More and more, printers are turning to anilox sleeves to run faster speeds with tighter tolerances and hasten set-ups. At the same time, operators are enjoying easier handling, operation and storage due to their light weight. Dave Burgess, Vice President of Sales and Marketing at Pamarco Global Graphics, a worldwide supplier of parts to the flexographic, gravure, offset, and embossing markets, sums up their impact on the industry: “The biggest advantage of sleeves is that they really are a fast-change, relatively low cost option for printers, giving them the ability to inventory a large selection of screen and volume ranges.” He continues, “In addition, they are easily transportable, reducing shipping costs.” Bill Bower, Director of Sales and Marketing, North America, for Rotec, one of only a handful of sleeve manufacturers worldwide, also maintains that the primary benefit is “definitely the efficiency gained through quick changeover. A printer changes out his anilox rolls in a fraction of the time it would take for integral anilox rolls, allowing him to use the exact configuration he needs for a given print job.”

Construction
In simple terms, an anilox sleeve consists of a hollow base sleeve which is mounted on a round cylinder for insertion into the press. As compared with a traditional steel roll, the anilox sleeve base is typically made from composite or fiberglass materials covered with an aluminum outer layer. A nickel bond coat is then applied as a protective barrier against chemicals and ink components to prevent them from migrating through the porous ceramic and damaging the aluminum underneath. Finally, a ceramic exterior coating is applied and its surface is engraved using CO2, YAG laser or other traditional anilox engraving process.

The inner wall of the sleeve contains an expandable foam layer which functions as an air bladder or expandable aluminum rings to allow for easy installation and removal from the press mandrel. Highly compressed air is propelled from tiny holes in the mandrel to expand the sleeve’s air bladder or rings, creating a cushion as the sleeve is slid onto the roll. Once in place, the air pressure is removed, and the sleeve adheres snugly to the mandrel.

According to Aaron Lessing, Director of Sales and Marketing for Apex, North America, an anilox sleeve manufacturer, “The undercoat and the process in which it is applied is perhaps the most influential part of the entire manufacturing process.” He draws a comparison to the relationship between paint and primer whereby, “The paint is only as good as the primer – in this case, the ceramic is only as good as the nickel undercoat applied beneath it.” The importance of this inner barrier becomes evident with regard to cleaning practices as discussed below.

Dimensional Tolerance
As with traditional anilox rolls, dimensional stability is critical to ensure proper performance of the sleeve. Circularity, cylindricity, concentricity and total indicated runout are dimensional tolerance measurements that can predict press performance. While circularity and cylindricity measure the tolerance within the surface of the roll, total indicated runout, or TIR, and concentricity measure the roundness with respect to the center axis of rotation. TIR measures the distance from the exterior surface of the roll to the center axis when rotating and is expressed as a measurement over the entire surface of the roll. When compared to traditional steel rolls, these dimensional factors are particularly important with anilox sleeves given the added variables of hollow inner cores and expandable components. To take a TIR measurement, a dial indicator is moved along the entire length of the sleeve while it is rotating. Concentricity is more difficult to quantify as it measures deviation between the center of rotation of the bearing area and the center of rotation of the roll face. It is important to consider these measurements during anilox processing as well as on-press. According to Mr. Lessing, “Final TIR is extremely critical, whether it be a standard anilox base or an anilox sleeve. If a roll is out-of-round, it can cause inconsistencies in the engraving process, which could easily be picked up in a print job in the form of inconsistent density. With respect to sleeves, this is an extremely hot topic.”

As market conditions continue to demand higher quality print, these dimensional tolerances are getting tighter, and accurate measurement is becoming critical to ensure that the sleeves meet performance requirements. Mr. Burgess maintains that, “A TIR of 0.0004 today is very obtainable. The key is to make sure that the manufacturer of the sleeve as well as the engraver has the correct high-precision mandrels on which to process the sleeves.”

Issues to Consider
While the operational benefits of anilox sleeves are clear, careful consideration is warranted when handling, cleaning and storing. Although their lighter weight makes them easier to change over and store, the sleeves are susceptible to mishandling by operators. When installing and removing, the sleeves should never be wiggled, rather twisted gently to ease onto and off of the mandrel. The outer ceramic coating can chip or crack easily if the roll is placed on its end or dropped. When storing vertically, it is important to place sleeves on cushioned padding and use end caps. If storing horizontally, sleeves should be properly stored on a cart or storage rack, or on a large mandrel to prevent hanging or drooping. The construction is vulnerable to dents and punctures, and the circularity of the inner hollow cylinder can become out-of-round. These factors can result in TIR issues, sticking or slipping on the mandrel, damage to end seals and doctor blades as well as ink leakage and contamination of the inner core.

