Inkjet Innovation

The story of the inkjet printer is one of continual innovation and astonishing success, as a technology that once seemed little more than a low-cost alternative to laser has grown dramatically in terms of speed, reliability, running costs and quality. Today, it’s the print technology that pretty much does it all. You’ll find inkjet printers in the home printing homework, art projects or family photos, and inkjets in the office handling the kind of high-speed, high-volume workloads that used to be reserved for lasers. You’ll find inkjets putting out professional-quality prints in design studios and print shops, and inkjets being used to print out fine-art photography for galleries. Where the earliest inkjets printed at speeds of 2ppm (pages per minute) at a low resolution of 300dpi, today’s models are capable of speeds of 70ppm and resolutions in excess of 1,200dpi – or up to 9,600dpi with optimisation.

The majority of today’s inkjet printers still work along the same lines as the original HP DeskJet, launched in 1988. In a conventional thermal inkjet, a print head moves left to right and right to left across the paper, dispensing tiny droplets of ink along the line. The ink is fired onto the paper from a multitude of tiny chambers in the head, each containing ink supplied from an ink reservoir, a nozzle and a heating element. A pulse of current passing through the element causes the ink to vaporize and form a bubble, which bursts through the nozzle propelling ink onto the sheet. Surface tension then pulls a further charge of ink from the reservoir into each chamber. Once each line is completed, the paper is moved upwards by a tiny amount to print the next, and so on until the current page is finished and the paper hits the output tray.

Pioneered by Canon engineer Ichiro Endo, this mechanism became the basis for thermal inkjet printers from Canon, HP and a range of others. Engineers at Epson developed a rival system, Piezoelectric Inkjet printing. This used a similar idea but with the thermal element replaced by a piezoelectric material, which changes shape when current is applied. This generates a pulse of pressure in the ink, forcing a droplet through the nozzle.

The HP ThinkJet and the Canon BJ-80 Bubblejet were the first inkjet printers to hit the market, but it was HP’s DeskJet that bought the technology into the mainstream. It was the first single-sheet printer that could actually sit on a desk, and was priced at a level small businesses could afford. It sold over one million units in its first year on sale.

By 1991, the first mass-market colour inkjets had appeared, including HP’s DeskJet 500C. The first colour inkjets worked by the same principals as the original monochrome DeskJets, but used three inks – Cyan, Magenta and Yellow – to create patterns of tiny coloured dots that create the illusion of a full-colour image. Black had to be formed by mixing the three process colours together, but the result was often more of a muddy dark green, so the next generation of colour inkjets added a separate black cartridge that either replaced or co-existed with the three-colour cartridge.

Along the way, inkjets developed in terms of speed and resolution, reaching resolutions of 600 or 720dpi and speeds of 4ppm in mono or 0.5ppm in colour. Meanwhile, more and more intelligent optimisation techniques like HP’s REt or ColorSmart enhanced the definition of black and white prints, while improving the inklets’ reproduction of a wider range of colours.

The evolution of inkjet technology has always focused on the development of new print-heads and mechanisms, yet this has necessarily gone hand-in-hand with the development of new inks and even new papers. The drops deposited by the original DeskJet were 85pl, and the ThinkJet before that had drops of 180pl. By 1998 it was possible to create dots under 10pl in volume. New inks enabled smaller and more accurate print-heads to fire without clogging, and also allowed for more vibrant and accurate colours, which were also more resistant to the effects of sunlight and time. New specialist papers could hold these smaller ink drops without the ink soaking into the grain, spoiling clarity and losing colour.

During the mid-to-late 1990s, resolutions climbed further to 1,200 and 1,440dpi, and this, along with the developments in ink and media allowed manufacturers to talk meaningfully about photo-quality printing for the first time. They started to experiment with dedicated photo cartridges, which contained additional light cyan and light magenta inks for photo printing and replaced the standard black ink. New Inkjets didn’t simply rely on dithered patterns of coloured dots, either, but on the precise layering of one dot on top of another to create a wider range of tones. Print-heads were also developed that could fire droplets of different sizes to make dithering even more effective. By the end of the nineties, HP was producing 1,200dpi printers capable of producing optimised prints that looked like 2,400dpi, at speeds of 12ppm in black and white and 10ppm in colour.

Meanwhile, inkjet printers were growing more flexible and versatile. Manufacturers began adding scanning and fax capabilities to inkjet printers, transforming them into multi-function devices that could print, scan, fax and make full-colour copies at a fraction of the price of dedicated appliances. USB connectivity made it easier to get a printer up and running, before the introduction of first Bluetooth and then Wi-Fi wireless communications made it possible for a PC and a printer to talk without a cable of any kind at all. During the last decade we’ve seen more Internet features being added, enabling you to send prints to a printer from almost anywhere and any device.

Today’s Inkjet printers are faster and more capable of incredible results than ever before, reaching speeds in excess of 30ppm in black and white and 20ppm in colour. Costs-per-page now reach below some laser printer levels, and with recycled cartridges, efficient power management and more effective cleaning routines, they’re more environmentally friendly than they’ve ever been.

Yet the development of the Inkjet isn’t over yet.  New full-page-width printers replace the moving print head of the conventional Inkjet with a static head that spreads across the width of the page, dispensing drops 1pl in size at speeds in excess of 60ppm in black and white or colour. HP’s PageWide technology, as found in the latest OfficeJet Pro X series printers, can print at 70ppm in standard mode or 42ppm in high-quality black-and-white or colour. These are laser-beating speeds at laser-beating prices; although for high duty cycle offices, laser printing will still work out the better option. Inkjet is a technology that has triumphed over every challenge, and it doesn’t look like it’s going to stop any time soon.

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