A variety of systems are available for restoring clogged anilox rolls to functional condition.
By Jack Kenny
Some things can function just fine when they are dirty. Small children, for example. Most things cannot, and the anilox roll is most certainly among them. If the cells of an anilox roll are not free of dried inks or coatings, they are unable to deliver the right amount of ink to the substrate. There’s no getting around that truth.
Flexographers clean their anilox rolls in a variety of ways, as well as at different frequencies. Joe Walczak, president of Sonic Solutions, a manufacturer of ultrasonic cleaning systems, says that he has a customer “who faithfully cleans his anilox rolls once a year.” Seasoned flexo people might choke at that, although some clean their rolls monthly. The consensus among most converters is to clean the rolls as often as possible. If they cannot be cleaned using one of the four methods discussed herein – water wash, ultrasonic, soda blast, and plastic media blast – they should at the very least be brushed with a detergent and the proper type of brush.
“A lot of people still clean by hand, using stainless steel brushes and cleaners,” says Dave Burgess, vice president of sales for MicroClean, a plastic media blast system. “The mechanical action at the top of the cell with the brush can get it clean. We’re not talking about 700 or 800 line count rolls here, just the lower count aniloxes. Brush cleaning is not very consistent from operator to operator. Even if it’s the same operator it might differ, depending on how much time he has.”
Hand cleaning is truly inexpensive. Other methods require capital investment with the goal of keeping those other investments – the anilox rolls – performing well every time. Here we examine four such systems, each different, that have shown to be effective in removing unwanted materials from the cells of anilox rolls.
The SS-6500 ultrasonic cleaner for anilox rolls
manufactured by Sonic Solutions
The ultrasonic cleaning systems produced by Sonic Solutions have succeeded in the narrow and midweb markets. Today, says Walczak, the company is working with engineers to develop a system for the wide web market, where moving anilox rolls around the shop is no small matter.
In the ultrasonic system, the anilox roll is exposed to a bath of solution that facilitates the cleaning process. “The ultrasonic process acts more like a vacuum cleaner to remove the debris of the cells,” Walczak says. “We have developed the 90-10-max5 rule to help people understand how it works best: 90 percent of the cleaning process is allowing the rolls to soak. That allows all dirt and debris to soften up. 10 percent of the work is the application of ultrasonics, no more than five minutes at a time.
“If it works all the way, the ultrasound vacuums the debris off the roll. It can clean thoroughly regardless of cell count. You are approaching the cleaning process in a logical way: If the debris in the cells is not soft, you will not clean anything out of them. Soften first, then apply the ultrasound.”
The roll being cleaned rests across the top of the unit, so that the lower half only is resting in the solution, and turning during the cleaning process. The length of time in the ultrasonic bath varies according to how dirty the roll is. “The normal routine is 10 to 12 minutes to soak, then a short application of ultrasound,” he adds.
The solution used in the ultrasonic unit is a high alkaline product, around 13 pH, Walczak says. Sonic Solutions is testing one that is a bit milder, he adds.
The solution is fairly long lasting, its life depending (again) on how clogged the anilox rolls are. Walczak says a converter can typically get 30-40 cleanings per batch.
Spent solution is disposed of according to local disposal requirements. “Typically it ends up being how you dispose of your waste inks,” he adds.
Sonic Solutions manufactures a range of systems. These include the SS-2800, which will accommodate rolls up to 10" long; the SS-6500, the most common version, which will handle rolls up to 18"; and the SS-6530, for rolls up to 30" in length.
Flexo Wash manufactures a system that cleans anilox rolls – and other parts as well – using just water and a detergent. According to Michael Potter, president of the company, it’s a familiar process.
“Our equipment cleans like a touchless car wash or a dishwasher. You put a roll into the machine, set the length of time that you want to clean – whether it’s heavy, normal or whatever. If it’s a coating roll with a catalyst or bonding agent, the cleaning process could take you 20 to 25 minutes,” Potter says. “Otherwise, an anilox roll used with water based or UV ink, or even solvent ink, can be cleaned in 10 in 15 minutes.”
