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ink-jet printing today

Introduction

The quality of ink-jet printing has come a long way in the past ten years. "An ink-jet was a poor man's substitute for a laser printer," I was told at the time. Of course, in the late eighties, few people were talking about color in the desktop environment.

So what has changed so radically in the intervening period? It is the general availability of in-house color printing and the democratization of the technology. After all, in the early nineties it was perfectly possible to buy a color Printer which produced high-quality results. The machine was so expensive, however, that it was kept in a service bureau or printing shop where the only way of amortizing the investment was to make sure it was occupied day and night with well-paid commercial orders. As for the home office, Hewlett Packard had just launched the first monochrome ink-jet at a price of almost $1700.

Today it is possible to buy a color ink-jet printer which can produce results so close to a real photograph that you have to take a magnifying glass to see the difference (more below) and the price of the hardware is now very reasonable. Indeed, you will more readily perceive the halftone screening in a top-quality four-color page (i.e., offset). Recent consumer research revealed that when a printer is bought today by the general public, nine out of ten machines are of the ink-jet type.

Good resolutions

The resolution of the printing heads has increased in the meantime from 360 to 1440 dots per inch. This enables the printer to squirt much finer drops of ink, 6 picoliters  in the case of the Epson Stylus 1200, 4 pl for the model 1160 and soon 3 pl. The first generation of jets used three primary colors plus black , but some entry-level models produced black (closer to purple-brown) through mixing all three primaries. Recent versions of Canon and Epson printers now feature six or seven colours to improve pastel tones.

More than 15 years ago, laser printers already provided outstandingly sharp text, have come down somewhat in price and are the answer for general office use where more than 50 pages have to churned out per day. Yet, the color lasers have not developed at the same rate as the ink-jet family - and for good reasons. But, wait a minute, whereas the home user buys a budget-priced ink-jet because he can switch from black and white to color whenever he wants (polyvalent), the graphic designer, photographer, artist as well as the liberal professions have other considerations in mind. From A3/tabloid upwards, where are the lasers? Well, all right, there is the Minolta or the Canon CLC series, but these big copiers (with associated RIP) are in the five-figure dollar bracket. The answer is that this graphics market is dominated by the thermal transfer, sublimation and ink-jet types.

So after a generation in which ink-jet printers served individuals and the small-to-medium office, later began to penetrate the domains of digital photography and pre press in the form of proofing machines, such as the Iris (Scitex), Stork and Epson 5000, the ink-jet technique is now in the throes of advancing into the territory of wide-format printing. The Calcomp CrystalJet, RasterGraphics PiezoPrint, Roland CammJet , Hewlett Packard DesignJet, the Novajet Pro series and the Mimaki JV 1300 are examples of machines which look a little like the former plotters for architecture and CAO but integrate an ink-jet head instead of a pen-holder.

The principles

How do these ink-jets function? There are quite a number of ways of getting ink, pigment or wax onto a sheet of paper or other substrate, yet only three main methods are commercially exploited today: spitting, heating and zapping. The first category spits individual dots at the paper. The second applies heat - directly - to a wax or resin matrix, ribbon or other proprietary consumable to transfer the colors individually to the paper. And the 'zappers'? Well, these are the lasers or electrophotographic type. Of course, there are sub-categories and hybrids in each group. What complicates the verbal specification is that manufacturers are not in agreement as to what each type of machine should be called. For instance, a thermal dye transfer printer is sometimes known as a dye sublimation printer (dye sub) while other purists insist on dye diffusion printers. But that is not the real issue here. On this particular site I am concerned solely with the spitters (ink-jets), with a preference for the piezo family.

The ink-jet quartet

1. In the pièzo-electric system, of which Epson is the major exponent, a slice of pièzo-electric quartz flexes when it is subjected to pulses of electric current, thus ejecting a droplet of ink towards the paper via an extremely fine orifice.
2. The bubble-jet system is employed by the majority of other popular desktop printers, the most notable contender being Canon. Here the droplet is expelled because its container is suddenly heated.

3. The solid wax type is still relatively rare. The leading manufacturer in this sector is Tektronix. These used to be called phase-change printers, because the colorant changed from a solid to a liquid and then back to a solid. Just remember they are fed with solid sticks of wax and spit wax instead of ink. The results are of the very best, but these machines still represent a relatively big investment.

4. Whereas the above types are 'drop-on-demand', there is one monster which just sprays all the time. Ink not needed for the image is deflected and recycled The most famous of this breed is the wide-format Iris made by Scitex. The image is in fact continuous.

Piezo in particular

It is not difficult to understand that if a multi-layer pièzo-electric element is associated with a tiny piston and current applied to the former, the latter will oscillate as a result. It is then possible to imagine how a droplet of ink squirts through an opening at the other end. What is so amazing is the degree of miniaturization which Epson and others have obtained in this respect. After all, each nozzle requires one of these minuscule piezo-pistons behind it. The Stylus Photo EX, for example, has 160 color nozzles in quite a small head. In some of the larger, high-output ink-jets, there are over 1000 nozzles. A drop of 10 picoliters ( 1 pl = a trillionth of a liter) measures 26.7 micron in diameter. Yet Epson has dropped below the volume of 6 pl for each dot. These are said to measure between 30 and 45 micron in diameter after splashing. (0ne micron is a millionth of a meter). If one takes a resolution of 1440 dpi, this would leave a space of about 18 micron between the dots. You would need quite a high-power microscope to measure all this yourself.

Hewlett Packard prefers to change the print head with every fresh ink cartridge. Nice argument against blocked nozzles. Yet, the life of the piezo head is considerably longer, and then what about calibration? With such microscopic manufacturing tolerances, the droplets are bound to emerge in a slightly different fashion. The custom color profile can only apply to one set of circumstances.

The disadvantages

As is many walks of life, there is often a catch somewhere. Ask Canon, HP or Epson to send you a genuine sample produced by their top "photo-centric" ink-jets and you will be amazed at the brilliance and reality. Yet, they are bound to have printed that vintage automobile on special glossy paper which costs more than an equivalent sheet of photo paper, and the ink comes in at about the same price, per ccm, as Guerlain perfume. Thus, the consumables are an important factor to take into account when considering employing ink-jets for volume work. Of course, it is not always necessary to use double-weight glossy paper. There are other possibilities which provide excellent results, depending on the application. Indeed, in the larger formats, a matt surface, watercolor paper or other textured substrate appears to please the art world to a greater extent. What critics tend to overlook here is the fact that classic artist's materials have never been all that cheap. If you are not one of the painting fraternity, drop into an art store the next time you have a chance and look what a even a 42 x 60 cm canvas costs plus a handful of oil or acrylic paint tubes.

Will it last?

As for the archival issue and those who would like to be sure that their prints will still be visible for the next generation, this is a serious question. Hang an unprotected print on your office wall in the sun and it will fade within a year. Yet, solutions to these problems are on the way, there are immediate precautions anyone can take to slow down the deterioration and it will be the purpose of a separate column to share news of current progress and provide advice on these and allied subjects. The safeguard is to keep a copy of your masterpiece not only in the dark but also on digital media. Will your descendants be able to print the file again in seventy years? Who can tell....

The authority on print permanence is Henry Wilhelm at:   www.wilhlem-research.com

See also:  Wide-format printing

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Copyright©: Brian Morrison

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