Flexographic Label Printing
Narrow web (continuous roll) flexographic printing, often called flexo printing, is the most prevalent pressure sensitive label printing process in use today. Flexography economically produces exceptional quality labels at blazing speeds (6000 to 24000 feet per hour).
Flexo inks are very thin, water-based or in some cases solvent-based inks which dry rapidly and are transparent, making them ideal for four color process printing (CMYK). Variable data printing, die-cutting and image verification are all accomplished in-line, which when combined with its exceptional speed, makes flexography very efficient for pressure sensitive label manufacturing.
Flexo Printing Process
Flexography is a rotary relief printing process. The substrate to be printed is fed through a series of inking stations and optional laminating, die cutting. waste striping and 100% visual inspection stations.
The printed image is achieved by means of a soft, flexible plate which contains the image to be printed in relief, much like a rubber stamp. The plate is adhered to a roller called the plate cylinder and placed on the press. Each color of ink to be applied must have its own plate and inking assembly.
Diagram of flexo inking assembly
Each color station contains a shallow tray of ink which goes through a series of cylinders before it is applied to the substrate. The fountain cylinder is partially submerged in the ink tray. As the fountain cylinder turns, it draws ink from the tray and applies it to the anilox cylinder. The anilox cylinder contains thousands of precision engraved cells which receive the ink in measured quantities and a doctor blade which removes excess ink to ensure an even coating. The anilox roller then deposits a thin layer of the ink onto the flexible plate where it is ready to be applied to the substrate.
After passing through each of the ink stations an in line laminating station may apply an optional protective over- laminate. The material then passes through a die cutting station which is set to cut through the label and adhesive but leaving the liner in tact. Finally, the waste area outside the labels may be stripped away from the liner before they are rewound onto the uptake roll.