Web offset printing or just simply “offset printing” is a commonly used printing technique in which the inked image is transferred (or “offset”) from a plate to a rubber blanket, and then to the printing surface (usually paper). The modern “web” process uses a large roll / reel of paper that feeds through a large printing press which continually prints as the paper is fed through. When using individual sheets of paper this process is called sheet fed offset printing.
The Steps in the Offset Printing Process
- The ink duct roller delivers ink from the ink duct to the ink pyramid, also called the Ink Train.
- The ductor roller, sometimes called a vibrator roller due to its rapid back and forth motion, transfers ink from the duct roller to the first distribution roller. It is never in contact with both rollers at the same time.
- The distribution rollers evenly distribute the ink. The first distribution roller picks up the ink from driving rollers, and the last distribution rollers transfer the ink to the form rollers.
- The transfer rollers transfer ink between the ink-absorbing and ink-delivering driving rollers.
- Driving rollers roll against the distribution rollers and either absorb or deliver ink, depending on their placement.
- Ink form rollers transfer ink from the last distribution rollers on to the printing plate.
- The printing plate transfers the ink to the offset cylinder (typically called the blanket cylinder) usually covered with a rubber “blanket.”
- The paper is then pressed against the blanket cylinder by the impression cylinder, transferring the ink onto the paper to form the printed image.
Want to learn more? Visit HowStuffWorks.com to see the process from start to finish.