An anilox roll manufactured by Harper Corporation of America
Improvements in laser technology, coatings and finishing make today’s anilox rolls better equipped to deliver precise quantities of flexo ink to plates.
By Jack Kenny
The anilox roll has been described over the years as the heart of the flexographic printing process. The description was popularized in a book by Joseph Trungale titled, The Anilox Roll: Heart of the Flexo Process. It is a fitting designation, because the anilox roll is unlike anything to be found, historically, in other printing processes. The description, however, is questioned by David Lanska in his book, Common Sense Flexography. Building on the anatomy metaphor, Lanska says that the anilox roll more appropriately corresponds to the vessels that carry precise amounts of blood to specific parts of the body. The ink pump, he maintains, is the heart; the fountain roll corresponds to the arteries that move large amounts of blood.
Heart or capillaries, the anilox roll is extremely critical to the creation of a quality print job on a flexographic press. Its microscopic cells transfer the ink to the printing plate, and it must deliver the exact amount of ink desired.
Most anilox rolls today, and for the past couple of decades, are engraved by lasers that create cells in the surface of a ceramic coating. For the most part the cells are not visible to the naked eye, but they are large enough to accept ink from the metering roll. The larger the cell, the more ink will be contained in the cells and transferred to the photopolymer plate as the rollers turn. Anilox rolls with large cells have low cell counts – the number of cells per linear inch – and are used to transfer relatively copious amounts of ink to the plate. As cells grow smaller, the cell count rises and the volume of ink contained is less. Typically, in narrow web, anilox cell counts can range from 150 at the low end, up to 1,200 or 1,400 and more at the highest end. High cell count rolls are employed in print jobs in which very light ink laydown is desired, as in a vignette.
Before the use of lasers in the engraving process, the cells in anilox rolls were created mechanically by use of a knurling tool. The engravings were made in copper and coated with chrome, which is much harder than copper. Chrome-surfaced anilox rolls are still made today, but in the narrow web industry they are pretty much unknown. A disadvantage with chrome rollers is that they damage easily and have low resistance to wear. Exposure of the underlying copper leads to rapid degradation of the surface and inhibits its performance.
Knurled cells tended to be squarish in appearance. With the advent of the laser engraved anilox roll in the late 1970s, that changed. The ceramic surface that now coats the anilox roll is extremely hard, and the cells can be different shapes – four-sided diamonds or hexagons, for example. The ceramic also offers the advantage of being corrosion resistant, and when it wears out, a new layer of ceramic can be placed atop the old surface and engraved anew.
The engraving angle is critical in the creation of the anilox roll. The term “refers to how the cells in subsequent rows of engraving line up in closest proximity to one another,” writes Lanska. “It is a way of differentiating alternative cell placement patterns and describes the spatial relationship of cells in one row of engraving with those in preceding and subsequent rows of engraving. There are three standard patterns typically described simply by the angle: 30°, 45° and 60°.”
Angles of 30° and 60° are similar in shape – their hexagonal appearance resembles a honeycomb – and are used mostly with water-based or solvent-based inks. In some cases, the 30° angle performs better when viscous inks are in play. The diamond-shaped 45° angle, which harks back to the days of chrome engravings, is not common today.
The volume of ink that an anilox roll cell carries is also a critical specification. Cell volume is measured in BCMs, or BCM/in2, which means billions of cubic microns per square inch, or cm3/m2 in metric societies. “Cell volume tells how much the cells can hold,” says Lanska, “which can be very different from what they can deliver to the plates. The percentage of ink that transfers from the cells to the plates is known as the transfer factor. The transfer factor is determined by the flow of characteristics of the ink or coating material and surface tension of the plates – and their ability to draw the ink from the cells. It is also affected by the absorptive qualities of the substrate, as well as press speeds, doctoring method and pressure, and impression settings.”
Laser technology has given anilox manufacturers the opportunity to experiment with all of the variables that go into production of the roller, and has given today’s printers superior tools with which to transfer ink to plates.
“The technology used to engrave anilox allows you to control consistency and predictability from roll to roll, thus allowing the printer to have predictable results with the goal of less downtime, waste, sustainability and make ready,” says Sean Teufler of Harper Corporation of America. Teufler adds that the 60° engraving angle “is still by far the most predominant type of engraving that allows for repeatability and predictable results.”
“The current technologies used in the manufacture of anilox rolls are improved coating and finishing stations that have affected the overall quality of the rolls,” states John Batistatos, the North American sales director for Apex Narrow Web Division. “Also, newer laser technology allows for better defined cells, thus improving overall printability. The new laser technology also cuts down the time to engrave a roll and reduces lead times to the end users.”
