thing on the horizon might be, should be basic guidelines for both the raw materials manufacturers and their end-users.

At Evonik, we are diligently working to support the further development of inkjet by contributing to the next generation of additives enabling the development of even smaller particle size, lower-viscosity pigment dispersions with outstanding storage stability features, and eventually enabling the formulation of higher pigment loading inkjet fluids. Also, having recognized that the curing speed will be one of the areas in which both print head and print engine development will go, we are designing new molecules to fit with the criteria of the required highly reactive ink systems.

The number of ideas in our Innovation Pipeline is indeed vast and we certainly have the ability to recognize the so-called ‘golden nuggets’ of the industry. With highly competent and motivated people and with the inclusive nature of our values, we have the ability to tackle any challenge the industry has lined up.