Drying water based inks – the challenges

For many reasons, ranging from ecology, through health and safety to economics and profitability, the world of print has a strong desire to move to water-based, or aqueous, inks. The inkjet world is no different with both printhead manufacturers and ink developers driving their R&D teams in this direction and many of the resultant products now arriving in our market place are aimed this way. With the current speeds specified for digital presses and printheads, and the broadening acceptability of the inkjet process into a wider and wider set of applications, many manufacturers are finding they must address the situation of using water as the “carrier” for the first time.

Whatever their motivation and experience however, once this water has been deposited as a component of the ink, it must be removed from the surface of the substrate to allow the desired quality image to be left behind in a fixed and rub-resistant form. How can this be achieved?

Many R&D teams bogged down in trying to keep a printhead operational with an ink set which is being developed at the same time as the printhead, have little time to devote to thinking hard about this dilemma and to design the drier wisely – they often just reach for the drying component that they have used for years, or ask their existing supplier for a suitable drier to integrate.

This critical error is resulting in printers reaching end users, who have purchased against the sellers marketing specification, where the printer is incapable of meeting the expectation of the customer. Yes, the printer can run at the specified maximum speed, yes, the printer can print the ink weights & image quality desired, yes, the printer can image onto a wide range of substrates –but you actually want to do all three of these at the same time? – oh dear! Who on earth was naïve enough to expect that!?

Printer manufacturers are going through a lengthy learning curve: they are learning about stocks, they are learning about drying technologies and they are learning about ink recipes.

Clearly carrier fluids and humectants in the ink recipe can be absorbed by the surface of the substrate, as in “inkjet treated papers” – here the paper manufacturers create a surface layer of the paper with a “honey-comb” of spaces so that when a ink drop arrives on the surface, some of the water and humectant can be held in these sub-surface spaces and dry-off over time. Unfortunately they wish to charge for their extremely sophisticated developments and these stocks are more expensive than conventional paper.

Some digital press manufacturers, wishing to resolve their customer issues and to capture a new revenue stream, have developed coatings and coaters which apply a surface layer to a substrate to deliver a similar result. Unfortunately they too wish to charge handsomely for this benefit.

As the end user market gets wiser, often through harsh and expensive lessons, they are forcing their digital press suppliers to think a little harder up front and to foresee these end-user penalties and iron them out in the design stage of the digital printer.

Ink recipes are being honed, not just to make the life of the print head development team easier, but also looking at how the customer intends to use the equipment. This is resulting in much learning. Substrate manufacturers are being enlisted to help in the design and specification of presses and often presses are sold with “approved” substrates. R&D teams are also devoting more time and looking more closely at drying technologies.

So what are the commonly used technologies in our digital printing field that can be applied to drying water based inks and fluids? Typically these are all using heat, usually created by radiated light energy, and some form of air movement. This drying element of the process will remove the water in part or in whole, but it may also “cook” or distort your substrate. This can make paper brittle and difficult to handle and can “resize” film stocks. Therefore it must be defined and specified well.

A second element often included under the drying banner is rub-resistance, does the ink smear? Drying is the removal of the water from the ink, however with vast percentages (sometimes up towards 50%) of humectants now being placed into the ink recipe as well (to keep the printhead operational and the small nozzles operational) often this is left on the substrate surface. Typically these humectants are high boiling point solvents such as glycol, which require temperatures of 200-300degrees centigrade to boil and evaporate them – clearly destructive to the substrate if applied. So how do you prevent this “oily substance” from smearing and damaging your image quality, from rubbing off on your rollers, or from gluing your stock together in the roll to form one giant firelighter?


Answering these questions requires experts who understand the subject, who know how to apply energy efficiently and effectively, who know about printing and the effects of water and humectants on printers, printheads and substrates. One such company is adphos, with a track record of removing the one litre of water per minute that the Kodak Prosper press places on to glossy paper stocks at 300mpm; as well as enhancing the performance of the HP T system presses by broadening the stock range usable and enhancing rub resistance. Adphos uses near-IR drying technology, and this technology will be described as part of the Inkjet Drying & Curing course to be held at IMI Europe’s Inkjet Summer School in Cambridge, 10-14 June 2019. Come along and find out more!

James Burbidge, adphos