Sleeves have been used for years by wide web printers, but only recently have narrow web converters begun to explore this alternative technology, both for image and ink transfer.
By Jack Kenny
Narrow web sleeves from Rossini, an Italian sleeve manufacturer with global locations. From the top: ThinA fiberglass, Everglass fiberglass, Photoflex with elastomer for printing solid colors, and an anilox sleeve ready to be ceramicized and laser engraved.
Sleeves are a boon to the wide web printing and converting industries. Mounting a plate on a cylinder 60" or longer is a formidable task, and moving it into position on press requires large, expensive equipment and a good degree of care. Same with anilox rollers. In wide web the sleeves have been the savior of money, time and labor, not to mention a contributor to a healthier workforce.
A growing number of midweb presses use anilox sleeves and print sleeves. That’s because the design of the newer generation of presses – those equipped with servo drives – often feature cantilevered rollers that accept sleeves easily.
Narrow web converters have been slow to adopt sleeve technology simply because most of them don’t really have to. Mounting a printing plate onto a solid cylinder is a routine procedure done well dozens of times a day in thousands of factories around the world. Mounting a fiberglass or nickel sleeve onto an air mandrel means that the converter has to possess air mandrels of various dimensions. Unless the job is of endless duration without variation, the sleeve question often doesn’t arise.
But sleeves have come a long way over time. Today you can buy a rubber sleeve that is laser engraved with the image of your choice. Today you can produce a seamless photopolymer sleeve on digital laser imaging equipment. And sleeves still come with a bonus: time savings.
“The beauty of plate sleeves is the tremendous time savings realized in their use,” writes David Lanska in Common Sense Flexography: A User’s Guide to Improved Pressroom Productivity (2007, PIA/GATF Press). “During job changeovers, sleeves slide on and off in a few seconds, as opposed to the time consuming chore of changing out conventional plate cylinders. While one job is running in the press, another can be mounted off-line on a separate mounting cylinder. Sleeves take up much less space and weigh considerably less than plate cylinders. This means they can be stacked in specially designed cardboard boxes on lightweight racking. Conventional cylinders require heavy carts or massive reinforced racks.”
Lanska goes on to point out that sleeve-mounted plates are not removed from the sleeves when the job is finished. “This maintains the condition of the plates and keeps them ready for reinstallation at any time the job gets rerun.”
One of the most basic types of sleeve is the tint sleeve, also known as a flood coater or a flood coat tube. This is a rubber product generally used to meter ink.
According to Tammy Wright, account representative for Mid American Rubber, Three Rivers, MI, USA, tint sleeves are used to apply inks, adhesives, primers, clear overcoats, and also for creating continuous stripes on a web. “Depending on the type of rubber that you have, you can use a tint sleeve with any type of ink, whether it’s water based or UV curable,” she says.
“In a traditional meter roll the rubber is vulcanized, and once it wears out or breaks down, it has to be sent out to have the old rubber stripped off and new rubber put on. If you use a tint sleeve you can take off the old one, toss it, and put on a new one.”
The most popular diameter for a tint sleeve, Wright says, is 3" inside and 3.5" outside. “I’m surprised by the number of new customers calling in and asking about metering rolls, and they don’t even know about the sleeves.” (Rubber coated sleeves aren’t just for printing, adds Wright. Mid American Rubber has a customer in Florida who uses them for a jet ski ramp.)
Laser engraved rubber
Luminite Products Corporation, of Salamanca, NY, USA, manufactures rubber rolls and sleeves and engraves images into them to be printed. “The advantage is that vulcanized rubber is directly adhered to the sleeve, and there is no chance of cupping and curling,” says Curt Smith, technical sales support representative.
“The sleeve is reusable, and it can be reconstructed. The image is applied using digital direct laser ablation – there’s no mask or film involved. The laser is driven digitally by the artwork, and removes everything that’s not supposed to be there. It’s a finished product, and requires no washout or processing.” Moreover, there is no distortion in the engraving. “The artwork is prepared at 100 percent,” Smith says. “We don’t change a thing.”
