The Offset Lithographic Process

In this section, we discuss the steps involved in the offset lithography process. 

The press run comprises the set of operations that are used to print the information contained on the printing plate on paper. These operations are highly automated and begin with a huge roll of paper that is fed through hanks of rollers. The paper is fed through the press as one continuous stream pulled from the rolls of paper. Each roller adds one color at a time. Some of these operations are briefly described below. 

In the inking step, the plates are first dampened by water rollers, followed by ink rollers, which distribute the ink from the ink fountain onto the plates. The image areas of the plate absorb ink from the ink rollers, while the water rollers keep the ink off the nonimage areas of the plate through sheer repulsion between the ink and water. With the image and nonimage areas of the plate now fuUy defined. 

Color control is achieved through the blending of the ink and is coordinated with plate registration. The image quality is determined by the amount of ink released into the ink rollers, which in turn is adjusted via the control panel, a part of the overall control console. Before being placed on the press, the plates are scanned and the data transferred to a microcassette, which serves as the master that directs the release of ink to preset values. 

The printing process is completed at the bindery, where the huge rolls of now-printed paper are cut and put together so that the pages fall in the correct order in which they are to be bound, stapled, or glued. 

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