Drive for printing quality boosts flexo

Marketplace demand for high-quality graphic reproduction, fast turnaround and consistency-plus lower cost-points converters to flexo. Check it out at CMM Intl. 2001 this month.

By Contributing Technical Editor Steve Utschig -- Converting Magazine, 4/1/2001

Flexography as a printing process of choice for converters has come into its own over the past several years, due to many factors. The new and improved flexo press technology that converters will be able to see at this year's CMM International in Chicago is only a part of the reason for flexo's steady progress.

Developments in the various component parts of the process, market demands for improved quality and consistency, while still maintaining lower costs, are driving the need for increased improvements in flexographic printing presses. The new flexo products being developed now and in the future will respond to those market demands.

Let's review some of these flexo developments:

Anilox rolls: This technology continues to improve. Cells are becoming better formed, smoother and more efficient in accepting and voiding ink. Metering technology using doctor-blade chambers has advanced, improving dwell times and controlling the ink film all the way to the surface of the plate.

Flexographic inks: Ink suppliers continue to work feverishly to develop systems that will work better under very low ink-film transfer constraints and still maintain good density properties and lay on both the printing plate and the substrate.

Printing plates: Until recently, the printing plate has been the last stumbling block to high-quality graphic reproduction because of the minimum size dot the plate could realistically hold. Numerous advancements have been made to address this issue. New plate materials, thin plate technology, laser imaging, laser engraving and plate-processing improvements are allowing at least the possibility of better tonal range and color gamut enhancements.

The press itself

As improvements proceed in the other component parts of the flexo printing process, the need increases for presses that have the capability to work within the much-reduced tolerances that are now the norm.

Most press manufacturers have converted to CNC (computer-controlled machining centers) to produce the components of their respective presses. This allows for tighter, more accurate and consistent tolerances, greatly reducing performance problems on the press.

With customers demanding shorter lead times, shorter runs and JIT deliveries, there's a continuing trend to develop presses with faster turnaround or changeover. Press designs are taking advantage of ever-improving sleeve technologies both on the plate cylinder and anilox-roll portion of the print decks. This usually involves some type of cantilever system.

Web handling and web-tension zone controls, allowing for driven unwind instead of more passive systems, improve the overall print quality. Between-color and overhead drying technology has also advanced, allowing higher speeds and greater production capacity.

Automatic deck positioning involving ball screws and stepping motors (derived from CNC technology) has been around for a while, but improvements and ease of use continue to be implemented. This is vital for reproducing high-quality graphics by allowing for minimal dot gain in the finished print if the other component requirements are met. Adjustments are made by the use of PLC or touchscreen technology. In fact, on some new presses the only actual control dials or buttons are the emergency stops!

Go gearless

The biggest advancement made in flexo presses to date, however, is the introduction of gearless technology. Gears coming in contact with each other show wear at different rates and can cause registration error and other related problems. Instead of trying to match the surface speeds of the various press components in the ink train with gears, this is now accomplished with the use of servomotors under PLC control. This technology has literally put to rest most registration issues within the flexo process.

With gearless technology also comes the ability to print to infinite repeat lengths, which was only occasionally possible with gears and extensible films. This opens up new opportunities for the flexo package printer. Price alone usually will not guarantee sales, but quality, consistency, and price will.

It's important to note that if improvements are made in only one or two of the component parts of the flexo process, quality and consistency are not guaranteed. All improvement is driven by market demands. As one component of the process is improved, all of the other components must adapt to that change. Use of today's advanced presses requires equal application of the latest technologies in the other components as well.

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