The printhead manufacturers are busy defining future printing technology by addressing a number of concerns such as print quality, productivity, reliability, and ease of integration.
The technology advancements are all round irrespective of industries or domain. No wonder printheads for graphics applications have also jumped on to the bandwagon, in turn, unlocking new opportunities in graphics production and beyond. Piezoelectric drop-on-demand inkjet printheads are one of the most important components to wide-format and other inkjet-based imaging devices, and the on-going developments in inkjet head design and manufacture have greatly improved print speed, quality, the ability to produce unique effects and many more.
The world of inkjet can be split into Continuous Inkjet (CIJ) and Drop-on-Demand (DOD). CIJ, being primarily associated with date-coding food products like operation, is not of our concern. Going forward, the DOD arena breaks into Thermal Inkjet (TIJ) and Piezoelectric Inkjet (PIJ). TIJ is widely used in the graphic arts market — notably by HP and Canon, while manufacturers and users of PIJ printheads are in abundance. PIJ heads work by applying voltage pulses to a piezoelectric material, which deforms in response and so ejects ink droplets from a chamber via a carefully engineered nozzle. Each printhead has hundreds or thousands of such chambers and nozzles.
For unfolding the latest, Sign & POP World contacted leading printhead manufacturers from across the globe. Since the time constraint couldn’t allow us wait for all the responses, we restricted ourselves with what we received from the three majors – Fujifilm Dimatix, Epson and Konica Minolta. These giants shared their inputs on various aspects including what new they have added in their respective kitties recently in the name of advanced technology and how these advancements are going to change the market dynamics in time to come.
While silicon MEMS (Micro-Electro-Mechanical Systems) technology emerged as the common attribute in the repertoire presented by the technology giants, the other factors like ‘greyscale’ or variable drop sizes, recirculating ink paths, compatibility of printheads with different types of media and inks, and high-speed operations have also got mentions from all the players owing to some improvement or the other.
Fujifilm Dimatix Inc. boasts of its bunch of pretty advanced printheads comprising Q-Class, Starfire, Samba, and other legacy products catering to any of the markets adopting digital printing. “Our products are designed to accurately disperse a wide range of fluid types in micro-amounts for demanding imaging and fabricating applications. We are constantly testing new fluids to continue to improve the breadth of our understanding and capabilities,” asserts Timothy N. Rosario, Senior Program Manager at Fujifilm Dimatix Inc. Rosario adds that the company is focusing on its industrial Silicon MEMS (SiMEMS) as a core technology for the products of the future.
According to him, SiMEMS allows for precisely high density features resulting in a high DPI and small & fast drop size. Fujifilm Dimatix also has a patented sputtered PZT, which is at the core of Samba printheads providing the engine for its high productivity. “Together, these result in a very high productivity and superb image quality, which are exemplified by the Fujifilm Jetpress 720S. We will continue the development in the sPZT and SiMEMS areas into its products to serve all the markets whether high-speed single pass or highly productive scanning systems,” he shares.
Another technology major, Epson Inc. does have a wide range of next generation printheads that includes MicroPiezo AMC – known for its accurate & consistent dot placement for maximum resolution, Precision Core TFP that features outstanding speed & output quality, and Precision Core Micro TFP. “All these fast-speed printheads offer professional quality prints and use less power thus bring economical printing solutions. Our entire signage products are using Precision Core Thin Film Piezo (TFP) printhead technology, wherein the TFP print chips facilitate maximum output of ink with an increased density of print,” avers Vasudevan L K, Deputy General Manager – Prographic Products, Sales & Marketing, Epson Inc.
According to him, the major benefit of Epson’s new Precision Core printhead technology is its print chip core. “It is no longer just a printhead with a giant array, but a little itty-bitty chip core with the ability to produce sharp, clear and accurate dots. This technology has also enabled Epson to utilize more advanced forms of chemistry to create that piezo crystal, and the result is an extremely durable printhead. This new head has exceptional ink flexibility to print virtually with any ink – be it normal water-based pigment, hard solvent or mild solvent. Above all this is its scalability,” avers Vasudevan adding that Epson makes a single little chip that can be put together to build any array as per the need, in any colour space, for any application. “This is completely new technology.”
