For all digital print's many advantages, there are some applications that have remained stubbornly the preserve of more conventional processes. And this is a problem for anyone wanting to produce short-run jobs economically, while exploiting print's unique tactile and aesthetic qualities.
For print to compete with other media, it needs to play to its sensory strengths while addressing its cost weaknesses. If you want to add value to short runs, then you need to be able to do so without incurring the extra processing and materials costs that go along with conventional processes.
Some added-value print and finishing techniques have already been addressed by toner and inkjet technologies. Coating and varnishing, for example, both for protection and effects such as spot varnishing and even textured finishes, are available from the likes of Kodak with the Nexpress, Canon with the Imagepress C1+ and MGi and FFEI with their inkjet spot coaters. Spot colours are offered by several toner-based systems and many wide-format inkjet machines use extended-gamut inks to help to hit brand colours. Inkjet machines are also increasingly able to offer white ink for use with clear and coloured substrates, much as screen process and flexo do.
But one of the best ways of adding a bit of extra sparkle to print has proved to be particularly difficult: metallic finishes.
"Metallic is the last bastion of conventional printing," says Xaar ink product manager Jill Woods. "This could open up so many new applications for digital. You have to consider that both hot- and cold-foil stampers already run slower than printing presses. So speed is not such an issue as it is for printing CMYK - you always need to slow the press down. And there will always be less waste if you are producing metallics using digital than if using hot- or cold-foil."
So why have metal effects proved to be such a problem for digital print processes?
With the toner-based technologies (both the dry toner of likes of Xerox, Xeikon, Kodak, Canon, Konica Minolta et al and HP Indigo's liquid toner/ElectroInk technology), electrostatic forces are used to apply inks or coating, but that doesn't work with metallics as their conductivity means they leak the charge that is needed to hold them where they are wanted.
As for inkjet, it had been thought that the relatively large particle size of metallic inks would make it impossible for them to be fired through minuscule inkjet nozzles.
"The old school thought was that you couldn't do it because it would rip the printheads to shreds," says EFI's ink business general manager Scott Schinlever.
That is all about to change following research by pigment specialist Eckart, which claims to have cracked the problem of jetting metallics. Tucked away at last year's Drupa, the company was quietly demonstrating the work it has done in this area. Then much more prominently, at Fespa Digital in Amsterdam this May, it was showing further developments.
At Fespa it had two inkjet presses printing metallics: a modified Mimaki wide-format solvent printer, and a custom-made narrow-web UV-cured printing rig produced by UK engineering firm JF Machines.
"At Fespa the feedback was amazing," says Eckart's head of graphic arts digital inks Colin Appleyard. "It's absolutely clear that the market wants it. All the samples we could produce and all the product marketing literature was taken."
Of course, concept machines on display at a trade show are one thing, making production-ready metallic inks a commercial reality is entirely another.
Eckart has been working on bringing its metallic ink expertise into the digital realm for the past two and a half years. Appleyard says the chief question was economics, not technology, and that previously the market wasn't large enough to make development worthwhile.
"We decided the market was ready. We did a study and proved that we could make a flake that could jet," he says.
Eckart has since been working away behind the scenes with all the major printhead vendors to ensure its pigments and the inks made from them will be suitable.
"We've tested the ink in Epson, Konica Minolta, Spectra, Toshiba Tec, Trident and Xaar printheads," says Appleyard. "All of those have been tested under lab conditions and some have been beta tested in production machines."
Beta tests
He remains tight-lipped about which printer vendors the firm is working with, although the solvent ink is already in beta testing and the UV ink has been run on a couple of wide-format multi-pass printers plus a couple of card printers.
Eckart will be in commercial production of its ink this summer. As the route to market will be via digital equipment manufacturers and ink suppliers, Appleyard can't be specific about what the first commercial products will be and who they will come from.
"We have great expectations and we can say that in the last quarter of the year there will be metallic inkjet products in the market," he says.
The printer vendors also are remaining tight-lipped about their involvement.
"We're keeping an eye on it. We've seen some demos and it looks good," says EFI's Schinlever. "We're looking at it. That's all I'm comfortable saying."
While Eckart has focused on bringing a solvent ink to market (and one that has been shown on a wide-format machine), it is label and packaging printers that have the most to gain from such a technology and who will probably be most interested in the UV-cured ink.
"In super-wide format, most customers are happy with process colour," says Schinlever. "But there's definitely interest from the flexo, screen and narrow-web side."
Retail aid
Xaar's Woods agrees that packaging will be a primary market, but she feels that metallic inks will also prove to be very appealing to one of wide-format's biggest applications, point-of-sale (POS) displays.
"For luxury packaging, metallic inkjet would reduce the need to use analogue print processes and to print more than is needed," she says. "When brand owners have the ability to print metallics digitally, it will become available for use on POS displays, rather than the current faux metallic finishes. Basically if the process helps them to sell products, then brand owners will use it."
She also believes it will be attractive for other applications, including greetings cards. Many cards use metal or foil effects and, increasingly, personalised digitally printed cards are sold online, although at the moment it's impossible to combine personalisation and metallics.
Woods also reports strong interest in digital metallics for use in combination with various varnish effects and with process colour.
However, Eckart's decision to show its narrow-web test rig points to the importance of the packaging and labels market for metallics. The JF Machines press was fitted with Xaar's latest generation 1001 heads, which are already used in machines serving this market such as the Nilpeter/FFEI Caslon and the EFI Jetrion 4000.
"The Xaar 1001 printhead is designed for single-pass printing and by far the biggest market for metallics is primary packaging and decorative labels," says Woods. "We feel it is a very good fit."
As the technology stands, printers still have to make an either-or decision about whether a product would benefit most from digital production or from the added impact of a metallic finish. Come the end of the year there will be no need for compromise as another analogue process falls under digital's cross-hairs.
INKJET METALLICS
Metallic inks use flakes of aluminium to produce a silver appearance. Achieving a highly reflective result is dependent on getting the flakes to lie flat on the surface to create a mirror-like finish. The key to that is the shape of the flakes – they need to be very thin relative to the surface area to ensure they lie flat. Typical flakes in conventional inks are around 10microns across. A micron is a millionth of a metre. For comparison, a human hair is 100microns thick. Inkjet nozzles are in the region of 20-70nm wide, which means particles of the size of the flakes used in conventional inks risk blocking the printheads.
Metallic particles are almost designed to block printhead nozzles, says Xaar ink product manager Jill Woods. If you get the shape wrong then they don’t lay right on the substrate and you get a dull grey result rather than something shiny. The biggest challenge is to get the particles small enough to jet, but to still retain the distinctive shape needed to produce a high gloss.
Eckart’s breakthrough has been to develop a proprietary process to make particles of the right size and shape.
They’re nanoflakes, says Appleyard. These pigments have a thickness in the nanometre scale and a particle size of 2microns.
Another crucial factor is ensuring a narrow particle-size distribution.
With standard pigments, 98% of particles are in spec and 2% are outside, and that’s acceptable, he says. In this case you need to get rid of all the particles that are bigger than average. Just one that is too big would kill a printhead. Multiple particles could block many separate printheads.
Inkjet printers use filters in the ink lines to stop oversized particles or particles of the wrong shape from reaching the printheads, which presents another challenge for Eckart.
Many of these filters are designed to let round particles pass, but not a flake, says Appleyard. It may be necessary to change the type of filters used in some systems to ensure they work with our inks – that’s why we need to work with equipment suppliers and not just the vendors of the print heads.