The process involves a 10-minute wash cycle, a two-minute drying cycle, and a two-minue rinse and dry cycle.
The water in a Flexo Wash system contains an alkaline detergent containing some surfactants. “The wetting agent is the key,” Potter says. “You can put the roll in wet or dry, because it’s going to get wet during the cleaning.” With the blasting cleaning systems the inks have to be completely dry in order to remove debris from the cells.
In operation, the roller is suspended in the air and is turning. The washing solution comes out of the nozzle at low pressure and at about 120° F. “That process causes the ink to dissolve,” notes Potter. “It could take five, 10 or 20 minutes, depending on the coating. Then, for two minutes, all we are doing is recapturing the liquid that has dripped off and down the drain to be filtered and used again. When that’s over the valve closes. We rinse with warm water, 85° F at high pressure, about 1,500 psi at 2.3 gallons a minute. That runs in one, two or three passes, usually two. Finally it undergoes two passes of air to dry.”
As Potter mentions, the Flexo Wash unit recaptures the liquid and filters it for reuse multiple times. Ink will migrate to the bottom of the tank, he says. The liquid containing the ink then goes through a 50 micron filter and catches whatever ink remains, which is then disposed of according to local procedures.
Water, says Potter, is the basic element in the system for penetrating the microscopic cells of the anilox roll. “Water will break down into the smallest molecular particle there is, and it will get into the cell. There is no damage, no corrosion.”
Flexo Wash manufactures equipment of several sizes. The narrow web units range from 36 to 53 inches in width.
Baking soda – sodium bicarbonate (NaHCO3) – is what Sani-Blast uses in its equipment to clean anilox rolls. This well known process is described by the company as “an efficient method of deep cleaning anilox rolls while being environmentally safe.”
A Sani-Blast anilox cleaning machine
Mulheran notes that the company offers a system that can clean large rolls on press to reduce downtime. Any roll that has a diameter greater than 4" and width in excess of 20" can be cleaned on press. With this operation, the blast and vacuum head goes up against the roll, and while the roll is idling the blaster traverses its length and blasts the cells clean with the baking soda.
“Another option,” he says, “is to clean rolls off press using an Anilox Roll Rotating Cart. The soda blaster traverses the blast nozzle while it rotates the roll being cleaned at proportional speeds. The soda is delivered via a device that assures a consistent volume and pressure. A vacuum head on the cleaning nozzle gathers the non-hazardous soda in one container for disposal in normal waste systems. The original soda blasting systems sometimes had problems controlling dust while cleaning, but improved vacuum and filtration technology has eliminated this problem.
Noting that sodium bicarbonate is friable, Mulheran says that the diameter of a grain of the medium “is under 7 microns when hits the face of the anilox roll. It cleans every last bit right to the bottom of the cells.”
MicroClean, a product of Flexo Concepts, is also a blasting system, but instead the dirty work is accomplished by plastic media.
MicroClean’s plastic media
MicroClean has three different grades of media, which are used according to the line counts and cell volumes of the anilox rolls being treated. “Fine media is for high screens,” says Burgess. “Laser media is for rolls from 150 line count up to the 600-700 range. The multi-media covers a very wide range, and is a blend of the fine and the laser.”
The media, he says, takes a long time to break down. “A single particle might go through the system up to 150 times before it breaks down.” He adds that it is “non hazardous, non-reportable waste. The end result looks like talcum powder. It can go into a waste stream.” The removed ink adheres to the media, and is then taken away through a cyclone and a series of dust filter banks. “The good media is filtered and passed over magnets before being returned to the process.
The volume of waste media that is sent to the dust drawer is replaced with an equal amount of new media.
The anilox cleaning takes place in an enclosed cabinet, the smallest of which will accommodate a roll up to 34" in length, journals and all.