Sheet-fed offset press illustrating the research progress of ink transfer

This paper mainly describes the experimental study of ink transfer through a sheet-fed offset press and how scientific research methods are applied to current research. Industry-oriented scientific research goals are to find the most up-to-date methods for solving problems in the system. In the new industry development framework, it is to increase technological capabilities and increase production capacity; it is also to save experimental time and costs through intensive theoretical discussions and research. To achieve a high degree of automation in the printing industry and increase economic efficiency.

At present, the printing quality and production capacity required by an offset press require high accuracy and high reliability. The maximum error of the ink layer thickness during printing is approximately 0.05 μm, or the deviation of the color image position of the color image. The maximum distance error of a color separation image from the edge of another color separation image is 0.02 mm. This is a technically acceptable range for general printing conditions and corresponding printing parameters.

Such requirements can only be met through intensive research on the core process of offset printing, which in turn promotes the development and production of the printing press. The complexity of the printing process and printing press requires the help of a large amount of scientific research.

In addition to the discovery of research activities from non-specialty printing machinery for printing press engineering, there are also special printing press research activities conducted by printers and printing equipment system manufacturers and many research institutes around the world. Companies and research institutes have also participated in joint research projects. These research projects are mainly aimed at basic research, improvement of production capacity and further development.

There are commonly used tools and methods for these experiments and theoretical explorations in research activities, as well as the development of new tools and the development of further research methods. This article mainly introduces scientific experimental research of ink transfer.

Design and Calculation of Ink Transfer System

1. Ink transfer system design

The ink transfer system for offset printing transfers ink from the ink fountain to the printing plate, forming a thin layer of ink on the printing plate. It is apparent that the amount of ink transferred depends on the image to be printed, and the number of inks in the transverse direction to be printed varies due to the difference in the printed image. For this reason, ink control is generally performed in zones. Due to the precise requirements of the thickness of the ink layer and the prevention of diffusion effects, the design of the ink delivery system is one of the technically extremely difficult to solve and more complex components of the printing press.

The development of each type of offset press depends mainly on the design of the ink transfer system. The ink transfer system must be able to best meet the following requirements:

a, a highly uniform ink layer in the longitudinal and transverse directions of the printed paper;

b, rapid adjustment, sensitive response;

c. The separation between the thin layers of the ink in each separation image is small, that is, the low sensitivity to the effect of splitting (for example, changes in temperature and humidity);

d, there is a wide range of control variables for the amount of ink and wetting fluid;

e, economic benefits, etc.

The parameters for designing the ink roller are mainly material, diameter, arrangement and movement, and the number of ink rollers. In the process of optimizing the development, time, and cost of the ink transfer system, most of the mechanisms adopted by the ink transfer system in the conventional design are based on empirical and experimental methods. Therefore, through the systematic investigation of the ink transfer process of the ink transfer system, the purpose is to establish its theoretical basis and in order to accurately design the ink transfer system in most cases. In the early days, someone was already looking for the regularity of the ink transfer system.

2. Calculation and simulation methods

In 1960, Mill first proposed a method for calculating the ink layer thickness in ink transfer systems. A balance system was established by establishing a balance equation for the amount of ink at each ink outlet. In this system, the ink layer thickness is unknown. In order to determine the ink layer thickness for the geometric parameters of the ink transfer system, Ruder proposed a precise and simple method.

Under Ruder's proposed two algorithms, only the average ink thickness can be calculated. It is impossible to calculate the inclination of the ink layer thickness in the circumferential direction of the ink roller and the printing plate. In 1971, this problem was first proposed by Rech and solved by computer.

For this calculation based on the angle increase method, all the ink roller and drum circumferences are divided into the same size zones. The thickness of the ink layer at each ink outlet is obtained by establishing equations and solving equations. Based on this algorithm, a further calculation method has come into being. It takes into account more and more parameters of the ink transfer system, so that it should be able to better approximate the actual thickness of the ink layer. In finding and simulating calculations that are as close as possible to the actual situation, it is crucial to determine the regularity, legitimacy, and ink transfer parameters.

The NKTEAM simulation program proposed by Patzelt and Ruder in the FGD research project reflects the latest developments in technology. It mainly considers the following parameters:

a, geometric parameters of the ink transfer system; b. Continuous or intermittent ink transfer; c, transfer of ink in circumferential and transverse directions; d, transfer and evaporation of wetting fluid; e, temperature; f. Horizontal partitioning; g, ink absorption.

INKTEAM ink transfer system is a simulation system. In the beginning, the ink transfer system is empty, the ink is separated, the ink is transferred throughout the ink transfer system, and each simulation calculation project recalculates the printing equipment until the ink layer thickness in the transverse direction of the print sheet no longer changes, that is, until Achieve stable conditions. From the calculated thickness curve of the ink layer, it can be seen that it is tested with two ink transfer systems in the length direction of the print sheet.

In the first case, all ink rollers and water rollers contacted the plate cylinder one after another, and the consistency between the simulation and the test was not satisfactory. This can be attributed to the interaction between many of the parameters considered and the accuracy of their settings. Simply changing the percentage of the percentage of factors that affect ink splitting can lead to completely different results.

In the second case, the ink and the wetting fluid are passed through the wetting roller and transferred to the plate cylinder at the same time. This produces a good effect. In other words, there are actually three ink rollers that are idle and wetting the system and the ink roller. The bridge between the wetting roller and the ink is delivered.

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 measurement systems require 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)
Two 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.

Source: HC Security Business Network