Fast, cheap and top quality: Offset Printing

In the printing industry, offset printing has become the most widespread printing process, especially for classic paper products and long runs. In this way, magazines, leaflets or flyers can not only be produced quickly but also cheaply.

In principle, offset printing is a further development of lithography that emerged at the end of the 18th century. Thereby, printing forms were made from stone, which served as a template, more or less a stamp. Initially in relief and gravure printing, later also in planographic printing. This is based on the specific properties of water and fat, which repel each other. In this way, printing and non-printing elements could be placed on one level and the processing of the stone was less time-consuming. Because the ink only adhered to areas that were covered with a lipophilic (fat-friendly) layer, while the areas that were not to be printed were moistened with water. This principle was continuously developed and finally led at the beginning of the 20th century to the offset printing process as we know and use it today.

High pressure

• Printing areas are raised.
• Ink roller colors raised areas.
• Raised areas transfer the color to the paper.

Gravure

• Printing areas are lower.
• The entire printing form is colored.
• Squeegee removes excess ink from raised areas.
• Color only remains in recessed areas.
• Paper soaks up ink from recessed areas.

Flat printing

• Printing and non-printing areas are on the same level.
• Basic principle: water and fat repel each other.
• Paint only sticks to grease-friendly areas.
• Fat-friendly areas transfer ink to the paper.

The printing process

The basic principle of lipophilic (grease-friendly) and hydrophilic (water-friendly) areas on the printing form has remained, but materials and technology have changed over the decades. Today, printing plates made of aluminum are usually used, which are coated with a lipophilic photopolymer layer. After exposure and development, parts of this layer are left that will eventually take up the fat-based colors. The plate with the correct side motifs is stretched on a rotating cylinder in the printing unit and wetted with water and ink with every rotation. In terms of repulsion, the non-printing, water-friendly areas on the printing plate run color-free. The print image now available is transferred to a rubber blanket that is fixed to a cylinder below. Here the motif is reversed like a stamp and is ultimately transferred back to the sheet of paper with the correct side. Because of this intermediate step over the rubber blanket, offset printing is also referred to as an indirect flat printing process.

An offset printing machine usually has four printing units. Accordingly, four printing plates are exposed, which absorb the individual colors (black, cyan, magenta, and yellow) and which make up the final print motif. Special and spot colors each have their own printing unit, which can be retrofitted.