The chemistry of inkjet printer ink
Whatever technology is applied to printer hardware, the final product consists of ink on media, so these two elements are vitally important when it comes to producing quality results. The quality of output from inkjet printers ranges from poor, with dull colors and visible banding, to excellent, near-photographic quality.
Two entirely different types of ink are used in inkjet printers: one is slow and penetrating and takes about ten seconds to dry, and the other is fast-drying ink which dries about 100 times faster. The former is generally better suited to straightforward monochrome printing, while the latter is typically used for color printing. Because different inks are mixed to create colors, they need to dry as quickly as possible to avoid blurring. If slow-drying ink is used for color printing, the colors tend to bleed into one another before they’ve dried.
The ink used in inkjet technology is water-based, and this caused the results from some of the earlier printer models to be prone to smudging and running. Oil-based ink is not really a solution for this 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 output from inkjet printers is still generally poorer than from laser printing.
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 light fastness and water fastness, and suitability for printing on a wide variety of media.
Today's inkjets use dyes, based on small molecules (<50 nm), for the cyan, magenta and yellow inks. These have high brilliance and wide color gamut, but are neither light- or water-fast enough. Pigments, based on larger (50 to 100 nm) molecules, are more waterproof and fade-resistant, but they aren't transparent and cannot yet deliver the range of colors available from dye-based inks. This means that pigments are currently only used for the black ink. Future developments will likely concentrate on creating water-fast and light-fast CMY inks based on smaller pigment-type molecules.