Gravure Printing
A method of printing; this process creates an image by engraving a negative of the image being printed onto a gravure cylinder, which is then coated with ink and the image is transferred to the substrate using pressure. Also known as rotogravure, or “roto” for short, this method is a form of intaglio printing, which involves an image being incised into a surface (rather than raised as in relief printing).
The image carrier in gravure printing is usually a steel cylinder that is electroplated with copper (some modern gravure presses use aluminium or plastic). A negative of the image being printed is created on the gravure cylinder as a pattern of cells, which can be of a uniform or varying depth, with as many as 50,000 or more cells per square inch. The image areas are created in recess, leaving the non-image areas in relief. The image can be created using an analogue or a digital method; traditionally, a photographic film negative of the image is placed over the gravure cylinder and the image areas are either engraved onto the gravure cylinder using a laser or diamond tool or chemically etched in place (with the film protecting the non-image areas from the chemicals, while the image areas are etched onto the cylinder). Modern gravure printing sometimes uses a digital image of the image being printed to instruct a computer driven laser or diamond tool to engrave the correct areas of the gravure cylinder to recreate the image. Once the gravure cylinder has been engraved or etched, it is usually plated with chrome to protect the copper during the remainder of the printing process.
The gravure cylinder collects ink from an ink fountain, before a doctor blade removes excess ink from the non-image areas to ensure that only the engraved cells (image areas) contain ink. The substrate is then passed between the gravure cylinder and an impression cylinder (usually steel with a rubber coating) to transfer the ink (and therefore the image) from the gravure cylinder to the substrate. The use of a gravure cylinder (image cylinder) and an impression cylinder makes this process a form of rotary printing, and the rubber surface of the impression cylinder allows the substrate to be pressed firmly into the cells to ensure that the ink is transferred successfully onto the substrate.