Durst Gives Insight On Water-Based Inks

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According to Durst, water-based polymeric inkjet inks are characterised by two important components: water as the main carrier and polymer as the glue to make the ink stick to various substrates. These are mainly paper-based materials and plastics, but include glass, metal and other materials.

The motivation to use water-based inkjet inks is relatively simple: there is no extraction needed, there are no monomer problems and water-based inks are generally seen as a ‘green’ solution. However, while water-based inks are prevalent on the desktop, penetration into industrial applications has been slow: water-based inks had widely been seen to require porous or specially treated substrates and to suffer from problems in adhesion to non-porous substrates.

These issues have mostly been solved by ‘glue’ included in the ink. This ‘glue’ is called binder, polymer, resin and so on, dependent on the manufacturer of the ink. It has the simple purpose of making durable colourants stick to the substrate.

The process of how the inks work is as follows:

1. Ink droplets are deposited onto the substrate. Due to polymers and formulation chemistry, the liquid droplets are immediately fixed to the surface of the substrate, leading to round spots. Adjacent spots should not mix.

2. Drying, meaning getting rid of all of the liquids (water and humectants). Water inhibits quite a significant evaporation enthalpy, requiring drying systems to be well-focused and sophisticated; non-uniform drying does negatively influence print quality (banding). For adsorbing media within roll to roll printers, certain adjustments to media transport are necessary as media shrinks during the drying process. At the end of the drying process, the film is touch-dry but not finally inhibiting all of its final properties.

3. Film forming: the polymers inside the ink film combine which each other more closely and start interacting. The physico-chemical mechanisms behind it are not fully understood on a scientific basis and do vary, dependent on the ink system. The final characteristics of the ink film develop during that process. It is the aim of ink chemists to shorten this time period. Ideally, by the time the media does leave the drying station, the process is finished and further processing of the printed product is possible.

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