Offset ink balance discussion - ink transfer (1)

In the printing process, the ink is transferred, transported and transferred to the surface of the printing material (Figure 5-7), always maintaining the ink transfer and transfer stability, evenness and amount, is to ensure the quality of the print.

The quality of ink transfer and transfer is not only related to the performance and accuracy of offset presses, but also related to the printability of paper inks, and also related to the design and implementation of printing processes.

Figure 5-7 Ink layout

Flow and distribution of ink between ink rollers

The ink between two inter-ink rollers is in a flowing state with respect to the ink roller (as shown in Fig. 5-8). An elastic roller and a rigid roller roll, and the outer edges of the two rollers form a two-way speaker. In the gap between the mouths, each layer of ink is accompanied by a layer of ink before the two rollers contact. After confluence, they enter the gap. After passing through the narrowest part of the gap, the ink is first pulled into filaments, and the ink is broken at one or more places. The ink adheres to the two rollers respectively, and a small part of the ink may be released to form an ink mist, which is the flow of the ink between the ink rollers.

Figure 5-8 Flow of ink between ink rollers

In the process of ink breakage (or ink layer splitting), the ability of the ink itself to prevent breakage is called stickiness, as described above. In drawing breakage, the work done to the ink is called splitting work.
Under normal printing and proper printing pressure, the ink separation between the ink rollers is in a stable state, that is, after the ink passes through the ink roller gap, the thickness of the ink layer distributed on each ink roller is the same, which is all before passing through the nip. The thickness of the ink layer (Figure 5-8) can be calculated from the distribution rule of the ink film thickness on the ink roller surface: the ink between each ink roller is a certain percentage, the ink roller The thinnest ink film, the closer the ink roller to the ink transfer roller, the thicker the ink film.

Figure 5-9 Thickness of ink conveyed by a pair of ink rollers

When the printing is interrupted (roller off pressure), the printing plate stops transferring ink to the surface of the printing material, and the stable state after the printing transition is destroyed. The ink system will enter a new stable state. The inks attached to all the ink rollers will be redistributed. At the same time, the several inks printed at the beginning of printing will be very dark, often waste, and generally need to print more than 10 sheets. In order to achieve the original stable state, the normal transfer of ink. Therefore, the number of printing stops should be reduced as much as possible during printing.