A continuous rubber sleeve has no seam or gap. “You can produce continuous strikes, any design where you need a continuous background or continuous stripes, or small fine type,” Smith adds. “The sleeve comes ready to use: no plate mount or prepress time at all. Also, on a multicolor job with very tight registration, because there is no seam and the image is produced digitally, there is so much less waste at startup trying to get registered. The sleeve pays for itself in one or two setups.”
Transfer is another benefit, according to Smith. Surface tensions on rubber can range from 23 to 32 dynes. “We can set a very low surface tension for fine screens and dropouts, or if you need opacity, we can give you a high dyne count.”
Luminite carries 37 different rubber materials in a range of dyne levels, durometer and composition. Rubbers are matched to ink types, whether solvent, water based, UV curable, offset, letterpress, or flexo.
“As narrow web presses get wider – 22" and 24" – those bases weigh a good amount, they are hard to work with, and shipping gets expensive. Sleeves are much more efficient as far as handling and shipping,” says Smith.
“We generally talk millions of impressions for our rolls and sleeves,” Smith adds. “Vulcanized rubber doesn’t have the stress of having been engraved and wrapped, and that stress is one of the reasons photopolymer wears so quickly. Rubber doesn’t have that pre-made tension. It flows and crosslinks.”
The engraved rubber sleeve and roller costs more than a conventional plate. “If you were to compare a 20" repeat for a plate and for a continuous cylinder, we would be more expensive, but we would outlast three or four sets of plates. On a long run job suddenly we are not as expensive. Factor in no prepress: mounting, remounting, adjusting. Also, considering the waste of material to get those plates up and running, the cost of an engraved sleeve or roller is actually under what you would spend on plates.”
Stork Prints was the original producer of sleeves for flexographic printing, says Gene Proffit, business unit manager for Stork Prints America, Charlotte, NC, USA. “We developed the seamless photopolymer sleeve in the late 1980s, called Seamex. About 1990 we sold that process to several companies worldwide, because we were not a graphics company and they were better suited to grow that business. We continued with the nickel based sleeve for flexo, and also for gravure and offset blankets.
“We had a business relationship with the composite manufacturing company ICI in the mid- to late 1990s. That changed as MacDermid bought ICI. Our most recent developments are twofold: We purchased AKL, a composite manufacturing company in Germany, which has an extensive sleeve product line for flexo; and we have been working on a gravure imaging sleeve.”
Proffit acknowledges that the narrow web printer is faced with a tough economic decision whether to use sleeves. “The smaller the cylinder, the tougher it is from an economic standpoint,” he says.
“As the quality level has improved in flexo sleeve offerings, that together with the economic benefit of the sleeve concept has become of more interest in narrow web. The quality improvements have come from two sources. One is the evolution of a higher quality level, better consistency in the sleeves themselves. More recently, new technology has been introduced by two organizations: Stork AKL and the DuPont/Rotec partnership. That technology is seamless photopolymer thin sleeves that are used on a permanent cushion adaptor. The performance of these sleeves has demonstrated a step up in print quality, and that comes from the precision of registration, and also from the performance of the cushion, which has allowed an improvement in combination print on a sleeve. That means line work and fine process imaged on the same sleeve that prints very nicely. We have seen better success with that than ever before previously.”
Stork Prints’ gravure sleeve, says Proffit, is getting “quite a bit of use in narrow web. It’s a nickel structure with an engravable copper layer, so that it is delivered to the engraver who doesn’t have to add copper and do any grinding.”
Digital ITR plate sleeves
In 1995 at Drupa, the technology for digital flexo plate production was demonstrated by Barco Graphics and DuPont Europe. By 1997, when the first five devices were sold, all were capable of imaging sleeves or plates. After a couple of incarnations and name changes, Barco Graphics is now EskoArtwork, based in Belgium and known worldwide for its digital laser ablation plate imaging technology, among other systems.