Vasudevan further elucidates that with the flexibility to deliver high-speed solutions for commercial, industrial and office printing, Precision Core enables superior output quality & durability on the widest range of media. “All our printheads are manufactured using Micro Electro Mechanical Systems (MEMS) for high-accuracy ink channels, enabling precise, high-speed ink ejection for precise & high-quality prints,” he underscores adding that the printheads from Epson are designed specifically for meeting requirements at high-demands of production environment and feature two one inch-wide printheads with 1440 nozzles per colour for efficient, precise and repeatable performance with best-in-class image quality.
Konica Minolta (KM) goes deep in to the specifications when it comes to referring its solutions for pretty diversified Indian market. “We offer state-of-the-art printheads to our Indian customers i.e. printer manufacturers, depending upon the suitability to the respective applications keeping in view the variability of diverse requirements. For instance, KM512, KM512i, and KM1024 series are widely used on solvent printers for signage market because of their compact and economic features. Similarly, KM1024i and KM1800i are meant for barcode, label and high-resolution UV printing with high speed; while water-based heads KM512iMAB-C and KM1024iSAE-C/MAE-C are used specifically in textile printers,” explains Toshio Tsuzuku, Senior Manager, Sales Division–Component Business Group, Inkjet Business Unit, Konica Minolta Inc.
For KM’s 1024 and 1024i series, each model has 1024 nozzles, but the older 1024 series uses two rows of 180dpi actuators operating in ‘shared wall’ or ‘three-cycle’ mode, whereas the newer 1024i series uses four rows of 90dpi actuators to achieve the same nozzle density but with significantly higher frequencies of operation. Remarkably, all the heads have an identical (and narrow) footprint: 106/18 mm. Each of the two families comes in small, medium and large-drop versions, and the similarity of mechanical mounting, electrical connection and ink connection provides greater flexibility for customers.
According to Tsuzuku, the strength of KM printhead is the base material technology, and the mechanical design that emphasises the ease and simplicity of printhead use and its handling. “Of course, KM printheads incorporate cutting-edge technologies and innovations, but for us the most important part to make printheads is the verification of effects. All thanks to our R&D team that meticulously keeps integrating the day-to-day improvement in the printhead design to lead the innovation,” he elaborates adding that at KM, the core technology of printhead is the comprehensive capabilities of the base material technology, the mechanical design technology, and the processing technology.
Tsuzuku insists that signage printing is the most widely-used application of KM printheads. The long-usage history of catering to the needs of signage printing fraternity with our printheads has already proved the worth, following which, KM is now getting into the next stage of improvements in the precision and productivity.
The change in technology is further adding to the print quality as well as improving productivity. “For instance, our printhead using independent driving method can achieve triple productivity comparing to three-cycle-driving method – standard printhead technology, used widely by leading manufacturers such as Xaar. Also, because of the improvement on the inside flow of the printhead, and integration of the laser processing technology on the nozzles with increased accuracy, our printheads today are developed to disperse small drop size (6pl or even 3.5pl), which is suitable not only for industrial application but also for signage printing,” reinstates Tsuzuku.
It’s aptly clear that when it comes to print quality, there are factors like drop velocity, drop volume, jet straightness and jet-to-jet uniformity, which are of greater importance. Industry experts advise that a printhead with a high jetting velocity allows for high stand-off distance. Therefore, depending upon the application, for a flatbed moving heads over a large area, a higher stand-off is going to limit the amount of head strikes. It is also important to get uniform drop volume out of every jet as any inconsistency in the drop sizes or the wide tolerance may lead to deteriorating imaging in the final output. Further, the jet straightness is also very critical to avoid fuzzy images. Jet-to-jet uniformity means all these components are consistent.
Ease of Integration
Amidst all this, the market wants a printhead that can facilitate easier and faster integration as well as compatibility – be it for media or inks. “Fujifilm Dimatix has several product families in which different printhead types are interchangeable. For example, the Q-class products come in over 100 varieties that allow for native drop size, nozzle plate technology, recirculation, greyscale/binary, ink connections, frame configurations, and the like. Adding to it is the absence of any wear out mechanisms such that when properly designed into a system and maintained as per instructions, they would have a very long life. In some cases, like the Galaxy and Starfire, the products are repairable such that if an event occurs that does cause damage the heads can be removed from the system, repaired, and put back into service,” elaborates Rosario.
Rosario mentions that couple of factors affects drop placement and the impact can be seen in the final output if necessary measures are not taken. For instance, the manufacturing tolerance of the printhead wherein tolerance in terms of manufacturing nozzle plates, which often experience unwanted scratches, dust accumulation, cured ink building up around, which together make the nozzle plate to pull the jet over. “Keeping all this in mind, Fujifilm has developed its VersaDrop technology that allows its printheads to be tuned to many inks with an open architecture. VersaDrop is actually our greyscale technology where we can have very small drops for high resolution and closer viewing; large drops for long-distance viewing or the greyscale, variable drops to achieve text or flesh-tones,” he says.
