Rotary Letterpress Printing
Rotary letterpress printing is commonly employed for the production of newspapers and magazines. Rotary letterpress machines require a curved printing plate that can be affixed to cylinder. Ink is fed and applied to roller from an ink tray. This roller may feed ink onto secondary metering rollers or may apply ink directly onto the printing plate. It is common for the roller that applies ink to the plate to be scraped to avoid excess inking, which can ruin the print. The paper is pressed against the print plate by another cylinder, referred to as the impression cylinder, and the ink is transferred to the printable surface in use. Rotary presses can be either sheet-fed or have paper fed off a large roll called a web, referred to as web printing.
There are two types of rotary letterpresses, sheet-fed and web-fed. Web-fed rotary presses are the most popular type of letter press printing. Sheetfed rotary presses are also declining in use; in fact these sheetfed rotary presses are no longer manufactured in the U.S. Like all rotary presses, rotary letterpress requires curved image carrying plates. The most popular types of plates used are stereotype, electrotype, and molded plastic or rubber. When printing on coated papers, rotary presses use heat-set inks and are equipped with dryers, usually the high-velocity hot air type.
Web-fed rotary letterpress presses are used primarily for printing newspapers. These presses are designed to print both sides of the web simultaneously. Typically, they can print up to four pages across the web; however, some of the new presses can print up to six pages across a 90-inch web. Rotary letterpress is also used for long-run commercial, packaging, book, and magazine printing.
Platen-type Letterpress Printing
Platen letterpress printing is often used for announcements, letterheads and forms. On platen printing presses, the plate is fixed to a chase (a type of frame) and placed into the print bed. Paper is fed onto the platen, a flat surface that is opposite of the print bed. Ink is applied to the plate by a roller or rollers. The platen and bed are then closed together. Think of this like a clam shell being closed. The ink is transferred to the substrate (usually a paper product) and the process is complete.
A platen press is made up of two flat surfaces called the bed and the platen. The platen provides a smooth backing for the paper or other substrate that is to be printed. The raised plate (image to be printed) is locked onto a flat surface. The plate is inked, the substrate is then placed on another flat surface called the bed and pressed against the inked plate producing the impression.
The platen and bed carry both the paper and the type form. The press then opens and closes like a clam shell. Platen printing is typically used for short runs such as invitations, name cards, and stationary. Larger platen presses are used for die-cutting and embossing. Some platen presses are arranged with the bed and platen in the vertical plane.
The plate is inked with an inking roller that transfers ink from an inking plate to the image carrier. Ink is placed on the inking plate by an ink fountain roller. The platen style press has been widely used in printing small-town newspapers since the late 1800s. The printing area is usually limited to a maximum of 18 inches by 24 inches. These presses are also used to print letterhead, billheads, forms, posters, announcements, and many other types of printed products, as well as for imprinting, embossing, and hot-leaf stamping.
Flat-Bed Cylinder Letterpress Printing
Flatbed letterpress printing is a slow process and, as such, is rarely done in the United States. On flatbed printing presses, the plate is affixed in the same manner as on a platen press. The printing plate is inked by a roller. The impression cylinder pulls a sheet paper around it by way of small grippers that are attached to the cylinder. As the paper is pulled around the impression cylinder, the entire bed with the plate moves under the impression cylinder, transferring the ink to the substrate as it goes.
Flat-bed cylinder presses use either vertical or horizontal beds. The plate is locked to a bed which passes over an inking roller and then against the substrate. The substrate passes around an impression cylinder on its way from the feed stack to the delivery stack. Another way of describing this is that a single revolution of the cylinder moves over the bed while in a vertical position so that both the bed holding the substrate and cylinder move up and down in a reciprocating motion. Ink is supplied to the plate cylinder by an inking roller and an ink fountain. The presses can print either one or two-color impressions. Flat-bed cylinder presses, which operate in a manner similar to the platen press, will print stock as large as 42 inches by 56 inches.
Flat-bed cylinder presses operate very slowly, having a production rate of not more than 5,000 impressions per hour. As a result, much of the printing formerly done on this type of press is now done using rotary letterpress or lithography. The horizontal bed press, the slower of the two types of flat-bed cylinder press, is no longer manufactured in the United States.Example of letter press: