Offset printing is a commonly used printing technique where the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. the offset technique employs utilises the the lithographic process based on the repulsion of oil and water . Here a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film. thus the ink does not appear on non printable areas.

Applications
applications include: newspapers, magazines, brochures, stationery, and books.computer to plate systems are used in modern offset presses instead of computer to film work flows.

Advantages:
-Consistent high image quality. Offset printing produces sharp and clean images and type more easily
-Longer printing plate life than on direct litho presses
-Quick and easy production of printing plates.


Types:
Photo offset:
It is the most common process and uses light-sensitive chemicals and photographic techniques to transfer images and type from original materials to printing plates.

Types of paper feed:
Sheet-fed litho:
individual sheets of paper or paperboard are fed into a press.

Web-fed litho:
rolls of paper supplied to the printing press.

for details, visit this link:
http://en.wikipediawiki/Offset_printing

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