How Does offset Printing work

WHAT IS OFFSET PRINTING

Offset printing is a common printing technique in which the inked image is transferred from a plate to a rubber blanket and then to the printing surface. Offset printing is also called Lithography.

Lithography is a method of mass-production printing in which the images on metal plates are transferred.

An offset printer includes three cylinders

  1. Plate cylinder
  2. Offset blanket cylinder
  3. Impression Cylinder

In offset lithography works on the principle of oil and water separation. the plates have been treated to make image areas attract ink and non-image areas attracts water to repel the ink. When water and ink are applied by the rollers to the plate, the oil based ink sticks to the image while water sticking to the non-image area repels it.

Some offset printing presses use four basic ink colours. cyan, Magenta, yellow and black. Each colour is applied separately, one plate per one colour.

HOW TO START AN OFFSET PRINTING RUN

Before starting a new print run, the printing plates must be replaced and a number of pages are printed to check if the quality is optimal. this is called the “make ready time” which can last up to 15 minutes depending on the complexity of the printing job. if you are printing on a single-colour press, you must completely clean the ink systems first before printing another colour.

To start the ”make ready process the image plates are clamped onto the plate cylinders and the settings are adjusted for ink density. an initial batch of sheets is printed at a low speed and the colour registration as well as the ink/water balance inspected.

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