Flexographic Process

As stated earlier, flexography is like letterpress in that both print from a raised image surface. Flexo plates, whether molded from rubber or imaged from photopolymer, are generally made from flexible materials. Flexo inks generally are low viscosity, highly fluid and quick drying, although there is a trend toward higher viscosity inks. The inks are made from a dispersion of resins, solvents, color and additives, which are either organic or aqueous based.

In the simplest and most common form, the flexo process consists of four components;

1) fountain roll,

2) ink-metering (anilox) roll,

3) plate cylinder and impression cylinder.

These are illustrated in the figure below. The fountain roll is generally covered with rubber.

It rotates in a reservoir of ink and its purpose is to pick-up and deliver a relatively heavy flow of ink from the fountain.

The anilox roll is usually chrome or ceramic plated and is covered with tiny engraved cells. The number of cells varies from 80 to 1000 cells per linear inch. The roll of the anilox is to supply a fine film of ink to the printing plates. Thus, the fountain and anilox rolls are set to rotate against one another with the least amount of pressure required to form a puddle behind the nip. The anilox roll is often used with a (reverse angle) doctor blade to wipe excess ink for the roll.

The plate cylinder is usually steel and in installed between the anilox roll and the impression cylinder. Printing plates are attached to the plate cylinder with stickyback (a special double sided tape). The plates raised surface picks up ink from the anilox and transfers it to the substrate. The impression cylinder is smooth, highly polished and supports the substrate when it contacts the plate. Its speed must match that of the plate cylinder, the anilox roll and the substrate.