Ink and paper

The ink used in inkjet technology is water-based, which poses certain problems. The results from some of the early inkjet printers were prone to smudging and running, but since then there have been enormous improvements in ink chemistry. Oil-based ink is not really a solution to the problem because it would impose a far higher maintenance cost on the hardware. Printer manufacturers are making continual progress in the development of water-resistant inks, but the results from inkjet printers are still weak compared to laser printers.

One of the major goals of inkjet manufacturers is to develop the ability to print on almost any media. The secret to this is ink chemistry, and most inkjet manufacturers will jealously protect their own formulas. Companies like Hewlett-Packard, Canon and Epson invest large sums of money in research to make continual advancements in ink pigments, qualities of lightfastness and waterfastness, and suitability for printing on a wide variety of media.

By the early 2000s most inkjets used dye-based colour inks and pigment-based black. Pigment molecules are much larger and more complex than dye molecules and consequently break down more slowly than dye molecules. Dyes are much more susceptible to UV radiation and pollution for the same reason. For example, when light hits the small dye molecule it entirely damages it, but when light hits much larger pigment molecules only the surface is damaged. Dye molecules' smaller size also precipitates bleeding and spreading on a marked surface to a greater extent than pigments. The net result is that pigments are more fade-resistent than dyes.

By the early 2000s most inkjets used small molecule dyes for coloured inks - capitalising on their wider colour gamut - and larger molecule pigment-based black ink - because of its better waterproof and fade-resistance characteristics. The world-wide trend in the development of inkjet ink was, however, clearly towards pigment inks with high water fastness.

The following table summarises the characteristics of pigment and dye inks:

     

Characteristic	Pigment Ink	Dye Ink
Light Fastness			Superior	Inferior
Colour Gamut	Narrow Colour Gamut	Wide Colour Gamut
Water fastness			Superior	Inferior
Colour Impression	Relatively Dull			Relatively Bright/Vivid
Overall fastness	Relatively superior	Relatively Inferior
Stability of Head	Relatively Inferior	Relatively superior

While there are many different types of paper, most fall into either of two groups, porous and non-porous. Non-porous (also referred to as swellable polymer) coatings are composed of ozone-resistant polymer materials, which cause ink to take longer to dry. With microporous coatings, on the other hand, ink dries almost instantly because it is absorbed into the surface and held there. The downside is that is never completely seals, and the paper is so absorbent that its more susceptible to fading from harmful light and ozone.

Vendors optimise their printers for specific kinds of ink and paper, usually their own proprietary brand - Epson, for example, has its own proprietary paper which is optimised for use with its piezo-electric technology. Whilst being tied to proprietary consumables can be expensive, it is also the surest way of achieving optimum results. Paper produced by independent companies is much cheaper than that supplied directly by printer manufacturers, but it tends to rely on its universal properties and rarely takes advantage of the idiosyncratic features of particular printer models. One of the ultimate aims of inkjet printer manufacturers is to make colour printing media-independent, and the attainment of this goal is generally measured by the output quality achieved on plain copier paper. This has vastly improved over the past few years, but coated or glossy paper is still needed to achieve full-colour photographic quality.

Paper pre-conditioning seeks to improve inkjet quality on plain paper by priming the media to receive ink with an agent that binds pigment to the paper, reducing dot gain and smearing. A great deal of effort is going in to trying to achieve this without incurring a dramatic performance hit - if this yields results, one of the major barriers to widespread use of inkjet technology will have been removed.