Taking the cure

Ink got to cure, print got to dry. The whys are immutable; less so the wherefores. And as the converting industry is shortly going to discover: it ain’t what you do - it’s the way that that you do it; that’s what gets results.

Drying and curing inks and coatings at speed on the press is pretty much the de facto standard for most volume packaging print applications. Likewise, UV: not least due to its inherent fast-drying attributes resulting from the less penetrative interaction between ink and substrate; the hard, gloss appearance it engenders; and its capability to mask any risk of imperfections on a quality finish – arguably of considerable significance in balancing comparisons between flexo and offset.

Water or solvent based inks dry by a process of absorption that can take up to several hours prior to sending the print through for finishing. UV inks and varnishes, however, sit largely on top of the substrate – so curing is virtually instantaneous as soon as the UV light triggers a chemical reaction with photo-initiators contained within the liquid. The process technology is centred on the inter-decking of relatively power-hungry arc lamps at strategic points along the press.

Whilst there is a market for upgrades and retro-fitting, most UV curing systems are sold on an OEM basis as part of a total package via press manufacturers. “I would estimate that over 90% of all our packaging customers opt for a curing facility as part of the specification,” says manroland UK sheetfed systems sales manager Adam Robotham.

“Some of the larger groups may buy a press that’s prepared for a UV system, then go out and do their own assessment and fit it themselves – but the advantage in buying a one-stop solution is in the unlikely event of there being an issue with any of the component parts, then there’s just the one supplier to deal with.”

The integration of a curing system could amount to over 10% of the overall installation price. With a Roland 700 fully equipped with all the necessary bells and whistles costing about £1.5 million, the ability to dry inks on the run doesn’t come cheap. On a 6 or 7-colour + coating configuration, that would entail two or three inter-deck dryers plus a unit or two at the end of the press to cure the more viscous varnish top-coat.

Whilst inter-decking mitigates cost to an extent, as these dryers are relatively expensive, it would never pay to install one per station, says Mr Robotham: there are other ways of easing the production budget. With sufficient skill, a converter can restrict the application of UV just to the varnish by printing with conventional inks and adding a water-based coating to act as primer before running the UV top coat.

Careful maintenance will also prolong arc lamp life expectancy; another practical way of controlling ongoing cost. Manroland users can also take advantage of a software programme that automatically reverts the lamp to standby mode of 30% viability during wash-up periods, thereby reducing unnecessary power consumption.

GEW’s Green Timer software also aims to optimise stand-by power, already a low 15% of full capacity, and targeting the practice amongst converters of typically leaving a UV system on stand-by for long periods - instead of switching off - so that they are always ready to run when the press is started.

Commonly, this happens during make-ready and work breaks. Green Timer allows the operator to program the system to start automatically after the desired amount of time, and to power down after a pre-determined time on stand-by. In addition, the total number of hours in which the system has been ‘intelligently’ switched off is logged so that managers can easily quantify savings. GEW lamps can be powered on and off for an infinite number of times, so their warranties are not affected by the increased activities created by the software.

High output, low energy

According to IST UK MD Simon Mitchell, who supplies UV curing systems to most OEMs and is Heidelberg’s preferred partner, despite its cost the mercury vapour lamp is the established high output, low energy consumption technology. “Life expectancy of a lamp can vary considerably subject to rate of use, and standards of maintenance. We warranty 1,000 hours as a matter of course, but in reality a lamp can run for several more times that long without having to be changed,” he says.

Also amongst the market leaders as one of the first developers of UV curing, Nordson numbers Komori amongst its principal OEM customers. A recent notable refinement for packaging applications has been the work done by the company to reduce odour; a natural effect of photo-initiator interaction, which it has successfully cracked by introducing nitrogen inerting technology.

Mercury falling

Whilst it has proved to be a viable alternative to mercury vapour arc lamps in the USA, electron beam (EB) technology has had a less enthusiastic reception within the UK and European converting sector; this despite the versatility it affords, its capability with the more opaque coatings, and its significantly reduced power requirement. The reason has largely been down to price; EB systems can triple the cost of installation. There’s also a relative lack of awareness or understanding of the technology, one of the less-informed misconceptions being that lead shielding is required as an operational protective measure.

A more likely contender, however, is emerging from the digital inkjet sector in the form of solid-state LED. Leading the charge is 2009 Queen’s Award for Export winner Integration Technology Ltd (ITL), which claims to supply over 57% of the global market – largely as an OEM orientated business in support of the likes of HP, Agfa and FujiFilm.

That level of market penetration has been achieved as a result of a succession of informed hunches, says MD Adrian Lockwood. “We first saw the potential of digital inkjet almost 10 years ago, and to develop the market we had to design UV systems that were quite different from the ones that had been made before. Along the way, we predicted that it would extend into the broader-based packaging market. We also anticipated that arc lamps would become outdated, and started working on solid-state LED driven light sources six years ago.”

Having successfully commercialised LED UV in inkjet, ITL is now developing the technology for wider applications such as flexo and ultimately offset, confirms Mr Lockwood: “Although currently double or more the price - on a 330mm narrow-web flexo press around £15,000/unit, and capable of 120-150m/min curing speed – there are two key compensatory factors. Firstly, the price will fall significantly as semiconductors move into volume production; and secondly, there’s an on-going benefit through significantly reduced operational costs.” In effect, a higher spend on an LED solution equals a higher saving against the business.

“There’s a huge environmental case for LED as it uses considerably less power than an ordinary UV system,” he adds. “It depends on the application, but you’re looking at a minimum of 40% reduction, and arguably as much as 60%. Also, because LEDs switch on and off instantly, there are more opportunities for energy saving in operation. Basically, you shut the whole system down when you’re not printing. With an arc light system, normal practice is to go into stand-by, so even at reduced power they’re still running all the time. We can also reduce it for width: if you’re printing only half the width of the machine, for example, then you’re only using half the LEDs.”

There are still some issues with LED compatible inks: more a matter of availability than price necessarily. But with lamp operating life expectancy of up to 30,000 hours, and its presence as a viable alternative to the in-situ UV technology renewing scrutiny of mercury vapour lamps as contravening EU regulations, when Adrian Lockwood says: “I prophecy that this is the technology of the future,” given his track record it’s a claim to be taken seriously.

Whilst linking its LEDZero Solidcure system with OEMs, ITL is also enlisting established distribution channels to assist sales into sectors where it is less well known. These, inevitably, are where it can expect to meet competition from established UV curing suppliers. Notable amongst these are both Nordson with its UVED LED system - just launched into the web market and designed to work in arrays using standard modules of 62mm up to a maximum of 1,984mm - and IST with a new system due to be launched at IPEX in May.

Meanwhile, a near infra-red system (NIR) developed for the rapid drying of water and solvent-based inks has also emerged from the digital inkjet sector. “At the short-wave end of infra-red, there’s a very high power density at 800 nanometers,” explains Adphos UK’s MD, David Pelling. “At that wavelength, paper and plastics tend to be almost transparent to the energy, so it’s very penetrative through the ink or coating without raising the temperature of the substrate, while forcing the moisture up to the surface. Drying is virtually instantaneous.”

NIR has the same switch on, switch off power-saving facility as LED, and can be installed direct on the press in a similar configuration to a UV curing system. Entry point price for a basic NIR 120 inkjet solution running labels at 80m/min would be as low as £5,000/unit.