According to Peter Schottland’s presentation, the main commercial printing technologies used for producing flexible packaging are rotogravure and flexography.
To provide a brief review of these processes, unlike offset lithography rorogravure does not use plates. Instead, the text and images of a page or package are engraved directly into the rotogravure cylinder using lasers, diamond-tipped tools, or chemicals. The deeper the wells engraved on the cylinder (with images, solids, screens, and type composed of dots), the darker the ink. The ink from the ink fountain fills the wells as the rotary press cylinder turns. Then a doctor blade removes the excess ink. Then the rotating rotogravure cylinder makes contact with the web of paper (a roll, not sheets) and deposits the ink on the substrate. Heat dries the ink before the paper enters the next color unit.
As you can see, the process involves a direct deposit of ink, unlike offset lithography (in which the image is transferred from the plate to the blanket to the printed substrate). Also, this is an intaglio process (as opposed to a relief process), since the ink wells are recessed into the rotogravure cylinder.
Rotogravure is a good choice for flexible packaging because it maintains exceptional quality over exceptionally long press runs (millions of images, for instance). In addition, it will allow for custom printing on webs of foil, film, or paper. According to Wikipedia, rotogravure has the “ability to print on thin films such as polyester, OPP, nylon, and PE, which come in a wide range of thicknesses, commonly 10 to 30 micrometers.”