Care must also be exercised when cleaning anilox sleeves. Chemical cleaners and submersible tanks have proven harmful to the inner core and aluminum cladding, and the industry has been challenged with finding safe and effective methods of cleaning. Many chemical cleaners contain harmful solutions which can penetrate the natural pores in the ceramic coating, corroding the aluminum underneath and damaging the inner core of the sleeve. For this reason, sleeve manufacturers typically recommend avoiding chemical cleaners, ultrasonic and chemical cleaning tanks, and any submersible methods for deep cleaning. Dry cleaning using plastic media or baking soda is widely recognized as the preferred method of deep cleaning.

While initial versions of anilox sleeves could not be reprocessed, it is now widely regarded that sleeves can be reconditioned and re-engraved. Mr. Burgess points to this misbelief as the number one myth surrounding sleeves. In his words, “Anilox sleeves are very reworkable and durable. The biggest problem is the sleeve going out of round due to the way it is being loaded and unloaded on the press.” As a matter of fact, he sees damage from mishandling as the only disadvantage of using sleeves. However, the number of times a sleeve can be reconditioned seems to be dependent on how well it is cared for by the user. Mr. Bower explains, “An anilox sleeve is considered a semi-consumable product and is not intended to last forever. Anilox sleeves can be reconditioned, but the biggest factor in determining how many times is based on how well the sleeves are maintained by the printer.”

Current Limitations
Manufacturers have overcome many obstacles since sleeves were introduced about nine years ago. As a manufacturer, Mr. Lessing of Apex maintains, “The goal is to make a sleeve that will hold up the way a traditional integral base anilox will; you must have TIR, dimensional accuracy, durability and reworkability. Without these, the sleeve is a throwaway, and in our opinion, the market will not accept this.”

With virtually every new wide web press manufactured today being gearless, the use of anilox sleeves has rocketed in the past few years. Gearless presses presently account for only a small percentage of the narrow web market and none of the corrugated, but these markets are rapidly following suit. According to Mr. Lessing, two words to describe the direction of the gearless press market and the use of anilox sleeves are “bigger” and “faster” with sleeves now available in excess of 144” long and press speeds running up to 3,000 feet per minute.

As sleeve technology continues to transform the flexographic industry, manufacturers are working to further improve construction and reduce long lead times caused in part by only a small number of anilox sleeve suppliers worldwide. As presses become faster, the industry is moving toward longer-lasting sleeve cores and continually tighter and consistent TIR specifications. Mr. Lessing comments, “TIR is absolutely critical on anilox sleeves. Many of these gearless presses routinely run at 1,500-3,000 feet per minute. Any bounce or TIR issues will be exaggerated as press speeds go faster.” With advances in composite technology allowing for better rigidity, longer face lengths are becoming possible. Research is presently being done on a disposable anilox sleeve for a single use with a cost to justify this convenience. As industry continues to upgrade and replace its presses with gearless, anilox sleeves will continue to dominate the anilox market.

The MicroClean System is an off-press anilox cleaning machine which uses specially designed plastic media to gently remove dried inks and coatings from the engraving, restoring cells to their original volume. This method has been shown to do a thorough job of cleaning traditional anilox rolls as well as sleeves with a wide range of line screens repeatedly without damage. The system uses dry plastic media and, as a result, is one of the few safe and effective methods of cleaning anilox sleeves on the market today. As an added benefit, the plastic media is recyclable, making MicroClean the lowest per-roll cost cleaning method of any on the market today.

Due to its proven success in cleaning traditional rolls and in response to the industry’s need for a safe and effective sleeve cleaner, Flexo Concepts has equipped all of its MicroClean models with optional sleeve adaptors to enable a sleeve to fit into the cleaning machine. The line was also expanded with two new models, 60 and 90, to provide sizes well-suited to the mid-web and wide-web markets, respectively. Both models are available with a sleeve adaptor kit, dual-gun for faster cleaning, and the SmartDrive System to pre-program roll and sleeve sizes for quicker set-up. The new models provide these markets with a safe and economical alternative for thorough cleaning of their anilox sleeves.