A jewel in the crown of jet printing

Diamond Dispersions' director Peter Callahan, with one of the mills that can break particles of pigment down to 100 nanometres in diameter
Diamond Dispersions' director Peter Callahan, with one of the mills that can break particles of pigment down to 100 nanometres in diameter
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MENTION ink jet printers to most people and the image you conjure up is of a box of tricks that sits next to the computer and costs less to buy than replacement ink cartridges.

In reality, they are highly complex machines that are finding their way into applications that range from instantly printing complete books to creating detailed patterns on textiles.

Diamond Dispersions director Sue Wright with a sample of material printed using dye sublimation inks developed by the Darnall company.

Diamond Dispersions director Sue Wright with a sample of material printed using dye sublimation inks developed by the Darnall company.

Some of the most advanced machines may use as many as 16 different coloured inks, including more than one tone of black and a white, too.

If the print heads are highly engineered, then so too is the ink and the half way house between the original pigment and the finished ink – known as a dispersion, because the tiny solid particles of pigment are evenly dispersed in super clean de-ionised water.

Mixing the pigment with the water is only half the battle – the heavier than water particles of pigment have to be “persuaded” to remain suspended for anything up to two years.

To do that, they have to be broken up in a high shear mixer to create particles that are two or three microns – a millionth of a metre - in diameter and then put through a special mill containing tiny balls of zirconium that reduce the diameter of the particles to around 100 nanometres, or a tenth of a micron.

“Getting the particles down to 100 nanometres in a mill is clever, but not unique,” says Diamond Dispersions’ director Peter Callahan.

“What’s unique is the chemistry we use to keep particles that are heavier than water apart.”

Quality control is vital, with each batch of a particular dispersion being put through a battery of tests to ensure its viscosity, surface tension, particle size and colour is just as it should be before being dispatched.

Having started out with just one product – like Henry Ford you could have any pigment you liked, as long as it was black – Diamond Dispersions now supplies more than 40, including dyes, dye sublimations and UV sensitive inks.

“When we started out, the only market was for refill inks and you printed on paper. Now, you can print on anything,” says Peter Callahan.

While pigments aren’t soluble in water, dyes are and dye sublimations are a half way house – a dye that doesn’t dissolve in water and turns straight from a solid to a gas when heated, allowing it to permeate fabrics, put permanent images on plastic products or be used for producing high quality photographic prints.

Dye sublimation is widely used on sports gear and, increasingly, for fashion products, as high street stores switch to short runs of patterns that may be on their shelves for no more than six weeks.

Meanwhile, UV sensitive inks offer the benefit of curing instantly, with no drying time, producing a water and weatherproof image that is ideal for hoardings and building wraps.

So why don’t ink manufacturers make the dispersions themselves?

The answer probably lies in the fact that the market is changing so fast, with new applications arising every day and the ink manufacturer’s expertise is in developing the chemistry of the medium the dispersion is mixed with to create the finished ink.