Water-Based Ink Cleaning Tips
One of the most common mistakes made when cleaning water-based ink is using just H2O. Operators may pull the anilox rolls and bring them directly to the sink to be cleaned with only water.
Water-based ink has a pH of approximately 8.5-9.5, depending on the ink system. This pH level keeps the pigment particles suspended and the ink functioning properly. Water has a pH of about 7 and when used to clean up anilox rolls, it drops the pH of the ink it contacts. This shocks the ink, throwing it out of balance and making it more difficult to clean up. It can even lock the ink in the bottom of cells and reduce the roll’s volume.
Do not fall into the misconception that if two points higher is good, then four must be awesome. This is just not true; in fact, it is worse
To aid in the cleaning up of water-based ink, a cleaning solution with a pH of two points higher than the ink is recommended. This pH level helps to re solubilize the ink and makes clean up remarkably easier. Please note: The maximum acceptable pH level of roll cleaners is 11.8 and exceeding that allows for potential damage to the anilox. Do not fall into the misconception that if two points higher is good, then four must be awesome. This is just not true; in fact, it is worse.
Another abused technique is the use of soak tanks. To increase productivity during changeovers, the operators will pull the rolls out of press and put them in a soak tank. The aniloxes sit in the tanks until they are cleaned. The theory behind this is that by soaking the rolls, it prevents the ink from drying. This is not a good practice and I do not recommend it.
Why? The mystery solution in the tanks is usually just water and as we discussed, this is not a good cleanup solution. If the pH of the solution is high, it can damage the rolls, especially if they are soaking for a while. This allows the cleaner to work its way through the ceramic to the base metal of the roll. Many times, these soak tanks are used for more than one ink chemistry and that only complicates the issue. Different ink chemistries typically do not mix well and can cause a cleaning nightmare by locking up the inks in the cells or creating residues that are almost impossible to remove.
More often than not, these soak tanks are not cleaned on a regular basis. The solution on the inside looks like sewage with floating debris. To make matters worse, the tanks are usually lined with dried ink. Dried ink is extremely hard and if an anilox is rubbed against it, the potential for a scratch is high. The use of soak tanks typically means the gears and bearing of the rolls are being submerged in water or cleaner. It is never a good idea to submerge gears and bearings—It will only cause them to fail sooner.
UV-Based Ink Cleaning Tips
UV ink is cured, not dried. This curing process is started by exciting the photoinitiators in the ink with intense UV lights at a specific wavelength.
Some shops will pull their anilox rolls out of the press and let them sit under shop lights. The lighting in your shop—whether it is fluorescent or incandescent—contains stray UV energy to initiate the crosslinking process of the photoinitiators. Granted, it is not as intense as the bulbs used in press, but it will begin to cure the ink. The longer you leave the rolls exposed to the light, the more the ink will cure. The ink will not cure overnight, but over time you will see a reduction in volume. Once the ink is cured in the cells, it becomes difficult to remove it. I always recommend thoroughly cleaning the rolls if they are not going to be used. At the very least, cover the rolls to prevent the UV rays from reaching the ink.
Granted, it is not as intense as the bulbs used in press, but it will begin to cure the ink. The longer you leave the rolls exposed to the light, the more the ink will cure.
When cleaning UV ink, it is also important to select a cleaner that is formulated to break the ink down. I stay away from fast solvents for cleaning, because they tend to cause more issues. Many UV cleaners are a slow solvent, so they can get in and break down the ink. The slow solvents do not evaporate quickly, so it is critical to rinse them using an alcohol or a fast solvent.
Off-Press Cleaning of Anilox Rolls
It is of paramount importance to keep anilox rolls clean. There are many off press cleaning systems that work well; however, be sure to follow the OEM’s specs. Increasing pressures or temperatures outside the recommendation can damage the roll.
If using ultrasonic cleaners, keep in mind the soak and ultrasonic times. Operators like to put the anilox rolls in with the ultrasonic on for much longer than recommended. With ultrasonic cleaning, the rotational soaking time is important. If a roll is not getting clean when adhering to OEM specs, something within the system is not functioning properly and I would recommend contacting the supplier.
If you inspect your anilox rolls and the cells are plugged, there are two things you need to do:
- Thoroughly clean the rolls (in an appropriate fashion) to get all of the dried ink out and restore the cells to their original condition. This is where many people go wrong. In a panic, they attempt to free up the cells with abrasive devices, or soaking with corrosive cleaners. In the end, they only end up damaging the rolls and causing thousands of dollars of irreparable damage. I can’t stress it enough: If you are unsure of how to clean your anilox rolls, ask questions. It could save you thousands of dollars
- Once the rolls are clean, put in place a cleaning process to maintain them. One of the most challenging things to accomplish is changing the process after people have been doing it a certain way for years. Take the time to properly train and explain to your employees the new process. All too often, companies have good intentions; however, the new process is not fully explained. Questions are not answered and they wind up in the same spot they were before
The No. 1 thing any printer can do is properly train employees. I find that lack of training is the single greatest cause of mistakes at print shops. Take the time to educate your employees on the importance of proper care and maintenance of anilox rolls. It is a small investment of time that will decrease damage and increase repeatability, consistency, and ultimately your customer satisfaction.
About the Author: Greg Harms has amassed more than 20 years of experience in production and management throughout the flexographic industry. Greg joined Harper Corporation of America in May 2012 as the Southeast HGS advisor and currently holds the position of technical account manager for narrow web in the Great Lakes region. Prior to joining Harper, Greg was the operations manager at St. Louis Pressure Sensitive. As operations manager, he focused on team building, lean manufacturing and cost reduction.