the limitations of inkjet: future applications

People have been adopting inkjet technologies for home and industry use primarily because of their advantages over analog and other digital methods. One indust r y obser ver descr ibed the momentum of inkjet adoption as unstoppable.1 Considerable evidence substantiates his projections over the next five to 10 years, but existing inkjet technologies also have limitations and challenges that are worth considering for future planning and purchases. Additionally, some analog print methods can perform some tasks as well or better than current digital technologies and are more cost effective.

Developers of analog printing systems are improving their technologies to stay competitive. They have added digital plate and screen making along with rapid make-ready systems to the front end of their processes that have kept them viable for medium to long print runs. Here, we discuss areas where inkjet is unlikely to displace current analog printing. We list and describe the pros and cons of the various inkjet technologies, examining how and where they provide value and what they can and cannot perform.

An Array of TechnologiesThe term “inkjet technologies” covers a variety of print- and material-depositing methods including continuous (CIJ), drop-on-demand (DOD), and spray-on-demand systems (see Chart 1). CIJ covers binary drop deflection, multidrop deflection, Hertz and multidot (see Chart 2). DOD includes thermal inkjet (TIJ) in Chart 3, piezo inkjet (PIJ) in Chart 4, electrostatic inkjet and acoustic inkjet. Spray-on-demand encompasses valve jet/airbrush and flat-jet that inkjet guru Alan Hudd, Founder of Alchemie Technology Ltd, is now promoting under the name Jetronica.

Each of these technologies offers both advantages and disadvantages. All share the ability to vary the print image and text from one print to the next, and all do not directly contact the print surface, which enables the printing of delicate and fragile materials from silicon PCB boards to cupcake icing. Inkjets can print substrates directly or indirectly to transfer papers, e.g. dye sublimation, or to an offset blanket, as with nanography, before transferring the print image to a substrate. As digitally controlled print methods, all inkjet systems

Vince Cahill, ASDPT Member, and Owner of VCE Solutions; with contribution from Dene Taylor, Ph.D., SPF-Inc.

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The Limitations of Inkjet: Future Applications

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can run from online-communicated files facilitating distribution, print and web-to-print business models virtually anywhere connected to the Internet. In addition, most inkjet methods provide cost-effective short print runs due to fewer prepress steps and expenses. They do not require the making of plates as with offset and other analog methods, nor do they require screens as with screen print. They do not incur the expense of film, plate or screen making, or storage common to analog print methods. They can produce less ink and cleanup waste, although DOD solvent- and aqueous-based ink systems waste ink when refreshing nozzles to prevent their drying. Inkjet systems enable very fast market sampling, personalizing, customizing and prototyping for both 2D and 3D print applications.

The Right ApplicationInkjet methods differ from each other in the ways they perform and for which applications they are best suited. Some inkjet printheads, like the Epson PrecisionCore PIJ, use small volume primary drops and grayscale, i.e. depositing multiple-sized dots from combinations of primary drops to produce high-resolution photographic quality images, while others jet larger drops to print low-resolution billboard graphics or carpet patterns, or jet live cells to build body parts.

Some inkjet engines can print satisfactorily in dusty environments while others would quickly fail. Trident push mode PIJ heads print corrugated card in environments rich with paper dust. They are even able to jet through some dust that might contaminate their nozzle plates. Alchemie Technology Ltd now offers the stainless steel Trident heads as part of their print solutions for dispensing a wide range of functional and biologic fluids. Some inkjet printheads can deposit precise amounts of material very accurately, while others print less precisely and accurately, but provide other qualities such as thicker deposit or faster print speed that are desirable for other applications.

Analog Isn’t Going AnywhereWhile some inkjet methods of fer advantages over certain analog print methods for particular applications, analog methods still supply the most cost-effective solutions for many. Inkjet methods can print electronic circuits, but analog methods produce the overwhelming number of printed circuits today and for the foreseeable future. Screen printing,

Chart 1: Inkjet Technologies

Chart 2: Continuous Inkjet (CIJ)

for instance, can print thicker and more robust circuit lines of lower cost conductive materials that can flow greater amounts of current and produce circuits at much faster speeds than current inkjet methods. But inkjet can print circuits competitively and cost effectively for prototypes and short run applications.

