ELECTRONIC ROTOGRAVURE PRINTING CYLINDER

Gravure printing is a high-speed roll-to-roll printing technique which can overcome the disadvantages of inkjet and reproduce the process flow in Figure 1 with much higher throughput. Gravure is commonly used in the graphic arts industry for medium to long print runs where uniformity and versatility are required. Gravure printed products span a wide range, including bank notes, gift wrap, magazines, and postage stamps.

Gravure is an intaglio printing process, which means that the image carrier has the image etched below the surface of the non-image area. The gravure image carrier is an engraved cylinder patterned with individual wells that form a continuous image when printed. There are five main aspects of the gravure printing press: an engraved cylinder, doctor blade, ink fountain, impression roller, and drying press [GAA]. Figure 2 shows a schematic of a typical gravure printing process.

In gravure printing, the engraved cylinder is submerged in an ink fountain and then rolled over the substrate. A tightly pressed blade, called the doctor blade, wipes off excess ink from the non-image areas of the cylinder surface before contact with the substrate. The gravure cylinder most commonly consists of a steel core covered by a layer of copper, which is then patterned and covered with a thin layer of chrome to protect against wear from the doctor blade. The average lifetime for copper-chrome cylinders is between two to three million impressions, which is equivalent to a week of nonstop printing. Cylinders can be reused by stripping the chrome and copper layers. Modern engraving systems are capable of transferring digital images directly to the cylinder surface, which has helped to reduce the lead time for engravings to a few hours [GAA].

Gravure has a number of advantages over inkjet. First, gravure has a higher throughput because of its wider print area and its faster printing speed of up to 2000 ft/min. Gravure is also capable of simultaneously depositing multiple drops in a parallel fashion, as opposed to inkjet which must deposit drops one at a time in a serial fashion. Second, gravure can sustain long print runs because the cells are continuously refilled with ink as the roll is rotated into the ink fountain, and the roll is not subject to clogging. Finally, gravure is a very versatile process capable of printing on a broad range of substrates with a wide range of ink viscosities. These advantages also help gravure compete against other high-speed printing processes such as flexography, letterpress, lithography, and screen printing. Gravure is a mechanically simple process with fewer controlling variables than other printing processes, which tends to give it a more consistent image quality.