14-A Flexography (Description)

Flexography (also called surface printing), often abbreviated to flexo, is a method of printing most commonly used for packaging (labels, tape, bags, boxes, banners, etc.).A flexographic print is made by creating a positive mirrored master of the required image as a 3D relief in a rubber or polymer material. A measured amount of ink is deposited upon the surface of the printing plate (or printing cylinder) using an engraved anilox roll whose texture holds a specific amount of ink. The print surface then rotates, contacting the print material which transfers the ink.One method of plate development uses light-sensitive polymer. A film negative is placed over the plate, which is exposed to ultra-violet light. The polymer hardens where light passes through the film. The remaining polymer has the consistency of chewed gum. It is washed away in a tank of either water or solvent. Brushes scrub the plate to facilitate the "washout" process. This method is considered "old-fashioned," but is still widely used in smaller operations, and is still taught in most high school and college flexo programs.Originally flexographic printing was basic in quality. Labels requiring high quality have generally been printed using the offset process until recently. In the last few years great advances have been made to the quality of flexographic printing presses.The greatest advances in flexographic printing have been in the area of photopolymer printing plates, including improvements to the plate material and the method of plate creation, usually photographic exposure followed by chemical etching, though also by direct laser engraving.Digital direct to plate systems have dominated the industry recently with their better resolution and the ability to print four color process (or more) as well as offset. Companies like Dupont in DE and PlateCrafters in Colmar, PA have pioneered the latest technologies with advances in FAST washout and the latest screening technology, even companies who make plates in house are going to trade shops to get these high quality plates.Laser-etched anilox rolls also play a part in the improvement of print quality. Full color picture printing is now possible, and some of the finer presses available today, in combination with a skilled operator, allow quality that rivals the lithographic process. One ongoing improvement has been the increasing ability to reproduce highlight tonal values, thereby providing a workaround for the very high dot gain associated with flexographic printing.Flexo has an advantage over lithography in that it can use a wider range of inks, water based rather than oil based inks, and is good at printing on a variety of different materials. Flexographic inks, like those used in gravure and unlike those used in lithography, generally have a low viscosity. This enables faster drying and, as a result, faster production, which results in lower costs.Printing press speeds of up to 600 meters (2000 FPM) per minute are achieveable now with modern technology high-end printers, like Flexotecnica [1], which introduced the world's first 12-color central impression (CI) drum press at Drupa 2008. Other press formats, such as in-line and stack presses, are available from Tresu and other suppliers.