In genera l, major ana log print technologies, including screen print, gravure, offset lithography and flexography, tend to be more cost effective and retain their market position for longer print runs of the same image, while inkjet and other digital methods prove more cost effective for short print runs or where images vary in a print run. Analog contact print methods apply lateral and downward forces during their print process. These forces are often sufficient to overcome or reduce the effects of surface energy incompatibilities between ink and substrate. On the other hand, since inkjet is a noncontact print method, ink and substrate energy interaction is critical to the adhesion of ink to its intended substrate. As a general rule for noncontact inkjet printing, material surface energy minus ink surface tension should be equal or greater than 20 mN/m. While analog methods can apply forces to adhere ink to print surfaces that overcome some surface incompatibilities, such pressures can make it difficult to impossible to print on some

materials. Noncontact inkjet can print delicate and dimensional substrates that most analog methods cannot. Inkjet also is typically a preferred choice for printing personalized and custom images, and for placing unique codes on packaging and beverage cans.

Continuous Inkjet SystemsCont inuous inkjet sy stems (CIJ) have provided the main method for automatically marking dates and codes on beverage cans and other packaging as well as digital postal franking with single-pass speed for almost 50 years. Continuous inkjet technology typically generates drops at about 100 kHz, with one type capable of ejecting drops at 1,000 kHz. CIJ heads can also jet and place their drops accurately over greater throw distances than PIJ DOD and TIJ DOD heads. Their continuous jetting action prevents nozzle clogging that can happen with DOD heads that use solvent and aqueous-based inks. While CIJ systems have dominated the narrow-format marking and coding industry, the initial capital cost of these primarily single nozzle heads and the relatively low resolution that CIJ head arrays can produce have restricted their use for most wide-format applications. Some of the early super-wide format inkjet billboard printers employed


Chart 3: Piezo Inkjet (PIJ)


CIJ technology. For example, Scitex used Imaje CIJ heads for its billboard models. But these systems used inks containing aggressive and toxic solvents, such as MEK, to bite into vinyl and other plastic banner substrates and evaporate rapidly to control dot gain. Scitex, with its Hertz CIJ Iris printer, and Stork, with its print proofing devices created digital capabilities for printing textiles and producing commercial print color proofs. But their drum-based configurations limited the size of their prints. Though relatively high resolution, they took a long time to produce a print. The arrival of faster and less expensive high-resolution DOD printers resulted in manufacturers discontinuing these Hertz CIJ proofing devices. Imaje also promoted the use of its CIJ heads for printing textiles. They

supply their CIJ heads for the Osiris Isis single-pass textile printing system that TenCate, headquartered in the Netherlands, has acquired. Despite its high throughput speed, its high capital cost and low resolution of the Isis system has inhibited its market adoption.

Corrugated Packaging and BeyondScanning printhead or scanning table inkjet systems are typically slower in producing prints than comparable analog and other digital print systems that cover the full print width and print with one pass. In the last 10 years, inkjet equipment manufacturers have acted

to reduce the processing time of their products by developing printing systems that employ scanning printhead arrays that print a larger swath and full print-width arrays of printheads. During the first years of this century, Sun Chemical enlisted and sponsored the innovative team at Inca Digital to create a single-pass PIJ printer for imaging corrugated board used in box packaging. About a decade ago, I visited a company in Ely, United Kingdom that used the resulting beta version of Inca Digital’s engineering known as the FastJet UV. Sun Chemical stepped away from the project a few years later, even though users of the device would have consumed considerable volumes of Sun’s ink. System glitches eventually led to FastJet’s cancelation. Sun Chemical placed only three beta versions of the device, all of which are no longer operating. Inca Digital continued to develop inkjet printers for corrugated and other flat card and sheet applications. Its current Onset line of flatbed inkjet printers produces high-quality, UV-cured prints automatically. While offering large arrays of printheads on the fast Onset print line, Inca’s printhead configuration does not yield the even faster single-pass print speeds. Durst, first with its now discontinued Rhopac and more recently with the Rho 1300, also addressed the demands for an inkjet folding carton automated flatbed system. Scitex Vision, now part of HP, and others have also targeted corrugated and folding carton markets with their scanning head inkjet machines.

