Cleaning methods for anilox rollers are always a hot topic in the flexo world. To help make sense of the many options available, the following discussion outlines the most common off-press anilox cleaning systems and chemical cleaners available in today's marketplace.
(Please Note: The following cleaning systems are not listed in any particular order.)
Baking Soda Blast (Sodium Bicarbonate) Systems:
A baking soda blast cleaning system uses air pressure to deliver baking soda media to an anilox roll. The spent media is then recovered using a vacuum unit.
Baking soda blasting works on the concept of refracture. Large sodium bicarbonate crystals break into smaller crystals upon impact. Blasting pressures reach 20-25 psi for chrome and mechanically engraved ceramic anilox, and 30-35 psi for laser engraved ceramic anilox. The baking soda actually gets inside of the anilox cells to break-up dried ink. The process seems to be effective for removing stains and dried ink.This method is capable of cleaning wide web rolls either off- or on-press, and narrow web rolls off-press only.
Off-press cleaning requires an enclosed blast cabinet, while on-press cleaning units are mobile and can be moved from press to press. Corrugated box printers typically use on-press systems to take advantage of the time saved by leaving their large rolls in the press during cleaning. In all cases, the anilox roll rotates while a nozzle mechanically travels across the roll during cleaning. Used under the manufacturer's parameters, these units are generally safe, quick and effective for cleaning anilox rolls.Following are some suppliers of baking soda blast units:
Plastic (Poly) Bead Systems:
Plastic bead systems use air and plastic bead media to impact upon anilox surfaces at an air pressure of 35-70 psi. These systems are normally off-press units with enclosed cabinets. The anilox roll rotates while the nozzle traverses the length of the roll. The plastic or poly beads actually get inside of the anilox cells to break-up dried ink.
The process seems to be effective for removing stains and dried ink.Used under the manufacturer's parameters, these units are generally safe, quick and effective for cleaning anilox rolls. Following are some suppliers of bead media units:
Ultrasonic Cleaning Systems:
Ultrasonic is sound energy that creates cavitation when introduced into a liquid. The cavitation is caused by pressure differentials, providing the cleaning action of this process. When using ultrasonic cleaning systems, be aware that excessive exposure time can cause cell damage.
To monitor this, ultrasonic generators are generally controlled by timers to limit exposure time and minimize damage to anilox cells. As a rule, higher line screen engravings require shorter cleaning times and are more susceptible to damage, as shown in the following examples:
Example 1: An 800-line screen roll contains 736,000 cells per square inch (wall width is 3 microns; cell depth is 8 microns.) The exposure time recommended to clean an 800-line screen roll should not exceed 3 minutes. Example
Example 2: A 200-line screen roll contains 46,000 cells per square inch (wall width is 7 microns; cell depth is 34 microns.) This lower line screen roll takes longer to clean, and can tolerate an exposure time of up to 20 minutes because wider walls are not as susceptible to damage.
The following reference table outlines exposure time recommendations for cleaning anilox rolls using ultrasonics:
|Line Screen||Recommended Time in Ultrasonic Cleaner|
|360 and below||20 minutes|
|380 - 440||15 minutes|
|460 - 660||10 minutes|
|680 - 800||3 minutes|
Any line count above 800-line screen should be cleaned manually.
Chemical cleaners are used daily in the flexo printing industry and for the most part they work. Many of these cleaners are caustic, permitting a fast and thorough cleaning. When choosing your chemical cleaner make sure you address the following items:
1. Understand EPA and OSHA issues. Make sure your cleaners are safe for use in your shop. Strict EPA and OSHA standards vary by state, and it is important to make sure your shop is in compliance.
2. Review Material Safety and Data Sheets. These documents contain valuable information about the chemical make-up of a cleaner. Be sure you understand the product and that you are taking the proper precautions when using a cleaner.
3. Consult with Your Ink Company. Before you begin using a chemical cleaner, contact your ink supplier. Some chemical cleaners may have a negative reaction with your ink, and hinder your ink's performance.
4. Keep in Mind that Ceramics are Porous. Acidic or alkaline chemicals can migrate through ceramic and can attack the ceramic's bond to the metal base. When ceramic is chipped, chemicals can migrate to the metal base even quicker causing the ceramic to blister and delaminate.
5. Take Care of Your Staff. The first and foremost goal is to protect the health of your employees. Normal health and safety practices require the use of safety glasses and rubber gloves when using a chemical cleaner. Understand that the pH of a chemical solution can damage your anilox roll if it is not in the safe range of approximately 4 to 11.8.
Additionally, the pH for water-based ink is typically 8.5 to 9.4, and the pH of the cleaner should always be higher than the pH of the ink to be effective. Although extremely effective at cleaning, anilox cleaners outside of the safe pH range can damage engravings with prolonged exposure. Because pH is such a vital component of anilox cleaners, having a pH meter on-hand is definitely a plus.
Generally, only anilox rolls with stainless-steel bases should be used with corrosive cleaners, because stainless steel is more corrosion-resistant than most other materials used for anilox construction. For instance, aluminum bases are much more easily corroded than steel. In fact, standard water-based inks can be harmful to aluminum-based rolls in many cases.
A stainless steel brush should be used with chemical cleaners on ceramic anilox rolls, and a brass brush should be used for chrome rolls. These brushes will agitate the cleaner on the roll surface and into the anilox cells. A good brush has bristles with small diameters of .003 (3 thousandths) or less. At this diameter, bristles can reach the bottom of cell engravings of 280 line screen and below because the cell opening on a 280 line screen is 85 microns, or 3.34 thousandths. This does not mean brushes will not work on high line screen anilox rolls. On the contrary, brushes with chemical cleaners work well to agitate the cosmetics of the ceramic as well as the tops of the cell walls to loosen up the ink. In addition, a steel brush will not damage the anilox rolls or the cells.
Your Maintenance Routine
Achieving adequate color density and reproducing it on each successive run is the common goal of flexo printers. With the same anilox roller volume every day, you can significantly reduce color matching time. The objective is to standardize the printing process and good cleaning and maintenance routine is a part of the process. Take the time to develop a maintenance plan that works for you, and then stick with it. Taking care of your anilox rolls will save you time, money and energy in the future.
Want to Attend A Complimentary Harper WalkingSeminar™?