EskoArtwork’s new cantilevered digital sleeve processor
“Flexible packaging – over 50" wide – is recognized as being the attractive market for digital sleeves,” says Ian Hole, vice president of market development for EskoArtwork. “There are other markets that will go to sleeve eventually: the lower midweb – 20"-30" range – and right down to narrow web.
“We announced the large cantilever sleeve device in March, and by the end of this year we will have a smaller version as well. It will be a 1450mm sleeve device for the slightly narrower flexible packaging market. Whether it will go further down into label market is yet to be seen.”
In North America, says Hole, “sleeves are not very prolific. There are only about four or five known traditional sleeve makers. Europe is the only place where there has been growth in the last four or five years.”
Photopolymer for flat flexo plates is made in thousands of square feet each day. “Sleeves are made one at a time and put onto a base sleeve. You start with a cylinder made of carbon fiber, Kevlar, fiberglass; then you put polymer around that and it has to be seamless. There are several methods: Wrap the plate around, warm it up and get rid of the joint, or build polymer up on the sleeve whereby the base slowly turns around and you add polymer. Whichever method is used, it is a much more machine- and time-intensive process. For the same amount of square footage you have to do a lot more. That’s why it’s more expensive.
“Sleeves are more popular in Europe because Europeans are sold on the idea of the other advantages of having a sleeve on the press: no mounting, no positional issue. You simply put the sleeve on the press,” says Hole. “Second, because there are no joins in the polymer, they enjoy running the press between 10 and 30 percent faster. Third, quality for a sleeve that has been imaged and processed in the round gives you an optimal type of opportunity to get your product right on that surface. Europeans tend to believe that benefits and savings from those advantages override costs.”
Hole says he believes that sleeve use will increase in North America. “Having a process without chemicals adds to the attraction. That’s one objection you can strike through: no solvents and chemicals.”
“The use of anilox sleeves has penetrated very well in wide web,” says Tony Donato, product and process development engineer for Harper Corporation of America, Charlotte, NC. “In narrow web, on the other hand, it has doubled in the past year. Total shipments, however, are less than 10 percent.” So it’s a tiny but growing segment.
“With the extensive engineering involved in their manufacture, anilox sleeves tend to be much more expensive to purchase than conventional anilox rolls, writes David Lanska in Common Sense Flexography. (Lanska is sales and business development manager for Stork Cellramic, an anilox roll manufacturer based in Milwaukee, WI, USA.) “They, however, can be driven by servo motors, which saves on the cost of the motors, as well as the electricity to run them…
“Anilox sleeves can be easy to use, or they can be a nightmare. Proper installation requires the following: a highly polished, precision machined cylinder, a high volume of compressed air, and a clean, dry surface on the cylinder. If any of these conditions is not met, it becomes a chore to install and remove sleeves. The cylinder surface is a big key to success. Scratches, dents and corrosion provide channels to dissipate the compressed air. Dirt, ink and other contaminants do not allow proper air flow across the face of the cylinder.”
Donato says that Harper is “spending more and more time educating people about anilox sleeves.” Indeed, the company produced a seminar on the topic in late August at Central Piedmont State College in Charlotte. “Converters need to know that an anilox sleeve doesn’t have the long endurance of a journaled anilox, that it can be more easily damaged. The primary material is aluminum, and some cleaners can cause blistering out on the ends. There are a lot of issues that require knowledge.”
The inner liner of an anilox sleeve is fiberglass, Donato says. Atop that is applied an expansion foam layer, then a fiberglass filler layer, then aluminum cladding. The ceramic to be laser engraved is applied as the final layer. “The final cost could be double what a roller is,” he adds.
