Printing Secrets from Print Acumen
Gravure Printing
The long run, high quality printing process
Applications:
Products printed by the Gravure printing process include:
- Food packaging
- Wall paper
- Wrapping paper
- Furniture laminates
- Panelling
- Greeting cards
- Magazines
Process Overview
Gravure printing is characteristically used for long run, high quality printing producing a sharp, fine image. The number of printing plants offering gravure printing gravure in is significantly lower than other printing processes. This is due, in part, to the cost of presses and components. While a lithographic press will cost in the range of $100,000 the cost of gravure press will be in the range of $1 million.
A single gravure cylinder will cost around $5000 versus around $15 for a lithographic plate how the gravure cylinder will last much longer than a lithographic plate.
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 cylindrical plates. 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 stocks 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 used in rotogravure printing can be from 75mm (three inches) in diameter by 50mm (two inch) wide to 91.5cm (three feet) in diameter by 6.09m (20 feet) wide.
Publication presses are from 1.82m to 2.43m (six to eight) feet wide while presses used for printing packaging rarely exceed 1.52m (five feet) in width.
Product gravure presses show great variation in size, ranging from presses with cylinders 50mm (two inches) wide, designed to print wood grain edge trim, to cylinders 6.09m (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
Gravure printing is an example of intaglio printing. It uses a depressed or sunken surface for the image. The image areas consist of honeycomb shaped cells or wells that are etched or engraved into a copper cylinder. The unetched areas of the cylinder represent the non-image or unprinted areas. The cylinder rotates in a bath of ink called the ink pan.
As the cylinder turns, the excess ink is wiped off the cylinder by a flexible steel doctor blade. The ink remaining in the recessed cells forms the image by direct transfer to the stock (paper or other material) as it passes between the plate cylinder and the impression cylinder.
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 stock.
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 vapour 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% 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 vapour 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.
Now, you can save big $$$'s on all your
company printing by downloading our
FREE Printing Perth Guide.
The 9 big insider secrets and proven methods
guaranteed to slash your printing costs... forever.
"Their service & quality has been exemplary"
"I have no hesitation recommending Print Acumen to any business
requiring a professional printing service"
Michael Burges
Bursar, Trinity College