Need For Speed

By Graham Galliford //

San Diego, California, USA -- As we are greeted by Jeff Bean, VP of Brand and Communication for Memjet, it is clear we are entering an environment of new technology and innovation. The energy present on Memjet’s premises can be felt from the moment you step over the threshold: one has obviously stepped into Memjet’s world of new technology and innovation.

For more than 15 years, the page-wide ink jet array based technology has been observed by industry pundits who have sometimes struggled to pierce the veil of mystery surrounding the new technology that was the subject of curiosity, speculation, enthusiasm and, from some quarters, doubt. I felt very privileged to have been invited to visit Memjet recently, to discuss in depth and at length the technology behind the “Memjet miracle”.

Historic Perspectives Shattered
Throughout the more recent history of digital printing, there has been the discussion about the potential for the supremacy of one of either ink jet printing or toner based printing technologies. Historically, the two competing digital printing techniques have had their advantages and disadvantages. During the past developments of these technologies, this has meant that, while there has been some overlapping application competition between these two techniques for instant printing, there have been application areas that have been the exclusive province for each. Ink jet printing, for example, has been able to economically address full-color printing for decades in contrast to the much more recent economically available toner-based print solutions. Ink jet printing has also been able to address the needs of the printing community for the instant printing of full color prints. We typically refer to both ink jet printing and toner-based printing as non-impact printing. However, ink jet printing is actually the only true non-impact (strike that for non-contact) printing technology in current use. Toner-based printing needs contact between the medium and the final toner transfer step to create the image on the media. This differentiating factor has enabled some bizarre but interesting technology demonstrations such as printing on an egg yolk using an ink jet printer.

On the technology downside, there have been the limitations for ink jet printing technologies of slow print speed and limitations in the media able to be used due to the need for the absorption of liquid from the ink jet ink for “drying”. Solutions to these limitations have been the subject of technology research and development efforts ever since the technology emerged from the lab into common use. There have been such successful developments as hot melt ink jet to overcome the media limitations and the development of ink jet array based printers to overcome the speed limiting “head shuttling”. Memjet has, without doubt, been the most successful practitioner of the array head as a means to increase speed.

In actual use printing on rigid surfaces, conductive media such as metal and irregular objects like electric wiring, has been the exclusive province for instant printing of ink jet technology. With the development of the technology to break down the historic barriers for ink jet, it is no wonder that it has found use in all in the following fields:
- Bar Code Labels
- Business Documents
- Business Forms
- Business Photos
- Direct Mail
- In-house Marketing
- Indoor Signage
- Packaging
- Production Graphics
- Publishing
- Retail Tags
- Secondary Labels
- TransPromo
- Well Log Printing

With models using Memjet, custom designed by their engineering partner company, there have been implementations or high speed production printing of continuous roll fed media for such things as labels as well as, on the other hand, high speed wide format printing for posters, engineering drawings, plan printing, etc.

The Memjet Secret

The secrets to Memjet’s success lie in its printhead design which has also demanded their development of a new controller chip and software. Memjet color printheads use what they call "waterfall" technology. The array printhead has 70,400 jets that can eject millions of ink drops per second, which the company claims enables print speeds up to eight times faster than competing technologies. The printhead enables an 8.77 inch (222.8 mm) printable width and can print at two different speed rates in the current two different modes, 6 inches (152mm) per second or 12 inches (305mm) per second. To calibrate the reader, that means a full color print process achieves speeds of about 32 or 64 letter pages per minute. This is all accomplished at a true cross process resolution of either 800 dots per inch at slow speed and 1,600 dots per inch in “in-process” direction. Each head has 11 Integrated Circuit (IC) Chips which are the structures that form the ink jet nozzle arrays with a total of 70,400 nozzles and 6,400 per IC Chip. These heads are produced using typical IC fabrication techniques by Memjet’s partner company in Taiwan.

This printhead is the heart of the Memjet print secret. Memjet claims that their Waterfall Print Technology achieves high-speed color printing at low cost. The print system requires some head conditioning time before printing commences, but this is the analog of warm up in a toner-based printer from the typical stand-by state. While dramatically improving the print speed, the fixed-head array based printer architecture also reduces the noise, vibration and mechanical complexity of print engines. Memjet’s printheads are designed as long-life, customer-replaceable components. The occurrence of ink jet nozzle failure is said by Memjet to be a relatively unusual occurrence, though ultimately inevitable during the life of the printer.

The heart of the Memjet print secret may be the printhead but the speed of a Memjet system is achieved through the integration and optimization of software and firmware as well as the printhead technology. The number of nozzle quantity and their density in the array mean that the system typically produces continuously up to 750 million drops per second. The system speed and quality is achieved simultaneously because there are enough tightly packed nozzles, firing with adequate speed, to achieve sufficient coverage and quality in a single pass. In addition, because the printhead does not “shuttle” from side to side, ink drop placement is also extremely accurate. The ink droplet size is 1.4 picoliters, which is the smallest of any commercial ink jet printing system.

