Each of the primary colours; black, cyan (blue), magenta (red), and yellow has a separate plate. Even though you see many, colours in the finished product, only these four colours are used.
Ink is then distributed onto the plates through a series of rollers. On the press, the plates are dampened, first by water rollers, then ink rollers. The rollers distribute the ink from the ink fountain onto the plates.
The image area of the plate picks up ink from the ink rollers. The water rollers keep the ink off of the non-image areas of the plate. Each plate then transfers its image to a rubber blanket that in turn transfers the image to the paper. The plate itself does not actually touch the paper, thus the term "offset" lithography.
The paper is fed through the press as one continuous stream pulled from rolls of paper. A roll can weigh as much as 1 ton. The paper is cut to size after printing. Offset lithography can also be done with pre-cut paper in sheet-fed presses. Web presses print at very high speeds and use very large sheets of paper.
The paper is left slightly wet by all of the ink and water being applied. Obviously, there is a risk of the ink smudging. The smudging is avoided by having the paper pass through an oven. The paper is then run through a short series of large metal rollers that have refrigerated water flowing through them. These chill rollers cool the paper down instantly and set the ink into the paper. If this were not done, the ink would rub off on your fingers.
The bindery is where the printed product is completed. The huge rolls of now-printed paper are cut and put together so that the pages fall in the correct order.
At this stage if required pages are bound together, by staples or glue. A machine called a stitcher takes the folded printed paper and collates them together. Then stitches (staples) bind them together.
The final components in the stitcher machine are the knives, which trim the paper to the final delivered size. The product is then ready to be shipped to the end destination.
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By: Jamal Atcha
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