Under the bonnet
Printheads and inks are key to the smooth running of any inkjet printer. Sophie Matthew-Paul looks at the developments that optimise performance.
Printheads tend not to receive the same levels of criticism as inks, although frequent nozzle drop-outs, crashes and inconsistencies can mean all is not well - whether it's the head or the ink or, even, the wrong allowance for material type or thickness which is causing the problem, the printing machine overall usually gets the blame. Inks can behave badly but very often this is the result of an allied factor which can range from the wrong colour profile, media with a poor coating or inappropriate surface quality or a drying or curing method which doesn't suit the process being applied. Adhesion with inks has always been a matter for conjecture with wide-format digital print, along with durability. Everyone knows that, with aqueous-based products, to gain any kind of long-term life then some form of lamination or coating is required. Even photographic prints are likely to be framed, and not many applications would be left exposed to the world without some kind of exterior treatment to bring about longevity without compromising the quality of the end print. The harder the solvent used in an ink's formulation, the more it keys with the material surface and the longer its life. Yet eco-solvents have now been fine-tuned to bring about a family of products which serve to produce very low odour and, in some cases, claims of no smell at all and no need for users to incorporate additional ventilation before running printers in enclosed spaces. Not surprisingly, this now widens the potential customer base for manufacturers wanting to target in-plants and smaller companies who don't want to have to get involved in complicated ducting and other health and safety issues. Many eco-solvent printers also run off a standard 13 amp socket, and this removes the necessity for potential investors to have to up their power capabilities to incorporate single or three phase capacity. Thoughts of the demise of solventbased inks haven't really been justified as Jeff Biggs, managing director of Colourgen, endorses. "We feel that as the solvent-based printer market has matured, customers are looking for more - more quality, more reliability and more ease of use. They are also looking for less in terms of smell. The newer low- or mild-solvent products, such as the Epson Stylus Pro GS6000 range, tick all these boxes and we're finding this machine being installed in production areas where it is not possible to ventilate, with no odour problems at all."
The gap between aqueous-based inks for display printing and solvent-based production has, of course, been filled by HP's latex printing technologies and the company's Designjet L65500 has now been adopted by users wanting to acknowledge the green benefits as well as durability. The introduction of this ink type, which has no hazardous components, has also meant that it can be used in environments such as the food and medical industries. HP's linked the printer with a range of recyclable materials, too, to enhance the eco-friendly attributes of this product. The move towards UV-curable inks continues for direct-tosubstrate printing as well as for use with roll-fed materials but the adhesion properties on some products has led to chipping and cracking with some media, a problem which can be helped by adjusting the curing. However, the need to be able to meet the requirements of many materials and more demanding applications has also seen the development of more flexible inks. Certainly, with Roland's VersaUV roll-fed machine, the combination of ink and LED curing options has resulted in the ability to print high-gloss output, bringing it new markets in areas such as labels and decals. Mimaki, too, has taken up the challenge of ink flexibility, again marrying it with the way the prints are cured. "One of the questions we were often being asked about our printers was the suitability of UV-curable inks on applications which, traditionally, have been produced on solvent-based systems," says Duncan Jefferies, marketing manager of Hybrid Services, exclusive UK and Ireland distributor for Mimaki. "Our competitively priced Mimaki UJV- 160 flatbed/roll-to-roll machine uses LED curing technology, as does our latest arrival in the form of the grand-format flatbed JFX-1631, and this means that we can be more versatile in the types of ink we supply. Both printers come with a choice of formulations, one being flexible and the other a more traditional hard UV-curable product. Developed in conjunction with 3M, the first of these ink types removes problems of cracking because it can stretch to 200 percent without compromising adhesion. In addition, the use of LED curing means that more heat sensitive materials can be used, too."
