Closing the Loop

Flexo plate sleeves are rounding out the process for higher quality, faster turnaround packaging.

by Terri McConnell, PrePress Editor

IN A MARKETING study recently conducted by the High Definition Flexo Consortium, end users across several consumer product industries were asked to identify the most important printing technology advancements over the past three to five years. The respondents were senior packaging engineers, packaging procurement managers, and senior designers from the food, beverage, pharmaceutical, chemical, and health and beauty segments.

These professionals, key to influencing and specifying packaging print methods, overwhelmingly agreed computer-to-plate imaging has made a substantial positive impact on print quality. They also consistently cited quick press changeover systems as a major economic facilitator to faster turnarounds and shorter runs.

In the ultra-fast growing flexible packaging segment, where promotional campaigns and test product migrations are driving quality requirements up, and run sizes down, a full 69 percent of the polled end users said CTP and quick-change—in particular the use of plate sleeves—were the two most significant breakthroughs. In this article we'll examine how those two technologies complement each other in the race to put cost-effective, graphically appealing packaging on the shelves faster.

The basics of sleeve technology

The use of sleeves as plate carriers first reached the North American shores from Europe in the early 1980s. Nickel, and then fiberglass and Kevlar composite sleeves, were accepted initially for their job storage and plate mounting convenience, and were found primarily in wider-web central impression pressrooms.

Over the next decade sleeves gradually became more popular as printers came to appreciate the cost-effectiveness of a sleeve workflow; press downtimes were reduced, and productivity improved. These benefits were especially apparent in situations where the printer had many jobs of the same repeat and needed faster access to plate cylinders for changeovers.

Recognizing the growing acceptance of sleeves, and seizing the opportunity to pare press downtimes even further, CI press manufacturer Windmoeller & Hoelscher introduced a cantilevered quick changeover press in 1993; according to Hans Deamer, W&H Corp. president, his company has sold more than 150 machines to date. Today, nearly every major CI press manufacturer offers a quick sleeve change system, and marketers estimate as much as 50 percent of presses sold into wider-web packaging applications are sleeve-dedicated with a cantilevered changeover feature.

Four years ago W&H introduced another groundbreaking technology that accelerated the use of sleeves—the infinitely variable repeat, gearless direct drive system. Sleeves are a strong complement to gearless technology because they can suit any repeat length at lower cost than conventional plate cylinders.

While sleeve adoption continues to gain ground across all packaging applications except corrugated, there are still limits to the payback. "Composite plastic sleeves are simply not as durable as steel cylinders, and some brands are easily damaged," explains Deamer. "Also, as we look at bigger presses, with more colors and web widths over 52˝, sleeves no longer have as great an ergonomic benefit. At that point, automated handling systems may be required as the sleeves become too heavy to handle manually."

Even within traditional wide-web markets printers have had mixed results with sleeves. In response, consumable suppliers have focused on developing new products to improve the process. Comments Brett Scherrman, worldwide marketing manager for sleeve manufacturer Rotec North America, "Sticky back suppliers have formulated new tapes with better adhesion properties for sleeves. And sleeve suppliers are improving their material selection and their ability to grind surfaces more accurately. Both are critical to achieving the excellent results."

Rotec, and other sleeve manufacturers such as Polywest and Axcyl, are pioneering the next generation of sleeves with softer, compressible surfaces. According to Scherrman, Rotec's Print Pro compressible surface can be ground to within ±0.0005˝ on the sleeve diameter, thereby eliminating a number of press variants caused by inconsistent gauge thickness inherent in sticky back foam. Says Scherrman, "When you start out with a surface that is more accurate, you can give a lot less impression to get good ink transfer in solid areas. Less impression extends your plate life and minimizes dot gain."

Printers who migrate to compressible surfaces from hard sleeves report significant improvements in printing combination plates, with solids and screens in the same image. They also point to ease of use, greater consistency, and better registration on tight trapping scenarios—primarily because the print height of the plate is more consistent from sleeve to sleeve.

Imaging in the round

From a prepress standpoint, sleeves are an enabling technology for plate imaging "in-the-round." Most digital platesetter manufacturers, like Barco Graphics, CreoScitex, and Schepers-Ohio, offer the ability to laser image plate sleeves directly from digital data. Because it's a digital process, in-the-round imaging provides all the benefits of flat digital plates: greater integrity to digital proofs; improved reverses; sharper text; extended tonal range; smoother vignettes; higher contrast; much lower dot gain; and tighter register.

At first, in-the-round imaging was used almost exclusively for seamless applications—printing of continuous patterns and random cut packages, where there are no discernible breaks for trimming within the design. But the potential is far greater. From a quality standpoint, in-the-round imaging represents a huge positive step-change in the flexo process. "It's the ultimate implementation of digital accuracy for color-to-color registration," says Ian Hole, packaging business development manager for Barco Graphics. "Five or six laser imaged sleeves can be put on press within 5 microns of register. This isn't even conceivable with pre-imaged and pre-processed flat plates that are subsequently mounted on cylinders." Further, printers and converters using sleeves imaged in-the-round report they have faster makeready and come up to sellable color much quicker.

While sleeves are here to stay, we've still got a long way to go before imaging-in-the-round becomes the norm. It may take years before we can resolve the prohibitive cost of platesetting and processing equipment, and the logistics of supply chains, shipping, and inventorying. In the meantime, end users will continue to watch, and wait, for us to make the ultimate connection.