Web printing.

Runs get shorter Flexo gets better Narrow webs get wider

Shorter printing runs are driving many of the improvements in today's wide- and narrow-web printing presses. Reduced inventory levels, just-in-time deliveries, and short-term merchandising programs in flexible packaging are resulting in smaller print orders. Average print runs have shrunk by a factor of 10 since the early 1990s, says technical manager Garnett Hobson at press maker Rotomec America.

Short runs entail just as much downtime for set-up and job changeover as longer runs - but that downtime represents a much larger percentage of the total press time for the job. To help untie that economic knot, press makers have engineered newer models to speed job changes and set-ups.

One example is the emergence of a new breed of flexographic equipment: so-called intermediate-width presses for webs of 24 to 37 in. These are central-impression, eight-color presses that offer the same sophisticated graphics and electronic controls as their wide-web counterparts, but with quicker changeover, often requiting just one operator.

In-line flexo and rotogravure presses are also keeping up with shorter runs. Interchangeable cartridge trolleys, for example, allow very quick, off-line make-ready. Automatic pre-registration, available for years on flexo presses, has been moving into gravure models. Ensuring that all colors are in register at start-up can save a lot of time and material.

FLEXO IS TAKING OVER

While rotogravure long held the title of highest-quality web-printing process, press makers and converters agree that the latest flexographic systems come so close in quality that consumers often cannot tell the difference. Flexo machinery still costs less. Price of an eight-color gravure press generally runs from $4 million to $10 million, while eight-color CI flexo machines can start at $700,000 and go up to $4 million with in-line lamination and coating.

Consequently, gravure printing has suffered a declining share of the plastic film market. About 70% of web presses currently sold in the U.S. are flexo type, 10% are gravure, and the rest are a combination of letterpress, dry-offset, and a few screen printers, says Kurt Freye, director of sales and marketing at Windmoeller & Hoelscher.

CI CYLINDERS DOMINATE FLEXO

In recent years, the largest trend in flexographic printing, particularly in the wide-web arena, has been the move away from stack and in-line presses toward eight-color central-impression (CI) cylinder machines. W&H's Freye estimates that CI presses account for 98% of all new flexo machines today.

Moreover, suppliers say the trend toward more sophisticated graphics will yield presses with more color options. Ten-color machines are already here. Kidder Inc., for example, has added the 10-color Model 1006 to its Gold Series. The machine has a 106-in. CI drum that prints on webs 35-65 in. wide at up to 1500 ft/min.

Other key changes that have become the norm in new flexo presses include improved recipe-retrieval software that allows computer storage of all job parameters and automatically resets the press. Today's machines also feature automatic positioning of printing decks, as well as robotics that allow safe automatic loading and unloading of anilox and press cylinders.

Another safety-related innovation on both intermediate and wide-web flexo machines is the replacement of integral cylinders with sleeves, notes Mark Gillis, director of sales and marketing at Paper Converting Machine Co. "Sleeves are much lighter in weight, easier to change, and, in some cases, lower in cost."

New quick-change technology has emerged for doctor blades. Kidder now offers a "flow-through" system that reportedly allows very accurate and easy setting of the blades. "They allow for quick changeover and eliminate seal problems because the ink flows through the blade and through a small ink collector," explains president Chuck Rae. They are now standard on the company's machines and are being retrofitted on many existing presses, including those of competitors.

Infinitely variable print-repeat length - previously restricted to gravure printing - is about to make its debut on CI flexo machines. Fischer & Krecke has a new patent-pending technology that will be used for the first time on wide-web and intermediate (33-39 in.) presses now under construction. Sales manager Kurt Flathmann says these machines will offer all the advantages of CI flexo presses, with all cylinders still driven by a single gear. Without revealing details of the technology, he says, "Converters will be able to move into jobs currently being printed by gravure without compromising package size."

'NARROW' GROWS WIDER

Narrow-web flexo presses are now following in the footsteps of their wider counterparts. They are now much more highly automated and often come with value-added downstream operations such as front and back coaters and laminators.

The biggest news is the advent of CI flexo presses for narrow webs, which up until five years ago were dominated by in-line or stack presses. Traditionally, the narrow-web field was defined as label printing on webs from 4 to 14 in. In recent years, the term "narrow" has come to mean anything under 24 in.

In addition, there are now intermediate-web CI flexo presses for widths of 24-37 in. Chuck Rae of Kidder - a pioneer in this type of press - calls them "half-web" presses, since they print on roughly half the width of a traditional "wide" web of 36-56 in. These eight-color machines reportedly permit changeovers as fast as 10 min per color vs. up to 1 hr/color on wide-web presses. "These presses have much higher speeds - up to 1000 ft/min - than in-line flexo machines," says Rae. "Compared with in-line presses, they are more rugged and allow quicker changeover since they are smaller, with easily accessible stations. They hold excellent registration and have no trouble handling extensible films."

