High-Level Anilox Performance

Three industry experts offer tips on maintaining anilox functionality, including the use and care of anilox sleeves.

Anilox Program: Care, Cleaning, and Handling
David Skellie, president, Interflex 
Laser Engravers

From the perspective of the anilox engraver, the pressroom anilox program for the care, cleaning, and handling of the anilox tool is very crucial to the performance of the roll in the press. The engraver must fully understand the pressroom's anilox processing conditions to ensure the roll or sleeve engraving is executed correctly to perform within the specified environment. These conditions include understanding the print process, types of inks or coatings applied, handling methods, cleaning methods, and general housekeeping procedures for the anilox.

The engraving process entails adding value to a tool supplied by the tool supply fabricator. In today's flexographic market, there is a higher trend toward selecting anilox sleeves based upon efficient handling and changeover speed. For this reason, many sleeves are fabricated from aluminum, which needs protection from corrosive applications. The engraver must understand the press applications to ensure the proper barrier coat is applied to protect this aluminum base. Of course, the more corrosive the environment, the higher the level of barrier protection required, in turn equating to higher processing costs.

A ceramic layer is added on top of the barrier coat as the medium for laser engraving. This ceramic is known for being very hard and having a long life in regards to wear. However, ceramic is also inherently porous, which allows migration of whatever it comes into contact with. This again emphasizes the importance of the barrier coat layer to protect the base aluminum. An integral steel base also needs barrier protection as required from the application, although steel is not as vulnerable as aluminum

The pressroom must also determine the best anilox cleaning method for the application. With today's more environmentally friendly ink systems and the processing abilities for much higher print quality, it is imperative for the operator team to continually monitor the anilox cleaning process. The laser engraver can now supply high-definition anilox rolls, which have cell structures that require more attentive cleaning after the print process. With proper cleaning, the anilox will perform to specification immediately on install and minimize press set-up time.

The care and handling of the anilox is essential to the engraving print performance and life span of the tool. It is a fact that most rework engravings come from contact damage or some form of mishandling of the engraving tool. A properly documented and executed anilox program will ensure print quality and minimize future rework costs. Most engravers offer the expertise to assist and educate your press crew with a proper anilox program.

Sleeve Care
Michael Potter, FlexoWash LLC

Gradually, printers/converters are replacing their older generation presses with anilox journals in favor of sleeved presses. Anilox sleeves are lighter, easier to remove from the press, and easier to handle. These anilox sleeves have been manufactured using various thicknesses of carbon fiber, aluminum, and other metals cores with bladders or mechanical configurations for ease of mounting and demounting to and from the mandrel. Anilox sleeves have now been in the marketplace long enough for OEMs and end users alike to better understand how to manufacture, clean, handle, and store them.

Aluminum is the metal of choice because of its relative strength in relation to its light weight. It is a smooth and less porous metal than stainless steel, which is used for journaled rolls. Because of these characteristics, sleeve manufacturers are continuing to experiment with various types and bond-coat thicknesses between the aluminum and ceramic. This bond coat prevents separation of the ceramic from the aluminum and protects the soft metal from corrosion. Inks, manual cleaners, on-press auto-wash cleaners, and off-press cleaners must be used under strict guidelines in this environment.

The development of anilox sleeves and cutting-edge engraving technologies have created much higher line screen counts and deeper cells with higher volumes. These innovations have created challenges that require converters to use on-press automated wash-up systems, manual hand cleaners, and off-press automated equipment cleaners under the guidelines provided by each supplier (that should be read and understood). Even ink and water by themselves are corrosives! All of these methods and systems can be very effective in cleaning sleeves, if used according to instructions and in the correct environment.

The following "dos and don'ts" are a result of many discussions with anilox sleeve OEMs in the U.S. and Europe, as well as with you, the printer/converter user.

• Don't flex a sleeve while placing or removing from the mandrel or storage cart. Aluminum is slightly flexible. Ceramic is not flexible at all, and will crack, breaking the bond to the sleeve.
• Don't subject sleeves to temperatures higher than 130° F for periods longer than a few minutes. Allow the sleeve to cool down slowly. Never leave sleeves in an enclosed unit for periods greater than one hour, overnight, over the weekend, or a long holiday.
• Do wipe out and prevent cleaners, inks, dirt, grease, etc. from spilling and migrating into the interior of the sleeve. This causes difficulty with mounting and demounting from the mandrel. Eventually, this could cause problems with the interior core.
• Don't force sleeves on and off the press by striking the end ring and dead band area with any hard objects. This causes chipping of the ceramic, loosening of the end ring and possibly damaging the bond coat, which would then allow cleaners to seep under the surface.
• Don't use harsh chemicals such as oven cleaners or other similar materials that are not specifically developed for cleaning sleeves.
• Do thoroughly rinse off spray-on, paste, or liquid cleaners from the sleeve; wiping with a wet cloth is not rinsing!
• Do conduct frequent training of your operating personnel.