Inkjet printhead manufacturers have developed and are continuing to develop DOD inkjet heads with larger print widths for both PIJ and TIJ heads, along with continuous inkflow features for PIJ heads to overcome other limitations of inkjet. The larger print width reduces the

Chart 4: Thermal Inkjet (TIJ)

Durst Rho 1300

cost per nozzle of these heads in addition to facilitating faster, more accurate head alignment. For the Xaar 1001 and 1002, Fujifilm Dimatix Starfire, and the newly announced Ricoh MH2830 Flow Through model, continuous f luid f low through the printhead prevents pigment and other particles from settling and air pockets from developing and clogging printhead ink channels and nozzles. The ceramics industry has adopted print systems using the Xaar and Dimatix flow through heads to the point where these PIJ inkjet printers are replacing screen printing as the primary means for decorating ceramic tile.

A number of production equipment manufacturers have also developed DOD single-pass printer systems, targeting various applications including packaging, rigid materials, textiles and commercial paper printing. All of these systems are very fast and are beginning to compete with analog print methods, but they have their own limitations.

Product SolutionsSun Automation Group (not part of Sun Chemical) and Barberan of Barcelona, Spa in have developed automated single-pass inkjet printing systems for corrugated-folding carton applications. Sun Automation has designed it s CorrStream line of single-pass inkjets using Kyocera heads jetting aqueous based pigmented inks. It reportedly has placed its CorrStream 20, which offers a 557 millimeters (about 20 inches) print width. The company also offers the CorrStream in 40 and 66-inch print width models. Barberan also produces its JetMaster single-pass inkjet printer in three widths, 840 millimeters (33 inches), 1050 millimeters (41.3 inches) and 1260 millimeters (49.6 inches). Barberan designed its single-pass inkjet systems for printing high-resolution images on not just cardboard, but wood, melamine, paper, particleboard, MDF, HDF and other materials, each requiring coating or other preparation before printing. Barberan offers preprint and finishing equipment to work with the JetMaster printers, and the JetMaster BIJB printer can be used as a stand-alone machine or in line with other manufacturing lines. They offer a maximum throughput printing speed of 55 meters per minute with physical resolution of 360 dpi, and 1200 dpi apparent resolution due to its CYMK heads’ grayscale capabilities.

According to Barberan, the JetMaster models offer three processing modes:

1. Discrete mode: The machine prints the same picture on all boards.

2. Roller mode: The machine prints an endless design on all boards. The start and the end of the picture match perfectly the design on the next and the board before.

3. Random mode: This is similar to the roller mode, but in this case the picture of the boards will not coincide with the one on the next and prior board as the start is always different.

The CorrStream line prints aqueous pigmented inks through Kyocera KJ4 PIJ heads. Their CYMK inks produce flat color prints that lack attention grabbing “pop” that product promoters desire for their primary product packaging, but have found acceptable for secondary box packages. Jetting pigment particles in aqueous-based ink consistently through KJ4 heads can prove challenging due to the tendency of pigment particles to block its nozzles and ink channels resulting in streaking and rejected prints. Ink recirculation and nozzle monitoring can help to limit the damage. Sun Automation’s CorrStream printers are just entering the market and will have the opportunity to prove themselves.

The Barberan JetMaster printers, on the other hand, print UV curable inks. They can print images that stand out with a gloss finish, and can also print many more substrate types — not just coated corrugated card. UV inks also do not typically dry in nozzles as solvent and aqueous inks can. But free radical-curing UV inks suffer from oxygen inhibition and do not fully polymerize. Their photo initiators and unconnected monomers can migrate from their print film, which should be kept from contact with food.