Newer examples of these intermediate-width machines include the Vision Press from Paper Converting Machine Co., which is designed for runs as short as 4000 ft. It prints on film up to 37 in. wide with 10-24 in. repeat lengths. W&H recently introduced the Soloflex 8L, suitable for web widths to 33.25 in. and repeat lengths of 24 in. Says Freye, "We aim these machines at applications requiring quick changeovers and very short runs - under 50,000 ft. But many converters who have them are using them for long runs and are simply not getting the flexibility and improved productivity they would get with a wider-web press."

IN-LINE FLEXO ADVANCES

A major breakthrough for in-line flexo presses was the infinitely variable print-repeat technology introduced in 1992 by BHS Printing Machinery. It allows flexo printing to be applied in cases that formerly required gravure methods. "Now you can print just like gravure, whereas repeat lengths had been limited by the gear pitch used - typically to 1/8-in. increments on narrow-web machines and 1/4-in. on wide-web presses. Further, it's possible to print longer or shorter using the same size cylinder or plate circumference," explains BHS president Dieter Langendorf. BHS replaced gears with a gearless electronic direct-drive system.

Other advances include improved electronic register control and thinner photopolymer plates that can reduce dot gain and slur and can print with higher contrast. Also, newer sleeves are larger so one small-diameter print cylinder can cover a larger range of repeats.

Faster changeovers have also come to in-line flexo presses. BHS recently built a 40-in.-wide, nine-color custom press that allows changeover on the fly. The press can be running with four or five print decks while the remaining decks are being changed.

Webtron, a maker of narrow-web, in-line flexo presses, recently introduced "instant-change" technology that reportedly allows complete make-ready or changeover in under 10 min. The new Instaflex presses have inking cassettes (including ink pans and anilox rolls) that are prepared off-line and placed on a loading cart where they are ready to be installed on the press.

RAISING FLEXO QUALITY

Improvements in anilox rolls, printing plates, and inks have contributed to much finer flexo print quality that can compete with traditional gravure or dry-offset printing. For example, today's laser-engraved ceramic anilox rolls can handle 800-1000 lines/in. vs. 360 lines/in. on chrome rolls a few years ago. Photopolymer plates are also much thinner, allowing better ink transfer.

Meanwhile, in-line flexo presses are leading the way toward adoption of non-solvent inks. Although solvent-based inks still predominate on wide-web CI flexo and gravure presses, the switch to water-based inks has already taken place for in-line narrow-web printing. However, Freye of W&H says water-based inks have scuff-resistance problems. "As a result, people tend to reverse-print and laminate to enclose the printing surface and get the gloss required. These approaches can be too costly for certain markets," he says.

Meanwhile, interest is growing in uv-curable inks. Unlike water-based types, uv inks don't tend to "fan out" and thus provide a cleaner and crisper print, explains Webtron v.p. of marketing Ted Stitzer. BHS's Langendorf adds that his firm has sold several presses for food and medical packaging that use cationic uv inks, which allegedly run better than free-radical uv types on in-line presses.

Kidder's Rae says, "UV inks are growing in acceptance because their rheology is now more suitable for CI flexo presses, and uv lamps have been redesigned to fit in the same space as traditional between-color dryers."

Converters and press suppliers note that uv inks also have a downside - namely higher cost, fewer color choices, and sometimes less rich or less uniform effects than traditional inks. Langendorf of BHS replies that despite their higher cost, uv inks can provide better overall economics because of shorter cleaning time and less start-up waste. Also, uv types reduce ink inventories because they are more universally applicable, he says.

Langendorf adds that uv inks may fit better with in-line than CI presses because the uv lamps' temperature will not affect the in-line print units, saving the capital and energy costs that would be required to cool the CI cylinder.

ROTOGRAVURE IMPROVES, TOO

Major technical improvements in rotogravure presses over the last few years include automatic impression and cylinder engagements, automatic wash-up systems, servo-drive systems that electronically register each gravure cylinder, and improved diagnostic and maintenance software. In addition, dryers are said to be 50% more efficient than in the past, so that dwell times can be shortened from 15 ft down to 6-8 ft.

Perhaps the biggest news is in reduced make-ready and changeover times - often down to 30 min from 6-8 hr. Several press makers now offer slide-in print trolleys that carry the cylinder, inking system, and viscosity controller. These are manually locked in position between the side walls of the print station, allowing quick set-up by one operator. Presses offering this feature include Rotomec's Rototec 3000 and W&H's Mercur Heliostar and Heliostar 2000.

A fully automatic version of this technology is the feed-through trolley system used by North American Cerutti on its high-speed (2000 ft/min) Model 950 presses. This system permits automatic off-line make-ready of print cylinders, inking system, doctor blades, and registration system. When the press comes to a stop at the end of production, one operator initiates trolley changeover on all printing units by means of a single command at the main control desk (see schematic). Automatic functions include sidelay alignment, damping of the printing cylinder, and connection of pneumatic pressure and sidelay drive for the doctor blades.

Suppliers are now building multi-duty presses that allow converters to print on a variety of substrates with just a trolley cartridge change. W&H designed its Heliostar 2000 to permit variable printing widths from 39.5 to 65 in. by means of movable gravure-cylinder bearing brackets. Changeover operations such as doctor-blade adjustment and locking the gravure-cylinder bearing housings are performed manually without tools.