Early Name: "Aniline"
The aniline printing process was introduced in the United States on a fairly broad scale in the early 1920's. Practically all the early aniline presses were imported from Germany, where the process is still termed gummidruck or rubber plate printing.

In America the process was called aniline printing because at the time coal tar dyestuffs - their parent substance being aniline oil - were used as the colouring ingredient in the inks.

Definition:
Flexography is a method of direct rotary printing using resilient raised image printing plates, affixable to plate cylinders of various repeat lengths, inked by a roll or doctor blade wiped metering roll, carrying fluid or paste type inks to virtually any substance.

Flexo Moves into Many Industries
With the war period over shortly after 1946, aniline as a printing method experienced a surge of rapid growth and acceptance in an ever increasing number of industries and substrate materials. The process was found adaptable to printing materials ranging from news stock to vinyl shower curtains. Aniline printing now established its own position. The number of converters, usually staffed by skilled craftsmen, multiplied rapidly. A new era had begun for an industry that was to grow by leaps and bounds.

Flexography Today
Flexographic printing units in use today consist of three basic types: the two roll unit, the two roll unit with a doctor blade, and the dual doctor ink chamber system. Two roll units are usually found on older flexographic presses, and on narrow web presses. Narrow web presses equipped for process colors often use the two roll unit with a doctor blade, and more modern wide web presses use the dual doctor ink chamber system.

Mechanical Principles of Flexography
In its simplest and most common form, the flexographic printing system consists of four basic parts:

· Fountain Roll
· Ink Metering Roll (Anilox)
· Plate Cylinder
· Impression Cylinder

Fountain Roll
The fountain roll is generally a rubber-covered roll of either natural or synthetic rubber. It is positioned to rotate in a reservoir of thin ink. Its main purpose is to pick up and deliver a relatively heavy flow from the reservoir or fountain to the metering roll. The fountain roll is usually driven much slower than the metering in order to effect a wiping action with the metering roll it presses against.

Ink Metering (Anilox) Roll
The ink metering roll, generally called the anilox roll, is usually a metal or ceramic coated roll, engraved over its entire surface with tiny cells numbering from 80 to over 500 per lineal inch. The purpose of the metering roll is to supply a controlled, metered, fine film of ink to the printing plates affixed to the next roller in the train which is the plate cylinder.

Anilox rolls are carefully selected for specific types of printing, substrates, and customer requirements. Often the flexographic printer will perform test runs to determine the ideal anilox for producing the desired ink distribution for halftones, spot color, and solids.

Plate Cylinder
The plate cylinder is generally a steel cylinder placed between the ink transfer (anilox) roll and the impression cylinder. Printing plates are adhered to it through the use of a double-sided adhesive tape called stickyback. Other methods include metal-backed plates magnetically held to the plate cylinder.

The ink transfer roll then transfers a finely metered film of ink to the raised surface of the plate, which in turn transfers the ink to the surface of the substrate.

Impression Cylinder
The impression cylinder is a smooth polished metal cylinder which services to back up and support the substrate as it comes in contact with the printing plate. The surface speed of the impression cylinder must be identical to that of the plate cylinder, anilox roll, and substrate. Otherwise, slurring, halos, smeared printing and reduced plate life will result.

Also, for quality printing, the accuracy of cylinder diameters, concentricity, gearing and bearing fit cannot be over stressed.

Configurations of Presses
The design of the flexographic printing unit enables press manufacturers to build presses in any one of three configurations: the stack press, the inline press (including corrugated presses), and the common impression cylinder press. Each configuration can be equipped with any of the basic printing units, depending upon the needs of the flexographic printer.

Flexographic Ink Delivery System
On a two-roll flexographic printing unit, the rubber covered fountain roll rotates in a fluid ink bath, dragging ink from the pan to the cells of the anilox roll. The soft rubber fountain roll is held in tight contact with the anilox roll. As the anilox rotates past the nip point, the fountain roll wipes excess ink from non-cell areas. Once past the nip point, each cell is filled with ink, and a measured, repeatable amount of ink is available to the printing plate. The metered anilox roll is moving into light kiss contact with the image areas of the plate, and the plate cylinder is moved into kiss contact with the substrate to transfer the image. The steel impression cylinder supports the substrate. When a thin metal or polyethylene doctor blade is used with a two-roll unit, the nip-point between the fountain and the anilox roll is opened to allow ink to flood the anilox and fill the cells. The doctor blade comes into contact with the anilox to clear excess ink from non-cell areas. With a dual doctor ink chamber, the fountain roll and inking pan can be eliminated; ink is delivered directly to the anilox through an enclosed chamber.