The flexographic printing process continues to improve in both quality and consistency in an effort to meet end-user customers' increasing demands.

Press manufacturers have met this challenge by developing more accurate printing presses with tighter tolerances in registration, settings, and drying capabilities. Also, because timing is also a factor, presses have started to use all kinds of quick-changeover technologies.

These new generation presses are more like fine instruments than machines, and it is this accuracy that will now show the weaknesses, albeit small, of the conventional photopolymer printing plate. The two most pronounced weaknesses are registration due to exposure and caliper variation due to processing.

As everyone in this industry is aware, digital prepress has become the standard. Artwork, separations, screening, trapping and distortion are all done now almost exclusively via the computer.

Creating images on film with the use of laser technologies is the accepted prepress practice today. It is when the film is used to image a photopolymer plate that small inaccuracies can occur. The film itself may expand or contract slightly due to environmental changes, thus causing registration concerns not so much noticeable with older presses but with the new, more accurate generation. Dot gain due to caliper variation within the plate from processing can also take a toll in print quality and consistency.

There are technologies available today to address the possible shortcomings that exist when imaging and making a photopolymer printing plate. These include laser imaging the plate directly and employing a solventless-washout system for photopolymer plate processing.

Laser imaging of plates eliminates most registration errors, as there is no film involved. The newer generation of lasers is also much faster, speeding up the exposure process and, in some cases, manipulating the dot structure, which is so critical for good process-color work.

If the digitally-imaged and UV-exposed plate is made of a specially formulated, thermal photopolymer material, it can now be put in a thermal developer (and development medium) that will create the relief structure of the plate. Because no solvent is used, the plates will not undergo the typical swelling and unswelling of conventional platemaking, which can lead to caliper variations affecting plate life and dot gain.

As a further upside to this new platemaking technology, there's a significant timesaving element. It reportedly takes only 25 percent of the time compared to conventional platemaking. This technology seems to be a very good fit with the quick-change characteristics of the newer generation flexo presses.

While these developing technologies hold much promise for the industry, they won't be an end-all cure for the quality and consistency concerns still prevalent in flexo printing. Continued cooperation between the prepress companies or departments and the printers themselves is needed to make the flexo process grow and further compete with other major printing methods.