In the main, UV-curable inks have stuck with free radical chemistry because it's tried and trusted throughout this industry now and, generally, performs as it should. The variant to this is, of course, in Spandex's Gerber Solara Ion duo, now available in four and eight printhead options, which incorporates cationic inks that claim to give a strong yet flexible bond to the material, thus improving adhesion. Perhaps surprisingly the Ion doesn't use LED curing but incorporates a system of UV lamps which run the length of the gantry to match the wavelength needed to cure this ink type and, again, this combination has been designed to be suitable for more sensitive and delicate materials. The other perennial discussion amongst users of wideformat printers regarding inks is the value of staying with the original manufacturer or venturing into third-party products. In times of recession users are always looking for ways to save money and to see if performance and coverage can be improved by using after-market options. Certainly notable names, like Sun Chemical, are striving to fill this perceived need as are smaller independent manufacturers. UK ink manufacturer ITL GB's Peter Williams, sales and marketing director, comments: "Since the recession was announced the OEM, on average, has increased prices by around 30%. This has had the knock-on effect with our enquiries rising by about 40% for the UK with a strong conversion rate. More people are now willing to try third-party products. But there are scare stories about manufacturers refusing to look at machines until they've been converted back to their original inks, and implying that the third-party products were the cause of the problem." Colorific, which secured the rights to the original Uniform inks, is another independent company. "As users have gained experience and confidence on their printing hardware, their interest in alternative non-OEM ink products has also grown," says Colm Garvey, European sales director. "We see many users now prepared to experiment to a greater degree - the ability to reduce ink costs by as much as 50% is a compelling argument.
"Current third party vendors, not least Colorific, are now able to offer colour-matched performance, as well as alternative warranty provision. This ability simply to pull out an OEM cartridge, and replace it with a plug-and-play alternative, without colour issues, has removed many of the sales objections," he continues. "Accordingly we are seeing, for the first time, UK market share growing at a rapid rate. The UK has traditionally been seen as a cautious and conservative market, yet current economic conditions, specifically the weak sterling, have played a significant part in this shifting attitude. When customers realise that conversion to lowercost non-OEM inks can be painless, and the savings immediate, the uptake naturally increases." The relationship between inks and printheads has never been so important as printer speeds increase and reliability becomes vital so that printer manufacturers can retain their credibility and reputations. Xaar's Mark Alexander, director of marketing, states: "The drive is towards speed, performance, quality and reliability - all at reduced cost. We are always evaluating architecture and manufacturing methods to produce printheads that produce the best cost/performance ratio. This is shown by the greyscale Xaar 1001 printhead which is revolutionising wide-format production quality and performance in new machines now coming to market. The tendency towards smaller drop sizes was evident at Fespa digital show, was significant in showing continued momentum for inkjet both within and beyond wide- and grandformat printing."
Talk of MEMS (micro-electro mechanical systems) has really only been followed through to date in our sector by HP with its Scitex FB7500 which incorporates its X2 printheads. But other manufacturers of high-speed industrial machines, such as Inca Digital with its Onset models and Durst with the recently launched Rho 1000 stay with established technologies instead of venturing into new territory. Again, Alexander comments on these trends: "Customers don't really care what substrate printhead manufacturers use; they do care about price and performance. When people talk about inkjet MEMS they are generally referring to the fabrication of inkjet actuators from a silicon wafer. However, silicon is not a piezo-electric material; so, if you wish to create a piezo printhead, you need to marry piezo elements with silicon processing. We looked into this technology more than six years ago and found that the cost benefits are only really experienced by mass volume markets. Plus the performance advantages claimed could be achieved via alternate methods. So we to continue to develop our ceramic MEMS technology." Printhead developments don't only affect complex greyscale technologies at the high-end of the digital print spectrum. Xaar's introduced two new options, the Electron and the Proton - both of which are binary models - to target entry-level and high productivity requirements and, already, Chinese printer manufacturers are adopting these in their latest products.
