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Offset printing

Offset printing
Today, offset printing is the most common method of printing large runs (over several thousand copies). Its principle of operation includes several stages of image transfer, a traditional method with exposure of the image from film to plaque or more modern - directly from a file. The final transfer of the image on the paper is done by means of an intermediate rubber offset cylinder (in English: offset). When combined with the lithographic process of forming the image for printing, it also includes a flat carrier, which is inked only in the parts to be printed. This medium is called a printing plate or plate - most often a plate with a photosensitive coating (as a rule, the plates are made of aluminum alloys). [1] [2]
The technology thus described is for one color ink only. For a multicolor image, two methods are used - either repeat printing separately for each color, or printing with a multicolor printing machine. Both methods are based on the decomposition of each color used into several color components, such as CMYK. A set of printed forms is prepared for each color page, and the image on each of them corresponds to one of the composite colors of the CMYK system. These plates are either loaded one by one in a machine with one set of shafts, or simultaneously with the corresponding shaft in the multi-color machine. The most common types of multi-color machines have their own names: two-color, three-color, etc. Various control systems based on densitometry, colorimetry and color sampling are used to ensure quality color in printing.

There are two types of offset printing machines:

sheet-fed offset printing - separate sheets of paper are fed into the machine, and they can be pre-cut in their final form or cut later
web offset printing - these are larger and faster machines. They are fed with large rolls of paper and the individual pages are separated and shaped afterwards. They are used for large circulations and printing of newspapers [3]