HP’s Web Press uses the company’s advanced TIJ DOD printhead arrays to print for a number of targeted markets, including packaging and commercial printing. HP has placed and maintained many of these devices and has invested the time and expense to refine its offerings. TIJ heads, however, suffer with a limited life due to the build up of burnt ink, called kogation (from the Japanese word “koga,” meaning burnt rice), on its thermal bubble actuators. HP has formulated its inks to reduce the buildup and extend the life of its heads, but they typically do not last as long as PIJ heads.

MS Srl, a company recently acquired by Dover Holding Group which also owns Markem-Imaje, has placed 12 (as of February 2015) of its LaRio single-pass textile printers. The LaRio and the Reggiani ReNOIR use Kyocera KJ4B printheads that can generate as many as 16 grayscale, 15-sized drops from 4–72 pl. The LaRio uses a large full-width array of the heads, while the Reggiani uses a large head array that traverses across the print surface as it moves. The LaRio is rated to print 75 meters per minute of full color 600x600 dpi images. The inkjet ReNOIR is rated to print at about 150 meters per hour at 600x600 dpi. While primarily for textile printing, one user of the LaRio in Italy reports printing paper for sublimation transfers at 100 meters per minute. MS and Reggiani had recommended printing dye-based inks with these devices. Molecules dissolved in solution constitute dye-based inks, whereas pigment-based inks are composed of particles containing typically over 10,000 molecules that are coated with surfactants, dispersants and other chemicals suspended in solutions. Dye-based inks are significantly less likely to clog ink channels in the Kyocera KJ4B printheads than pigmented inks. In the fourth quarter of 2014, Reggiani and MS


Regianni Renoir


offered pigment solutions for use with their LaRio and ReNOIR printers. MS, with a dozen machines operating in the market, is gaining experience with the issue and challenges of single-pass textile printing. SPG Prints, formerly Stork Prints, is developing its own single-pass textile printer using Fujifilm’s Dimatix Samba variable drop PIJ printhead with continuous ink flow.

Keep It CleanAnother major concern for inkjet textile printing is that lint from textiles and garments can migrate to inkjet nozzle plates and block nozzles resulting in print streaks, rejects and wasted materials and effort. As previously mentioned, some inkjet printheads can tolerate some build up, but the Kyocera KJ4 is not one of them. OEMs of inkjet textile and corrugated board printers, including MS, Reggiani, La Meccanica, Durst, Konica Minolta, Mimaki, Mutoh and others, need to monitor nozzles for jet outs and incorporate automatic cleaning and recovery protocols with their print systems. They could also include some engineered solutions to eliminate lint or contain it from blocking inkjet nozzles in the first place. Also, print plant management should use other means to remove lint and dust from substrates and in their print environment.

OEMs have developed many single-pass inkjet solutions for printing labels, commercial paper and card that have been operationally successful, but also experience occasional lint contamination. Recirculating ink in PIJ heads also prevents jet outs from particles agglomerating and air bubbles forming to block nozzles.

Size LimitationsThe diameters of inkjet nozzles limit all inkjet printheads. As a general rule, the largest dimension of every ink particle needs to be no larger than one-fiftieth of the diameter of the nozzle through which it is jetted to prevent particles log jamming. For example:

• Epson PrecisionCore has nozzles with 20µm in diameter and should not have particles larger than 0.4µm in the ink.

• Fujifilm Dimatix Galaxy PH 256/80 have nozzles with 52µm diameters and should not have particles larger than 1µm in the ink.

The finer grinding of pigment particles that is necessary for jetting through most inkjet nozzles requires significantly more

grinding time and resulting expense. Four-color process pigments are often ground to a point where the largest particle dimension is less than half the wavelength of light, about 0.2 µm, thus making them inherently transparent, a desirable characteristic for process color. Most analog print methods use much coarser and less expensive pigment particle grinds resulting in significantly less expensive ink.