The structure of the assembled head is of 5 ink channels with 10 rows of nozzles, 2 per ink channel. The Memjet printhead contains 11 IC chips placed side by side across the printhead with an approximately 1-micron gap between the IC chips. At the join in the adjacent IC array sub-systems there is a patented triangular “wedge” element that is also part of the IC-based array. The nozzles in the wedge overlap those nozzles in the two adjacent IC sub-systems. The nozzles in the “wedge” that are in the correct lateral position with respect to those in the adjacent IC are used to ensure the “seamless” cross process ability of the full width array when printing.

The Ink – the blood that flows through the heart of the system

The inks used in the Memjet system are aqueous dye based inks. The inks are, in this way, similar to other ink jet inks in daily use in the market. There are currently no pigmented inks available for the Memjet technology printers. This is in contrast to recent trends in ink formulation for the latest ink jet products and this trend is the industry’s efforts to improve the durability of prints. It is, however, not surprising that the Memjet suite of ink products does not include such ink as the nozzle size in a Memjet is much smaller than those of typical commercial products. The nozzle size is 0.5 microns and pigment particles in pigmented inks can easily be of a size close to this level.

Drying for ink jet has always been a challenge and in a world where we are trying to avoid VOC emissions and water is the preferred medium this will not change any time soon. The printers using the Memjet technology are also subject to this issue though much has been done to overcome the issues of instant dry touch characteristic in the prints. Such things depend not only on the ink technology but also on the characteristics of the media used. There is no “forced drying” used in the Memjet technology-based commercialized systems today. Image permanence is also an area that may be addressed in the future. Dyes themselves, as chromophores for printers like the Memjet, are subject to limitations in light-fastness and the potential for bleed in wet or damp conditions. These factors are the reason for the development of pigmented ink products by other companies and it may be anticipated that there will be new technology development efforts by Memjet to work on these issues in the future.

With drop volumes comparable to the smallest in current commercial use, Memjet is capable of amazingly high-quality print results. The fact is, however, that to achieve adequate optical density, whatever the print system, a certain amount of dye must be delivered to the print medium and typically therefore the same amount of ink (including water) must also be delivered. In this there is the implication that drying for all ink jet systems is broadly the same. Memjet has, however, with a printhead that is eight times faster than traditional inkjet printheads, optimized and specially formulated their ink for optimal printing at high speeds.

Memjet inks are water-based, four-color (CMYK) ink formulations, customized to work in conjunction with Memjet printheads. Memjet inks are said by the company to be unique to meet the demands of high-speed drop ejection, single-pass printing, and to ensure reliable, high-quality color printing for the life of the printhead. Memjet selected advanced dye colorants to achieve the highest image quality and reliability at high speeds. The printheads’ small 1.4 picoliter ink droplets absorb into typical substrates in milliseconds, so absorbent media of all types that are printed with a Memjet printhead and ink are dry to the touch when they exit the printer. The inks are also said to be extremely low in impurity levels to ensure maximum printhead life.

Environmentally Friendly Supplies with Remanufacturability Designed In—A Remanfacturer’s Dream or is it a Nightmare?
In the office applications of the technology, Memjet claims the use of significantly less energy than monochrome and color laser technologies by any measure. The “OEM ink tanks” can be refilled by using authorized refilling systems provided by Memjet’s OEM partners. This built-in remanufacturability gives the products a “green” image though the supplies cannot currently be remanufactured by any organization. Only authorized remanufacturing can be performed using authorized Memjet inks and refilling systems. It seems that the razor blade paradigm will still prevail with these printers.

In addition, the remanufacturing industry may find itself in a similar position as with the Tektronix/Xerox hot melt ink jet printers with respect to the printhead warranty and the validity of this with the use of third party inks. To be certain, Memjet is the only source of replacement heads at this stage and it would seem challenging to consider that third part printheads would ever be made available.

For the printer models there are ink tanks that are flat and “rectangular-ish” in appearance. They sit inside slots of varying position and height in the printers, the relative height between the ink tank and the respective color print head being of key importance to avoid too high a “water head height” so as to avoid the dripping of ink at its given designed viscosity. The population of the printers in world markets is small at present but when “critical mass” is reached it will be interesting to see how the remanufacturers respond to the challenges and opportunities presented.

The Need for Speed?
This high-speed ink jet technology has certainly found favor in a variety of applications where there is a big gain in marketability to be had. For sure high speed full-color printing in the office environment is of potential advantage too, and 60 pages per minute color printing on the desktop is an amazing achievement. More significant is that this can be provided at competitive cost versus the best toner-based solutions out there today. However, with desktop office color printing in its current mode demanding relatively low-duty cycles even for typical currently commercialized lower speed devices, it remains to be seen if any benefit can be derived for the user from the immensely high speed. What is probably more important is that these high speeds can be provided at competitive cost. Absent any unforeseen disadvantages to the print technology, it would seem that the latter could be a driving force for the products in the market.

Memjet technology is certainly impressive in its performance characteristics and potentials. A very good start has been made in the realization of commercial products using it. In the writer’s view, the situation that has prevailed since the competing technologies were developed will prevail. There will be coexistence of the technologies in the market with each exploited for the unique performance capabilities they bring to the print market.

Read more articles in our May 2013 issue

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