Rotogravure (Roto or Gravure for short) is a type of intaglio printing process, which involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset printing and flexography, it uses a rotary printing press.
Once a staple of newspaper photo features, the rotogravure process is
still used for commercial printing of magazines, postcards, and
corrugated (cardboard) product packaging.
In direct image carriers such as gravure cylinders, the ink is
applied directly to the cylinder and from the cylinder it is transferred
to the substrate
While the press is in operation, the engraved cylinder is partially
immersed in the ink fountain, filling the recessed cells. As the
cylinder rotates, it draws ink out of the fountain with it. Acting as a squeegee,
the doctor blade scrapes the cylinder before it makes contact with the
paper, removing excess ink from the non-printing (non-recessed) areas
and leaving in the cells the right amount of ink required: this tool is
located quite close to the paper so that the ink left in the cells does
not have enough time to dry. Next, the paper gets sandwiched between the
impression roller and the gravure cylinder: this is where the ink gets
transferred from the recessed cells to the paper. The purpose of the
impression roller is to apply force, pressing the paper onto the gravure
cylinder, ensuring even and maximum coverage of the ink. The capillary
action of the substrate and the pressure from impression rollers force
the ink out of the cell cavity and transfer it to the substrate (Figure
1). Then the paper goes through a dryer because it must be completely
dry before going through the next color unit and absorbing another coat
of ink.
Because gravure is capable of transferring more ink to the paper than
other printing processes, it is noted for its remarkable density range
(light to shadow) and hence is a process of choice for fine art and
photography reproduction, though not typically as clean an image as that
of offset lithography.
Gravure's major quality shortcoming is that all images, including type
and "solids," are actually printed as dots, and the screen pattern of
these dots is readily visible to the naked eye.
Gravure is an industrial printing process capable of consistent high
quality printing. Since the Gravure printing process requires the
creation of one cylinder for each colour of the final image, it is
expensive for short runs and best suited for high volume printing.
Typical uses include long-run magazines in excess of 1 million copies,
mail order catalogs, consumer packaging, Sunday newspaper ad inserts,
wallpaper and laminates for furniture where quality and consistency are
desired. Another application area of gravure printing is in the
flexible-packaging sector. A wide range of substrates such as
polyethylene, polypropylene, polyester, BOPP, etc. can be printed in the
gravure press. Gravure printing is one of the common processes used in
the converting industry.
Rotogravure presses for publication run at 45 feet (14 m) per second
and more, with paper reel widths of over 10 feet (3 m), enabling an
eight-unit press to print about seven million four-color pages per hour.
The vast majority of gravure presses print on rolls (also known as webs) of paper
or other substrates, rather than sheets. (Sheetfed gravure is a small,
specialty market.) Rotary gravure presses are the fastest and widest
presses in operation, printing everything from narrow labels to
12-foot-wide (3.66-meter-wide) rolls of vinyl flooring. For maximum
efficiency, gravure presses operate at high speeds producing large
diameter, wide rolls. These are then cut or slit down to the finished
roll size on a slitting machine or slitter rewinder. Additional operations may be in line with a gravure press, such as saddle stitching facilities for magazine or brochure work.
