Lord Rayleigh

Who would have thought that Inkjet technology is one of the oldest technologies? Yes, you hear right. While the printing industry has only discovered it in the last 20 years, it has been around much longer. Sabine A Slaughter investigates its roots.

The triumphant success that inkjet technology has attained within the last 10 to 20 years is based on science and research covering almost 300 years of history. Although commercialisation and professional availability only cover a short period in history, the principles and basis theories referring to inkjet have been researched more than 200 years ago. The French scholar and cleric Abbé Jean Antoine Nollet already published a report in 1749 on the effects exerted by static charge on a drop. As part of his research on osmotic pressure and only a year after, he invented the electroscope, a device for detection of electric charge, this has only been one of the many discoveries the 18th century had to offer.

It took many years – up to 1833 – when an elaboration from Savart was published. This one dealt with the usage of acoustic energy to produce uniform drops. Some years later, in 1859, Magnus presented his experiments with electrostatic drop deflection.

During this time, a young scholar, William Thomson, the later Lord Kelvin of Largs, was already actively engaged in the study of electricity and magnetism. At the age of 22 years, William Thomson was appointed as a professor at the University of Glasgow. During his tenure lasting 53 years, interrupted by some studies that he performed in his free period (at the time university years were calculated by half year studies and half year free time), he developed many groundbreaking inventions, among other things within the area of telegraphic communication. In his time, not only a temporary cable for telegraphic transfer between Calais and Dover – across the English Channel – has been laid, not only due to his findings.

The dream to also connect the Old and New world was born. However, difficulties such as not only time delays but also the attenuation of the signals over long distances were an issue. As a solution for the latter, he invented the mirror galvanometer. After receiving knighthood from Queen Victoria in 1866 for laying a transatlantic cable and with this the possibility to send messages, Lord Kelvin found that, in his opinion the mirror-galvanometer did not work efficiently enough. He replaced this, after years of research with a siphon recorder consisting of a small pin that looks out of a glass tube shaped like siphon. One end of the pen dipped in an ink tank, the other end wrote little messages in zigzag-lines on a paper that mechanically moved vertically along. The pen was triggered and moved horizontally by small signal charges that ran through a small coil between two electromagnetic poles. The ink then flows in small successive drops from the pen onto the paper. This method was made possible my electrification of the ink container and the ink as well as the contact of paper with a non-isolated metal roller. The magnetic attraction between both, the electrified and non-electrified materials – ink and paper – draws the ink drops that subsequently ended up on the paper without the pen touching it. The first – still rough – continuous inkjet system has been born when it was patented in 1874. Just two years later, telegraph systems were equipped with the Kelvin-recorder. Later, towards the end of the century, this technology was also used for oscillograph recordings.

A further important discovery in connection with inkjet technology was made by the future Nobel Prize winner Lord Rayleigh in 1882. In his research he found that electrically charged droplets change shape and form an ellipse during free fall under certain conditions. At both poles of the ellipse, fluid "rays" consisting of about 100 miniature drops, called jets, form. This instability of droplets calculated by the researcher, whose bourgeois name was John Willian Strutt. The calculation, the so-called Rayleigh limit, has been so accurate that it could only be recently confirmed by physicists at the University of Illmenau who watched the phenomenon with a special microscope and thereby confirmed the theory.

Mousemill motor for siphon recorderAfter Magnus, in 1859, already published the first studies relating to deflect electrostatic drops Hansell published further research results in 1929. In the beginnings of the 30s of the last century, RCA Communications used an ink jet recorder that pressed ink through a nozzle thus "broke" them into smaller droplets and sprayed those onto a rotating drum with paper. This was followed by experiments with pulsed output options regulated by compressive force.

The next big step towards inkjet systems was taken with the introduction of inkjet recorders in the 1950s and the subsequent developments in the 60s. Ascoli presented the first textprinter based on inkjet technology in 1955. After Richard G. Sweet received a patent on electrostatic deflecting ink jets in 1964, Paillard presented the first inkjet typewriter in 1965. All those presented writing devices worked with continuous flow technology based on an electrostatic pulling method. A perforated metal foil sits between nozzle and paper that only allows those drops to pass that are required to represent the respective character. The intensity of the charge of the individual ink drops thereby determines the reproduction. Print quality, due to the big distance between paper and nozzle, was very rough. The first inkjet printer was introduced two years later, in 1967, by IBM. Two more years passed until the first commercial inkjet printer from A.B. Dick Information Products Division (IPD), that after several name changes is now Videojet Technologies, was launched.

Images of a falling drop forming an ellipseDuring the 70s researchers worked feverishly on various technologies to develop and evolve inkjet printing, that already by then was predicted to have lots of potential. Zoltan received a patent on an inkjet method that used pulse technology in 1972. This drop-on-demand technology however was not mature at that time resulting in the fact that inkjet printers entering the market in the 70s employed continuous flow technology.

