Now, on top of the various inkjet, solid and liquid toner, nano – and of course litho – presses, we have an unlikely new entrant in the form of the Coventry-based start-up Lumejet and its ‘photonic’ print technology.
Lumejet first appeared in PrintWeek in January 2013 when it announced its inaugural product, the Lumejet S200 – a 250-A4-sheets/min printer that combined one brand new technology, the photonic digital printhead (DPH), with one that many assumed was destined for the scrapheap: silver halide (AgX).
At the heart of the S200 was Lumejet’s photonic printhead, an array of 300 LEDs (100 each for red, green and blue light) combined with a tapered fibre lens and associated electronics. The tapered lens enables the device to produce a four-micron dot – chosen for the approximate size of the photo receptors in the media – while the fact that silver halide uses the RGB colourspace, rather than CMYK, means photonic printing has a much wider gamut than other processes without needing spot colours.
In terms of quality, the device is in a class of its own, capable of producing an equivalent inkjet resolution of 4,000dpi from just 400dpi exposure, thanks to the fact it is a continuous tone (contone) process. Meanwhile, the micro-dots enabled by the tapered lens mean it can print very fine text, down to less than 1pt, without losing edge definition – even with reversed out coloured text.
Frank Romano, of the Rochester Institute of Technology, describes the result as “the highest quality printing I have ever seen”.
“This is beyond inkjet. This is beyond toner. This is where the material itself has the colour built into it and the quality of it is photographic in nature,” he adds.
The sample in question was printed on the S200, which uses a dual printhead travelling across the paper width, imaging a 12mm swathe with each pass. This device can print at around 24mm/second or around 1m in about 40 seconds. At that speed, it obviously isn’t designed for long runs or even medium runs, but rather for short runs of very high-end photo books or other specialist products for which quality is the prime concern and not cost, such as pitch books for ad agencies.
Next step
However, notwithstanding the fact that its first product is barely out of beta, Trevor Elworthy, director of innovation at Lumejet and inventor of photonic printing, has been busy working on the next iteration of the technology, the Lumebar: a high-speed device, incorporating multiple printheads across the full paper width. This has the potential to dramatically increase the output speed – from 24mm to 1.5m per second (the speed at which the DPH currently traverses the paper width).
However, it is not simply a case of bolting together a few extra printheads onto a bar the width of the substrate. The Lumebar will feature 14,400 micro-LEDs (4,800 per colour) versus just 600 LEDs on the DPH. This poses a significant challenge in terms of timing. “We use a constant current per LED and what is called pulse width modulation (PWM) to govern the time the LED is left on for,” explains Elworthy. “We should in theory be able to run the paper under the bar at 1.5m/sec, assuming that the micro-LEDs can produce as much power as the DPH and that we can time this number of LEDs in the same manner.”
This is where Lumejet is currently focusing its research – on the microLED and microLENs chip designs plus the associated drivers and bus architecture needed to achieve the required data rates. “On paper at least this all looks doable,” says Elworthy, with the caveat that a commercial product is still two or three years away.
An interesting snippet from the press release announcing the Lumebar, is the fact that Lumejet is already working with “leading labeling technology manufacturers”, suggesting not only a growing interest in the Coventry-based firm’s photonic printing, but also a potential lifeline for silver halide. Elworthy highlights the fact that Fujifilm is increasing capacity and the number of finishes it offers for AgX media, while Kodak’s document imaging and personalised imaging businesses have secured their future with their sale to the UK-based Kodak Pension Plan and re-launch as Kodak Alaris. That said there are obviously limitations in terms of the variety of AgX substrates available. “We are not sure if [AgX] is the correct media for high-volume labels or cartonboard, although it could be applied as a dressing layer,” says Elworthy. “But we are investigating new classes of photo-activated inks that may be part of a longer-term solution.”
Whether these inks work in a similar way to AgX in terms of containing photo-activated RGB dyes is the subject of an NDA, as is the process by which these inks would be applied – including whether the ink would be applied uniformly as a flood coat, or selectively (which could raise the prospect of some sort of hybrid process, perhaps flexo/photonic given the reference to “leading labeling technology manufacturers”) and whether this would be inline with the photonic printheads or nearline/offline.
Photonic printing has the clear advantage over inkjet and toner of being non-contact, which means it doesn’t face the same challenges at high speed around precise placement of fine droplets or particles in turbulent air. It also doesn’t have registration to contend with as all three layers are imaged at once. “And light travels at 300,000,000m/s – ink at 10m/s!” adds Elworthy. It may seem far fetched, but could it really be back to the future for silver halide?
