Diagram of rotogravure process Rotogravure (gravure for short) is a type of intaglio printing process, in that it involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset and flexography, it is a rotary printing press. This means that gravure presses print on rolls of paper, rather than sheets of paper.
Gravure cylinders nowadays are typically engraved digitally by a diamond tipped or laser tipped etching machine. On the gravure cylinder, the engraved image is composed of small recessed cells (or 'dots') that act as tiny wells. Their depth and size control the amount of ink that gets transferred to the paper.
A rotogravure printing press has one printing unit for each color. The number of units vary depending on what colors are required to produce the final image. There are five basic components in each color unit: an engraved cylinder, the ink fountain, the doctor blade, the impression roller, and the dryer. 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 ink from the non-printing (non-recessed) areas. 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. 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.
|
