What you should know about Flexo printing
Flexo printing is the dominant printing technology for printing flexible packaging in Europe and North America. Over the past decades, flexo pre-press and printing technology have evolved to a level of quality close to that of offset and rotogravure printing. The latest developments in flexo prepress and plate technology allowed flexo to close the gap, however not without significant cost increase.
Flexo printing is characterized by the use of flexible printing plates in combination with anilox rollers for ink metering. The anilox rollers supply ink from the ink chamber onto the flexo printing plates. The use of anilox rollers and low-pressure ink transfer make the use of liquid inks mandatory in flexo printing.
Flexo printing plate
Flexo printing plates are polymer-based. Flexo plates hold the image as a positive relief on their surface. Imaging of Flexo plates is an extensive and time-consuming process that, after CTP imaging, includes drying and a hardening step. An imaged flexo plate is several times more expensive than for example an offset plate, which has a negative impact on short-run economics. Polymer flexo plates cannot be recycled.
Inks for Flexo printing
Flexo inks are liquid, having a low viscosity in the range of 0,05 up to 0,5 Pa·s. A variety of ink systems is available for flexo printing, including UV, LED-UV, and EB energy-curable, water-based, and solvent-based inks. The drying system can be configured to match the application of choice. The majority of Flexo inks contain significant amounts of solvent or water with solvent, up to 60 to 80 mass-%. Maintaining constant and stable viscosity requires continuous monitoring and adjustment of the solvent components in the ink. During printing the solvent, or water with solvent, is evaporated from the ink by the use of hot air dryers. Depending on the emission quantity, and local applicable regulations, solvent-loaded air cannot be vented freely into the environment. The solvents in the air must be removed for example through thermal oxidation. This requires investments in installations and additional costs for operations and energy.
Flexo Narrow-web, Wide-web, and Flexo in-line
Flexo presses and printing units can be found in a variety of designs, from Ci-presses to wide-web inline and narrow-web. Ci-presses are commonly used for flexible packaging printing, wide-web inline flexo presses are typically for certain cardboard applications, and board is for liquid packaging. Narrow-web flexo presses are typically used for low-volume label printing. Most narrow-web flexo presses utilize UV or LED-UV inks, avoiding costs and handling hot-air drying.
DG press hybrid web-press configurations
Integration of one or more flexo units inline in DG press’s web-offset presses is common practice. Web-offset press series DG-AUXO and DG-Vision can be equipped with up- or down-stream flexo units, for lacquers, varnish, specialty inks/coatings, or first- or last-down whites. Available drying technologies are hot-air drying tunnels for water-based and solvent-based flexo inks and lacquers or electron beam or UV curing for energy-curable flexo inks and lacquers.