Flexo Sleeves Gain Traction

Digital imaging of flexographic plates has brought about many improvements when compared to conventional platemaking methods. Sleeve technology offers further refinements to the process. Advances in flexo sleeve technology are yielding opportunities in markets traditionally dominated by offset and gravure—markets such as folding cartons and shrink sleeves.

Lightweight, durable, easy-to-handle flexo sleeves not only work well with less expensive substrates such as tissue, napkins, and paper towels, but also provide excellent laydown of solid and metallic inks in packaging applications. Flexo sleeves are being used in two ways: as carrier rolls for flat, imaged plates mounted on the surface or with the image directly engraved (in-the-round) on the sleeve surface. Each provides productivity enhancements for package printers.

With sleeves that serve solely as carrier rolls, imaged printing plates can be mounted to the sleeves offline, which can then be installed onto cylinders in the print stations using compressed air to expand the sleeves, allowing them to slide into position on the cylinders. The use of sleeves in this way provides increased production flexibility by using the premounted plates to provide quick changeovers for short runs and design changes. It is especially effective for short-run, repeat jobs, since the sleeves can be taken off the press and carefully stored with the plates mounted on the sleeves.

In-the-round (ITR) technology refers to digitally imaged, continuous polymer printing sleeves that permit flexographers to print images on a wide range of substrates by imaging and processing the printing form directly on the sleeve. The photopolymer sleeve may be a continuous pre-manufactured sleeve with a seamless layer of photopolymer topped by a laser ablation mask (LAM) coating, ready for imaging, exposure, and processing. It can also involve mounting individual pieces of photopolymer on a base sleeve with stickyback tape, then imaging, exposing, and processing them in the same manner as the photopolymer sleeve with the LAM coating.

Because photopolymer sleeves imaged in-the-round do not use plates to carry the image, a host of problems ­associated with conventional flexo plate mounting is eliminated. These problems include plate lift and bounce, misregistration, distortion, and waste.

“Flexographers used to image on a flat photopolymer plate and attach the plate to a round cylinder with stickyback tape,” says Mike Smoot, business manager for Xymid Print Sleeves, Xymid, LLC. “The thicker the plate and the smaller the diameter of the cylinder, the greater the potential for misregistration and distortion. In contrast, the alignment of sleeves is spot-on.”

Sleeves are made from various materials, including thermoplastic composites, thermoset composites, and nickel, and may or may not be reinforced with fiber to resist cracking and splitting. Long-run, reusable sleeves that incorporate a foam or cushion base are used for very high-quality printing. So-called “thin” sleeves, without foam or cushioning, have been developed to be thrown away after use to keep costs down.

Print sleeves manufactured by Xymid are polyester-based products with composite construction that creates a durable product to resist cracking and splitting. Xymid print sleeves are available in thicknesses from 0.010˝ to 0.320˝ and in unlimited widths. The wide range of thickness allows printers to run longer repeat lengths on existing print cylinders. Acknowledging that sleeves cost considerably more than traditional flat plates, Smoot explains that the decision to use sleeves tends to be a function of the quality requirements particular to a given job.

The thinner the better

Thin, seamless photopolymer sleeves mounted on a permanent cushion adapter or bridge mandrel are currently being commercialized in the U.S. Examples include DuPont’s Cyrel Round Thin and Stork Prints’ OptiFLEX sleeves ­designed to provide excellent print quality and registration in flexo environments when imaged in-the-round.

Stork OptiFLEX sleeves are composed of a very thin (0.013˝) composite, a seamless layer of photopolymer, and a black LAM. A high-performance fiber is required to achieve the thin structure. According to Gene Profitt, business unit manager for Stork, “Seamless ITR thin sleeves benefit the industry by promoting increased plate lifetime, faster press speeds, elimination of plate lift, elimination of cushion tape expense, and faster press job set up. Print quality gets a boost from near-perfect registration; high-quality, repeatable imaging; and better TIR (total indicated runout) tolerance when compared with a plate and separate sleeve cushion.” Stork also makes the mandrels and adapter for use with OptiFLEX sleeves.

Polywest Americas has recently introduced new sleeve adapter technology, called Spacer, which is designed for the safe mounting of thin sleeves. Using a separate Spacer-Mounter, the thin sleeve is mounted on the adapter offline, which enhances the ability to achieve precise positioning while reducing set-up time. Once the thin sleeve is mounted on the Spacer, the unit can be used like any other plate mounting sleeve.

Significant progress

Flexographic printing has made huge strides during the last decade in its ability to compete with the superior quality of both offset and gravure processes. Implementing state-of-the-art flexo sleeve technology is one example of how the industry has used digital technology with other techniques to reduce or eliminate variability in the flexo printing process. pP

New for large-format sleeve imaging

EskoArtwork recently introduced the Cyrel ­Digital Imager (CDI) Advance Cantilever targeted to trade shops, large-volume converters, and the flexible packaging market. The CDI Advance ­Cantilever handles the imaging of large-format sleeves, as well as optional large-format flexo plate imaging, and is built for the wide-web flexible packaging market. The new imager comes with a cantilever air cylinder for fast exchange of print sleeves without requiring additional handling equipment. Users can exchange drums for 50˝ x 80˝ or 42˝ x 60˝ plates, as well as for sleeves up to a length of 83.1˝. A fiber laser with multibeam optics enables the CDI Advance Cantilever to operate at speeds to 8.0 m²/hr.

“There is a definite global trend toward the use of sleeves,” says Jan Buchweitz, EskoArtwork CDI product manager. “Converters find that sleeves allow them to increase press speed on certain types of substrates. . .With the CDI Cantilever Advance, EskoArtwork is providing an imager that makes the entire process—from imaging, to mounting, to printing—as easy as possible.”

DuPont has recently developed the Cyrel FAST Round solution for processing Cyrel Fast round sleeves. Not only does this system shorten processing time, it also fits seamlessly onto the CDI Advance Cantilever for production of high-volume flexible packaging. DuPont describes Cyrel Round as the only complete digital sleeve production solution, consisting of a family of “ready-to-image” Cyrel printing sleeves, supported by complementary DuPont equipment for UV exposure, processing, drying, and finishing. The new Cyrel FAST Round system uses thermal technology and offers “thermal continuous development,” a smart processing technique for developing sleeves.