Gravure Printing - What is gravure printing?
Definition of 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.
Gravure printing requires the use of low viscosity liquid inks, which are made up of a pigment (for colour), a binder (for adhesion and finish), and a solvent (as the vehicle, which evaporates as the ink dries). The quality of the print is often determined by the viscosity of the ink and the dimensions of the cells on the gravure cylinder; the cell dimensions (whether uniform or variable) determine how much ink those cells can hold, which in turn determines the range and intensity of colours that can be produced (the more ink a cell can hold, the better the density of colour). Gravure printing is capable of producing full colour prints; it usually uses the four process colours (cyan, magenta, yellow, and black) to mix the colours that are required, with each of the four process colours having its own unit, including its own gravure cylinder, ink fountain, doctor blade, impression roller, and dryer. The process can also use specific spot colours that may be needed to produce fine art prints, such as metallic or fluorescent inks.
This process dates back to the late 19th century but remains a popular method for high volume commercial printing jobs, including magazines, catalogues, packaging, postcards, wallpaper, and laminates. Gravure printing is mostly web fed, but can also be a sheet fed process, which is usually chosen for the production of printing proofs, fine art posters and prints, and some packaging items such as cartons.
It is capable of processing a wide range of substrates (including thin flexible films of polyester, polyethylene, polypropylene, and vinyl), and the gravure cylinders are extremely durable, which means they can be used for high volume jobs over a longer period of time, which reduces production costs. However, the high start up costs (particularly when printing in colour, which requires one cylinder per colour) mean that the process is highly unsuitable for small volume jobs, and, while the process is capable of high quality print, it doesn’t produce as clean a print as other methods (such as lithographic printing) because the image is created using cells; the image is effectively a pattern of dots, which tend to be visible to the naked eye.Go Back to Glossary