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Printers: Cleaning Anilox Rollers
The key factor in metering ink in the flexographic printing process is the anilox roller. Etched with cells that act as the carriers of exact quantities of ink to the printing plate, the anilox roller must maintain its integrity through cleanliness. An anilox roller with plugged cells will deliver reduced amounts of ink, shifting color from the acceptable standards for the graphics.
The use of solvents to clean the cells and maintain the quantity of ink transferred and, thereby, the quality of the graphics, has an effect on the environment. Air pollutants are released and hazardous waste is generated. As the amount of solvents used and converted to waste increases, so do demands on the printer to comply with increased regulatory requirements. Thus, the need to maintain the cleanliness of the anilox rollers becomes a critical event in the conduct of business. The cost of cleaning properly and environmentally responsibly must be weighed against the cost and liabilities of allowing rollers to plug and degenerate graphic quality, as well as the cost and exposure experienced by the printer after hazardous waste is generated.
REGULATIONS DRIVE NEED TO CHANGE CLEAN-UP METHODS
There are a number of basic areas of concern involving the use of chemistry for cleaning printing presses:
PHILOSOPHIES IN CLEANING ROLLERS
There are two approaches presently vying for the attention of the flexo printer. One contends that the answer lies in the equipment that can be used off-press to maintain the fidelity of the engraved anilox cells; the second deals with efforts to find solutions that work well on the press. The off-press approach argues that better cleaning can be done away from the printing station, utilizing either high fluid pressure or soaking to dislodge dried inks. The conventional thought is that a better, more thorough cleaning can be done away from the press environment. The technologies cited are similar in some ways, but different enough to stimulate discussion as to which can do a more effective job.
The on-press approach has sought new, safer solvents for use as cleaning agents, and contends that production is maximized if presses are not taken apart for cleaning. A press that is running is producing saleable product. A press that is down costs money, as profits are lowered by reduced production of saleable product.
Conditions vary by press size and configuration. While it may take minutes to remove and clean an anilox roll from a tape and label press, a wide web press may requires hours for the same function. The sophistication of the graphics also weighs heavily in a decision to shut a press down for anilox roll cleaning.
Neither of these two cleaning approaches can be the sole option employed. They must work together. To consider one as the ultimate, without recognizing the advantages of the other, can only lead to the confusion that currently exists, as each of the new approaches to clean-up technology claims superiority.
Cleaning lies in a three-pronged attack on the plugging and drying of inks in anilox roll cells.
For on-press cleaning, with water-based or solvent-based inks, select a cleaning agent that will remove the inks quickly and will be compatible with your plates and ink system. In the event that the cleaning agent finds its way into the ink train, you do not want it to contaminate the ink. Compatibility will enable the ink to continue performing without affecting the quality of your graphics or the stability of the ink formulations.
There are many such cleaners on the market. The key is to select a formulation that will adequately re-wet or dissolve the wet ink and return it to the ink reservoir for re-use. If your cleaning solution will render contacted ink unusable, you will want to select a solution that is either reusable through solvent recovery or water treatment, or can be disposed or discharged as a non-hazardous waste.
Among the recently available cleaning solutions are solvents with very high boiling points, where evaporation is so slight that it is almost unmeasurable. A number of these agents are also biodegradable and may not be considered hazardous wastes. Investigate thoroughly to make sure these cleaners will penetrate the inks and maintain the cells in top condition.
The chemistry is only as effective as the methods by which rolls are cleaned. Establish a procedure and train your press personnel to follow these guidelines. Predictability comes from the consistent use of the method and the proper application of the cleaning chemicals. A major problem associated with on-press cleaning is inadequately clean cells due to the reaction between two different ink systems, which allows for build-up of dry ink in the cells.
Companies frequently resort to a very high caustic cleaner—(i.e., oven cleaner)—to get the cells relatively clean. This is not safe for the roller or the press personnel and should be avoided. Regardless of which off-press option you select, it is necessary to have regular cleaning done on press to assure that product quality is maintained. In this scenario, the time lost due to offpress cleaning is minimized.
Periodic use of the proper anilox bristle brush can help dislodge stubborn ink solids. Spray bottles can be used to limit the amount of solvent or aqueous cleaning solution, as well as allowing the solution to be applied into the cells where it is most needed.
ON-PRESS AUTOMATIC CLEANING OPTIONS
Press personnel may neglect to perform proper cleaning for a variety of reasons. Whether they are too busy, overworked, or simply bogged down under too many other demands on their time, one of the easiest things to let slide is cleaning the press, which is why most plants look for more predictable press cleaning systems.
One alternative are systems that can be used on the press. These include the relatively new system that uses a chamber blade system with built-in air pressure cleaning jets, and the variety of add-on cleaning systems, that can be attached to the press station for the cleaning sequence.
OFF-PRESS CLEANING SOLUTIONS
There are five basic options for cleaning the press parts away from the print station:
The baking soda (sodium bicarbonate) and plastic bead techniques are both considered effective by their respective users. Roller companies are concerned about the ramification of the powders beating on very thin walls of high cell count rollers. The possibility exists for breaking down walls and creating ink transfer inconsistencies.
A more effective system, from the perspective of minimal waste in the operation, would be the dry ice technique. This uses particles of dry ice in place of the powder and plastic beads. The dry ice removes the ink, then evaporates. However, there is a concern that high air pressure is not able to force the dry ice into the cells.
An established cleaning system is the ultrasonic tank. The success of this method relies on the additive used in the cleaning tank water. There are formulations that prevent a film from coating the surface of the rollers and creating problems with adequate transfer of inks. However, there are concerns regarding the ability of thin cell walls to withstand the pressure of the ultrasonic waves.
Cleaning tanks using caustic soda solutions or aggressive solvents offer the ability to allow parts to soak, literally burning the ink out of the anilox roll cells or off the parts of the press. In some tanks, the liquid is circulated to create motion and promote cleansing. Racks allow parts to be suspended for total exposure to cleaning solutions. Appropriate safety measures are a must for all personnel working in this cleaning environment, these solvents may be caustic, toxic and/or highly flammable.
MAKING THE CHOICE
Consider the following factors as they relate to your facility:
Reprinted with permission from pneac.org/.