Roll Up Your Sleeves
Quality and damage control for higher line screens demands renewed attention to anilox roll cleaning practices and methods.
By Susan Friedman
Oven cleaner just won't cut it. When it comes to anilox roll cleaning, package printers are having to muster some heavier duty enthusiasm...and exercise care.
"Before higher line screens, cleaning didn't have to be as thorough because anilox rolls didn't provide the quality they provide now," says Torben Rasmussen, president, Flexo Wash. Anilox roll prices have doubled right along with line screens, and now the concern is preventing these rolls, which have thinner cell walls, from being damaged, he adds.
Converters continue to favor less rigorous cleaning routines. According to Steve Woodard, sales and service manager at ARC International, manually cleaning rolls with stainless steel or brass brushes is still the most common method. "It can do an adequate job if done regularly, before problems start," he states.
Cleaning agents used with brushes can create roll surface erosion if they have a higher ph than the inks. Laser-engraved anilox rolls that hold up best are those with a corrosion-resistant undercoat, which functions as a barrier between the roll's steel core and ceramic coating, Woodard notes.
Hand cleaning can also take a lot of trial and error, because few solvents can remove all types of inks and other contaminants, notes Praxair Region Sales Manager Jan Ashfield. "One cleaner that works perfectly well with ink A may not work well with ink B," he comments, adding that ink suppliers are the best source of guidance on this issue.
Brushes' popularity often leads them to be used even when they are ineffectual. "After 440 line screens, using brushes and powders is like putting a square peg into a round hole," says Ray Marro Jr., president of CR Products.
Heavy-duty cleaning methods that package printers have already taken a shine toincluding baking soda blasting, plastic media blasting, ultrasonics and heated solutionsare heeding the industry's call for faster, damage-free cleaning at 1,200 to 1,500 lpi.
Baking soda blasting can generally keep rolls clean for four to six months, if, between treatments, rolls are cleaned after each use with a non-hazardous chemical solvent. The baking soda media is a lower ph blend of surfactants that lift away inks and other residue. A complete baking soda system should include the applicator, a handling device for the roll and a vacuum system.
The baking soda exits the applicator as a jagged, 70 micron particle, and then shatters down to 8 microns to clean the cells. The best applicators, explains Jim Heffer, president of Anilox Roller Cleaning Systems, meter the media and contain flow additives to ensure even dispersion into rollers' cells.
Rolls need to be rinsed with water after blasting to remove media residue. Heffer says baking soda can currently clean 1,200 line screens. Cleaning tests are underway with 1,500 line screens. Each treatment costs about one-tenth the price of a new roll. A 10ý roll can be cleaned in two and a half minutes, and larger rolls can be cleaned on- or off-press.
Plastic media blasting, available for the past year and a half, employs "a malleable plastic media that can fold, bend, bounce back and be recycled," says Bob Temple, CEO, Absolutely Micro*Clean International. Average life cycle for the media is 120 cleanings.
Once the roll is positioned on a centering unit within a cabinet, a computer-driven gun applies a medium pressure, dry blast of the media. Plastic bead blasting can currently clean 1,200 line screens without wear, and has undergone testing for higher line screens. A fourth-generation blend of the plastic media, Micro*Clean IV, uses a "sharper bite" to cut cleaning time in halfabout ten minutes for small, narrow-web rolls, and 30 to 45 minutes for wide-web rolls. Narrow-web plastic media systems can run about $13,000, while a wide-web system is around $28,000.
In ultrasonic cleaning, transducer-generated sound waves create bubbles that use a vacuum effect to remove material from a roll's cells. Marro says ultrasonics' submicron-size bubbles are the key to its effectiveness for higher line screens. He recommends adding a chemical such as CR Products' CR 1 to the cleaning solution to aid the breakdown of polymer (a scuff-resistant ink additive) build-up on rolls. Otherwise, ultrasonic cleaning may take several hours, causing damage. Normally, ultrasonics cleans a roll in two to seven minutes.
Sandy Mueller, technical sales representative at Daetwyler, stresses that proper usage eradicates the chance of damage with ultrasonics. Users should ensure that the roll is rotating during cleaning, and that the solution in the tank cavitates, or bubbles, well. Newer systems offer adjustable sweep frequencies. A table-top ultrasonic unit can run as low as $500, while a complete system for extremely large rolls could cost up to $50,000, Mueller estimates.
Heated solutions with a ph similar to that of inks aim to dissolve away inks and other dirt. Up to three rolls can be submerged and rotated in Flexo Wash's enclosed units, explains Rasmussen. Cleaning takes five to ten minutes, and then a high-pressure spray of water finishes the job.
Rasmussen says rolls can be left in the solution for an hour, even overnight, without fear of cell wall damage. In addition, units are small enough to be installed right next to the press, encouraging higher cleaning frequencies. The heated solution method is also claimed a safe haven for 1,500 line screens, and is moving into wider-web applications. Unit costs range from $5,000 to $40,000, depending on roll size and custom configurations.
Easing into a routine
Converters must make a conscious effort to avoid sweeping roll cleaning practices under the rugand suppliers offer several approaches to making roll cleaning as automatic as breathing.
"The most common mistake by far is that, regardless of method, anilox rolls are not cleaned frequently enough," observes Mueller, who adds that there is no easy frequency formulathe appropriate time frame can depend on inks used, line screen count, length of time in the press and other variables. Printers' best bet is to simply integrate anilox roll cleaning into their regular maintenance routine, she says.
Marro believes convenience will foster cleaning motivation. "If you are using a tedious method that requires cleaning one roll at a time...you will wait for a problem to clean," he says. "And then you miss the objective of cleaning, which is to be running with clean rolls all the time."
It might take the trouble of a close examination to determine the best cleaning approach. "Have the proper tools to evaluate your anilox," Temple states. "I would encourage anyone with a large inventory of rolls to invest in a microscope so they can see what's happening."
At the same time, the definition of a clean roll may soon come down to a numerical value. Heffer predicts that new volume testing procedures will allow stricter cleaning method standardizations. This may soon enable printers to achieve volume consistency throughout a monthly cleaning cycle, and from plant to plant.
Zapping Away Contaminants
Fresh on the market is a laser anilox roll cleaning process developed by Datasphere, in which a "softened" laser beam heats and removes ink, polymer plate material, ink additives and even embedded metal from the surface of the roll. Laser cleaning is said to restore a ceramic roll surface's rewetting ability, which can be sapped by ink additives for release and scuff-resistance.
Laser cleaning is designed to be a saving grace to rolls returned for reengraving that "just got to the point where they wouldn't print," says Datasphere President Jerry Jenkins, who patented the anilox laser engraving process. "This is something that you do when you decide that the roll cannot be cleaned with a standard process," he adds. Many rolls get to this point of no return because printers add water to water-based inks, reducing ink ph and releasing additives and other contaminants onto the roll.
Rolls up to 80ý, with 1,200 line screens, can be laser cleaned at 10 percent to 15 percent of the cost of reengraving. Converters who want to spring for their own system will need to invest about $80,000, Jenkins says.