Yet in some ways the advances in flexo have been more exciting than those in litho. 

In the narrow-web sector of flexo that’s largely used for labels, many of the advances have been in hybrid technologies that integrate a digital print engine onto a modified flexo press chassis that provides the material transport and can also incorporate conventional flexo, screen and finishing units inline. This is leading to a shift in emphasis to mid-widths for pure flexo presses, says Phil Baldwin, European sales manager for flexo press maker Mark Andy. “A lot of the traditional narrow-web market is being taken by hybrids or roll-to-roll inkjets. The reason Mark Andy has concentrated on hybrids here is that customers can have digital, or flexo, or both. However, the pure flexo technology is moving to mid-web widths of 510, 560, 580mm, for non-hybrids. 

“They are taking the benefits of narrow flexo over the past five to 10 years of no-waste automation, with AI de-skilling the press, basically. You can have the benefits of narrow-web but now within mid-web. Meantime the widest webs, 660mm, are likely to decline as run lengths come down.”

Baldwin reckons that food packaging is the weak spot for inkjets. Xeikon dry toner and HP Indigo liquid toner digital presses have food-safe inks, but they are much slower than UV-cure inkjets. Baldwin says: “With inkjet, even with an approved low-migration ink, over a certain amount of coverage it isn’t going to pass the migration test. It’s a matter of how much uncured photo-initiators and other components are left in that volume, which is much more than in a thin flexo ink film.

“This is where flexo can still beat digital, in the mid-web arena. You can use barrier films and things with digital, but the best way is just to go flexo.” 

Rebalancing the market

Digital has no plate costs, but inkjet inks cost three to four times as much as flexo, Baldwin says, so there’s a broad balance of costs. “I think in the next three to four years the narrow-web label market will become predominantly inkjet or hybrid, with flexo complementing it for longer runs for many years to come. But the all-flexo presses will be mid-width and that will become the predominant space.”

Since around 2013 the multi-developer Revo alliance has overseen the development of what it terms ‘digital flexo,’ meaning that all aspects of the pre-press and press operations are automated and computer controlled. Revo comprises Bobst (flexo presses), Esko (pre-press workflows), DuPont (flexo plates), X-Rite (colour measurement instruments), AVT (verification systems), Apex International (anilox rollers), Flint Group (inks) and UPM Raflatacs (label materials). 

The original press supplier in Revo was the innovative Italian press maker Gidue Nuova, which was acquired by Bobst in 2015 and incorporated in its Italian Bobst Firenze operation. Gidue and now Bobst developed the narrow and mid-width M-series of flexo presses that are highly automated, with pre-loaded cylinder changes on the fly as the previous job completes, resulting in instant job changes with only about half a metre of waste. 

Federico D’Annunzio was president of Gidue and is now Bobst’s senior press innovation advisor and hybrid programme manager. 

In April Bobst announced what D’Annunzio says is the “last mile” in the digital flexo project, a new inking system called Ink-on-Demand (IoD). This replaces the standard flexo unit’s ink tray with a digitally controlled ink dispensing system and automatic wash-up. The result is a dramatic reduction in the amount of ink circulating in the system, explains D’Annunzio, using just 30g of ink compared to 1.5 litres in a conventional ink tray system. “It’s a one minute operation to clean and replace 30g of ink,” says D’Annunzio.

This makes it much quicker and cheaper to change special ink colours between jobs. However, it also fits in with another Revo system, which uses a ‘fixed duct’ seven-colour process ink set, instead of special colours. 

This has also allowed this year’s introduction of a new automatic ink density control method, says D’Annunzio. “Instead of running one ink per print unit, we feed two inks, one extremely dark and one extremely light. Then we mix them before going into the print unit. Let’s say I start with 50-50, and if I see that I need it darker, I adjust the mix to 70% dark and 30% light.” The whole system is monitored by a spectrophotometer on the press so colour adjustment is completely automatic on the run.

Bobst’s technologies seem to have taken the potential of automation the furthest so far, but other companies aren’t far behind. Mark Andy’s most automated mid-range presses are the Performance series. These can also run fixed duct seven colour process inks. “The idea was to go up against digital, i.e. HP or Xeikon,” says Baldwin. “So we have very small print repeats of 5.5 inches, so you run one round instead of three around.” 

The UK’s own Edale has developed its own AiiR technology for its Fl3 and FL5 flexo presses, standing for Autonomous, Inking, Impression and Registration. It is a camera-based, closed loop inspection system which will bring the print into register without operator input.

Pre-setting of Edale and Mark Andy presses allows the next job to be set up on unused units. In theory this can be done while the previous job is running, though Baldwin is dubious about the safety implications. “It only takes 30 seconds to change a cylinder. We stop the press, remove the cylinders and put the new ones in. We have pre-register that brings it very close and automatic register for when you’re running.”

Koenig & Bauer Flexotecnica presses also take advantage of the past decade’s improvements in flexo quality, as well as seven-colour fixed palettes. “Our CI (central impression) presses used for flexible packaging don’t follow the same path as narrow-web label presses,” says Richard Warnick, sales manager. A recent development has been automatic impression setting that works from zero speed, which K&B has applied to patent. “We will show a new design of press specifically for quick turnrounds at the K Show in October,” says Warnick. Details haven’t been announced yet, but he says “it will be printing there, not just a mock-up”.

Argument for in-house

Traditional flexo platemaking is still often handled by outside service houses, but fast turnround flexo will inevitably drive demand for more plates, more quickly. Adopting platemaking in-house is a logical answer, though the cost of this is actually leading some flexo converters to choose entry-level digital presses instead for fast turnround work, says Baldwin. 

Chemistry-free thermal processing using heat and an absorbent blanket to remove uncured polymer is a much faster alternative to solvent washout. This process was originally introduced by DuPont in 2002 with its FAST system. Others followed, such as MacDermid with LAVA, and Flint with nyloflex Xpress. No drying is required, although a final UV blast is still needed to de-tack the polymer.

Aqueous washout is the main fast alternative, though favoured more in Japan and the far east than in Europe and North America. This uses hot air knife drying and is quicker than solvent washout as water isn’t absorbed by the polymer. It allows very small highlight dots and is better than thermal (although that’s improving). Asahi is the main promoter of aqueous plates in Europe, with its Flenex range. 

Both thermal and aqueous plates can be laser imaged and processed in less than 90 minutes. Once produced, plates can be re-used, with up to four runs being typical. 

Digital platesetters for flexo mostly use powerful lasers to ablate a LAM (laser ablation mask) that is factory-applied to the plate surface. Kodak’s Flexcel NX system – now sold by spin-off business Miraclon – is different in that it images a film the ‘thermal imaging layer’ of which is subsequently laminated onto a bare plate. Either way, after imaging the plate is exposed to UV light top and bottom to harden it, and then processed to remove unhardened polymer. 

Esko’s current CDI XLS Crystal range is particularly suited to in-house use, says Pascal Thomas, director of flexo business at Esko. It combines a CDI LAM laser platesetter with automatic transfer to an Esko LED UV exposure unit for both back and top layers. “Printers don’t want to fiddle with curves and tuning UV energy and lasers,” Thomas says. “It has to be a simple process, a one-button solution where a plate comes out and they have to be able to trust it. These people are paid for the printed plastic they ship, not the plates they make.”

Fully automatic lines combining processing are possible, says Thomas. “At Drupa 2016 we showed a completely automated system targeted mostly at trade shops. It was connected to a solvent processor. Next Drupa we will connect to another type of processor – I can’t tell you what but it should be something interesting!”