rotogravure printing, system of printing based on the transfer of fluid ink from depressions in a printing plate to the paper. It is an intaglio process, so-called because the design to be printed is etched or engraved below the surface of the printing plate. At the start of the gravure printing process, the plate is covered with ink and the surface is then wiped clean. When paper is pressed against the inked plate, the paper penetrates the sunken parts slightly and draws out the ink.
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All copy (the material to be reproduced, or printed) in rotogravure printing is prepared as positive film. A gravure printing plate made of copper is then prepared to accept photomechanical transfer by means of a gravure screen; this is a grid of closely intersecting lines that create thousands of tiny squares on the plate, which will in turn react differentially to an etching bath after the plate has been exposed to light through the positive film. The varying depths of the etched cells determine the tones of the printed image, with deeper cells holding more ink (and thus printing darker) than shallow cells, which may hold no ink at all.
In the printing process, the cylinder bearing the printing plates is usually arranged so that during its rotary movement it passes through a trough filled with a thin solution of fast-drying ink, or is sprayed with ink instead. A thin steel blade (called the doctor blade) moves across the cylinder and removes the ink from the plate’s surface but not from the tiny depressions in its cells. The plate cylinder then comes in contact with the paper, and the paper draws the ink out of the depressions in the plate. In colour rotogravure printing, a separate cylinder is prepared for each colour.
More From Britannica printing: RotogravureThe food packaging can be customized to make it more original, to enhance branding and make the product more appealing. One of the techniques available is rotogravure printing, also known as gravure printing.
It is a different printing method to flexographic printing, as it uses a different type of plate and specific gravure presses. Let’s see how and when gravure printing is used to customize the artwork on food packaging.
The rotogravure printing technique for food packaging is a particular printing method that achieves results with bright, quite dark and opaque colors. In traditional offset printing, the ink is pressed, while in gravure printing, it is picked up by the paper: printing occurs through direct contact between the material and the plate.
In gravure printing, the printing part is in a recess compared to the non-printing part, and the ink is transferred through a modular system of small cells of varying depths. This determines the quantity of ink and therefore the brightness of the color, which often appears darker than with other printing techniques.
How did gravure printing originate? The name of this printing method comes from newspaper and magazine printing – indeed gravure printing is widely used in this sector. That is why the technique took on the name rotogravure printing since it is mostly associated with printing news magazines.
Gravure printing involves the use of a specific gravure press, in which the inked mold transfers the ink onto the material to be printed. Then, it is pressed using a roll that has been specifically coated with quite a thick layer of natural rubber or rubber.
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The inked mold is a metal roll with a very thin copper coating onto which the printing pattern is engraved. After the first stage, when excess ink is removed by a blade, the engraved roll transfers the ink onto the material, which is then printed.
Gravure printing uses two printing cylinders: the lowest rotates in an ink trough, also called a rotogravure cylinder; and the printing cylinder at the top applies pressure to the material. The two cylinders are separated by a tape, where the print material is located.
This technique is used with paper or plastic and metal materials. Plastic and metal are the most widely used solution for flexible food packaging. In this type of application, specific inks are used that are formulated in accordance with food industry hygiene and safety standards and the technical characteristics of food packaging.
Gravure printing presses are the main element of this printing process. In fact, specific printing presses are used for each type of print, such as machines for press printing for printing newspapers and catalogs. They produce high-quality graphics to enhance illustrations and require the use of paper with a low gsm.
Forfood packaging, on the other hand, specific gravure presses are used for flexible packaging. These presses achieve excellent print quality and allow the ink to adapt to the type of material used, optimizing the formulation, while the use of volatile solvents enables a quick drying process and it is possible to use bronze and aluminum metallic inks to make the print brighter.
In general, these machines are designed to print at a lower speed and on smaller formats than press printing machines, with the possibility of using complete systems that print, laminate and perforate to perform the entire packaging process on one machine.
In order to optimize printing, some flexible packaging machines also use electrostatic units that help the ink cells to empty properly.
Today, the market is rapidly moving toward research about sustainable and eco-friendly food packaging, using innovative materials and processes with a low environmental impact. That’s why many players in the sector use more eco-friendly techniques alongside gravure printing, like flexo printing and digital printing. This makes it possible to create more eco-friendly flexable packaging, without compromising the shelf life of food products and the hygiene and safety standards that the food industry demands.
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