Technology of Flexography

Flexographic presses are capable of producing good quality impressions on many different substrates and is the least expensive and simplest of the printing processes used for decorating and packaging printing. The use of flexographic printing presses is on the rise. There are two primary reasons for this: 1) it is a relatively simple operation; and 2) it is easily adapted to the use of water-based inks. The widespread use of water-based inks in flexographic printing means a large reduction in VOC emission compared to the heatset web or gravure printing processes.

Packaging flexography is used for the production of folding cartons, labels, and packaging materials. Large quantities of inks are used during normal runs on flexographic presses; however, some printers are able to recycle a majority of their spent inks and wash waters. Major chemicals used in flexography include platemaking solution, water and solvent based inks, and blanket/roller cleaning solvents.

Flexography is a form of rotary web letterpress, combining features of both letterpress and rotogravure printing, using relief plates comprised of flexible rubber or photopolymer plates and fast drying, low viscosity solvent, water-based or UV curable inks fed from an "anilox" or two roller inking system. The flexible (rubber or photopolymer) plates are mounted onto the printing cylinder with double-faced adhesive.

The process of printing each color on a flexo press consists of a series of four rollers:

• Ink Roller
• Meter Roller
• Plate Cylinder
• Impression Cylinder

The first roller transfers the ink from an ink pan to the meter roller or Anilox Roll, which is the second roller. The Anilox roller meters the ink to a uniform thickness onto the plate cylinder. The substrate then moves between the plate cylinder and the impression cylinder, which is the fourth roller.

The impression cylinder applies pressure to the plate cylinder, thereby transferring the image onto the substrate. The web, which by now has been printed, is fed into the overhead dryer so the ink is dry before it goes to the next print unit.

After the substrate has been printed with all colors the web MAY be fed through an additional overhead tunnel dryer to remove most of the residual solvents or water. The finished product is then rewound onto a roll or is fed through the cutter.