It is a given that the flexographic anilox sleeve has become a welcomed standard on wide web, preprint, mid web and many narrow web presses.
Flexographic presses equipped with anilox sleeves allow for quicker setups of new jobs or color changes and also provide a safer environment when handling, due to the lightweight construction.
All photos courtesy of ARC International
Compared to conventional anilox rollers, manufactured with heavy steel tubing, headers and integral journals that take much longer to install or remove; anilox sleeves are mounted on fixed air mandrels in the print stations. Forcing compressed air through holes in the air mandrel enables the anilox sleeve to be mounted or removed in a matter of seconds.
Fiberglass = Affordability
Today’s flexographic printer has a choice when it comes to selecting the type of anilox sleeve to be utilized in the press. The most common anilox sleeves are 0.375-in. to 0.500-in. in thickness and constructed with an inner layer of fiberglass. This is a common type of fiber-reinforced plastic using silicon glass fibers that are woven together to form a material. Fiberglass has a lower tensile modulus than some other materials, which allows it to bend or expand for the purpose of mounting on or dismounting from an air mandrel.
This is achieved by having an expansion layer applied to the fiberglass, then a lightweight resin to reduce weight and an aluminum shell, which gives the sleeve its stability and provides a suitable surface for applying a corrosion-resistant undercoat and the subsequent chromium oxide ceramic for grinding, honing and laser engraving.
Many suppliers apply a protective end ring to the sleeve to minimize inks and cleaning agents penetrating the various layers and causing swelling, which results in distortion, added TIR (total indicated run-out) and inconsistent print quality.
While fiberglass anilox sleeves are most commonly used, there is a downside in relationship to sleeve durability and lifespan. Since the glass fibers in the fiberglass sleeves are not as tightly woven and rigid as carbon fiber, with continued mounting, dismounting, excessive air pressure and poor handling, the inner layer often cracks and is no longer suitable for reconditioning.
In addition, as the fiberglass inner layer becomes distorted over time, the operators often have trouble mounting or even worse, removing the sleeve from the air mandrel. Sometimes they have to use a wooden block and a mallet hammer to get the sleeve removed from the mandrel, which causes further damage.
When worn or damaged fiberglass anilox sleeves are sent to the anilox sleeve supplier for reconditioning, the supplier first inspects the inner layer for potential damage. If there are no cracks or holes in the sleeve it is then mounted on a production mandrel for processing. But, prior to removing the worn or damaged ceramic surface, the sleeve is checked for TIR.
If the sleeve layers have begun to separate, especially near the ends of the sleeve, it is likely that too much TIR will result in that sleeve being deemed unfit for reconditioning. Many anilox sleeve suppliers keep an inventory of the most popular anilox sleeve blanks, in order to replace rejected sleeves in a timely manner.
Thus, when printing requirements and tolerances aren’t too stringent and affordability is a factor, fiberglass anilox sleeves are certainly the best avenue. With proper handling, cleaning and storage practices, these fiberglass anilox sleeves can have a longer than normal life and produce exceptional graphics.
Carbon Fiber = Durability
For precision high graphics with exceedingly tight tolerances, many converters choose to utilize anilox sleeves with carbon fiber construction instead of fiberglass. Carbon fiber is made with small strands of carbon atoms that are combined into strands woven together to form an incredibly durable and lightweight material.
Carbon fiber is about three times stiffer than steel and aluminum for a given weight, thus its high tensile modulus minimizes any potential vibration and deflection issues, more so than fiberglass. In addition, its lowered rotational inertia allows for higher production speeds and easier start-ups and shutdowns with reduced web damage.
On the latest sophisticated flexographic preprinted liner presses, the anilox rollers/sleeves are very large, with face lengths ranging from approximately 100-in to 114-in and with outside diameters ranging from approximately 11.00-in to 14.00-in. This type of carbon fiber anilox sleeve construction is especially beneficial as these sleeves are mounted and removed with sophisticated robotic arms, operated at extremely high speeds with the highest graphic requirements.
While the addition of an aluminum sleeve is optional in this type of construction, it is the carbon fiber itself that provides the sleeve’s overall rigidity, as compared to the aluminum sleeve in the fiber glass construction.
Thus, if the highest quality graphics are demanded, cost is not a factor and better durability are factors in your decision when buying anilox sleeves, the carbon fiber constructed sleeves would be the perfect choice. It is also more likely that this type of sleeve construction will allow for more reworks over time when ceramic surfaces become worn, scratched or damaged.
Mandrels & Engraving
When considering the pros and cons of fiberglass versus carbon fiber, it is also worth noting that the mandrels on which the anilox sleeves are processed and operated are generally made of ground steel and chrome plated. Over time, the chrome plating can wear and lead to issues when mounting and removing various sleeves. A mandrel constructed with a carbon fiber body and steel headers and journals can provide greater rigidity and durability, similar to the sleeve itself.
Regardless of the construction of the anilox sleeve, it makes no difference if the engraving quality on the finished product is of poor quality or inconsistent. Make certain that your anilox supplier is using the highest quality chromium oxide ceramic, the most efficient corrosion-resistant undercoating and the latest laser engraving technology, along with precision inspection equipment.
If a flexographic printer utilizes his or her own inspection equipment, such as an Ani-CAM or MicroDynamics vertical scanning interferometry unit, they should ensure that their equipment is calibrated to that of the anilox supplier’s equipment in order to accurately compare the supplier’s findings with their incoming inspection.
Storage Do’s & Don’ts
Longer anilox sleeve life is also dependent upon cleanliness and storage. Ink should not be allowed to dry in cells, as this will affect color density and print quality. Properly diluted anilox cleaners should be used on a day-to-day basis. Harsh chemicals with low or high pH levels can certainly affect the ceramic surface and the bond between layers.
If rollers are being cleaned with soda blasting, plastic beads or dry ice equipment, make certain that the engraved surface is not degraded from too much pressure or being used too often. Ultrasonic and laser cleaning equipment, if not used properly, can lead to imagery in the roller surface that can show up in the print.
How your sleeves are stored can also contribute to their longevity. If stored vertically, make certain that the storage unit has a padded bottom, so the sleeve ends do not sustain damage. If stored horizontally on a rack with rods, be sure to rotate the sleeves fairly often to maintain proper roundness. A cushioned wrapping also gives extra protection to exposed ceramic surfaces.
The anilox roller or sleeve is the “heart” of the flexographic press as it provides the precise amount of ink, coating or laminate to the printing plate or substrate, just like the heart transfers blood throughout the body. Whatever its construction, steel, fiberglass or carbon fiber, take good care of your sleeve, just like you’d take care of your own heart!
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