The never-ending search for the right type of printer

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Want better photo prints? Try a mix of blue ink, grains of rice and Arizona road dust.

HP’s high-end A3 photo inkjet, the Photosmart 8750, uses nine colours of ink. As well as cyan, magenta, yellow and black, there is a dark and a light grey to improve skin colours (and back and white photos). Light cyan and magenta produce better colours and smoother tones, but they do not give extra colours.

The ink research and design team at HP tests 700 inks a month; one went through 1,000 black ink prototypes. There is also a black in the Vivera ink range as dense as a laser print-out, gives smooth edges on plain paper (where black usually has a jagged edge) and works well on photo paper. The secret is the surfactants.

Ink has to heat up to 300°C, squeeze through a nozzle that is barely large enough for a red blood cell and fire on to the page at 30 miles an hour. Getting more and smaller nozzles closer together, perfectly aligned and shooting ink more often gives better quality and faster printing; ink scientist Nils Miller calls it “Moore’s law for printers”.

Instead of welding a sheet of nozzles on top of the pipes that carry the ink, HP etches the whole printhead as one unit by photolithography, packing on 4,000 nozzles that fire 24,000 drops per second. That is twice as fast as a 1995 Deskjet – and 20 times faster than the original 1984 Thinkjet. HP calls it Scalable Print Technology because it can put printheads side by side to speed things up.

A fast-drying paper helps. This has a porous coating that the ink soaks into straight away. Usually prints on porous paper fade quickly; HP has worked out a way of dealing with ozone and other airborne pollutants that cause the problem.

Making coated paper more porous also gives better laser prints. Coated paper means glossy prints; the smoother the paper the more light it refracts and the richer and more vivid colours look. It also avoids printer jams. But a sheet of paper is 5 per cent water that will boil when the page meets the 180°C fuser inside the printer; if the coating traps the water the fibres of the paper will burst under the pressure, leaving blisters on the page. HP’s laser paper has a coating that looks like grains of rice under the microscope; the open structure is porous, lets out steam and stays glossier.

The laser printer paper has the coating on both sides. Inkjet photo paper does not, so HP has put a barcode on the back. Using the sensor that checks if there is enough paper in the tray the printer can tell if the paper is the right side up and the right way round. It can even change the settings to match the type of paper.

The printer has to be safe, sturdy and quiet – but not too quiet. When a printer lacks the familiar whirr when it starts to print, most will assume it is not working and hit the print button again (or waste time by getting up to check it). So the engineers at HP concentrate on making the noises they produce easier to suffer.

The printers are fried by static, bombarded with radio frequency interference in a $4m test chamber and exposed to 18 weather simulations (up to 80°C and 80 per cent humidity) while they churn out 11m pages a month on 400 kinds of paper (including Chinese paper made from grass fibre rather than wood pulp).

Because not everyone works in an office, the lab will soon have a dust chamber where Arizona road dust is fired at the printers (the closest match to Chinese dust). Printers are shaken, dropped and maltreated: again, China is the benchmark because the delivery system is a 12-foot high stack of printers on plywood sheets, tied in a cargo net and dragged behind bicycles down pot-holed paths. If a printer stands up to 18 months of this abuse, then you can buy it. Concentrating on R&D and quality rather than price is how HP plans to stay ahead.

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