Offset printing |
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Offset printing is also known as lithography or pantographic printing, when compared to relief printing the printing and non-printing surface areas of the plate, which is made of aluminium are almost on the same plane or level. Offset is an indirect printing process, during this process the ink is transferred from the printing plate to a rubber blanket and then set off onto the substrate, hence the name offset. The basic principle of offset printing is simple: ink and water do not mix. When the aluminium plate is exposed, an ink receptive coating is activated at the image area. On the press, the plate is dampened; first by water rollers, then by ink rollers, similar to a letterpress inking unit. The ink adheres to the image area and the water adheres to the non-image area. As the cylinders rotate, the image is transferred to the rubber blanket. The substrate passes between the blanket cylinder and the impression cylinder, where the image is applied onto the substrate.
Due to a well balanced ink-water-ratio the printing and non-printing areas are separated sharply, which allows a dot-for-dot reproduction. The resulting high resolution is important for vignetted halftone screens and very fine elements. |
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