‘Turbo-charged' Flexo Inks Keep Pace with High-speed Presses
When examining industry trends, the good news for printers in the flexographic market is higher speed presses and better productivity. The bad news for printers in the flexographic market is, well, high speed presses: Or, more specifically, speed-generated issues, including inks, plates and aniloxes.
At this point, relatively few operations are impacted. Many flexographic print jobs still fall within 15,000-to-30,000-foot run lengths handled by presses running at 600-800 feet per minute (fpm), with quick-changeover assists from automated systems. During the past few years, newer presses have quickened the pace to 1200-1300 fpm. Now some 2,000-2100 fpm machines are delivering the goods. Yet this year, presses at speeds over 3,000 fpm could have more flexo operations eyeing long-run jobs (500,000 feet and up) that have traditionally been considered gravure territory. And press makers probably haven’t reached their limit.
Other flexo providers, however, need to catch up.
Pressures and ProblemsThe prospect of taking on jobs where high-speed output means saving hours, not mere minutes, puts pressure on ink suppliers to solve problems that naturally arise when everything on-press is happening twice as fast (or faster) than before. These include multiple ink-related issues, recent advances in technology to resolve them.
The problem boils down to less ink transfer at higher speeds, and less time for ink to level out and lay smooth. While many printers rely on inks to resolve this issue, it’s not quite that simple. Granted, particularly with nonporous plastic substrates on many flexo applications, inks have to be more technically capable in order to properly adhere, more so than with paper where absorption helps.
Ink transfer, however, involves not only the ink itself, but the transfer process, which means the aniloxes need to be evaluated. Plates also need to be evaluated; even the type of plate mounting tape. There are many pieces to this puzzle; adjusting one affects them all.
For example, anilox rolls hold only a given volume of ink, about 50 percent of which is transferred to the plate – and only 50 percent of that (about 25 percent of original anilox volume) gets to the substrate. At today’s higher speeds, this could be reduced by another 25-30 percent to a mere 17.5 percent.
Presses themselves have new issues at high speeds, including greater vibration; and increased air flow around plates and aniloxes can impact run stability, ink flow, drying and more.
Recognizing these multiple related issues, manufacturers are taking steps to improve their technologies. Press makers have managed to reduce vibration. They’re improving ink delivery to the anilox in doctor blade chambers by using baffles, or widening the distance between blades to provide more time for ink to fill anilox cells.
New plate technology can probably increase ink transfer by 20 percent to 30 percent; in some cases, we have seen Magenta ink density improve from 1.4 to 1.65.
Walking a Fine Line with InksTwo primary ways ink manufacturers can improve ink flow and transferability is to adjust the resin/binder type and ink drying speed. The key to high-speed inks as press speeds continue to accelerate, however, will be developing new and unique resin systems. The right commercially available resin – sometimes like finding a needle in a haystack – can lead to formulations that work. Basic R&D capability improves the odds, because specific ink properties can be designed when formulating from scratch.
One developmental “speed bump” is that most R&D type printing presses cannot duplicate the latest press speeds. Ink companies bear considerable expense buying press time to finalize formulations. It all takes time, especially with laminating inks or those for food packaging. Knowing solvents that are acceptable for food packaging and suitable for end uses is key, too.
From a formulation standpoint, thinner inks work better at high speeds because they flow faster. But if the ink viscosity is too low, it can create other problems on press, and ink strength may become an issue, as well as an adherence to substrates.
In short, inks have to concurrently perform contrasting roles: they need to stay open on press, transfer easily and smoothly, and dry on command, while also sticking to substrates, interacting well with adhesives and standing up to the rigors of end use. It’s a balancing act involving two sides of the same coin. The challenge is to flip that coin and have it land on its edge, every time.
We have seen inks running well at about 2000 fpm, on presses upgradable to 2900 fpm. Printers can expect further developments that will enable them to push the high-speed flexo envelope with confidence.
Inx International Ink Co.