New Drying Process for UV Inks
I just read an article in PrintWeek about new directions in UV ink technology. The article is entitled “Will the Latest UV Drying Techs Win Over Sheetfed Litho?” (1/25/16, by Richard Stuart-Turner), and its implications reach far beyond the technical connotations of the title.
First of all (to provide a context for this new technology), when I started in the printing field back in the late 1970s, if you wanted to print on both sides of a press sheet you had two options. Either you used a perfecting press (one that printed both sides of the sheet simultaneously), or you printed one side of the press sheet first and then waited for it to dry before turning the stack of press sheets over to print the opposite side. This was called “backing up the sheet.”
Drying times could be problematic. Some inks seemed to never dry (certain blue inks, as I recall), and ink on uncoated paper took an amazingly long time to dry (up to three days). Moreover, inks that appeared vibrant on uncoated stock usually dulled back as they dried.
New Technology
A number of years ago developers created UV inks that would cure instantly when exposed to ultraviolet light. This was ideal, because you could print one side of a press sheet, expose the ink to UV wavelengths in the process, and end up with a completely dry press sheet at the delivery end of the press. You could then print the opposite side immediately (unless you had already perfected the sheet, or printed both sides simultaneously).
Having a press sheet immediately dry on one side and ready for printing the opposite side meant production schedules could be shortened dramatically. In addition, since the inks dried (or cured) immediately, they would sit up on top of the press sheet. This was especially beneficial when printing on an uncoated press sheet. It yielded a more glossy ink appearance, in contrast to the dulled surface of inks that had seeped into the fibers of an uncoated paper stock.
Akin to the new ease of printing uncoated press sheets was the ability to print on non-porous substrates. Printers could print on plastics and foils, as well as other high-surface-tension materials. The ink would dry instantly, sit on top of the substrate, and retain its gloss.
The Downside
Unfortunately, the mercury lamps used for curing the UV inks were very hot. This necessitated cooling the presses with water, which consumed energy and therefore increased the cost of UV printing. According to the PrintWeek article, “Will the Latest UV Drying Techs Win Over Sheetfed Litho?” there was even a risk of fire. Therefore, carbon dioxide fire fighting systems were needed, driving up the equipment costs even further.
Moreover, the mercury UV bulbs burned out quickly, which further increased the expense of UV printing, and the inks themselves cost up to three times as much as conventional inks.
Furthermore, according to Stuart-Turner's PrintWeek article, traditional UV printing released ozone, which had to be removed from the printing facility to protect the environment.
Back to the Present (in the PrintWeek Article)
This is the context for the new UV-LED technology described in “Will the Latest UV Drying Techs Win Over Sheetfed Litho?” The article describes LE-UV (low-energy UV) ink curing, also known as HUV (highly-reactive UV, because the inks are more sensitive and therefore need less energy for curing—i.e., lower-output UV lamps can be used effectively).
The article explains a maturing UV printing process, which uses light emitting diodes to cure UV inks. LEDs emit far less heat than conventional mercury lights and therefore minimize the need for (and energy cost of) cooling. They also last up to eighteen times longer than mercury lights.
As an additional benefit, this technology can be retrofitted onto existing presses, making the process accessible to a much larger user base.
The Implications of the New Technology Described in the PrintWeek Article
1. Since printers don't have to print one side of a press sheet and then store skids of sheets until the conventional ink dries, there can be less storage space in a printing plant.
2. Schedules can be shortened because printed jobs can move immediately into the finishing department for folding, trimming, etc.
3. Shorter print runs are economically feasible, since the process can move more quickly and without wait time for drying. This means offset lithography can compete head to head with digital printing for shorter press runs, affording options to printers and print buyers.
4. Since quick turn-arounds and short press runs are now the norm in business, the higher quality of offset printing can offer an economically feasible alternative for static print runs (print runs in which content does not vary from press sheet to press sheet).
5. Since the format of offset presses still exceeds that of most digital presses (compare a 28” x 40” press sheet to the largest of the digital press sheets, which is closer to 20” x 29”), offset printing is still ideal for larger jobs such as posters and 2- or 4-color book printing. In some cases the digital option, which might be a grand-format flatbed inkjet press, might not be as cost-effective as a large offset press, due to the length of the press run (or its nature, such as a press run for a print book).
6. The reduced operating costs of the newer UV inks, as well as the reduced emissions and reduced risk of fire, position UV offset and digital printing in a competitive stance with one another. And this competition will benefit the consumer, since it will spur innovation. Both technologies will be improved and made cheaper to satisfy buyer demand.
7. For short press runs, which are becoming economical for offset printing with the advent of LED-UV curing, the much higher costs of the inks will be less of a determining factor. That is, for a short press run, ink costs would be only a small percentage of the entire production expense.
8. In terms of environmental stewardship, not needing to generate as much electricity to run the traditional UV lights and not needing a coating tower or extended ink dryer (such as used in web-fed offset) will significantly reduce a printer's environmental footprint. In addition, the UV wavelength of the LED light is shorter than that of conventional lamps, so the lamps don't generate ozone (although they do still generate some heat).
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]