The difference and function of the setting of the

The difference and function of the setting of the intermediate roller on the multi-color offset press

first, the water ink balance of lithography

we all know that lithography uses the basic principle of oil-water immiscibility (except for water-free offset printing) to make the blank part absorb water first on the printing plate plane to resist oil ink. Then make the graphic part absorb ink to form lithography. Therefore, controlling the ink and water balance of the layout is a key issue in lithography, which is directly related to the operation: the internal quality of the process and products

what is ink balance? The concept of stillness is that the water in the blank part of the printing plate and the ink in the graphic part do not infiltrate each other. But in fact, this is impossible. Because the immiscibility of oil and water is only relative, under certain conditions, for example, under the action of force stirring and surfactant, oil and water will dissolve into emulsion. In the process of water and ink transmission of lithography, the ink and the fountain solution are always in the force extrusion plant. The inking roller and the water film of the blank part of the printing plate are mutually extruded, so that the ink on the inking roller contains fixed water. The water roller and the graphic part of the printing plate squeeze each other, so that the ink layer of the graphic part of the printing plate also contains fixed water. The more blank parts of the print and the more water on the water roller, the more water is squeezed into the ink. In addition, there are many kinds of surfactant in fountain solution and ink. It can be seen that ink emulsification is inevitable in lithography. The problem is how to control the emulsification value and first insert the probe into the maximum range to stabilize the emulsification value. The balance of water and ink in offset printing should be understood as adjusting various factors, using the minimum amount of water in the blank part of the printing plate to compete with the ink, forming a small diameter emulsion ink, and stabilizing the emulsion value of the ink. Less ink and less moisture in the layout; More ink and more water in the layout. In this way, a slightly stable emulsion ink can be formed. It is difficult to measure the slight emulsification value in actual production, but one thing is obvious: the greater the emulsification value, the greater the disadvantages. For example, the dot is seriously enlarged, the version is pasted, the ink color of the product is unstable, the back of the product is sticky and dirty, and the imprint is not easy to dry, etc

second, ink balance control

printing process, the control of ink balance is related to many aspects. For example, the adjustment ratio between ink volume and water volume, the nature of the fountain solution itself, the concentration and temperature of the fountain solution, the nature of the ink itself, the pressure of the ink roller, the ambient temperature and humidity, and so on. On the old machine, the control of these aspects is basically based on feeling and experience, and there are a lot of variable factors. In actual printing, it is easier to find out if there is less moisture. Because the water content of the layout is less than a certain degree, the layout will be dirty. Therefore, the ink imbalance occurs, mostly due to the large amount of water. If not adjusted in time, it will cause serious emulsification of ink. In the past two years, including those who used the single crystal form of hydroxyapatite for compounds with greater strength, workers in a printing plant said that their machine (old-fashioned machine) printed batch products, and the whole page (four open) had only about 20 bold characters of No. 1. They had adjusted the ink volume to the minimum (the water bucket roller and the ink bucket roller had almost stopped rotating), but when printing more than 2000 sheets, the ink was seriously emulsified, resulting in serious dirt on the back of the printing sheet. As a last resort, the ink roller can only be washed off and re inked, but the fundamental problem has not been solved. After more than 2000 copies, the old problems recur. Analysis of the reasons, on the one hand, they did not adjust the ink balance in this case. On the other hand, the objective conditions are also very important. Modern offset press, even if the ink path is set to separate state, the actual situation is very different. Comparing the water and ink delivery system of the old offset press with that of Heidelberg CP2000 offset press, there are many differences:

1. The dampening system of Heidelberg CP2000 offset press uses continuous water supply for loading. Bucket roll and metering roll are independent transmission components. The amount of water supply can be adjusted by the stepless speed of the bucket roll and the metering roll, and also by the gap between the bucket roll and the metering roll

2. this machine generally uses alcohol fountain solution. Alcohol fountain solution has low surface tension and good spreading property. A small amount of water in the blank part of the printing plate can form a uniform water film, which greatly reduces the water supply to the plate. Only

is rooted in the water roller, and there is no need to use the flannelette cover of the water roller

3. the machine is equipped with fountain solution circulation (which must be equipped when using alcohol fountain solution) and automatic control system. It can strictly control the alcohol concentration, stock solution concentration and the temperature of the fountain solution, so as to control the surface tension and pH value of the fountain solution

4. Relative to each ink area, there is an axial blowing in the fountain system, which can quickly volatilize the excess fountain solution in a certain area

5. The inking roller of this machine is equipped with circulating liquid with controllable temperature, so as to control the ink temperature of the whole inking system and reduce the change of ink viscosity in the printing process

6. equipped with a powerful CP console, which can pre fade and fine tune the ink volume; For the fountain solution, pre fountain, post fountain, set tracking fountain, set ink volume and speed characteristic curve, and so on

these factors are directly related to the balance of ink and water. Therefore, even if the modern offset press is set to separate the ink path, the traditional offset press cannot be compared with it. In other words, it is much easier for modern offset presses to control the ink balance

III. The characteristics of interlinked water and ink routes

as mentioned earlier, the water and ink balance of lithography is to form a slightly stable emulsion ink. If the ink road is separated, it takes a certain time (printing number) to achieve this balance. The more ink, the longer it usually takes. In other words, the ink color is unstable during this period. If the ink path is set to be connected and printing starts, the first inking roller supplies an emulsion ink to the printing plate. If all the factors affecting the ink balance have been effectively controlled, the ink balance can be reached and kept stable in a relatively short number of prints, so that the ink color of the product can reach uniformity and consistency quickly

further analysis, using alcohol fountain solution can make the water film on the water roller very thin. Therefore, while the water roller transmits water to the blank part of the printing plate, the ink of the graphic part of the printing plate is also transmitted to the water roller more or less. If the ink path is connected, a considerable part of the ink transferred to the water supply roller returns to the ink roller. The more ink in the layout, the more ink returned to the ink roller. If the machine is idled and reprinted in the printing process of these 45 year old samples, it is not easy to cause the ink color of the first few prints to be particularly dark, or it can make the ink color reach normal relatively quickly

if the ink path is set to separate, the situation is different. Because when the machine is idling, the ink layer thickness of the ink roller is quickly redistributed, and the ink layer thickness increases. After embossing, the ink transferred to the printing plate suddenly increases, especially for products with a large amount of ink. There are usually two situations: one is that there are more water on the water roller, and the ink on the printing plate can't be transferred to the water roller. Therefore, the ink color on the printing sheet can't return to normal until the ink layer thickness on the ink roller returns to normal (the specific number of sheets is related to the ink path design). Second, there is less water on the water roller, and the ink on the printing plate will be partially transferred to the water roller. If the pressure of the ink roller is correct and the ink balance is well controlled, the ink on the water roller will slowly seize the opportunity to stabilize the ink color by taking away the part of the printing plate. If the pressure of the ink roller is improper and the ink balance is not ideal, the ink on the water roller will form dead ink, and even gather more and more. Sometimes, you have to stop the machine and wash the ink on the water roller before opening it. Observe the four-color machine of some manufacturers. If it is set to the water ink separation state, it is mostly the first case, that is, there is more water on the water roller, and the water roller is basically not inked