The development of ink transfer through a sheet-fed offset press (Part 2)

In order to obtain accurate values ​​from the simulation as much as possible, it is necessary to consider all the influencing factors in the simulation model. In order to ensure this, it is necessary to do a lot of work to verify the simulation tools and adapt the simulation tools.

Jiang proposed a different simulation model. In the model, the ink transfer system is considered as a transfer system under control. Here, the supply of the ink represents the input signal, and the ink transferred to the photosensitive layer serves as an output signal. The split signal is the input of intermittent ink, the platen gap and the single print image. The complete ink transfer function of the ink transfer system consists of the independent transfer function of each pair of ink rollers. Simulations are performed in the frequency domain and ink transfer is a hysteresis factor. Due to changes in time and nonlinearity, recording the ink transferred to the plate is quite difficult and can only be calculated by simplified linearization.

When changing the supply of ink, the first model calculates the results of the response of the ink delivery system to time. In the lateral direction, the optimization of the average thickness of the ink layer is not possible.
Experimental Study of Ink Transfer

The regularity of ink transfer occupies a very important position in the design of the ink delivery system and the wetting system. Experimental studies in this field started early. Broetz and Hars obtained recent experimental results in two FGD research projects. In other studies, one of the goals of these research projects was to establish a simulation program for Patzelt and Ruder to determine the specific amount of ink split.

Experiments and independent studies have been conducted on all the relevant variables that have an influence on the amount of ink splitting, so that a complex set of experimental points is established. It includes a continuous-type ink delivery system with an ink roller driven by a cantilever bearing, control of ink temperature, printing equipment (print plate and impression cylinder), unwinding and rewinding equipment.

The measurement of ink layer thickness is extremely important and must be non-contact. In addition to the traditional instrument for measuring ink thickness, a measurement system established in the institution that is consistent with it is used to measure the ink layer thickness. Infrared is used in the operation of the ink thickness measurement instrument invented by FOGRA because the maximum absorption value of the wetting liquid and the ink overlap in the maximum range is expressed in this band. Due to the overlapping absorption spectrum of the wetting fluid and the ink in the largest range, the signal is completely separated. Absolute measurements of wetting fluid and ink layer thickness are only possible with precision scale dimensions. Since the measurement of the ink thickness gauge is only possible on the plate material, an additional roller is required to measure the thickness of the ink layer on the elastic ink roller. This has led to the development of the above-mentioned ink thickness sensor. The sensor uses visible light, but it can only be used without dampening fluid. Both measurements

The volume system needs calibration to determine the thickness of the ink layer by measurement.

All ink splitting factors. Or different ink layer splitting factor β is used as a parameter describing the ink transfer in accordance with the following equation:

Aij=s'j/(si+sj)
=s'j/(s'i+s'j)
Î’ij=(sj+sj)/(si-sj)
=(si- si')/(si-sj)
=W/(si- sj)
(aij is the total ink splitting factor, s is the thickness of the ink layer, βij is the difference in the ink layer splitting factor, and w is the thickness of the ink layer that was transferred)

The determination of most variable parameters requires experimentation, and it is more difficult to make a clear and comprehensive description of the results of the parameters. Thus, experiments and descriptions were performed with one parameter changed while the other parameters were unchanged.

Experiments have shown that there is an interdependence between the ink splitting frequencies on the ink splitting factor at a constant printing speed. In the case of experimental wetting fluids, the ink splitting factor was expected to increase faster than if no wetting fluid had been input.

Concluding remarks

The large number of parameters and methods described in the designed experiment are now applied more and more. By increasing the importance of these parameters and methods through multiple variables, it is allowed to reduce the number of experiments, that is, to change several variable parameters in each experiment. The ink thickness measurement instrument of FOGRA is a relatively advanced instrument in the world. It has practical value for the measurement of ink transfer transfer.

The experiments so far have led to a significant increase in the level of awareness of wetting fluid and ink transfer. However, a complete description of a set of formulae must consider all relevant parameters. This description is still not found.