One of the most frequently asked questions today is “What is waterless printing?” Unfortunately this is the least understood printing process within the two-piece can printing industry. First, let us dispel some commonly held misconceptions:
1: Waterless is not a new printing technology. In fact, waterless printing technology has been around from as early as 1977. (For a complete discussion of the history of waterless printing visit www.waterless.org, which is the web site of the Waterless Printing Association, of which Genesis Innovation is a sponsor member).
2: Waterless was not invented within or for the two-piece can industry. Waterless was designed for the paper industry and is today employed to some extent by that sector.
3: Waterless may not be printed on conventional two-piece decorators. Waterless printing, by definition, requires structural modifications to the decorator as well as new applications of physics and tight process controls or it simply does not work.
4: Waterless does not require in-plant direct-to-plate (DTP) technology. Although highly desirable for any printing technology, DTP is not a special requirement of waterless printing.
5: The stringent requirements for Waterless Printing may not be "relaxed." If we attempt to change the operating requirements, we may as well go back to traditional dry offset printing (in the case of two-piece printing) or water-based lithography (in the case of three-piece printing).
So, what exactly is waterless printing? To understand waterless is simply to understand lithography, which is based upon a mixture of ink and dampening solution (usually water), and single-plane plates, as opposed to the relief plates used in the two-piece industry. The plates are exposed in a manner (not discussed here) such that the print areas are oleophilic (or oil attracting) and therefore hydrophobic (or water repelling). Conversely, the non-print areas are oleophobic (or oil repelling) and therefore hydrophilic (or water attracting). The dampening fluid (water) is applied to the plate prior to the ink. Lithography is capable of extremely high line screens.
Waterless printing essentially is
lithography without the water. The dampening
solution is removed, to reveal a process that is mechanically (except for the
plates) identical to what we
do today. This is why it holds such high
attraction for our industry, and rightly so, because it provides the
advantages
of lithography without the complications of using a dampening solution.
However, waterless printing carries with it some special requirements. Besides the required machine design modifications referred to earlier, waterless printing requires by definition control of ink temperature. The plates used in waterless printing contain an extra layer over the photopolymer composed of hardened silicone. It is this layer that repels the ink, while areas where the silicone has been ablated attract the ink via the etched photopolymer. This has an advantage over conventional lithography, in that the walls of the silicone afford some semblance of support for the dot, thereby keeping mechanical and optical dot gain to a minimum. However, the inks are formulated to work within narrow bands of critical toning temperature (CTT) and critical mottling temperature (CMT). Wide temperature variations will inadvertently cause either not enough ink to be attracted to the photopolymer, or so much that ink begins to transfer to the silicone.
