Hints and tips

Size matters – Uvijet Digital Ink Technologies

Wide format inkjet technology is a merger of large and small. To produce large format point of sale material, the finest particles are required to achieve the quality needed.

Fujifilm Sericol’s reputation has been built on developing innovative products for the screen-printing process using a wide range of ink technologies. The screen printer will use different products depending on the application and substrate and can easily switch ink systems when they need to. In part this range of options has arisen through a longer development history, but it is also because it is relatively easy to replace one ink with another.

Digital inkjet technology is more complex and changing inks is not a practical option. It would take most of a day to change inks, eliminating the prime benefit the digital process offers – fast turnaround of finished print.

Recognising this fact Fujifilm Sericol and Inca were determined to move digital printing to the next level by developing a digital press, which used multi application UV curable inks.

Until recently manufacturers of digital printing equipment and inks have adopted a ‘product led’ strategy concentrating on the functional aspects of the machine rather than the application. The problem with this approach is that the choice of inks was of secondary importance and consequently utilised older established technology such as solvent-based. For solvent-based digital products the solid content (pigment / resin) is less than 20% with the remainder of the ink being made up of solvents. These solvents not only help to control the viscosity of the ink system but also assist with maintaining the fine dispersion of the pigments. However, UV inks are “100% solid”, which makes the viscosity of the ink more difficult to control.

What are UV curing Inks?

UV curing inks are those that change from a liquid to a solid state when polymerisation takes place under exposure to ultra-violet light. This UV light initiates a chemical reaction, which generates a matrix of cross-linked materials, giving the solid ink film chemical resistance, gloss and durability. The ink has a low molecular weight and low viscosity but the polymerisation reaction initiated by exposure to UV light generates a high impact solid, resulting in a cured ink film.

Combining UV inks and inkjet technology

For industrial and wide format graphic applications selecting the correct pigments and achieving the desired particle size is a major challenge for inkjet printing no matter what the ink technology used. Ultra Violet ink systems have a 30-year record within the screen-printing market where with a mesh hole size of, typically, 30 microns, particle size is not critical.

With inkjet, size matters. UV inkjet ink represents a radical departure from traditional inkjet technology and demands a new set of working parameters. Firstly, digital inks are approximately 50 times thinner than their nearest screen-printing equivalent. Secondly, an inkjet nozzle on the Inca machines has an opening similar to the diameter of a human hair and one oversize pigment particle could spell disaster. Uvijet digital inks feature pigment particles of less than a micron, which are evenly dispersed within the carrier and retain that dispersion. And finally, selecting the correct ratio and type of monomers (reactive diluents) Oligomers (reactive resins) and Photoinitiators (UV light absorbers) capable of producing stable low viscosity ink suitable for jetting effectively.

In developing Uvijet digital inks, Fujifilm Sericol have optimised the surface tension, viscosity and overall physical properties of the ink to control both print quality and end-user properties, including adhesion performance. This means that digital UV ink can apply to the widest range of substrates possible.

Dr Carole Noutary, Fujifilm Sericol Imaging Technical Manager says:
“As UV inks cure instantly when exposed to Ultra violet light it is the only ink technology able to keep up with the ever increasing speed achievable from Peizo inkjet printers. Also when you consider that the Inca Spdyer 320 has 16 print heads with 2,048 nozzles each nozzle with an opening the size of a human hair, particle size is a serious matter. Only the best dispersion techniques could achieve the desired quality and ultimately determine the success of UV digital printing. In addition, because UV curable inks are non-volatile products, the life of the print head increases, significantly reducing downtime. And UV digital inks uses non-flammable materials and therefore are more environmentally friendly.”

Without utilising UV ink technology the Inca machines could not offer many of their key benefits such as: production speeds in excess of 65m2(Spyder 320), wide adhesion range onto the broadest range of media, outdoor resilience and excellent colour strength.

With the development of the Inca machines and Uvijet inks the relationship between Inca and Fujifilm Sericol has flourished providing the synergy needed to keep these two dynamic companies at the leading edge of UV digital technology.

Research and development for both parties goes on - the UV inkjet potential is only just being realised.

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