Images from falling drops forming an ellipse seen through a microscope at TU IllmenauThe first industrial inkjet marking system got introduced by IPD in 1972. The first large format inkjet printer the "Mead Dijit", launched in 1974, also employed continuous flow technology. This printer could already print with a resolution of 100 dpi and had a performance of four meters/minute. A better resolution was achieved in 1976 by IBM's inkjet printer 6640. While the printers still employed continuous flow technology, IPD introduced the first printer with multiple head technology in 1977.

The biggest problem facing the researchers was that the drop-on-demand technology needed to be developed in such a way that individual drop are only then ejected if and when they were needed. For print quality reasons, the distance between the nozzle and paper was greatly reduced. The intermediate metal foil of the early inkjet printers had to disappear due to the small distance. A logical conclusion was therefore that ink drop development had to happen already in the print head.

Thus, piezo technology has already been developed during the 70s. This technology uses crystals, so-called piezo crystals which act as a pump. Depending on the voltage, the crystals expand whereby ink is ejected or they contract and the ink is drawn. Per nozzle, a crystal is thus needed at exactly the right position. The first devices of this type were already middle of the 70s on the market. Initially they featured seven nozzles that already offered a better resolution than the then popular matrix printers, but had not yet enough nozzles to be attractive for all areas, industries or purposes.

As so often the case with inventions, chance played an important role in the discovery of thermal technology. On August 2, 1977, Ichiro Endo, then head of a research team at Canon, who wanted to improve piezo technology, accidentally hit the tip of a syringe filled with ink with a soldering iron. The result was a discharge of ink from the needle. This initially stunned the researcher. After further experiments, he discovered that it is possible to heat ink via a temperature impulse at the tip of the needle in such a way, that a bubble forms whereby the excess pressure ejects ink in form of an ink drop for relief. The discovery was called "bubble jet technology". Thus the development of a printhead, that contains a heating element regulating the discharge of drops by means of heat, started. Shortly thereafter, a patent was applied for. In 1978 Canon already started a project whose aim was to develop a digital copy system employing bubble jet printheads. 1979 Canon presented a device employing the bubble jet technology, as well as Hewlett-Packard (HP) that presented a quite similar thermal technology in a device, as showcase.

Some hurdles in drop-on-demand printing technology still had to be circumnavigated: the individual print nozzles still clogged up and got easily dirty; strong dependencies between ink and substrates existed. In 1981, Canon then presented the first copier based on bubble jet technology, the Canon Ink Jet Printer, featuring eight nozzles per millimetre. It's speed was eight pages per minute and it allowed for enlargements and downsizing, cut-outs and two colour copying. Even colours could be changed. The printhead covered the whole of the page in A4 size and had 1680 nozzles that could be addressed individually.

HP's first inkjet printer was introduced in 1987, the 2225 ThinkJet. Shortly afterwards the development of disposable cartridges. Problems for the nozzles that were caused due to fast drying ink, especially when heated and the specially coated paper that had to be used quite often, took further years of research. The "Super High Speed Color Graphic Recorder" and the BJ-80 were introduced by Canon in 1985.

Many manufacturers of inkjet printers with continuous flow technology also recognised the potential of drop-on-demand technology and began feverishly to develop solutions. Videojet introduced the Videojet Maxum in the 80s. Nevertheless, inkjet technology was still a very expensive investment during this period. The interaction between ink and media, whereby during this time, it was especially a substrate – paper- issue was not yet mature and the resolution was still comparatively low.

The first colour inkjet printer was introduced in 1987 by HP. Towards the end of the decade slowly issues such as clogging of printheads, contamination of nozzles and the relationship between ink and media were solved. The first printers by Canon and HP that could print on normal paper were introduced. Developments during this time proved, that it is possible to influence the flow of ink even further.

Despite all the developments inkjet printers remained at the beginning of the 90s and expensive item in offices. Very slowly the took a step towards the industrial sector, but the commercial market was not yet accessible. This only happened in the 90s when prices for desktop printers were slowly affordable for ordinary consumers with around $1,000. The first black and white printer with a resolution of 600 x 300 dpi was launched by HP in 1992 and only a year later the first four colour printer could be purchased at an affordable price.

The introduction of the first inkjet printers that could reproduce photographic quality in 1996 and further developments of ink cartridges and their capacities triggered the advent of large format printing and the acceptance of inkjet as a viable printing technology in this sector.

Already in 1997 the first super wide format printer, the UltraVu 5300 from VuteK, featuring a print width of five meters was introduced. It already employed a PostScript rip. The same company introduced the first super wide six colour printer in 1999.

The last years of the last millennium shows that in the area of capacity, speed, resolution and colour the last word has not been spoken for a long time. At drupa 2000 VuteK then presented the first inkjet printer for industrial applications that could print on both, rigid as well as flexible media. The PressVu, an eight colour printer with 360 dpi resolution gave users the ability to produce both outdoor and indoor applications as well as photo prints.

Read what happened after drupa 2000 and further information about inkjet history, technologies and applications you can read in the upcoming parts on our special on inkjet technology.

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