Tuesday, 28 September 2010

Lithography (Rotary Printing - Litho - Planographic)

Lithographic printing is well suited for printing both text and illustrations in short to medium length runs of up to 1,000,000 impressions. Typical products printed with offset printing processes include:

General commercial printing Quick printing
Newspapers Books
Business Forms Financial and Legal Documents
Offset Lithographic Printing Process Overview

Lithography is an "offset" printing technique. Ink is not applied directly from the printing plate (or cylinder) to the substrate as it is in gravure, flexography and letterpress. Ink is applied to the printing plate to form the "image" (such as text or artwork to be printed) and then transferred or "offset to a rubber "blanket". The image on the blanket is then transferred to the substrate (typically paper or paperboard) to produce the printed product.

Sheet Fed:
In sheet-fed offset, “the printing is carried out on single sheets of paper as they are fed to the press one at a time.” Sheet-fed presses use mechanical registration to relate each sheet to one another to ensure that they are reproduced with the same imagery in the same position on every sheet running through the press.

Web fed:
A high run, speed printing press that uses rolls of paper rather than individual sheets.

Web Offset Perfector Presses are beneficial in long run printing jobs, typically press runs that exceed 10 or 20 thousand impressions. Speed is a huge factor when considering turn around time for press production; some web presses print at speeds of 3,000 feet per minute or faster. In addition to the benefits of speed and possible faster turn around times, some web presses have the inline ability to print, but also cut, perforate, and fold. Web offset perfector presses uses roll-fed paper and blanket to blanket method. The delivery system includes an oven that cooks the inks for higher speed (preventing ink offset), and then folds and trim the book. A book on a Web press is usually made-up of 16 or 32 pages depending on the size of the press.

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