Offset printing (offset lithography) is a common printing technique in which the inked image is transferred (or "offset") from a plate to a rubber blanket and then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier. Ink rollers transfer ink to the image areas of the image carrier, while a water roller applies a water-based film to the non-image areas.
Details about the process
The offset printing process relies on planographic principles, where both printing and non-printing elements exist on the same level but differ in their physicochemical properties. An offset press, typically equipped with a plate cylinder and an offset cylinder, is used to execute the printing process. The plate cylinder holds the printing plate containing the desired elements. As the plate cylinder rotates, the image is transferred to the intermediate cylinder, which then imprints the image onto the substrate.
Advantages of offset printing compared to other printing methods include:
- Consistent high image quality. Offset printing produces sharp and clean images and type more easily than, for example, letterpress printing; this is because the rubber blanket conforms to the texture of the printing surface.
- Quick and easy production of printing plates.
- Longer printing plate life than on direct presses because there is no direct contact between the plate and the printing surface. Properly developed plates used with optimized inks and fountain solution may achieve run lengths of more than a million impressions.
- Cost. Offset printing is the cheapest method for producing high quality prints in commercial printing quantities.
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