Waterless is a lithographic process that does not use fount solution. It is based on repulsion between the ink and siliconized zones. When the plates are exposed to light, siliconized and nonsiliconized zones are formed according to the exposure mask. The ink deposited is repulsed from the siliconized zones towards the non-siliconized zones, thereby forming the printing and non-printing zones. The ink is then transferred onto the blanket and deposited on the substrate.
The Waterless UV process employs the same differentiation principle, but drying takes place through photopolymerisation. The UV dryer systems used are the same as those in offset with fount solution.
WATERLESS UV ADVANTAGES
The advantages of waterless UV printing lie in the elimination of the fount solution :
• Qualitative advantages : Print quality is significantly improved by eliminating the fount solution :
• Dot sharpness (low dot gain).
• Constant reproducibility.
• Better colour density.
• Production advantages : The absence of water eliminates the need to adjust the water/ink balance, which reduces the start up and setting times and cuts waste. The elimination of the fount solution also enables other related drawbacks to be avoided : no need for a fount additive or need to maintain the fount solution tanks, elimination of problems of misting and piling, etc.
• Ecological advantages : The absence of isopropyl alcohol in the process eliminates any production of VOCs and ensures it is compliant with the objectives of the EPA (Environmental Protection Agency).
WATERLESS UV DISADVANTAGES
• Significant cost of consumables : Waterless UV printing requires appropriate consumables : blanket cleaners, inks, additives, plates, etc. These are in general 2 to 3 times more expensive (than conventional products), which remains a brake to the development of this technology.
• Relatively slow printing speeds : Although Waterless UV printing speeds can now reach around 30m/min, and even 60m/min in the case of new Aniflo® type technologies, they do not match those obtained in conventional UV offset printing.
• Demanding temperature adjustment : Although the Waterless process makes the inking for the print run easy to set up and maintain, specific care needs to be taken as regards the printing temperature. In fact, the “printing zone” / “non printing zone” differentiation is very temperature sensitive. The temperature of the ink ducts, inking rollers and plates has to be precisely adjusted (between 18 and 23°C). Lower temperatures can lead to an “orange peel” appearance in the print and higher temperatures can cause ink misting on the plates.