HP Scitex X2 print head technology

HP Scitex has come up with a revolutionary, brand new concept in print head design that promises a leap forward in print capability. John Taylor visits HP in Barcelona and lifts the lid off the new technology.

With a clean sheet approach to pioneering new technology to take piezo inkjet printing on to a new stage, HP Scitex, looking to bridge the productivity divide with more m2/hr output at highly sellable quality, has developed a stunning new print head, the X2.

Key to the new print head development, says HP’s Dr Ross Allen, is to take output levels to the hundreds mark in m2/hr with potential for the future in thousands. The route to that particular Xanadu he sees as via rapid dry inks, more nozzles per print head, higher reliability, longer print head life and easier maintenance and service, all revolving around the head and ink system for reliability. For the head: brand new technology and for the inks, UV curables.

The resultant new generation X2 print head is indeed a new generation in piezoelectric inkjet technology for industrial inkjet applications and, just for starters, using UV curable ink, it takes industrial wide format quality, productivity and reliability to that much vaunted new level. X2 boasts high durability and reliability, delivering the high ink flows needed for high speed printing, with necessary quality to boot.

In a definitive move to new manufacturing techniques, Scitex turned to silicon chip technology, moreover, wafer fabrication as the basis for producing the new head. The concept is truly stunning and Scitex promises the results to match! Key to the revolution is Silicon based MEMS, Micro Electro Mechanical Systems.

The resultant design features print head parts that come into contact with the ink fabricated in silicon, glass and epoxy, thus making it highly resistant to corrosion. Furthermore the wafer fabrication-based MEMS process delivers extremely high accuracy and repeatability manufacturing, ensuring uniformity and performance. This, says Ross Allen, is important as print heads are used in arrays of tens, hundreds or even a 1000 or more. For that, he adds, mounting and imaging accuracy, as well as speed are also benefits of the technology.

X2 is patented and destined for major integration. They feature on the newly previewed HP Scitex FB6500 flatbed and the forthcoming HP Scitex XL2200 wide format inkjet. Both are expected in the first half of 2007 for applications ranging from high quality, durable PoS and PoP displays to outdoor signage and building and vehicle graphics. The print head silicon chip features a two sided side shooter design. Sixty four nozzles, ink channels, and piezo actuators are formed on each side of the chip, delivering up to 30,000, 50pl drops per second per nozzle in a 32.5mm swathe.

Native resolution of the X2 is 100 nozzles/in and by assembling into multi-print head modules, resolutions up to 800dpi can be readily achieved. Measuring up at just 8x64mm at the delivery end, the slim, under 1mm thick profiled X2 is, says Ross Allen, ideal for building multiprint head modules with very high nozzle density. An ink channel at the top edge of the print head supplies all nozzles and ink up to 15cP viscosity can be delivered. Ink delivery, states Ross Allen, is incredible, quoting 100min to deliver one litre of ink.

The electronics packaging of the print head design uses anodic bonding and not adhesives, forming a permanent chemical bond and hermetic seal between the constituent materials. The result, as mentioned, is only silicon, glass and epoxy touch the ink, and the piezo actuators and electrodes within the assembly are completely isolated from the ink. The print head is reckoned to deliver dependable imaging performance over 15-45ºC.

Compact and modular in design, the heads snap accurately together to form banks and also snap accurately into place on to the machine. These are secured with just two screws, for precision location and hence accurate printing repeatability. Two location pins provide precision head location accuracy said to be better than 10microns without adjustment. X2 can deliver over 10ml of ink per minute at linear print speeds up to 2m/s. Notably, the new design increases the number of nozzles in the print zone by a factor of three over any other head in the industry, says Ross Allen.

Ink connections to the print head are via two ports, each sealed with an O-ring and without the need for tubes that have to be attached and tightened. Power and communications to the head are via a standard 26pin connector.

In operation, the piezo actuator deflects the glass plate a fraction of a micron into the ink channel when a voltage pulse is applied, ejecting an ink droplet. Nominal drop velocity is 8m/s, providing precision dot placement at high linear printing speeds. The piezo actuators and electrodes on the head are outside on the surface of the glass, completely away from the ink. Because the nozzles are formed in a polished silicon surface, there is no nozzle plate to align during print head manufacture or to delaminate with use. Silicon, says Ross Allen, provides an ideal surface for the nozzles because it is hard and durable, resisting abrasion and corrosion, even with low pH inks.

With the silicon design and the anodic bonding approach – restricting where ink can get to – ink capability of the X2 is tremendous – water based to highly corrosive solvents are said to be not a problem for the new design. In making a start for using the new technology, though, HP Scitex has plumped for rapidly growing in demand UV curable to hit the button on fast drying, high quantity, quality production. However, according to Scitex’s Itai Halevy, other platforms such as solvent, will be very much considered for X2 as and when they come along.

On its existing machine line up Itai Halevy points out that there are no plans to replace the existing heads on existing machines with X2. Changing to the new head is not easy, it needs a ground up development of new machines. But notably, he adds, that now with its own head, HP Scitex indeed feels comfortable not having to rely totally on anyone else’s head.

In developing a new UV curable ink for the new head, the company returned to basics. Essentially UV curable inks fall into two categories of free radical and cationic. Compared to aqueous and solvent inks, UV curable as complex. Around 95 per cent of UV curable inks are free radical based, produced using a wide range of raw materials and photo initiators, to deliver formulations that cure only under UV light exposure.

Cationic UV inks are more complex than free radical inks and also need heat to fully cure. The problem with cationic formulations is that they continue to cure through dark curing until all the ink is totally cured.

HP UV inks are free radical in formulation, produced from 100 per cent solids and invoking no evaporation. That means curing solidifies all the solids without producing VOCs. The ink stays where you put it says Ross Allen, delivering pin sharp edges and lines. The inks are plastic, forming a mechanical bond with the media, penetrating and keying to its surface as they dry. The result is a highly durable print where rapid curing under UV also minimises spreading and feathering of the ink.

With no VOCs generated, UV curable inks deliver a major health and safety advantage over other ink formulations. And in energy savings terms, no drier is needed. UV inks do not dry inside the head and thus the machine is easier to keep running, with real advantages in terms of ink efficiency. Ink supplies do not need capping and nearly all the ink delivered, says Ross Allen, ends up on the media.

The new HP Scitex water based, pigmented UV curable inks, as used on the new FB6500 flatbed and XL2200, are free radical curing and monomer based, solidifying with a photo initiator that polymerises the ink. Oligomers are added to keep the dry ink flexible on the media, producing very flexible print that otherwise would be brittle. The four, six and eight colour formulations deliver a wide colour gamut and are reckoned to be 24 months outdoor durable.

In production of its inks, HP carries out total end to end quality control. HP, according to Ross Allen, is the only manufacturer of inkjets that does it all: machine; head and inks, all end to end engineered and quality controlled. The inks can be used on rigid and flexible uncoated media at low cost per copy, high quality output. Print is water fast and fade resistant for two years or more on outdoor displays, whilst also resisting abrasion.

W: www.hp.com

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