Implementation of these guidelines will extend the performance and life of your sleeves, insure safe and effective cleaning habits and results, and build a strong and lasting relationship with your sleeve OEM.

Sleeve Design and Manufacture
Michael Bell, Rossini NA

Current anilox sleeve technology consists of having an aluminum tube as the outer surface upon which the ceramic is applied. As noted previously, aluminum provides a challenge to the engraver not only from an adherence perspective, but also from a sealing and corrosion perspective. Sleeve manufacturers use different aluminum alloys, which can help with adherence, sealing, and corrosion characteristics. In addition to these challenges, there are some additional factors in the manufacture of the anilox base sleeve that can cause problems for the printer.

There are two styles of anilox base sleeves on the market today. The majority of sleeves employ a core expansion style, while the remainder use a solid build-up style. Both have a composite core sleeve with a wall thickness of approximately 0.040 inches. The core expansion style relies on a polyurethane foam expansion layer that compresses as the core expands when the mandrel air supply is applied. There is a secondary composite build-up layer applied to the foam expansion layer that allows the aluminum tube to be pressed and glued in place without compressing the foam, as that would render the sleeve too tight.

The solid build-up style has no true expansion layer and relies upon a core that shrinks in wall thickness as the core is forced into internal cavities within the thicker aluminum tube mounted on top when the mandrel air supply is applied. The core is only attached to the aluminum tube at each end, which allows the core to move laterally as the core material expands into the internal cavities and causes the parts of the core in contact with the solid internal ribs to become "thinner" therefore allowing the sleeve to mount onto the mandrel. When air pressure is removed, the core in both styles relaxes and locks to the mandrel with an interference fit.

Chamber leaks and end seal leaks result in ink getting into the vicinity of the core sleeve. In expansion layer styles, some designs have end rings to try to protect the foam expansion layer, but, inevitably, ink penetrates the foam layer and leads to problems. Since the foam layer is compressed in a mounted state, any ink that penetrates the foam and dries results in elasticity being compromised. This can have an effect on sleeve surface concentricity and possible future fit problems.

In the solid build-up styles, any ink contamination on the inner core or leaking into the internal cavities compromises the thinning of the core and the ability to easily remove the sleeve from the mandrel. Additionally, internal wear due to the lateral movement of the core against the ribs can result in concentricity problems for the printer.

The foam expansion layer is the weak link in any expansion style sleeve, plate, or anilox. In the case of anilox sleeves, ink contamination or non-conforming cleaning procedures can lead to serious consequences to the printer. Sleeve faces should always be sealed when using dry media and liquid cleaning devices. Ultrasonic cleaning is not recommended for anilox sleeves as it can actually delaminate the various build-up layers. Damage to the expansion layer by dry media or cleaning solutions can result in significant challenges to the printer, mainly in the form of TIR (total indicated runout) problems.

Efforts are being made by sleeve suppliers to permanently seal the foam expansion layers and internal cavities, but a significant breakthrough has yet to be made. Some anilox suppliers have developed methods to refurbish anilox sleeves by removing the ink-encrusted expansion layer and replacing it with a silicone type sealant, but this will not always return the sleeve to an acceptable TIR.

The future of anilox sleeves likely lies in a hollow sleeve with a composite carbon fiber outer tube and hubs that "slide" on the mandrels without an expansion layer. Such sleeves are available to the industry as plate sleeve bridges and such technology in the anilox sector could significantly reduce ink and cleaner contamination and corrosion, as well as allow press speeds greater than 2,500 fpm. Sleeve suppliers are beginning to develop such composite anilox sleeves for the newer high-speed, wide-web presses.

Adhering to supplier developed cleaning procedures will certainly extend the life of any anilox sleeve, but care in mounting/de-mounting and reducing ink spillage will also go a long way to prevpPenting print-related anilox sleeve problems for the printer. pP