Print Production - Rotogravure

Typical gravure printed products include:

• Food packaging
• Wall paper
• Wrapping paper
• Furniture laminates
• Paneling 
• Greeting cards
• Magazines

The gravure process has its origins in the early seventeenth century when the intaglio printing process was developed to replace woodcuts in illustrating the best books of the time. In early intaglio printing, illustrations were etched on metal, inked, and pressed on paper. Gravure, still also known as intaglio printing, makes use of the ability of ink to adhere to a slight scratch or depression on a polished metal plate.

Currently, the dominant gravure printing process, referred to as rotogravure, employs web presses equipped with a cylindrical plates (image carrier). A number of other types of gravure presses are currently in use. Rotary sheet-fed gravure presses are used when high quality pictorial impressions are required. They find limited use, primarily in Europe. Intaglio plate printing presses are used in certain specialty applications such as printing currency and in fine arts printing. Offset gravure presses are used for printing substrates with irregular surfaces or on films and plastics.

Today almost all gravure printing is done using engraved copper cylinders protected from wear by the application of a thin electroplate of chromium. The cylinders (image carrier) used in rotogravure printing can be from three inches in diameter by two inch wide to three feet in diameter by 20 feet wide. Publication presses are from six to eight feet wide while presses used for printing packaging rarely exceed five feet. in width. Product gravure presses show great variation in size, ranging from presses with cylinders two inches wide, designed to print wood grain edge trim, to cylinders 20 feet wide, designed to print paper towels. The basics of Gravure printing is a fairly simple process which consists of a printing cylinder, a rubber covered impression roll, an ink fountain, a doctor blade, and a means of drying the ink.

The major unit operations in a gravure printing operation are:

• Image preparation
• Cylinder preparation
• Printing
• Finishing

Gravure Inks - Solvent Based, Water Based

Gravure inks are fluid inks with a very low viscosity that allows them to be drawn into the engraved cells in the cylinder then transferred onto the substrate. In order to dry the ink and drive off the solvents or water, which essentially replaces most of the solvent, the paper is run through Gas fired or electric fired driers. The ink will dry before the paper reaches the next printing station on the press. This is necessary because wet inks cannot be overprinted without smearing and smudging. Therefore, high volume air dryers are placed after each printing station.

The solvent-laden air from the dryers is passed through either a solvent recovery system or solvent vapor incinerator. A typical recovery system uses beds of activated carbon to absorb the solvent. Saturated beds are regenerated by steam. The solvent laden steam is then condensed and the water and solvent separate by gravity. Greater than 95 percent of the ink solvents can be recovered using this process (Buonicore). The solvents can either be reused or destroyed by incineration.

Water based inks, especially used for packaging and product gravure, require a higher temperature and longer drier exposure time in order to drive off the water and lower vapor pressure constituents. As mentioned subsequent sections, Flexo and Gravure inks are very similar and the constituents are essentially the same. Again, a pollution control device may be needed.

Gravure Press Design and Equipment

Web-fed gravure presses account for almost all publication, packaging, and product gravure printing. These presses are generally custom manufactured machines designed for a specific range of products. The typical press is highly automated and consists of multiple print units. The printing mechanism in a rotogravure press consists of a gravure cylinder and a smaller, rubber clad impression cylinder.

Other types of gravure presses in commercial use today are sheet-fed, intaglio plate, and offset gravure. These types of presses are used primarily for special printing applications.

sources http://www.pneac.org/printprocesses/gravure/webfed.cfm