Epson too claims that the flexibility to use a wide variety of media is its key strength. “We have successfully tested more than 200 different types & varieties of media used in the signage industry like flex banner, paper, film, one-way vision, wall coverings, canvas, backlit, vehicle wraps, textile and many more. This has gained the mind share of the Epson products among the signage converters,” shares Vasudevan adding that the company offers standard warranty that covers the printheads. Also, there is the Annual Maintenance Contract (AMC) for the convenience of the customers. Beside printheads, Epson also develops its own inks based on the feedback from the market to cater to the varying industry requirements.
Compatibility with Inks
Going forward, not only the differentiated media but also the market is brimming up for printers that do not require changing of inks for different applications. Following which, many manufacturers have started working on this front to develop printheads that can offer greater compatibility with a wide range of inks that are currently available in the market.
“Many of our heads are rated for the major ink types AQ, Solvent, UV. However, in some cases, like ceramic, we specify a different material set to be compatible with oil-based fluids. Back to our wide range of options though, we have variants that allow us to match the head to the ink type needed if a ‘universal’ material set isn’t available. Using proper flush and change over procedures allow the heads to be used with different inks even in the same system. One area that distinguishes Dimatix printheads is our RediJet technology. Speed between switchovers is the key here, and RediJet recirculation means heads will be primed and ready to print quickly,” asserts Rosario.
When it comes to compatibility, Epson offers different types of inks for different printhead technology to give the best results which the customers nowadays look for. For example, Micro Piezo AMC printhead along with Ultrachrome HD pigment ink is the best suited for professional photography print application.
According to Tsuzuku, since the inkjet printing technology is a non-contact printing, matching with the ink is the most important issue than that of the physical integration between media and inkjet head. “Especially, the printhead is required to be widely compatible with the ink parameters. KM printhead has the compatibility with both low viscosity water-based ink as well as high viscosity UV ink,” he says adding that for all this to happen in proper coordination, KM has a professional team that works closely with the ink manufacturers from across the world to help our customers (printer manufacturers) in verifying the compatibility of the ink they want to use. KM does posses an ink development team, but it doesn’t offer inks to its printhead customers. “Instead, we design our printhead for wide ink compatibility, and help our customers to test the ink they want to use.”
Tsuzuku further elaborates, “The compatibility is affected by various ink parameters, mainly the viscosity, the surface tension, the particle size, and the fluid-proof. KM has line-up of the printheads with the internal heater that heats up the high viscosity ink to lower its viscosity so as to make the same compatible for a different usage. When using big particle size ink, big printhead nozzle is needed to prevent ink clog. Moreover, if the ink uses strong solvent, the inside material of the printhead may be damaged. KM printheads use the high fluid-proof material to prevent this kind of damage.”
Interestingly, printheads have been present in digital printing, coding and marking for years, before wide-format graphics came-in to define new lines of opportunities, around a decade ago. It is further expanding encompassing huge potential as the number & type of substrate is continuously on the surge; urging the technology giants to come up with solution that can efficiently address most of the issues. These apart, the stakeholders may look forward to develop printheads for next generation printers, with further enhanced accuracy, improved print quality and increased speed to combat the comparatively faster-rolling future challenges. Meanwhile, commercial printing applications are growing, along with it 3D prototyping, functional applications, deposition applications in printed electronics, and bio-science applications, where printheads are used as a micro-pump or a precision dispensing tool in jetting fluids other than ink.
Printhead Design & Cleaning Mechanisms
There are two main design philosophies in inkjet head design: fixed-head and disposable head each with its own strengths and weaknesses.
The fixed-head philosophy provides an inbuilt print-head (often referred to as a gaiter-head) that is designed to last for the life of the printer. The idea is that because the head need not be replaced every time the ink runs out, consumable costs can be made lower and the head itself can be more precise than a cheap disposable one, typically requiring no calibration. On the other hand, if a fixed head is damaged, obtaining a replacement head can become expensive, if removing and replacing the head is even possible. If the printer’s head cannot be removed, the printer itself will then need to be replaced.