Fujifilm Dimatix hasn't been hiding its light behind a bushel either and when a printer like the Inca Onset has 576 printheads jetting up to three billion drops/second, there has to be a way to counteract the effect of a nozzle malfunction. How Dimatix Spectra does it is with its iNozzle technology which uses an onboard scanner to read a test pattern, find any nozzles that aren't perfect, and assign a reserve head to jet the ink to avoid any image quality compromise. When vast numbers of printheads are used, the likelihood of a head change naturally is increased and, today, even on smaller machine using smaller arrays, users don't want to have to wait for an engineer to appear before they can carry on printing. Certainly the layout on machines, such as the HP Scitex FB7500, makes it easy for an operator to lift the bonnet, snap out the old head and insert a new one. The million dollar question with inks and printheads is: "What happens next?" as machine developments continue relentlessly in their quest to make wide-format inkjet production increasingly versatile and cost-effective. Apart from improving the mix of speed and quality, the mainstream digital market has a good choice of 'under the bonnet' options which are reliable. Certainly we can expect specialist inks, such as metallics, to move into this market but the fine-tuning of what's available now should be sufficient to satisfy even the most demanding of print service providers for years to come.
Why shouldn't I use third-party inks?Most kit manufacturers find ways to invalidate warranties when users want to move to third party inks. Peter Williams of ITL GB says: "Whilst we do tell people that it is illegal for the OEMs to refuse to carry out warranty work no matter what inks they are using, we generally advice people to wait for their warranty to lapse before using our inks. We are then ready to step in with a fully insurance backed scheme, were we extend their warranty for up to ten years for a small monthly fee around 50% less than the OEM."
Which printheads are in my printer?
Many printer manufacturers are extraordinarily secretive about which heads are used in their systems but this knowledge is as relevant as knowing what engine you have in your car. Companies guilty of this oversight include Spandex with its Solara Ion and Mimaki with its UV-curable options (although one look at most heads will give the game away to the inkjet cognoscenti).
What's in this ink?
Health and safety issues in the UK demand that the MSDS (material safety data sheet) for all hazardous products must be made available to users and include full information and handling procedures. Thumbs up to ink manufacturers who have these details instantly available for download and whose data includes everything and not just a loosely-worded 'secret ingredient'.
How much is this ink going to cost me?
It's difficult to work out exact ink costs. It doesn't matter which standard is being used to gauge ink usage, people want to know the original cost of their inks by the litre because that's what they are physically having to pay for. Hats off to manufacturers who are prepared to provide prices according to coverage and by cartridge.
Why do my prints smell despite using low-odour solvent-based inks?
Even when using inks which carry virtually no odour, the drying process for solvent-based printing involves heat. And heat can cause the surface of the material to give off unpleasant smells, even when there's no nasty aroma in the ink itself. Prints need airing or out-gassing before being sent to the customer and being installed to minimise rejection on odours alone.
Top ten niggles
Why is the adhesion so poor on some materials printed with UV-curable ink?
Unlike hard solvents, which key with the material surface, UV-curable ink sits on the top. Claims that this technology can work with virtually all substrates is true to an extent but some inks can crack when put under pressure, such as being folded, and flake away at the edges when being cut. Ink manufacturers are increasingly developing more flexible products which offer better adhesion and even enable sufficient elasticity to make them suitable for vehicle wraps.
Why don't my inks match the colours I get on my screen?
It's usually a case of incorrect or possibly the calibration of the host computer screen where the job is being originated.
Why aren't my printheads covered under warranty?
Some manufacturers include all printheads in machine guarantees and warranties, some include none and others include only one. Today's printheads normally don't fail unless some third-party intervention has caused a problem. The most common cause of a wrecked printhead is probably a crash caused by attempts to print to the wrong media thickness or by a raised surface on the substrate's edges. In this instance, it's difficult to attribute blame to the printhead.
What causes nozzle blockages in printheads?
With solvent-based printers, the most common cause of blockages is lack of routine maintenance which should include purging of the printheads and nozzles. Problems can also arise from air bubbles in the ink flow and general lack of cleanliness in the area where the printer is used. Drifting swarf from a nearby cutter and other air-borne detritus can also reduce the performance from printheads.
Why can't I print without leaving the casing up on the front of the printer?
It might be considered beneficial to run a UV-curable printer with its protective casing open, thus making it easy to check the output as it dries but looking at a metal halide UV-curing lamp while it is in use can damage eyesight and is not to be recommended.