Offset printing

How does offset printing work?

The process is also referred to as "indirect printing," as the ink is not transferred directly onto the substrate. Instead, the color is transferred from aluminum plates to a rubber cylinder before reaching the substrate. The printing process itself is automated. The main effort lies in the preparation, as the printing plates must be exposed and mounted. Additionally, the precise overlay of the color layers must be controlled before a print job is started.

The color transfer is based on the principle of repelling water and grease. The printing plate has areas that are to be printed and areas that are not to be printed. The printable areas absorb the greasy ink and repel water from the dampening system, while the non-printable areas absorb water and repel the ink. In this way, the ink can be transferred with extreme precision to the rubber cylinder before it reaches the substrate.

Colors in offset printing

The printed colors are represented using the primary colors (Cyan, Magenta, Yellow, Key). However, it is also possible to use special colors such as metallic and fluorescent colors. Each of these colors is processed by its own printing unit on the machine. The substrate passes through each of these printing units in succession. The ink is applied to the substrate in the form of halftone dots. This halftoning simulates a gradient that is not visible to the human eye. Only upon close inspection with a magnifying glass can the individual dots be seen. This method is similar to the principle of a screen, where the pixels create the illusion of a gradient depending on the halftoning.

How does an offset printing machine work?
The printing machine is divided into different sections. The first section is the feeder, where a pallet with the sheets to be printed is loaded. From here, the sheets begin their journey through the printing machine. The central elements are the printing cylinders, which are located immediately after the feeder. Each of these cylinders applies one of the four CMYK colors to the sheet. Since the cylinders are arranged linearly in the machine, the layering on the sheet occurs step by step. A sheet that has passed through the first cylinder is only printed with one color at that point. The combination of all color layers creates the desired print image.

After the printing cylinders, at the end of the machine, is the delivery section. Here, the fully printed sheets are stacked on a pallet. Once the pallet is full, it can be replaced with an empty one. At the end of the machine is also the control center. The machine operator has an overview of the entire machine and can control all processes electronically.

Offset printing with cylinders offers the significant advantage of printing large formats at high speed. Additionally, offset printing is known for its extremely consistent and uniform print quality.