ViscosityViscosity is defined as a measure of a fluid’s resistance to flow and describes the internal friction of a moving fluid. Most inkjet printheads require very low viscosity for the fluids they jet, typically 20 cP or less. Two commonly used measures for viscosity are centipoise (cP) and mille Pascal.second (mPa.sec), where 1cP = 1mPa.sec. At 20 degrees Celsius, water’s viscosity = 1cP, corn oil = 72 cP, glycerin = 1490 cP, ketchup = >50,000 cP. When comparing inkjet ink viscosity with that of analog printing inks, we see how much more viscous analog inks are. UV-cure screen print inks range from about 1,000 to 3,000 cP, solvent and aqueous screen ink range from about 1,000 to about 10,000 cP, and plastisol inks have viscosity >20,000 cP. Offset lithographic inks range from 40,000 to 100,000 cP. Flexographic and gravure inks range from 50 to about 500 cP. In general for plastics, longer polymeric chains result in higher viscosities. More robust polymers typically have longer chains and higher viscosity.

Heating polymers and other materials lowers their viscosity. As a rule of thumb, viscosity decreases two percent for each degree Celsius rise in fluids. Heating inks can lower the viscosity of more substantive polymers to levels where inkjet heads can jet them. In the case of hot-melt inks, heated ink reservoirs and ink channels can melt wax-based solids and jet their drops to a substrate where they solidify on contact. Heaters and thermistors on ink reservoirs and printheads can also melt and jet some thermoplastic materials. Most PIJ printheads can function at temperatures of 40–45 degrees Celsius. Ricoh’s Gen 4 and 5 heads are rated to function at temperatures up to 60 degrees Celsius. The company certifies its Gen3 and Gen 4L heads to function at 80 degrees Celsius. Fujifilm Dimatix offers PIJ heads certified to jet fluids at 135 degrees Celsius. Xerox indicates that its T and M-series bend mode PIJ heads can tolerate 140 degrees Celsius. Océ

also created a high temperature hot melt CrystalPoint PIJ head. The amount and consistency of pressure moving fluid along to the printhead can also affect print consistency and quality.

Meeting Customer ExpectationDebbie Thorp2 , Business Development Director for Global Inkjet Systems of Cambridge, United Kingdom, emphasized in her recent IMI Inkjet Conference presentations the complexity of creating and controlling inkjet systems to produce the desired and customer expected image quality. She described how producing print quality that appeals and performs requires the integration of inks, substrates, encoders, RIP, linearization and color management software, printheads, print processes, mechanical devices and more. Each of these items includes a number of issues for which to account. For example, integrating ink into a PIJ graphics system to produce the desired result requires accounting for and controlling color gamut, ink temperature, dissolved gas, f low rate and meniscus pressure. Also changes to one item can impact others and require adjustments throughout the system, further underscoring the complex challenges that inkjet developers and integrators face.

They must also be aware of what others are developing and claiming as their property. Mike Willis of Pivotal Resources Limited and some others scan and review more than 300 national and international patents issued each month and help keep their clients abreast of developments. Willis recently described patents for new inkjet printheads featuring various fluid recirculation strategies from Konica Minolta, Océ and Samsung for PIJ heads, and from Hewlett Packard and Lexmark for TIJ heads. He also described offset indirect inkjet systems from Canon, Xerox, Landa, Hewlett Packard, Ricoh and Seiko Epson. As inkjet technology progresses, covering, comprehending and controlling its technical and legal aspects grows even more complex and challenging.

Moving to 3DAs we move from 2D inkjet to 3D, the challenges and limitations compound. Yet these challenges are also opportunities to innovate technology, satisfy customers and grow business. Also, many other digita l technologies, as well as the improvements of analog, compete with inkjet. Stereolithography, selective laser sintering and melting, fused deposition

modeling and many more outcompete inkjet for many applications. Inkjet 3D printers from Stratasys and 3D Systems have established their usefulness and market positions for rapid prototyping, tooling and casting, but have not gained a market foothold for building product and parts production. Direct inkjet deposit of materials requires the printing of support materials that are removed as waste before the object is finished. Also, the direct inkjet deposit systems use free radical UV-curable materials to build objects. These materials contain photoinitiators and uncured chemistry that interfere with build strength and limit their mechanical properties.

