Getting the right double-act

In former times, when discussions evolved around UV-curable printing the emphasis tended to lie on the ability to output direct to rigid substrates. These, after all, were the machines and inks which enabled users for the first time to print reliably onto all manner of materials up to reasonable thicknesses. In the wide-format inkjet sector there was a pressing need to be able to use a durable ink formulation on all manner of media, including wood, metal and corrugateds as well as more conventional sign-making materials. Solvent-based inks could play their part in the roll-fed sector where longevity of output was required but, with pre- and post-heat being needed in the drying process, it was obvious that many display products would be rendered unusable.

Flatbed wide-format inkjet printers first came into being nearly ten years ago, but even some of the very earliest of these had a combination feel to them. Think back to the Z?nd 215C and there is testimony to an astute belief that users moving to UV-curable output were going to want more than a means of printing onto boards.

Since these early days, we've witnessed UV-curable printers of all shapes, sizes and capabilities coming to market and, as this ink type became more popular as users wanted to move away from systems which emitted hazardous chemicals, so printer manufacturers complied with demand. At the high end of the manufacturing ladder, Inca Digital had only ever opted for UV-curable formulations in its machines whilst others in those days, such as NUR Macroprinters, and Vutek, had been busy with their solvent-based options. Changes within the industry saw consolidation of companies which brought together the good bits into a larger pot, and the timing for many of these acquisitions seemed neatly to coincide with a perception that UV-curable printers were going to grow in popularity and, in many cases, supersede their solvent-based counterparts.

Today, all the top-end manufacturers concentrate on UV-curable inks for the bulk of their equipment and, until a viable alternative comes along, the only true variations we're likely to see are in more refined formulations and improvements with the curing itself. Although the ability to print direct to rigid materials was an enormously tempting carrot for users across all sectors and every budget, it was inevitable that efficient ways of printing to roll-fed media had to follow.

This transition from flatbed to hybrid wasn't as simple as at first believed by print service providers. This type of unit needs to be able to work with rigid media and roll-fed materials and its design and construction needs to be conducive to ease of use with both types of media. More dedicated flatbed units often have the option to print onto flexible sheets but not all include a roll unit and, for those that do, there can be a limitation in the width of the printable area being less than the bed maximum. This might be fine for some users but many want to be able to handle rolls and rigids up to the optimum printable size offered by the system so, for these people, a true hybrid is what's needed.

Thus, there are many considerations required in a combination unit which offers no compromise between flexible or rigid media. The formula used in the development of these machines follows a basic principle, whether one is investing in a high-end Durst or an entry-level Agfa Anapurna. The printer must have the ability to handle and work with rolls of material as well as having the power to cater for heavyweight rigids, with all media passing from the rear of the machine, through the printing process and onto a stable platform once the job is cured. Options can include roll-to-roll and roll-to-sheet or a rewind unit for finishing away from the machine whilst, for rigid and flexible sheet materials, it's essential that there are feeding tables on both sides of the printer for accurate, stable delivery of the application before and after it's been printed.

Hybrid units tend to have movable tables which can added or taken away according to the media length, with many offering extensions to enable longer through printing to be accommodated. Again, Durst's continuous board printing feature means that successive sheets can be fed through the machine to allow contiguous output and, in this instance, a job comprising several panels can have guaranteed colour accuracy throughout all sections as it can be produced as a single application.

Even heavy duty options, such as EFI Vutek's existing QS and recently introduced GS 2 and 3.2 m flatbed printers offer easy manoeuvrability of its flatbed tables which, despite their sturdy design, are able to be removed by a single operator when a roll-fed application is needed. However, the logistics of loading a new roll of material involve considerably greater weight than merely shifting a couple of caster-based units out of the way and it goes without saying that, the wider the print area, the heavier a full roll is likely to be.

Even the lowly priced UV-curable printers need to have a good feed system which conveys the material in a stable manner through the production process, and combination systems cannot cut back on material handling for rigid and flexible media. Because of the processes involved, with printing being followed immediately by the curing, the nature of a hybrid system must take into account both the roll-fed performance and the ability to work with different thicknesses of sheet substrates. With the former, materials need to be held absolutely flat and steady across the printing area to produce even distribution of ink but, also, to prevent head crashes from the edges. The variation in thickness of products also means that there must be adjustability in the height of the printheads and, whilst this is often carried out automatically or electronically in more expensive machines, manual options are more common in lower cost models.

One of the disadvantages of some of the less feature-driven hybrid systems has been their inability to work to precisely optimised printhead heights and specific positioning of the material on the table. With an increasing range of substrates now being output using UV-curable inks, and demands likely to continue to increase in the foreseeable future, the ability to work with a wide range of thicknesses become ever more necessary. Similarly, it is difficult to standardise on any of the media currently available as different UV-curable inks and their curing parameters can vary which, if not set up to provide the best performance obtainable, might well affect adhesion and result in cracking and flaking.

Many of the businesses moving into UV-curable printing simply don't have the space to accommodate a dedicated flatbed machine which, because of its table design and functionality, necessarily has a large footprint which cannot be compromised in any way. Bigger organisations that have invested in systems such as those from Inca Digital and HP are normally in the type of production environment that had needed to accommodate screen-printing or offset litho presses. But for the many sign-makers and display producers operating from small premises, the size of a printing system is as crucial as its capabilities.

Certainly machines at the entry level of UV-curable printing, and which offer hybrid capacity, are priced and configured to suit users on a low budget but, of course, these will not offer the speed of throughput found in their senior counterparts although many of the current models can produce perfectly acceptable quality. Agfa has been particularly successful with its Anapurna series in this category, with individual members of the range offering varying options including white. Mutoh has entered the market with its Zephyr which, again, carries an attractive price tag. Another notable entry-level option is the Mimaki UJV-160 which comes with a choice of flexible or more conventional hard inks and features LED-curing. These 1.6 m options are targeted at users who want to print both to roll-fed and rigid materials.

Because of the additional strength in engineering and handling capabilities when printing to wider sizes, there is generally a noticeable price jump between a 1.6m entry-level machine and a 2.5m model. Not only are design parameters needed to ensure stability of material handling, the printheads have further to travel on each pass and, thus, must be configured in a gantry which allows them to travel consistently for uni- and bi-directional modes in all quality levels. The more solid the build of machine, the higher the chances of longer term reliability and you tend to get what you pay for. A machine such as the Screen Truepress Jet2500UV, for example, won't fulfil the budgetary requirements hoped for by many wanting an entry-level printer but its solid build provides reassurance of the quality it can produce.

Fespa Digital earlier this year also brought forward a rash of new options, from various manufacturers dotted around the globe, and this confirms the continuing upward trend across all price brackets for hybrid UV-curable printers. Whilst many users set out with the intention of printing direct to rigid substrates, the temptation of being able to output to roll-fed materials secures the popularity of these combination machines.