The cleaning issue is also critical. “Mistakes can be made,” adds Donato. “When you switch to sleeves and use ultrasonic tanks for cleaning, you have to have good end caps so that the cleaner won’t get on the end of the sleeve. The aluminum ring is exposed on that end, and most water based cleaners are high pH, and aluminum doesn’t like anything that’s caustic. Also, you don’t want liquid to get into the expansion foam. It will deteriorate.”
The blasting method of cleaning, whether it utilizes plastic media or baking soda, is fine as long as the end caps are solidly in place. “It’s important to keep the media out of the interior,” Donato says.
Sleeves, repeats and bridges
By Mike Smoot
An Accumount bridge sleeve from Xymid
With wide web presses, the ability to quickly change out a job using sleeves is more significant than with narrow web presses. This is primarily due to the greater weight of wide web cylinders versus narrow web cylinders. With wide web presses, a crane is typically needed to install or remove cylinders. This is very time consuming. With narrow web, the cylinders are much lighter and an operator can install or remove the cylinders with relative ease. Consequently, one might ask, “What is the value of using sleeves in narrow web?”
There are several advantages to using sleeves with narrow web presses. First, the price of a sleeve is less than the price of a cylinder. Therefore, the investment required to reach each repeat is lower. This is especially true the thinner the sleeve. Second, given that sleeves cost less than cylinders it makes more sense to keep jobs mounted. This is particularly true for short runs that come up month after month. Keeping jobs mounted reduces sticky back and labor costs as well as reduces plate damage. Third, using sleeves allow for readily imaging plates in-the-round as well as using continuous photopolymer on lower cost thin sleeves. Finally, storage space can be reduced because, when sleeves are used in conjunction with bridge mandrels, they can be stored inside each other when the diameter and thickness allows.
When using a sleeve press, printers must decide how they will reach their required repeats. The press comes with at least one fixed mandrel per print station. They need to fill the gap between the fixed mandrel diameter and the required print diameter. The choices are basically, “Do I use thick sleeves, or do I use bridge mandrels with thin sleeves to reach my desired repeats?”
A bridge mandrel is similar to a thick sleeve in that it has a certain thickness to increase the repeat size. The big difference is that the bridge mandrel has the ability for air to pass through its wall thickness, thus allowing a sleeve to be mounted over the top of the bridge. In some respects, a bridge mandrel is no different than a metal cylinder that has been drilled for air to accept sleeves. Both allow the printer to increase their repeats with the addition of a sleeve over the top.
The choice between thick sleeves alone versus bridges and thin sleeves is rarely either/or. For most printers it will involve a mix of both approaches because most printers have a variety of print needs. This includes the number of jobs at a given repeat, whether repeats are close together or far apart, whether they have more short runs versus long runs, and whether they keep any jobs mounted versus demounting most jobs after printing.
Two rules of thumb can be considered which can simplify the decision making process. The first is, “If two sets of sleeves are required for a given repeat, then it can be about the same cost to buy bridges and thin sleeves versus thick sleeves alone.” The second rule is, “If one set of sleeves is required for two repeats that are close to each other, then it can be about the same cost to buy bridges and thin sleeves versus thick sleeves alone.” These two rules apply when the thick sleeves are at least ¾" thick.
While having the cost be the same may not be very exciting, for the printer wanting more than two sets of sleeves at a given repeat or more than one set of sleeves for two or more repeats close together, the savings can be very significant. Depending on the thickness, thin sleeves can cost from 35 percent to 75 percent less than thick sleeves. These dramatically lower costs open up the opportunities to reduce makeready time and keep jobs mounted because the investment for additional sleeves can be economically justified.
In general, thin sleeves pay for themselves after four to five runs when jobs are kept mounted due to savings in sticky back, labor and plate damage. Of course, the actual savings with any of the examples given above depends on the product pricing for a given sleeve and bridge supplier. Regardless, the following is always true: Thin sleeves cost less than thick sleeves, and thick sleeves cost less than bridge mandrels. It is important that printers are aware of their options and that they “run the numbers” to see which approach minimizes their investment cost.