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Anilox Roll Cleaners



Proper care of the anilox roll a critical flexo tool can be achieved



Published September 7, 2005
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Anilox Roll Cleaners

Proper care of the anilox roll — a critical flexo tool — can be achieved


Above: An ultrasonic anilox roll cleaning unit from Max Daetwyler Corporation.
One type of roller among the many that inhabit a flexographic printing press receives the most attention, and with good reason. The anilox roll has been described as the heart of the flexo press, and as such is deserving of proper attention and care. Its surface is composed of millions of invisible cells that capture and transfer ink, and must continue to do so hour after hour at constant speed without failing.

Keeping anilox rolls clean is an industry unto itself, and a highly competitive one. There’s basic press-side cleaning, and then there are at least three or four deep-cleaning, off-press processes in use today. One doesn’t have to go too far to hear a tale of woe about how one particular system damaged an anilox roll, and why a converter switched to a different process. Experts agree, however, that most anilox damage is caused by human error in operation or in judgment, regardless of the type of machine used for the cleaning. All of the systems available on the market today will clean anilox rolls, but each has aspects whose appeal varies.

Day-to-day cleaning

No question about it: Anilox rolls have to be given a basic cleaning as soon as they are taken from the press. A general rule is to keep the other anilox rolls turning in their inks while one roll is being cleaned. “Use a press wash that has a chemical make-up that suits the chemistry of your inks well,” says David Lanska, narrow web sales manager for Stork Materials Technology, Milwaukee, WI, USA, an anilox roll manufacturer. “Rinse the rolls down with the press wash, using a rag or an anilox roll brush or some kind of pad to agitate that cleaning chemistry. Then wipe it clean with clean, dry rags. You might have to do it again.”

CTS Industries, of Cedartown, GA, USA, which also makes anilox rolls, recommends the use of a stainless steel wire brush (“Never use a brass brush to clean a laser engraved ceramic anilox roll. The brass bristles are soft and can imbed themselves into the cell structure of the anilox roller.”). “Work the brush in a circular motion, as if you were waxing a car. The bristles are larger than the cells of the anilox roll; therefore, they do not touch the bottom of the cells. However, the agitation created from the bristles will penetrate the cleaner to the bottom of the cells in order to lift up the ink for easier removal. Then flush the roller with solvent and wipe it down with a lint-free cloth. If you are using water based inks, pour alcohol over the roller to absorb any moisture which would be left in the cells.”

Ultrasonic cleaners

It’s difficult to say which deep-cleaning system has the lion’s share of the marketplace. Ultrasonic cleaning units are among the top choices, and several changes have been incorporated into the systems from several manufacturers in recent years to address the needs of printers.

This system utilizes two basic steps to thoroughly clean a roller. The first is treatment with a solution designed to loosen the ink that has dried in the cells. “The purpose of the solution is to soften up the resins that dry within the cells,” says Joe Walczak, president of Sonic Solutions, Lockport, IL, USA. “They dry clear and rock hard, and they take up a good amount of cell volume. That’s why 90 percent of the cleaning time is spent softening up the resins. And if you don’t have a strong enough solution you might end up overdoing the ultrasonic cleaning.”

Exposing the rolls to the solution can be accomplished in two ways. Some systems involve full immersion of the roll in the solution. Systems by Sonic Solutions and Daetwyler are among those that expose only part of the rolls to the solution at any given time, and these are always in rotation. “In our system about an eighth of the roll is submerged,” notes Walczak, “so the gears and bearings can be left on, typically.”

Sonic Solutions promotes what Walczak calls the 90/10 Max 5 Rule: “90 percent of the time you are soaking the roll; 10 percent is the application of ultrasonics, with no more than 5 percent of ultrasonics at a time.”

It is said that the ultrasonic process poses a potential threat to anilox rolls. “We have had people use the same roll in an ultrasonic cleaner for 10 years without damage,” says Walczak. “Using any system inappropriately will cause a problem. If you turn it on at night and come back in the morning, you’ll have some damage.”

 
Absolutely Micro*Clean’s anilox roll cleaner utilizes a plastic blast media that is re-usable for up to 100 cleanings.
The ultrasonic part of the process comes from transducers that are welded to the cleaning tank. These cause the metal tank to vibrate at a very high speed, so high that the liquid cannot keep pace with the vibrations, which creates millions of vacuum bubbles. “When those bubbles come into contact with the anilox roll they implode,” says Lanska. “It’s a way of agitating the cleaning chemistry on a microscopic level, so that it gets into the microstructure of the engraving.” Stork Materials Technology markets the Alphasonics ultrasonic cleaner in the United States.

