The ‘Inkjet Set’
Conferences, trade shows, and other gatherings of inkjet aficionados are growing in size and frequency every year, crossing technological and international boundaries. Up-and-coming inkjet industry leaders, engineers, and the otherwise curious are flocking to learn, exchange information, and see new gadgets fresh out of development and on the market.

One such gathering earlier this year, the 16th annual Inkjet Printing Conference (sponsored by Information Management Institute of Maine), attracted more than 150 participants and exhibitors from the U.S. and Canada to Japan, Korea, the UK, and Netherlands. This conference, among many others, was preceded by an informative Inkjet Academy – taught by influential industry founders – designed to bring the novice up to speed in a mere day and a half.

According to the “veterans” in this 20-something-year-old industry: as of January this year, over 100 inkjet-related patents are being published each month. Rapid advances are being made not only in the broadening variety of printhead technologies but also, in ink and substrate development, inkjet applications, and print quality improvements.

The Basics
Inkjet – the direct transfer of ink to substrate – is being called today’s “electronic fountain pen.” Some tout it as the simplest of printing technologies, involving only a printhead and ink. But as is often the case with the “simplest” anything, there are many exacting details to perfect before achieving widespread success.

The advantages of inkjet are many, including its non-contact nature, its speed and ink savings, its need for fewer consumable parts, its wide range of color capabilities, and its potential for large format printing. The disadvantages center mainly around the technology’s prime component: the inks. Inks bleed, leak, stain, clog, fade, dry at different rates, and – because they are an airborne liquid in this process– inks are subject to the laws of gravity and physics. Current jetting limitations and ink drying times require that printheads be very close to the substrate, thus limiting variations in surface depth and contours.

A Mere ‘Inkling’
Understanding inks ultimately involves understanding fluid dynamics; that is, how various liquids react and respond when subjected to different stresses and environments. These can be predicted, somewhat, by their contents. Inks can be water-based (aqueous,) oil-based, solvent-based, phase change (with waxes and long-chain organics), and UV curable. The ingredients include a liquid carrier (water, solvent, oil) plus binders (polymers), colorants (dyes and pigments), and additives (surfactants and conductivity salts).

The ink’s complexity influences the jets’ reliability and stability, and how well they perform in a given application. Further, reliability is a function of nearly a dozen components, including nozzle design and exit contact angle, plus the ink’s molecular weight and viscoelasticity. Streaking, lines, and print voids due to nozzle dropouts and clogging are just a few of the visible results of failed performance. Add that to the ink’s interaction with the substrate – whether it is plastic, paper, glass, or metal – and the equation is further complicated.

Ahead of the Curve
Researchers, in addition to tinkering with the inks, are currently expanding on two basic types of printheads: continuous drop and drop-on-demand. Continuous drop technology works as its name implies: drops are generated continuously from the printhead, and turned into print via a deflection and capture technology. Drop-on-demand (DOD) only generates drops when required, and is used in thermal/bubble jet and piezo/electrostatic printhead technologies.

Additionally, each technology “phylum” has its own related genus and species; i.e., piezo is divided into direct and acoustic-type head design, and direct is further split into roof, tube, moving wall, and piston-type jet designs. That diversification also holds true for thermal, electrostatic, and Micro Electrical Mechanical Systems (MEMS) classes of DOD technology.

How these technologies work is another wonder of modern science. With thermal or bubble jet, a heater inside the jet causes a bubble to form. The bubble expands rapidly, like a micro-explosion, and creates a pressure wave that forces a drop of ink from the jet. With the piezo and electrostatic technologies, the actuating materials are distorted when an electric field is introduced, thus forcing the ink from the chamber through the jet.

Time is Money
Each jetting method has its uses. Continuous heads are good for marking and coding (43 m2/hour at 60 dpi), proofing (6.1 m2/hour at 1,500 dpi), and high-speed web printing (6,100 m2/hour at 300 dpi). The continuous drop technology currently is seen with high-speed applications like time, date, and product codes on plastic packaging (it’s the lettering that looks like antique dot matrix type from the prehistoric days of printers with ribbons) or the printing of utility bills on a paper web.

The DOD thermal/bubble jets are prominent in home markets – as are the piezo letter-size printers for photos – and are capable of 1,200 to 1,400 dpi at a speed of 10 to 11 pages per minute. The DOD piezo flatbed for commercial photo-quality production can achieve up to 1,000 dpi with a speed of 130 m2/hour; and on an extra large web, the piezo technology can reach 900 m2/hour, with 300 dpi.

Of course, getting both high speed and high quality comes with a price tag. While the home peripheral costs under $100, industrial jet large scale webs start at $1 million and up… just a drop in the $30 billion-plus market that inkjet currently enjoys.

The Future is Now
As inkjet technology overcomes the logistical speed bumps of printheads and inks, more challenges are being presented in the guise of consumer and industry demands. The “more/faster” generation also wants bigger, shinier, easier, simpler, and cheaper. To that end, engineers are exploring new printhead materials like silicon that allow greater miniaturization and faster manufacturing techniques such as resist etching and laser burning.

Soon home users will be buying printers featuring page-wide inkjet arrays with tens of thousands of nozzles. As micro technologies become more streamlined, the current $30 billion market is predicted to at least double in the next few years for plastics decorators, high-volume office printers, light industrial production, retail photo, and other consumer printing sales.

And that’s not even counting the uses that lie ahead: X-treme scale weatherproof signage and outdoor decorating, widespread industrial uses, textile applications, and materials deposition for diverse fields such as Radio Frequency Identification (RFID) technology, printed circuit boards, and 3-D prototyping. Stretching the imagination, inkjet someday may be the preferred printing method for all types of packaging, wall and floor coverings, and even flat panel electronic displays.

For those wanting to immerse themselves in the growing field of inkjet, the upcoming Inkjet 2007 Technology Suppliers Showcase will be May 30 - June 1, 2007, in Barcelona, Spain, preceded by the Inkjet Academy: Theory of Inkjet Technology, taught by Mike Willis of Pivotal Resources and Alan Hudd of Xennia Technology. For more information about the event, visit www.imieurope.com.

Annette M. Sharon works as lead technical writer at Ink Jet Machinery of Vermont, a wholly owned subsidiary of Pad Print Machinery of Vermont. The company now offers a line of monochromatic industrial flatbed and rotary inkjet machines, and is developing a complete line of inkjet systems for broad industrial applications. For more information, call (802) 362-0844 ext. 233 or e-mail [email protected].