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What is offset printing?

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Wiki User
2011-09-07 11:29:47

Offset printing replaced expensive and labor intensive raised

metal type in the printing process with a photographic based system

that uses a flat rubber mat to transfer an image onto paper. It was

the predominant system for commercial printing from about 1960 into

the beginning of the 21st century. It is currently losing ground to

digital computer based systems that rely on colored toners to

create an image. Offset printing works because of hydrophobia, oil

and water don't mix. A photographic image in created on a flat

metal printing plate that has a grainy surface that holds liquids

well. The 'image area' on that plate has a coating that is

receptive to oil-based printing inks while the uncoated areas tend

to accept water and repel ink. Roller systems on an offset press

supply measured amounts of ink and water to that plate allowing an

image to form on it's flat surface. Other rollers transfer the

image from the metal plate to a cylinder covered with a flat rubber

mat called a 'blanket.' Finally, paper is delivered past the

blanket cylinder and squeezed slightly against it by a third

'impression' cylinder. The ink transfers from the blanket to the

paper and you have printed! In offset printing, the colors and

appearance of the objects on all the printed materials are the

same. For example, not one color is lighter or darker compared to

the other copy. So this means that the finish printed products are

consistent.


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