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Offset Process

di Antonio Abbate

Offset is a planographic process, that is the image and non-image areas are essentially on the same as the printing plate. In short the image areas are ink-receptive and non-image areas are ink-repellent.The basic principle of offset printing is simple: ink and water don't mix.The image area covered with ink is grease-receptive and the non-printing area is water-receptive. The offset process works by first transferring on image from an inked printing plate to an intermediate cylinder covered with a rubben blank and then to the substrate.Those the substrate picks is the impression of the image.Offset is used for a wide variety of printing jobs such as business form, newspaper, catalogues, books , encyclopedies and magazines.One of the reasons of its success is the possibility to print efficiently on coorse paper.Moreover the plate making process is simple and inexpensive.In plate making the ink.receptive images areas are generated on the water-receptive surface of the grained and anodized plate.This process is possible with presensitized plates or electrographic plates used in reprography and newspapers.The basic structure of an offset printing press consists of three cylinders revolving around their own axis.These cylinders are the plate cylinder, the blanket cylinder and the pressure cylinder.Moreover there are two distinguished groups of rolls which wet and ink each printed sheet.These rolls are called wetting rollers and the brayers and inking rollers.During every cycle, the plate meets the wetting rollers, then the brayers and the inking rollers.