The chemistry of dyes and pigments – what is the right ink for the right job?

Modern inks contain a range of different ingredients that ensure machines can print faster and more accurately.

Many people think of ink as an afterthought, that it’s the printer or software that makes all the processes work together and that one ink is as good as another. But in reality, just about any modern inkjet ink is a highly engineered component within the overall print system, one that’s formulated precisely for a specific printer, to deliver a defined set of properties at a pre-determined price point.

It goes without saying that almost every printer thinks the price they are paying for their ink is too high. But the price comes from a number of factors, including the value of the intellectual property used to create it, but mainly it’s down to the ingredients used. So, what are those ingredients?

Perhaps the most obvious place to start is the colourant. Many consumer-grade water-based inkjet inks, as well as many textile inks, still use dyes but commercial printers mostly use pigments, which offer much better resistance to fading for longer-lasting prints, particularly under direct sunlight for outdoor signage or posters in shop windows. Unlike dyes, these pigments remain solid after printing and sit on the surface of the media. The pigments are finely ground into micron-sized particles to ensure they are small enough to be jetted through the tiny nozzles found on high resolution inkjet printheads.

Up until the last few years, most ink vendors have opted for a relatively low density of ink particles in order to improve the jettability of the ink and limit the risk of the particles clogging the printheads. This in turn meant that several passes of the head carriage were needed to lay down enough colourant to produce a vibrant and well-saturated image. But most printheads can now handle a much higher pigment loading, meaning more colourant can be laid down in each pass, greatly speeding up the overall printing times.

The pigments themselves are suspended within a carrier fluid that is designed to ensure the pigments are evenly dispersed and do not simply fall to the bottom of the ink tank as sedimentation. One of the most common carrier fluids is water, which has the double advantage of being both relatively cheap and environmentally-friendly. As well as aqueous inks, water is also…