Nano ink wars are nothing new
Published: 3 August 2014 | No comments yet
A simulation of a halftone dot of Landa NanoInk on paper fibres. The pigment particles are ‘tens of nanometres’ but the eventual ink film is about 500 nm thick
Has Landa’s Nanographic ink been pipped at the post by Kodak? No, argues Simon Eccles, as the two processes are fundamentally different.
‘Kodak beats Landa in nano wars!’ was the gist of the more excitable reports following the former’s June announcement of its new Prosper 6000C and 6000P inkjet web presses. A line in the press release mentioned ‘newly formulated nanotechnology inks, offering a greater colour gamut and delivering print quality that rivals offset output on a wide range of uncoated, coated, and glossy papers’.
Actually the Prosper ink pigments have always been nano. The Prosper 6000XL represents a major rethink in press configuration compared to the previous colour Prosper 5000XLi and the black-only 1000. Its ink is reformulated so it does not wear the Stream heads out so quickly, but the particles were nano scale all along.
According to Erwin Busselot, European marketing director for digital printing, ‘we were always nano’ since Kodak first revealed its Stream continuous inkjet head technology at the end of 2007.
Stream heads are used in the Prosper press range and the Prosper S-series imprinting units. For the inks, a micro-milling technique was developed to give very small, fairly uniform particles. They are in the 10 to 80 nm range, which helps to avoid blocking the 10 micron diameter (ie 10,000 nanometres) print head nozzles. It is just that the company did not think it worth stressing the nanometres (nm) in 2007. Given that Landa has been getting huge publicity for its nanotechnology claims, why not jump on the same bandwagon?
Benny Landa is a showman as well as the inventor of two digital offset printing technologies. At drupa 2012, his spectacular theatre presentations constantly emphasised the nanometre scale pigment particles in the NanoInk that underpins the Nanographic process. There is a lot more to this process than tiny particles, but nano was the hook he chose to hang it on.
After selling Indigo to HP for a reported $800 million in 2001, he set up Landa Laboratories in Israel to develop new technologies. A new press was not uppermost in his mind, he revealed last year: ‘When I set up Landa Labs I never dreamt I’d be going back into printing,’ he said. ‘But then we had this breakthrough with nano particles that enabled us to make nano pigments, and I had no choice, I had to go back into printing, because it was like the Holy Grail of printing. But this was in the context of research into nanotechnology for energy. We’ve had a big project running for over ten years, of thermal energy conversion. It’s still years away.’
Whether you would call this nanotechnology or not is open to debate. The original use of the term was intended to describe ways of manipulating individual molecules or atoms, including hypothetical sub-microscopic machines such as gears and levers. That is not what you get in nano-scale pigments, which are very small but essentially passive lumps of pure colour.
Visible light wavelengths range from about 400 to 700 nm and so the Stream and NanoInk particles are about a tenth of that. By comparison Xeikon says that the pigments in its forthcoming Trillium liquid toner inks are two to three microns (a micron being 1000 nm) and that its current dry toner particles are about seven microns. Typical offset ink pigment particles are around 500 nm.
A Kodak research paper dated 2000 includes a graph showing that pigment particles below 100 nm exhibit dramatically less reflectance/scatter of unwanted colours than conventional pigments, falling to nearly zero below 50 nm. This means that the reflected cyan, magenta and yellow colours are very pure and dense, so you need less weight of pigment to build up the print. Landa makes much the same argument for its NanoInk, with both companies claiming significantly wider colour gamuts than conventional inkjet or offset CMY inksets.
So yes, Kodak is already delivering inkjet presses with nanometre-scale pigment particles and Landa is not yet. But otherwise the two printing technologies have almost nothing in common. They work differently and they are for largely different applications, though with some overlap.
Prosper presses and inkjet heads all use Stream print heads, with a continuous inkjet system (CIJ). Ink is continuously pumped out of the head nozzles, where it is broken up into small discrete drops. The drops are directed onto or away from the substrate by an air knife. Unused ink is directed into a catch gutter and recirculated. This process is amenable to high speeds: Prosper 6000 presses can print at up to 300 metres per minute.
Continuous-flow heads are inherently resistant to blocking, which is important for single-pass inkjets, but early Stream heads turned out to have shorter wear lifetimes than anticipated. The new ink is intended to extend this life.