According to Dave McBeth, global VP of sales and marketing in the Flexo Division of Pamarco Global, “Ceramic technology and laser technology play a significant part today in the quality of high-tech anilox rolls. The label industry in particular has been adopting higher anilox line screens – 1,500 lines per inch at volumes of around 1.8BCM. To achieve these finer screens along with consistent quality, anilox manufacturers have had to look at MBA laser technology (multiple beam). The multiple beam allows the laser to hit the anilox cells multiple times at very high power. The multiple beam allows not only for the higher anilox screens but also very little re-cast on the cell surface.
“CO2 lasers have limited capabilities in terms of line screens. Fiber lasers of approximately 200 watts have become the standard in many anilox companies, but the very latest technology is 500-watt MBA technology.
“Ceramic technology now is more critical than ever, and companies have moved to harder coatings such as Triplex ceramic. This coating overall produces a high quality cell formation, but due to the finer walls, the cells can be more susceptible to wall defragmentation at higher line screens.
“The latest ceramic technology is called ‘New Era’,” says McBeth. “This coating is ideal for MBA laser technology at higher screens; it’s a more durable coating that works in conjunction with the laser technology, allowing for the razor thin cell walls to stay intact with no defragmentation.”
Stork Cellramic also is making use of the new fiber technology. “Through the use of fiber optic technology in engraving anilox rolls, we have seen higher ink carrying capacity capabilities and smoother cell surfaces than in previous years,” says Tom Bass, East Coast sales manager. “This allows printers to utilize higher lines-per-inch plates to print combinations that will allow for a high resolution image and desired color densities.”
“The newer laser systems have digital front ends, and we have moved away from the CO2 lasers,” says Jean Jackson, global business development manager for Praxair Surface Technologies. “It has changed the resolution, but it has opened up the ability to change cell shapes.”
A microscopic view of Praxair’s Proline REV anilox cells.
The second new engraving is called REV, short for Revolutionary Engraving. “Proline REV engravings have a distinct slotted cell shape around the circumference of the roller. This engraving technology offers a blend of higher densities, better ink transfer, and excellent solids coverage,” says Jackson.
The printer’s challenge
Label printers face challenges when they interact with anilox rolls at several stages of the print process, and even before. These challenges can include color consistency, cleanliness and wear, and basic understanding of cell volume and line count.
Jim Kissner of Harper Corporation says printers should take steps to ensure that the roll they purchase is the roll they truly need for the job. “The biggest challenge with anilox rolls is making sure you are getting the engraving you have paid for,” he says. “We recommend that all printers put the engravings they receive to the test, so they know they are truly standardized. The material and ink dollars lost on unknown or unexpected anilox volumes easily dwarf the investment needed to get an anilox inventory into shape and monitored properly.
“Another challenge,” he adds, “is care and maintenance of anilox inventory. We see a high percentage of rolls that have to be re-manufactured due to poor handling, as opposed to rolls wearing out or losing volume.”
“The basic challenges that label printers have with anilox rolls is keeping the cells clean and monitoring wear,” says Batistatos of Apex. “Printers need to understand the rating of the ceramic on their roll as well as the shape of the cells. Hardness, as well as porosity, are key factors that determine the quality of the ceramic. Ceramic should be in the 1,500 Vickers range, which is a measure of its hardness. Just like your skin, ceramic has pores. The higher the porosity, the worse the ceramic. Porosity should be at 1 percent or less.
“All Apex plants analyze their ceramic by using a metallurgical lab that measures the key attributes to assure consistency and reliability. Newer laser methods allow the ceramic to fuse during engraving, which also can contribute to lower porosity.” Batistatos adds that Apex rolls have “extremely dense, smooth and even less porous” ceramic surfaces.
“Printers try to push quality without understanding the variables in the system,” says Jackson of Praxair. “As they do finer work, getting the balance of the metering system, the anilox and the plate are a challenge. For the fair amount of people printing solids, care and maintenance is fundamental, as is setting the blade, installing it properly, and maintaining the rolls. We see a lot more rolls coming back that are dirty. As you move up in the fineness of line count, the rolls are harder to keep clean because the cells are smaller. We see a lot of dirty rolls that are 1,000 line count and above.
“An anilox roll should be cleaned every time it comes out of the press, but the question is at what level should it be cleaned?” she asks. “I recommend that you work with your supplier. But if you can see color on the roll, it’s dirty.” (See the article about anilox cleaning systems on page 60.)
Magnified anilox cells in a 60° engraving angle.
