Letterpress Printing

Letterpress print process is referred to as a "relief" process because the printed image is produced from a plate in which the image area is slightly raised above the non-image surface of the plate. It is a direct printing method as the inked plate applies the image directly to the material. Letterpress is one of the oldest printing processes and was the most widely used process until the middle of the 20th century when technology advances in other printing processes made it obsolete. Flexography, which is an updated version of letterpress, is now the dominant relief printing process.

The letterpress process uses an ink that is thick in consistency and is well suited for relief printing. A set of rollers spread the ink on the raised image area of the type or plate, but ink is not deposited on the non-image areas. For this reason, letterpress plates do not require any dampening in order to keep the non-image areas free of ink. This makes the process a simple one and allows for consistent results, but the process still cannot match the quality of more sophisticated print processes such as lithography or gravure.

Press Types

Platen Press: platen press use movable metal type that are locked into a frame called a chase. The chase is then placed in the press bed and it is also locked into position. During the printing process, grippers move a sheet of paper from the feedboard, which contains a stack of paper, to the platen, which is the surface where the print impression is made. A set of rollers applies ink to the type on the press bed and then the press bed and the platen are pressed together which produces the image on the paper. When the impression is complete, the platen and the press bed spread apart and the grippers remove the paper, placing it on a delivery tray.

Flatbed Cylinder Press: The type or plate is locked in a chase which is then mounted on the flatbed of the press. Grippers on a “rotating impression cylinder” pick up a sheet of paper and as the cylinder revolves, the paper is pulled around it. The inked flatbed containing the letterpress plate then moves under the impression cylinder. The squeeze between the impression cylinder and the flatbed creates the printed impression on the paper. When the impression is complete, the flatbed returns to its original position and is inked for the next impression.

Rotary Sheet-Fed Press: The plate is mounted on a cylinder where a roller system applies ink to the raised area of the plate. The paper passes between the plate cylinder and an impression cylinder where the resulting squeeze between the two cylinders produces the printed impression on the paper.

Rotary Web-Fed Press: The web-fed system also uses a plate cylinder and impression cylinder, but instead of individual sheets passing between the two cylinders, the paper is a continuous web unwound from a large roll. After printing, the web is cut into individual sheets. Web-fed presses are used for larger print runs. Like other printing processes, the letterpress web-fed press usually contains several printing units so that multiple colours can be printed.