One recent change in ultrasonic anilox cleaning involves the incorporation of variable frequencies in the vibration. These are known as frequency sweeps. “With a single frequency, ultrasonic waves can collide and cancel each other out and create areas of inactivity,” Lanska says. “In other areas they can create greater intensity; those are the hot spots. That’s why some parts of the rolls might clean better than others, and some might still have ink residue in them.” The Alphasonics machines, he says, utilize a frequency sweep of ±5 percent of their operating frequencies to minimize the formation of hot spots. The units operate at 54 kHz for deep cleaning, compared with conventional units at 40 kHz. Many available systems have a second operating frequency of 92 kHz for extremely gentle daily cleaning or for the cleaning of ‘high definition’ engravings — ultrahigh line counts with high cell volumes.”

“Our ultrasonic cleaners can go as low as 25kHz, and up to a little more than 60kHz, but 40 is good for anilox rolls,” says Marty Cansler, national sales manager, pressroom products, for Max Daetwyler Corp., Huntersville, NC, USA. “We have power adjustments on our units, and when a printer gets to a higher line screen anilox roll, instead of limiting time in the cleaning process, we can limit the amount of power. It can stay in the tank for five to 10 minutes and still get the job done.

“Typically we don’t require that it spend any time soaking, but it depends on how long it’s been since the roller had been cleaned,” notes Cansler. “Every time they take it out of the press they can put it in the tank for five minutes to keep it clean. If it hasn’t been cleaned for a long time, they might have to soak it.” In the past, he adds, damage had been a concern, “but with the power control there will never be a problem with cleaning on a regular basis.”

Hessonic, a manufacturer of ultrasonic anilox cleaners based in Washington, UT, USA, makes a unit that fully immerses the anilox roll. “It can clean all sides of the roll simultaneously in 60 to 90 seconds when cleaned on a monthly basis with complete liquid immersion,” says Jim Hesson, president. “No rotation or pre-soaking is required,” he notes, adding that a bearing protector is supplied.

Dry blast cleaning

Two types of dry blast cleaners are prominent in the narrow web marketplace today. One uses baking soda — old-fashioned sodium bicarbonate.

“Our system features an automated blast cabinet,” says Dan Griffin, president of Sani-Blast, of Spring Grove, MN, USA. “You place the roll inside and blast it at 35 pounds per square inch (psi) with a crystallized form of Arm & Hammer baking soda called Armex blast media.”

The soda crystals are 70 microns in size, “but they are really soft and fracture on impact, reducing to 8 or 10 microns in size. That enables them to get inside the tiniest of cells to thoroughly clean the bottom of the cell.”

A 10" wide anilox roll, Griffin says, requires only about five minutes to clean, with no pre-treatment of any kind.


Sani-Blast’s cleaning system utilizes Armex baking soda at about 35 psi to dislodge ink resins from anilox cells. A finishing rinse with water completes the cleaning process.
“The roll rotates inside the cabinet,” he says. “The nozzle makes one pass and shuts off. Higher line count rolls are easier to clean than the lower count rolls because the cells are more shallow and have less capacity.”

One follow-up step is critical when using the soda blast process, Griffin notes. “Once you are finished blasting, just rinse the anilox roll with water to remove any Armex residue. If you don’t rinse it well and then put the roll back on the shelf, the residue can settle into the cells. After a while it can anchor to the roll itself and displace the ink.”

The nozzle speed in a blast cabinet is adjustable. On the Sani-Blast unit the adjustment is from two to four inches per minute traveling across the roll. The traverse speed, Griffin says, is determined by the roll diameter. “Rotating speed is constant: in the 20 rpm range.”

Air pressure is limited, he says, to prevent accidental damage. “Blasting at too high a pressure can damage the cell walls on high line count rolls. We have pressure regulators that limit the range to 40 psi.”

Frequency of cleaning with soda blast, Griffin observes, depends on the print job as well as the routine press-side anilox cleaning. “I’d say at least once a week, depending on how many roll changes are involved, how many runs the printer has, and how well cleaned the anilox rolls are between runs.”

Competitors note that a soda blast unit can be messy if the media escapes from the cleaning unit. “A large industrial vacuum captures the dust,” says Griffin. “If a hose gets a hole in it, some of the media can escape, but that’s why regular maintenance is important.”

Griffin points to the environmental benefit of soda blast: The used media is collected and can be disposed of in a landfill, “and the usage rate is only about a half-pound per minute.” An advantage that he cites over the ultrasonic cleaners and the water pressure cleaner (see below) is the absence of chemicals in the process. “We are dealing with food-grade product here,” he says. “We don’t have to inventory chemicals that are hazardous.”