Fixed head designs are available in consumer products, but are more likely to be found on industrial high-end printers and large format plotters. In the consumer space, fixed-head printers are manufactured primarily by Epson and Canon. HP also offers a few fixed-head models, such as the HP OfficeJet Pro X576dw. Industrial fixed-head print heads are manufactured by companies including Kodak Versamark, Trident, Xaar, Spectra (Dimatix), Hitachi / Ricoh, HP Scitex, Brother, Konica Minolta, Seiko Epson, and ToshibaTec (a licensee of Xaar).
The disposable head philosophy uses a printhead which is supplied as a part of a replaceable ink cartridge. Every time a cartridge is exhausted, the entire cartridge along with printhead is replaced with a new one. This adds to the cost of consumables and makes it more difficult to manufacture a high-precision head at a reasonable cost, but also means that a damaged or clogged print head is only a minor problem: the user can simply buy a new cartridge. HP has traditionally favoured the disposable print head, as did Canon in its early models. This type of construction can also be seen as an effort by printer manufacturers to stem third party ink cartridge assembly replacements, as these would-be suppliers don’t have the ability to manufacture specialized print heads.
However, an intermediate method does exist. A disposable ink tank connected to a disposable head, which is replaced infrequently (perhaps every tenth ink tank or so). Most high-volume Hewlett-Packard inkjet printers use this setup, with the disposable print heads used on lower volume models. A similar approach is used by Kodak, where the printhead intended for permanent use is nevertheless inexpensive and can be replaced by the user. Canon now uses (in most models) replaceable print heads which are designed to last the life of the printer, but can be replaced by the user should they become clogged.
Head Cleaning is a Must
The primary cause of inkjet printing problems is ink drying on the printhead’s nozzles, causing the pigments and dyes to dry out and form a solid block of hardened mass that plugs the microscopic ink passageways. Most printers attempt to prevent this drying from occurring by covering the printhead nozzles with a rubber cap when the printer is not in use. However, abrupt power losses, or unplugging the printer before it has capped the printhead, can cause the printhead to be left in an uncapped state. Even when the head is capped, this seal is not perfect, and over a period of several weeks the moisture (or other solvent) can still seep out, causing the ink to dry and harden. Once ink begins to collect and harden, the drop volume can be affected, drop trajectory can change, or the nozzle can completely fail to jet ink.
To combat this drying, nearly all inkjet printers include a mechanism to reapply moisture to the printhead. Typically there is no separate supply of pure ink-free solvent available to do this job, and so instead the ink itself is used to remoisten the printhead. The printer attempts to fire all nozzles at once, and as the ink sprays out, some of it wicks across the printhead to the dry channels and partially softens the hardened ink. After spraying, a rubber wiper blade is swept across the printhead to spread the moisture evenly across the printhead, and the jets are again all fired to dislodge any ink clumps blocking the channels.
Some printers use a supplemental air-suction pump, utilizing the rubber capping station to suck ink through a severely clogged cartridge. The suction pump mechanism is frequently driven by the page feed stepper motor: it is connected to the end of the shaft. The pump only engages when the shaft turns backwards, hence the rollers reversing while head cleaning. Due to the built-in head design, the suction pump is also needed to prime the ink channels inside a new printer, and to reprime the channels between ink tank changes.
Professional solvent- and UV-curable ink wide-format inkjet printers generally include a ‘manual clean’ mode that allows the operator to manually clean the print heads and capping mechanism and to replace the wiper blades and other parts used in the automated cleaning processes. The volume of ink used in these printers often leads to ‘overspray’ and therefore build-up of dried ink in many places that automated processes are not capable of cleaning.
The ink consumed in the cleaning process needs to be collected to prevent ink from leaking in the printer. The collection area is called the spittoon, an open plastic tray underneath the cleaning/wiping station. For printers several years old, it is common for the dried ink in the spittoon to form a pile that can stack up and touch the printheads, jamming the printer. Some larger professional printers using solvent inks may employ a replaceable plastic receptacle to contain waste ink and solvent which must be emptied or replaced when full.
There is a second type of ink drying that most printers are unable to prevent. For ink to spray from the cartridge, air must enter to displace the removed ink. The air enters via an extremely long, thin labyrinth tube, up to 10 cm long, wrapping back and forth across the ink tank. The channel is long and narrow to reduce moisture evaporation through the vent tube, but some evaporation still occurs and eventually the ink cartridge dries up from the inside out. To combat the issue, which is especially acute with professional fast-drying solvent inks, many wide-format printer cartridge designs contain the ink in an airtight, collapsible bag that requires no vent. The bag merely shrinks until the cartridge is empty.