Since the process of flexographic printing was conceived, an increasing demand for consistency, print quality and creative design elements has led to the application of continuous improvement across all channels.
Sophisticated point-of-sale packaging, or labeling, has been a key driver for the success, thanks to flexography’s proven posture. Simply put, it’s less expensive and more versatile than other print processes.
All photos courtesy of Harper Corporation of America
Greater demands can bring increases in makeready times, downtime and impact production speeds. Our industry is always reinventing and pushing the envelope with continuous improvement, so it is important to understand fundamentals—particularly how anilox rolls remain critical in keeping up with these changes. Proper anilox management and specifications can help eliminate a lot of the issues found daily in pressrooms.
History Lessons
In the early years of flexographic printing, the use of a chrome anilox was standard, utilizing a two-roll system. The rubber roll, or doctor roll, metered the ink to the anilox’s cells, which then delivered ink to the plate. A chrome roll was born as a mechanically engraved copper surface that was then chromed for durability, resistance to corrosion and ink release. The issue was inconsistencies developing in the rubber roll, which changed the inking of the anilox in a relatively short time.
Since the metering system itself was a deterrent to consistency, it created the need for blading to create consistent ink films at any speed. The price to pay to correct the consistency through the use of a blade was the rapid wear of the chrome anilox surface. The anilox did not serve well as the wear component, so something had to be done to create a longer-lasting surface. Here we have continuous improvement as a fundamental necessity.
The ceramic anilox made its introduction to the industry, allowing the ability to utilize doctor blades to create ink film consistency and make the much less expensive doctor blade the wear component. When blading systems are used correctly, they won’t damage the anilox roll. Since the introduction, the drive to improve on the ceramic anilox has been ongoing:
- Laser engraving technology has allowed for stronger cell walls, better volume consistency, tighter tolerances and smoother cell openings to allow for even more precise ink deposit efficiencies
- Improved ceramic formulation has allowed for better release, consistent cell shape, longer lifespan and a reduction in broken or missing cell walls, due to high porosity in the ceramic
- More powerful engraving lasers with smaller beams have also allowed for a wider variety of productive cell geometries. These technologies now deliver options for better laydowns of custom inks and coatings—like metallics, tactile, and adhesives
Banded roll trial
Fragile Nature
The need to maintain and monitor anilox condition is important to repeatability and predictability to the process. This need is met with the proper care and maintenance of the rolls. Anilox rolls are fragile by nature, but understanding what can damage one can increase the lifespan of this investment.
Ceramic is a hard substance, but it is important to understand scale when thinking of the cells themselves. A human hair is approximately 100 microns (μm) in diameter on average. On a 900 CPI anilox, the standard cell wall is 3-μm. with an opening of 25-μm. Simply put, a wall that is 3 percent the width of a human hair and an opening that is 25 percent of a human hair can easily be damaged if certain precautions are not taken.
More than 80 percent of the rolls returned to anilox manufacturers are damaged long before they wear out. As I mentioned already, correct use of metering blades (low-pressure contact with the anilox’s surface) helps prevent damage factors from developing. Damage to the anilox roll can be devastating when blades are misused. Metal wear from the doctor blades, not immediately captured by magnets, is a main source of score lines in anilox rolls.
Having slivers created at the contact point between anilox and blade puts the creator of damage right next to the recipient of the damage—Not an ideal situation, to be sure, hence the need to prevent the occurrence. Worn blade holders or chambers, poor chamber preventative maintenance and poor blade seating are also common sources of score lines.
Hazards & Happenstance
The easiest step to anilox care is planning and training when it comes to workflow. Before removing or putting a roll in the press, evaluate your work area for potential hazards. These can include blocked travel ways while handling or tools on the workbench where the anilox is being placed. Poor storage practices, like not using covers, using racks that do not protect the anilox rolls and placing the storage in high-traffic areas, all contribute to the butcher’s bill. Most commonly found in the work area on surfaces are metal rings, screws and other assorted tooling. Rolling a small roll on a bench can collide it with any of these loose items.
Keeping your anilox rolls covered is a good way to help protect them. For sleeve anilox rolls, ensure the roll bore and mandrels are clean to ensure the roll glides on smoothly rather than rocking it up and down, or side to side, to get it started. This can affect the total indicated runout (TIR) of the sleeve and thus render a host of issues with the anilox, such as poor inking, blading, remanufacturing abilities, or even direct damage to the inner liner.
The most common error with anilox rolls is in the way they are cleaned and what is used to clean them. The adage of “If some is good, more must be better” often takes place on the shop floor. You must choose from a management perspective to train employees on the proper cleaning and limit your cleaners to those that do not cause damage.
When careful cleaner selection and training is not the rule, the possibility of incorrect dilution rates or improper ink/anilox cleaners can cause a higher-than-wanted pH level of cleaner. This can lead to greater exposure and will ultimately cause a chemical attack that is hard to stop once started.
Blistering occurs when a high pH solution gets past the ceramic of the roll via prolonged exposure or through chips on the ends of the rolls. This allows the high pH cleaner to corrode the metal base, which shows up in the face of the roll and finally in the print. Always use the proper cleaners for your anilox rollers to prolong their lives and maintain the integrity of the cells. Always rinse.
Be sure to check with your anilox manufacturer to determine what’s best for your situation. Damage is not limited to press-side activities. Note that anilox damage can happen in high-pressure cleaners, ultrasonic cleaners, laser cleaners and media blasters, when the systems are not properly maintained or the settings are incorrect. Evaluate these systems for how well they clean and how well they maintain cell integrity. Introducing damage into your anilox inventory is not going to be a process improvement you will want to continue.