A cutaway of the Landa S10 web press, showing the four inkjet printbars building up the image onto the moving belt, which then transfers it to the paper web at the base of the machine
Longer head life
Because the heads are firing all the time, they have a more or less fixed lifetime in terms of so many hours. Prosper 6000 presses have a new and faster media transport system than the older 5000XLi. This means that you get more print through per hour of head life, thus lowering the cost-per-copy to about 0.003p per A4 page.
Kodak claims that the resolution (undisclosed but probably around 600 to 900 dpi) and ‘200 lpi equivalent’ print quality is the same as before. Both the 6000P (for publication) and 6000C (commercial/direct mail) presses can print at up to 300 metres per minute on matt and uncoated papers, while the 6000C has an enhanced drying system to handle heavyweight glossy and silk stocks at 200 metres per minute.
The alternative drop-on-demand (DoD) heads used by virtually everyone else, including HP for its T-series presses as well as Landa, only fire when they need to create an image. The lifetime depends on the image coverage and is harder to predict. Misfires and blockages are more common, though there are all sorts of measures to minimise these.
What makes the Landa presses really different is their use of an offset belt and the way this works with the inks. All other inkjet presses spray ink droplets directly into the substrate, where it dries or cures by heat or UV light, leaving the pigment bonded to the surface.
The Landa process uses off-the-shelf piezo printheads (though they are called ‘ejectors’) to jet into a moving, heated belt. The NanoInk comprises the nano-scale pigment particles that are coated or encapsulated by a heat-sensitive resin, in turn suspended within a water-based vehicle. The ejectors build up the image in mirror alignment on the moving belt, which then travels until it is brought into contact with the substrate (which can be paper, plastic or a range of other materials). As the belt travels, the heat evaporates the water, leaving the pigment inside the by now sticky resin. As it contacts the substrate, the resin transfers onto it. It is vital that the transfer is complete, so that the belt is clean when it passes under the heads again.
This is the clever bit, and means that a water-based ink can be used with a wide range of substrates at high speeds, while avoiding the high energy drying requirements and the risk of distortion that printing water directly onto paper entails. The process works with either sheet or web fed media transports, in a range of widths. The announced speeds are 100 metres per minute for the widest 1020 mm wide W10 web press, and 6500 sheets per hour for the largest B1 format sheet fed S10. Resolutions will be 1200 dpi, while Prospers are thought to be in the 600 to 900 dpi range.
There is no need for expensive special media coatings to control ink absorption and spread. While the Prosper 6000 models will work with offset grade papers, it seems that operators will have an easier life if an inkjet grade is used instead.
Mr Landa went into some detail: ‘All that I did at Indigo was to take offset printing and marry it to electrophotography, which nobody had done before, and made it work. All we have done now at Landa is to take inkjet printing and marry it to this offset process. Which nobody could make work before.
Taken from an early Kodak PowerPoint slide, this shows the size of conventional inkjet pigment particles versus the smaller Stream particles, alongside a Stream nozzle
‘The reason it’s not an obvious thing to make happen is this: in order for you to transfer an ink 100% efficiently from a blanket to paper, that means that the blanket surface needs what’s called very low surface energy. When you peel a label off a label stock carrier it peels very easily. When you stick it onto another surface it sticks tenaciously. That’s because the backing paper is like Teflon, it has a very low surface energy and it’s easy to peel things off it. That’s what you need for the blanket.
‘The trouble is, if you take a label stock and put a drop of water on it, you see that it beads. All those low energy surfaces are very hydrophobic, they repel water. So how are you going to make an image with water-based ink on a water-repellent surface? That’s what the magic is in our process. That’s what held it up for decades. There are patents from the 1980s envisaging ejection of ink drops onto a blanket and transfer to paper. None of them ever worked.’
The upshot is that Kodak really has indeed had nano scale inks for years, but it is only with this second generation colour web press that it is likely to really deliver the goods. Landa has not delivered anything yet, but assuming it works as predicted then its offset process will be substantially different and more flexible than any of the other inkjet digital presses to date. Remember that lithography did not really reach its potential until it went offset. Perhaps history will repeat itself.