WHAT IS PLANOGRAPHIC PRINTING?
Planographic printing processes are based on the different properties of oil and water.
In planography, the printing and non-printing sections are practically on the same plane. The principle is a simple one: the printing (image) sections attract oil and grease, while the non-printing (non-image) sections, which are moistened with water, repel the greasy, oil-based ink. As a result, the ink only adheres to those parts of the plate that have been chemically pre-treated beforehand.
Planographic printing methods include lithography and offset printing, which developed out of lithography.
WHAT IS OFFSET PRINTING?
Offset printing is the most widely used planographic printing process.
The fields of application for this printing method range from book printing through to packaging printing. It is an indirect planography process, in which the printing plate and the print substrate do not come into contact with each other. The ink is transferred from the printing plate to the printing surface by means of a rubber cylinder (blanket).
In this process, the printing plate is first moistened by the dampening form rollers and then covered with ink by the inking form rollers. The ink sticks to the pre-treated printing areas where, for instance, the test should later be visible. No ink sticks to the other areas, which previous attracted water. In many cases the printing plate is made of aluminium, anodised to hold the dampening solution. The printing areas are created using a photopolymer (light-sensitive synthetic material).