Over the years digital print has gained increased acceptance across a range of markets, both augmenting and in some cases supplanting the incumbent analogue printing methods. But if we take a historical view, some of the most successful implementations of inkjet machines have relied on combined technology approaches. For the purposes of our discussion we are calling these hybrid processes. In the main part they are single pass and have been designed to maximise application suitability by using rollers and inkjet heads from the start.
Some of the first machines to combine inkjet and flexo were applied to the label market and appeared very early in the industrial inkjet era of the noughties. Drupa 2000 saw demonstrators of Barco’s The.Factory (“dot factory”) as a standalone printer, but it was not long before the potential of combining this with flexo UV was captured with the Mark Andy DT2200. In fact, the retro-fit approach has been provided a steady income for inkjet integrators ever since. But these machines were not developed as an optimum solution and market acceptance relied on the inkjet print being perceived as having sufficient reliability not to hold up the analogue print.
For this reason, much of the rise of industrial-scale inkjet has taken hold in applications where the substrate can be a little more forgiving. Paper is a good example of this and the number of printers tackling the production inkjet space, like the Océ Jetstream, grew quickly in the space of Drupa 2000-2008, with new head options like Kyocera KJ4 opening the market. At the same time of course HP were busy pushing the boundaries of their TIJ technology into the same space in their Web Press platform.
In about the same timeline the Nilpeter/FFEI Caslon press and the Dotrix Modular, Agfa’s evolution of the dot factory both combined UV inkjet and UV flexo to create a value proposition that leveraged the benefits of flexo to mitigate the limitations of inkjet. In the former case, flatter spot colours could be produced at a lower cost per label, whilst for the Dotrix, the substrate applicability could be widened to accommodate the ink surface tension required by the print head. The approach is analogous to that other well-known HP technology, Indigo, which was using pre-coats and lacquers to overcome the limitation of the EP materials.
In a way, labels have always been a test bed for the flexible packaging dreams of the future. Indeed, packaging was already the target when the author joined the world’s biggest inkjet company bank in 2007 to help develop printers and, more critically, print processes for digital printing of labels and corrugated board. What became clear early on is that it was difficult to explain to converters why they couldn’t use their favourite (low cost) substrate even thought they paid multiple times the ink price. For this reason, the concept of priming became a theme for our work which was not always popular with the existing inkjet solution provider. Why work with the competition when we want to replace them? In practice though, reformulating a primer to get a different substrate function is a much more reasonable R&D program. One example of this was getting FastJet’s corrugated-focussed UV inks to adhere to polypropylene sheets by use of special primer.
Décor printing with UV inks is also a process relying on the integration of roller coating to prove the necessary base coating and protection that simply is not possible with the inkjet chemistry alone. Printing edge bands and MDF panels both benefit from this approach which extrapolates to lots of potential applications, like metals and glass, although outdoor lifetime is generally ≤ 10 years with organics pigments.
Many years later, with experience under our belt and amazing leaps in printhead technology and the true power of hybrid approaches is becoming clear in a range of markets, especially where the market is now demanding more sustainable materials and the drive is to water-based inks. What is clear from looking at the machine design is that you can’t make a printer and then decide which process you going to have a go at applying it to. This has the been the mistake of some OEMs who have developed their inkjet technology for one market and are looking to apply it to another by changing the ink. We can demonstrate this with some examples.
Production print onto coated paper stock has had to accede to pre-coating, and doing it inline make more sense from an active process control perspective. The Ricoh VH60000 is an example of this sort of implementation. Using a controlled pre-coating layer with a chemistry that increases the colour potential of the inkjet dispersion increases the cost-per-page, thus improving the return in investment. The drying must be able to adapt to the ink chemistry being used, and sufficient drying “footprint” should be allowed for balancing the needs for an energy efficient process with keeping the heads healthy.
In décor, there is an appetite for gravure-replacement in pre-print for high pressure lamination, for example. In this application the printer is not just helping the colour, it can provide some of the lamination function, thus making the process work. This is perhaps the most important example if we extrapolate to flexible packaging. Many of the challenges are common: varied substrates, different post-process conditions & expectation of high speed. Changing for ink for each material is obviously not an option. But doing that with the pre-coat is slightly easier to contemplate. The same goes for printer for corrugated packaging, whether UV post-print or water-based pre-print.
So, what does this mean for our “new” target of flexible packaging with aqueous inks? Well the first lesson is don’t assume you are building an inkjet box. Going hybrid with your process and thinking about the solution in modular design terms is likely to make all the difference to the market acceptability of the output. Many existing inkjet presses tend a standardised in-line head arrangement, whilst the analogue printing used a range of architectures. Is something like the below even possible?
Remember that for piezo drop-on-demand print heads being adopted in most machines, the service life is expected to be years (not months) so being able to balance the maintenance of the inkjet system relies on understand the head’s interaction with the ink in some detail. Trying to get an inkjet ink to dry quickly means that the heads has the chance to dry too and overloading the chemistry with functional materials means that can be a bad thing.
So, if we distil the learning of almost 20 years of industrial inkjet in single pass: don’t design a machine without at least some idea of the balance between these properties made possible by the fluids that are going to be used. Gaining methodical understanding of the print process is the key to “form follows function” when it come to a printer design that gets the best out of the chemistry available.
Mark Bale will present an invited talk - "Importance of hybrid print processes in the digital evolution" - at the IMI Europe Inkjet Development Conference, 17-18 April 2018 in Frankfurt, Germany.