ExOne has developed an inkjet binding system using Fujifilm Dimatix Q-class heads for building metal parts. But the inkjet build is only the first step toward making a product. Its process requires high heat to evaporate the inkjet binder and sinter the metal particles of the built part and further heating and infusion with additional metal to create marketable production parts. The results are impressive and ExOne is placing its systems, but inkjet is just the first step in production.

MicroFab of Plano, Texas uses PIJ heads to deposit different materials including biologic materials and cells. These systems are relatively slow, but enable the deposit of larger particles and more viscous substances than other inkjet systems. But nozzles constrain even these systems. Laser Induced Forward Transfer (LIFT), originally introduced in the mid 1980’s, deposits material without the constriction of a nozzle. Rather, it uses the focused energy of a laser to release drops from a film of material coated on a polyester sheet. The LIFT carrier, as with inkjet, does not contact the substrate. It has had limited application due to its dependence on a coated sheet that is not rechargeable and results in both waste and expense. Photon-Jet of Israel has invented and is developing a rechargeable LIFT type system. It has the ability to print materials with viscosities ranging from 2 to 20,000+cP. Since it is nozzleless, it can print much larger particles and cells than inkjet systems. It offers the promise of depositing inks that are much less expensive than current highly refined inkjet inks. It can print the less expensive inks that analog systems use, and can also deposit biologic materials and live cells with little cell loss. As an innovation in its early stages of development, however,



it has a way to go before it begins to work its magic commercially. But it could prove disruptive to inkjet technology in the long run, particularly where inkjet’s limitations prevent the use of less expensive, more durable or delicate materials.

Maintaining MomentumIn the past few years, inkjet has proven its value for 3D enhancement of 2D graphic prints. Scodix of Israel, MGI of France, Roland, Mimaki and Screen of Japan have added 3D textures and other effects using inkjet printheads. Direct Color System (Rocky Hill, Connecticut) has developed a 3D enhancement inkjet system that prints raised graphics that meet the Americans with Disabilities Act standards for printing Domed Grade 2 Braille characters with heights between 600–900 micrometers.

Inkjet has considerable momentum for the next decade. Its advantages and constant improvement fueled by large corporate investment will undoubtedly move forward with printer placements for packaging, variable data and images, commercial print, textile and garment printing, 3D rapid prototyping and casting,

ceramic tile printing and more. But one should not lose sight of the technology’s limitations and the complexities associated with its development and implementation. Also, developers of other technologies, both analog and digital, are not standing still. Many of these already best inkjet for providing many applications.

Vince Cahill, President of VCE Solutions, provides consulting services for Fortune 500 and other companies operating in the analog and digital printing industries. He has also served as a Principal in The Colorworks, where he has a 25-plus year career in specialty graphics. Previously, Cahill served as CEO of Datametrics Corp. as well as Principal and Technology Developer for Newhill Technologies and GDI, which are devoted to digital printings applications. He is a longtime volunteer with SGIA, serving on the Association's Textile Committee for several years. Cahill has contributed several articles to the SGIA Journal.

For more than three decades, Dr. Dene Taylor has been leading printing product and process developments. He has contributed to

SGIA conferences and publications for much of that time. His experience with digital printing began in 1987 at James River Graphics, a leader in inkjet and electrostatic wide format imaging. Developing systems for novel applications is core business at his consultancy, for SPF-Inc. Current activity is with UV and EB cure inkjet.

1 IMI Inkjet Conference 2015, Orlando, Mark Hanley’s presentation, “The Renaissance of the Print Industry: InkJet’s Unstoppable Forward Momentum”

2 IMI 2015 Inkjet Conference, Orlando, Florida. See also November-December 2014 SGIA Journal, “Inkjet Surface Decoration — Market Overview and Challenges”

the limitations of inkjet: future applications

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