- September 01, 2000, David Lanska, Stork Cellramic Inc.
There are some exciting new developments in anilox roll technology, but they won't bring the results you want until you fine-tune your print process by attending to basics.
Everyone is looking for that elusive competitive advantage. With press and accessories manufacturers constantly touting high-tech improvements, it's easy to assume these developments will give you that edge. This may not happen if you neglect the basics.
When to Fine-Tune?
Let's clarify "the basics" by discussing a few situations where the system is out of control and needs "fine tuning."
- When rubber nip rolls are used instead of doctor blades, they cannot provide precise control of the ink film on the anilox roll.
- When pH or ink viscosity (two critical factors that affect ink flow) are not monitored, color density can shift.
- Using gears with heavily worn or damaged teeth leads to inconsistent ink laydown because of the poor meshing of gear teeth.
- Worn and sloppy bearings result in inconsistent impression with the plates.
- Plates that are removed repeatedly and remounted stretch and distort.
- You can not expect one 800 lines per inch (lpi) roll to print like another if one was specified as 60 deg with a volume of 2.0 billion cubic microns (BCM) while the other was ordered as a 1.2 BCM at 30 deg.
- Worn and plugged anilox rolls will not deliver the same volume as rolls that are clean and well maintained, even if they were engraved to the same specifications.
Moreover, the print quality demanded has to justify the expense and effort needed to attain it. Otherwise, people will stick with what has worked for them in the past.
Line Counts Soar
FM (stochastic) and hybrid screening are gaining in popularity slowly, but conventional screening still has the lion's share of the market. It is a little premature to speculate on the growth potential of FM screening, but printers that conscientiously and methodically work to take advantage of new technologies often have a competitive advantage.
Anilox manufacturers seem to be in a fierce race to develop higher line count engravings. As their customers move up to plate screens above 150 line (some even beyond 200), the minimum recommended anilox exceeds 800 lpi, with better results being achieved at 1,000, 1,100, and 1,200 lpi, (engravings referred to as "ultra-high" line count).
For 20 years, 800 was as high as laser system and control technology would allow. Only in the last few years has the 800 line count barrier been shattered.
The benefit of new engraving technologies is fairly obvious. Higher line count engravings ensure a cell wall structure that provides better support to the highlight plate dots and reduces the occurrence of dot dipping. (Dot dipping is where the plate dot plunges into the cell opening and picks up ink on the sides of the dot. This results in plate muddying and significant dot gain.)
Although manufacturers currently produce up to 2,000 lpi, few customers actually are purchasing engravings of 1,500 or higher at this time. The cell openings are extremely small with incredibly thin cell walls. While this can produce excellent print results, the ultra-thin wall structure offers little support to stand up to the mechanical cleaning methods being used today such as ultrasonic and soda jet.
In addition to the concern about damage occurring during cleaning, most people simply do not need to go that high in line count to satisfy their own customers.
While producing rolls to 1,500 lpi is still a rare occurrence, there is a growing trend in the number of orders for rolls in the range of 900-1,200 lpi. Although these orders usually come from print shops that routinely print high quality process jobs, these shops come from the narrow, medium, and wide web segments.
When it is necessary to go beyond 800 lpi, it becomes critical that each component of the ink distribution system be optimized.
No Escaping Tradeoffs
CO2 lasers produce engravings that for many years have been the standard of the industry. YAG lasers are creating the new standard. YAG lasers work very well for producing extremely fine patterns, because the beam is a great deal narrower and can be focused down to a much finer point. They also have a sharper burst of energy, enabling them to drill cleaner cells with thinner cell walls. This translates into the ability to create greater cell volume from a 1,200 lpi than typically obtained from a 700 CO2. This is a desirable feature when you need to precisely place microscopic ink dots while still achieving the desired color strength.
As mentioned earlier, however, there are always tradeoffs to be made. Regardless of the engraving technology used, as cell count increases, wall thickness decreases. If a 400 lpi roll has twice the wall thickness of an 800, the 400 will be better able to stand up to day-to-day use (and abuse), and whatever cleaning method is used.
Those willing to commit to achieving litho quality in flexo also must commit to establishing standards, as well as monitoring (and eliminating) variables. Standardization of the print process includes standardizing volumes and cell placement angles for each line count used.
Interchangeability as well as predictability come as the system is brought under control. Once you have established control, it is critical to maintain the integrity of the system. This only happens with proper maintenance and upkeep of all press components.
You likely will find significant gains in print quality and predictability simply by doing the basics well and gaining control of the print process. If, after all that, you still need to go further to gain your competitive advantage, then it is time to go shopping.
David Lanska is a regional anilox sales manager for Stork Cellramic, Inc., Milwaukee, WI. David has been with Stork for more than 18 years and previously served as technical service/marketing coordinator. Prior to that, he was a quality assurance inspector and laser operator for nearly ten years. David has been a speaker at association forums, has performed numerous roll audits and training seminars across the US and Canada, and has written several articles on flexography. He recently received his MBA from Concordia University. He can be reached at 414/357-0260; firstname.lastname@example.org.