Sheet Offset Press

Offset printing is an indirect print process. This means that in the print process a cylinder covered with a rubber blanket is set up between the printing plate and the paper. This is so the printing ink is transferred indirectly on the printed sheet. This ensures an even print, so that the same quality can be produced in high print runs. Unlike the lithography printing process, offset printing processes are largely automated. Instead of stone, aluminum plates are used as the print template.

A sheetfed press consists of three main parts:

• The feeder and lay system

• The printing units

• The delivery system

• The control station

The feeder and lay system ensures that the sheets are fed into the press one by one in exactly the same position. The printing units each contain a plate cylinder plus ink and damping rollers, a blanket cylinder and the impression cylinder. Each unit prints a single color on only one side of the paper. In the video we saw, they have 5 color press which can print both sides of the paper in one pass by means of a perfecting cylinder, which re-aligns the paper for the second side. After that the delivery system receives the sheets from the press and stacks them in a pile on the delivery board. But during the printing process, the press operator takes some sample sheets from the press and checks them at the control station. Before the print run start in this 5 color press, we need to set up the ink. Once the ink is set up, the plates are mounted on each color unit, either by hand or automatically. Extreme care is needed because even small scratches on the plates would be visible in the printed image.