(Photo courtesy of Stork Prints)
Tom Bass of Stork Cellramic would like to see press operators gain a better understanding of how an anilox roll works. “The challenges have always been the level of knowledge of the press operators,” he says. “If the operator who is selecting the anilox rolls to run a new job does not realize the correlation between the lines per inch and BCM, he will not be in a position to make the best possible choice the first time, and will be more likely to have to change the anilox roll out to achieve the desired resolution and color densities. It is the combined efforts of the anilox and ink supplier to ensure that the proper level of support is offered to ensure the highest level of success.”
Some of today’s servo driven narrow web presses make use of anilox sleeves, which are much lighter than the standard solid anilox. Jean Jackson says that the trend in anilox sleeves began in narrow web, but has really taken off in the wide web arena. The use of sleeves is not an option: Either the press uses them or it doesn’t. “You don’t get a choice on the press whether you’re going to choose sleeves,” she says, adding that they can cost more than a conventional anilox roll. “The advantage is ease of handling and loading. On the narrow web side there is no difference in performance than with a conventional roll.” She adds that because they have an aluminum layer just beneath the ceramic, the printer must avoid caustic solutions during cleaning.
“Anilox sleeves initially were profiled in a scenario of short-run environments where anilox changes are very common and required, but have shown their usefulness regardless of the frequency of changeover,” says Mike Huey of Harper Corporation. “They are an operational advantage to printers, provided that the printer and operators receive proper training in how to handle, care for and install the anilox sleeves. We have discovered that training for proper care of anilox sleeves has helped to negate much of the concern and incidences of sleeve damage.”
“I see anilox sleeves gaining more acceptance, and I see more of them in the field today,” says John Batistatos. “Anilox sleeves are much easier to handle and are ideal for short runs. The advantages also coincide with the gearless press technology itself: increased automation and maintenance. Once the converter’s facility is adapted, sleeves are easier to store and inventory. The disadvantages of sleeves are their cost as well as the different care and handling that is required. Converters need to design special racks to store sleeves so that the chance of damage is minimized. In addition, sleeves cannot be cleaned in the same fashion as rolls, which may add more time and cost.”
Tom Bass sees the use of anilox sleeves taking on a limited role in narrow web. “Narrow Web sleeve presses are beginning to show up in more pressrooms, but I do not feel that they will be as widely accepted as in the wide web market, because the narrow web anilox rolls are nowhere near as difficult and time consuming to change. They can also tend to be more expensive than their journaled counterparts, and they can be resurfaced only a limited number of times.”
“There have been many debates about anilox sleeves for narrow web,” says Dave McBeth. “In general these have been adopted by some of the higher OEM companies on 16" to 21" face rolls, and have a significant advantage in terms of handling and changeovers. The quality of these sleeves is very high, and have a significant cost increase as opposed to a steel or aluminum base.”
New cell configurations are on the minds of anilox roll manufacturers. Jackson, noting that the purpose of the anilox roll is to distribute ink, says that the industry “is on the verge to break some paradigms with some laser capabilities.”
McBeth observes that the latest technology, a cell formation called EFLO, has shapes and angles “completely different from conventional 60 degree hexagonal engraving. It allows for more cells on the roll to be printed on the 1 percent dots and below on the printing plates. The technology allows for rolls to be engraved, for example, with an 800 lines-per-inch volume of 2.3BCM at a 1,300 lines-per-inch engraving. This means density and contrast levels are much higher and allows narrow web printers to use printing plates of approximately 200 lines-per-inch without sacrificing density.
Batistatos has similar thoughts: “The future of anilox rolls will be engraving geometries that are much different than standard cells. Future anilox technology will also consist of different ceramic coatings that will help with release as well as durability. Conventional anilox engravings have virtually exhausted their potential for improvement.” Apex, he says, has introduced a new type of roll that is not called an anilox roll but rather a metering roll, “because it’s manufactured by means of genetic transfer technology. One of its key characteristics is that the roll does not have cells. The unique coating is made with a combination of chromium and titanium oxide. The engraving profile is an open structure so there are no cell depths or line screens to specify the roll.”
Bass believes that anilox suppliers “will continue to tweak the engraving process and focus on supplying custom engravings that solve specific problems for printers. We may begin to see more customization in anilox engravings to allow the flexographic printing process to continue to be competitive.”
Sean Teufler of Harper says, “The future of anilox technology is based greatly on a customer’s ability to verify the volume of the engravings and getting the consistent performance every print challenge requires. We do not anticipate a day coming were anilox rollers become a ‘one size fits all’ type of product due to the unique needs and the requirements of tailoring to ink, plate and even substrate challenges for each printer.”