Sheet Feats

Sheetfed offset press advances have reached a level where neither sheet size—nor substrate—has to matter.

By Susan Friedman

Sheetfed offset press technologies have reached a nearly egalitarian state in which small-, medium- and large-size jobs can be handled in similar time with similar resources. But which format are most printers trying on for size?

A smaller sheet size that appears to have garnered appeal across printing markets is the 28˝ x 40˝. Achim Schmidt, manager for the packaging and label industry, Heidelberg, relates that the company's 40˝ Speedmaster CD, though introduced at DRUPA 86, took until the early '90s to really catch the sheetfed segment's attention. When it did, however, the press won customers not only in the carton printing industry but also in labels and commercial printing.

Sheetfed printers' approach to meeting shorter-run demands is not likely to translate into a steady downsizing. Current interest in sheet sizes smaller than 40˝ is mostly limited to prototyping and JIT production, Schmidt says.

"The industry still waits for a real half-sized press for folding carton," he adds. "Heidelberg is not ignoring this requirement, however at the moment many of our 40˝ customers take advantage of the quick size-presetting features of the CD 102 to go rapidly into the smaller sizes."

KBA recently answered to scaled-down sheet size needs with a 20˝ x 28˝ press, but Director of Marketing Bob McKinney sees this configuration, as well as the 40˝ machines, as more commercial application-oriented.

"The trend toward smaller sizes started five years ago and has practically ground to a halt," McKinney states. "Runs were getting shorter, and automation wasn't available on larger presses to achieve needed makeready and process speeds."

After automation for presses in the range of 51˝-64˝ was introduced at DRUPA '95, crew sizes, makeready times and speeds for small and large presses were finally comparable. As a result, McKinney estimates that only 20 percent of sheetfed presses sold today are as small as 40˝, while KBA's large format sales have increased four-fold.

In the past 12 months, MAN Roland has catered specifically to the large format crowd with the introduction of its Roland 900 series 44˝, 51˝ and 56˝ sheetfed presses, which can achieve speeds of 13,000 sheets per hour.

"The mainstay of the sheetfed industry is the large format, 40˝ x 56˝ machine," says Rudy Valenta, director of sheetfed press sales. "The larger presses allow printers to gang jobs differently—more efficiently—with twice the output at the end of a shift and only 33 percent additional operating costs."

In addition to requiring the same size crew and makeready time as a 40˝ press, the Roland 900 Series features one-minute set-up for automated feeder and delivery, and one-minute plate mounting. Preparation parameters for up to 5,000 jobs can be stored on the PECOM Press Center, a process electronics concept that links all areas of the plant into one data network.

Mitsubishi covers a wide sheet size spectrum with a product line of 28˝, 40˝, 51˝ and 56˝ presses. New Product Manager John Santie recommends printers have a realistic idea of the sheet sizes their presses can accommodate. Most presses are flexible, but only up to a point. "If a printer is interested in running sheet sizes outside the range of their current equipment, the purchase of a new press is something that must be considered," he says.

Process pressure?

Combination-process, web-press technologies have played handily into package printers' needs to produce multiple graphic effects and functionalities. Does this mean sheetfed suppliers are feeling pressure to push further development in this direction?

"Sheetfed presses do not offer the same type of finishing capabilities as web," acknowledges Santie. "The inline application of either aqueous or UV works best."

Mitsubishi rarely sells a press without a tower coater, he says, and some presses will have two coaters for the application of an aqueous UV primer followed by a UV coating. A chambered anilox roller system for the coater can apply blister pack coatings, specialty aqueous coatings or metallic ink applications.

When compared to sheetfed, web's weaker points are speed, expensive rotary dies and dot gain control, Valenta points out. He also believes sheetfed is ultimately more flexible. "Offline stations may add to the total cost of a printer's operation, but the stations also leave the presses open to handle any type of work," he explains.

Package printers' considerations typically go beyond offset technology when a decision between sheet and web must be made. "If it's going to be a web press, it's going to be flexo," McKinney states. "Both sheetfed offset and web flexo technologies can do in-line coating, so print quality continues to be the deciding factor."

Offset web presses can cost twice as much as offset sheetfed machines, making an apples-to-apples comparison difficult.

"Inline web offset solutions do offer an interesting alternative for some products," Schmidt comments. "There are many considerations, not the least of which is the cost of high-speed diecutting equipment, and the available quality from flexo not yet matching the litho process."

To give sheetfed offset printers more value-added process options, Heidelberg has increased its one-pass production range by integrating flexo-type coating units for metallic or spot coatings, multiple inline coatings, and perfecting capabilities.

Travel agents

The majority of sheetfed presses claim the ability to seamlessly process the thinnest paper, the thickest board and every substrate in between—but how do printers ensure that the proof will be in the pudding?

According to McKinney, presses with the most substrate versatility will include features such as timed air blast systems and double-size impression and transfer cylinders. He recommends assessing the overall ruggedness of the press to ensure accommodation of thicker paperboard over many years of production.

Very thin foil stocks and plastics remain the most problematic for sheetfed technologies, he notes, particularly due to the risk of scratching the substrate. Printers purchasing a sheetfed press for a plastic or foil application should ensure all surfaces contacting the substrate are highly polished, and that additional elements needed to guide a thin sheet, such as those on the KBA Rapida, are included.