Product Reviews

Rotary Screen

July 11, 2005

Once used by few narrow web printers, this technology is now in demand.

Rotary Screen

The pursuit of new frontiers in packaging, always the goal of product marketers, has propelled narrow web rotary screen technology to the forefront as a printing process to be desired. Particularly in such markets as cosmetics and health and beauty aids, the screen printed product has caught on and continues to rise in popularity.

From a converter’s perspective, the beauty of screen printing — aside from its appearance in finished form — is that it can be accomplished by the addition of a module on an existing press. Full-blown, multi-station screen printing presses are available and are well put to use by those who own them, but the popularity of rotary screen modules has breathed new life into the process.

For the past several years, retrofitting of rotary screen modules onto presses has increased. Press manufacturers are finding that more and more new machines are being produced with the addition of rotary screen printing units.

“We see a good level of activity and of interest,” says John Costenoble, sales manager for Stork Rotaform, Charlotte, N.C., which manufactures a modular rotary screen system called RSI. “The printers who are installing rotary screen printing stations are loaded with work, very busy. More and more of their work is long runs, such as for beverage products.”

“We’ve been successful with our retrofit screen head in many smaller companies,” says Tom Kirtz, president of Telstar Engineering, Burnsville, Minn. Some of the steady growth Kirtz sees is attributable to interest on the part of retail companies with private label brands. “The store brands are trying to improve their appearance, enhance their labels and keep up with the big boys,” he adds. “We’ve seen growth as a result of that, and smaller label companies are now adding screen equipment by retrofitting.

“I thought at one time that the market would be saturated,” Kirtz says, “that those in it would run the work that was available. But it continues to grow, and now there is interest in Mexico and South America. We’re getting leads from that part of the world.”

30 microns
Everyone knows that screen printing results in the laydown of a substantial quantity of ink onto the substrate. The amount can be impressive: UV letterpress can lay down ink to a thickness from 2 to 3.5 microns; UV offset is 1.5 to 2.5 microns; gravure is 2 to 5 microns, and UV flexo can deposit from 3 to 8 microns. UV screen, however, has an ink thickness range from 4 microns to 30 microns.

All rotary screen inks today are UV curable. According to George Ohlson, technical sales manager for DMS, Palatine, Ill., early efforts in rotary screen development used solvent and water based inks, “but they couldn’t get the speeds out of them, so they went to UV, which lends itself to a rotary system.”

Flat screen printing has been around for a long time, but rotary screen is relatively recent. Back in the 1960s the process was developed by George Reinke of Screen Printing Systems in Nevada. He came up with the idea to make a flat screen into a cylinder and squeegee the ink through the mesh from the inside while the screen rotated and the web moved.

Gallus, the Swiss press manufacturer, acquired rights to the process, and began manufacturing screen printing equipment, plus the screens themselves and the lab tools necessary to process them. Today Gallus is a major supplier of quality screens and equipment throughout the world.

In addition to Gallus and Screen Printing Systems of Sparks, Nev., screens for rotary printing are available from a new supplier, Microcircuit Engineering, of Mount Holly, N.J.

Screens today are made of stainless steel (with one exception), and nickel coated for stability. A wide variety of meshes are available, depending upon the desired printed product. Each screen is coated with a photosensitive emulsion — in all cases a proprietary compound — that will eventually yield the image to be printed.

During exposure of the screen in the prepress lab, a positive film image is laid over the emulsion coated screen. After exposure to light, the emulsion on the unexposed portion of the image washes away with water to become the print image. The emulsion that remains on the exposed part of the screen has bonded together under the light, sealing the openings in the mesh to prevent ink from going through.

New textures
Sensitive fingers can detect screen ink on a label surface, there’s that much of it. Because of its capability to lay down such amounts of ink, rotary screen has given rise to applications that cannot be achieved by other printing processes. One such application is that of the textured varnish.

“One of my customers took gold foil, screen printed a textured varnish onto it in the pattern of a candy company’s name, and the finished product looked like it was embossed,” says Kirtz of Telstar. “The varnish thickness was in the range of 15 microns, but the texture gave it the appearance of having much more depth than that.”

The look, he adds, is similar to a matte finish, with a pebbly quality to it. “Of course, the tactile look will change by alterations in the emulsion weight and screen count.”

Telstar recently sold a screen head to a company that intends to print Braille characters. “With tests we ran we were able to deposit nearly seven-thousandths of an inch of heavy bodied clear varnish.” For a person without sight, the presence of colorless varnish has no effect on the Braille lettering. “They can truly feel the text,” adds Kirtz. “Seven thousandths doesn’t sound like a lot, but if you print a perimeter of seven thousandths, even untrained people can feel and envision that shape.”

Telstar produces mostly custom screen print stations, and has the engineering capability to tailor the equipment to a specific press, even to make it portable for use on more than one machine. The company also retrofits screen units to central impression drum presses, such as Ko-Pack, Sanki and Sanjo letterpress machines.

Nonwoven mesh
The screens for Stork Rotaform’s RSI unit differ somewhat from other rotary screen systems in that they are manufactured of a nonwoven material rather than of steel, and then nickel-plated. The company sells its screen exposure equipment to converters, but keeps its proprietary welding technology at headquarters. Stork screens, moreover, are re-usable.

Stork has received significant attention from narrow web press manufacturers, and the company has OEM arrangements with Comco, Mark Andy, Chromas, Nilpeter, Arpeco, and others. The standard RSI module is 24" wide, though a 32" unit was sold in Europe for a security printing operation, according to John Costenoble.

“People think rotary screen printing is not simple, but difficult,” he says. “We try to make it simple. Sales people who work for converters don’t really have an understanding of how screen works, and what it can do for their customers.” Costenoble makes presentations to sales forces as well as instructing press operators. “Some printers want us to talk to their sales people, and we suggest it, too.”

Costenoble adds that ink suppliers should work harder to improve the consistency and quality of their inks. “If the inks don’t work, then the printer gets frustrated,” he says. “Rotary screen technology is new, and he doesn’t know what to do to get that ink to perform. If it’s not flexo, they don’t really know enough about it.” He adds, however, that more and more ink suppliers are offering rotary screen ink because more converters are working with it.

Stork Rotaform is working with Akzo Nobel Inks in planning for educational programs at Akzo’s Technical Center for Excellence. “We’re going to put together a lab at our headquarters in Charlotte in 2001 with our own technical programs,” he adds. “We’ll be able to develop new systems for people who are working on special projects.”

Costenoble sees potential for the rotary screen market in other areas of packaging as well. He’s been talking with flexible packaging converters, companies that run chip and pretzel bags at speeds of 600 to 700 feet per minute. “They’re showing interest,” he says. “It is commodity product, but what these converters are trying to do is to go their customers with something new — unusual packaging to help sell the products.

“Rotary screen will never be as big as narrow web flexo,” he adds. “But there are a lot of niches out there.”

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