A second type of blast cleaner for anilox rolls uses plastic media instead of baking soda. Bob Temple, president of Absolutely Micro*Clean, of Sacramento, CA, USA, says that a narrow web anilox roll can be cleaned for between 40 and 80 cents using his company’s process.


The Flexo Wash anilox roll cleaning unit uses a chemical solution and water pressure to remove ink.
The media is 100 percent dry plastic. After blasting it is automatically reclassified: ink particulate, dust and debris are removed; good media is recycled back into the hopper for the next roll cleaning. “You can get about 100 passes before the media fatigues,” Temple says. “Once it fatigues, it begins to shatter. Then you can get about 20 more passes before it becomes dust.” The system consumes about a pound of media per hour. Spent media is a non-hazardous, landfillable waste product, he says. “It’s like talcum powder, it’s that fine.”

Temple recommends that anilox rolls be cleaned in the plastic media blaster after each use. “Every time you take a roll off, go ahead and clean it and put it on the storage rack. That way the next time you go to use it, you know it’s clean. There’s no question that you will get the exact cell volume you need every time.”

An advantage of the plastic blast media, Temple says, is its safety with anilox rolls. “You can never really over-clean a roll. We clean up to 1,200 line count rolls comfortably. It doesn’t matter, because of the properties of the plastic. The media is soft and malleable.” Testing, he says, showed no damage to anilox rolls even after 400 cleanings. “This far exceeds the average life of an anilox roll.”

Water pressure cleaning

Flexo Wash is a company based in Denmark, with a subsidiary in the US, that has been attracting some attention in the anilox roll industry.

The Flexo Wash system utilizes a two-step cleaning process. First is a chemical sprayed at low pressure onto a rotating anilox roll, at a temperature of 130° F. “The pressure and the temperature loosen the ink, pulling it out of the cells,” says Ryan Potter, customer service manager for Flexo Wash in Louisville, KY, USA. “The second step is a high pressure water blast.” By high pressure, he’s talking 1,600 psi of warm water. “It blasts all of the loosened and softened ink right out of the cells. That’s followed by an air blow dry.”

Inside the cleaning tank, the anilox roll sits on two sets of gears, one for each journal. The roll rotates as the chemical is applied, a process that takes anywhere from five to 20 minutes, depending on the size and condition of the roll.

“Then the chemical is drained back into the tank, and is re-usable,” says Potter. “It never needs to be replaced, only replenished. Most of the particulate removed from the roll will settle to the bottom of the tank. If it’s in the solution it will be filtered the next time it is pulled for use.”

The water blast and subsequent blow dry lasts for only about four minutes.

“We recommend that the first time going through our system with an anilox roll you clean it for 10 to 20 minutes, depending on what’s in the cells. After that, it’s clean after five minutes, and we can pretty much guarantee 95 percent cell volume recovery.” The line count, he adds, makes no difference. “In Europe we are cleaning 2200 count aniloxes.”

The pH of the chemical used in the process is about 11 (“pretty harsh”, Potter says), and is mixed 1:1 with water. “Depending on where they are, about 95 percent of customers can just flush it down the drain. Some areas have stricter regulations.”

Water, Potter adds, has “absolutely no effect on the cell walls of anilox rolls. Harper Corporation ran it through about as rigorous a test as anyone could, and they concluded that there is no way to damage an anilox roll in a Flexo Wash machine. You can leave it at 1,600 psi for an hour.”

A closer look

Back to press-side, and the critical moment when the press operator must determine whether the anilox roll can stay on the press or go off to get cleaned.

“We’ve been preaching this for years, and some printers are catching on and really looking at their anilox rolls,” says Mike Huey, Midwest graphics technical advisor for Harper Graphic Solutions, Charlotte, NC, USA.

“I don’t care what cleaning system they are using, whether it’s soda or plastic media blast, ultrasonic or high water pressure — we always preach to clean it until it’s clean, not too much, not too little. The only way to do that is to look at the roll. Unfortunately, 95 percent of flexographers don’t have the equipment necessary to look at their anilox rolls.”

Huey is talking about a gravure scope or a digital microscope. “The best printers take the roll out of the press and put it under magnification. This takes a minute or two. They can tell if the cells are clean or not. And if they’re clean, then why clean something that costs X cents a roll to put through a cleaning system?

“Clean it off right now by hand and put it under a scope. Either it’s dirty or it’s clean. Anybody who has ever seen an anilox roll under a microscope can tell if it’s dirty. If there’s color in there, it really needs further cleaning.”



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