Flexography is the major process used to print packaging materials.
Flexography is used to print corrugated containers, folding cartons,
multiwall sacks, paper sacks, plastic bags, milk and beverage
cartons, disposable cups and containers, labels, adhesive tapes,
envelopes, newspapers, and wrappers (candy and food).
In the typical flexo printing sequence, the substrate is fed into
the press from a roll. The image is printed as substrate is pulled
through a series of stations, or print units. Each print unit
is printing a single color. As with Gravure and Lithographic printing,
the various tones and shading are achieved by overlaying the 4
basic shades of ink. These are magenta, cyan, yellow and black.
Magenta being the red tones and cyan being the blue.
The major unit operations in a flexographic printing operation
Below is a process flow diagram for flexographic printing:
Image preparation begins with camera-ready (mechanical) art/copy
or electronically produced art supplied by the customer. Images
are captured for printing by camera, scanner or computer. Components
of the image are manually assembled and positioned in a printing
flat when a camera is used. This process is called stripping.
When art/copy is scanned or digitally captured the image is assembled
by the computer with special software. A simple proof (brown print)
is prepared to check for position and accuracy. When color is
involved, a color proof is submitted to the customer for approval.
Flexographic Plate Making:
Flexographic and letterpress plates are made using the same basic
technologies utilizing a relief type plate. Both technologies
employ plates with raised images (relief) and only the raised
images come in contact with the substrate during printing. Flexographic
plates are made of a flexible material, such as plastic, rubber
or UV sensitive polymer (photopolymer), so that it can be attached
to a roller or cylinder for ink application. There are three primary
methods of making flexographic plates; photomechanical, photochemical
and laser engraved plates.
Flexographic Printing Presses:
The five types of printing presses used for flexographic printing
are the stack type, central impression cylinder (CIC), in-line,
newspaper unit, and dedicated 4-, 5-, or 6-color unit commercial
publication flexographic presses. All five types employ a plate
cylinder, a metering cylinder known as the anilox roll that applies
ink to the plate, and an ink pan. Some presses use a third roller
as a fountain roller and, in some cases, a doctor blade for improved
Flexographic inks are very similar to packaging gravure printing
inks in that they are fast drying and have a low viscosity. The
inks are formulated to lie on the surface of nonabsorbent substrates
and solidify when solvents are removed. Solvents are removed with
heat, unless U.V. curable inks are used.
After printing, the substrate may run through a number of operations
to be "finished" and ready for shipment to the customer.
Finishing may include operations such as coating, cutting, folding