Process of Letterpress Printing
Letterpress printing is the oldest form of press printing in the world. Letterpress has become an atypical method of printing, having been replaced in large part by faster and cheaper printing methods such as offset and flexographic printing. It is still available in many specialty printing shops and is used for a variety of purposes including business cards, letterheads and embossing. The letterpress process uses relief printing plates. On relief plates, the image is a raised surface. Historically, these plates were cast out of metal, but have been largely replaced with photopolymer material plates due to lower expense and reduction of chemical byproducts. There are three methods of letterpress printing: rotary, platen and flatbed.
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Rotary
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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.
Platen
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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.
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Flatbed
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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.
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