One, lithographic ink and water balance We all know that lithography is based on the basic principle of immiscible oil and water (except waterless offset printing), in which the blank part first adsorbs water to resist the ink. Then, the image part is adsorbed by ink to form lithographic printing. Therefore, controlling the layout ink balance is a key issue in lithography, which is directly related to the operation: the intrinsic quality of the process and the product. What is the balance between ink and water? The concept of motionlessness 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 reality this is impossible. Since oil/water incompatibility is only relative, under certain conditions, for example, in the stirring action of force and the action of surfactant, oil and water will dissolve into an emulsion. The lithographic process of transporting water and ink, the ink and the fountain solution are always in a force squeezing action factory. The ink application roller and the water film of the blank part of the printing plate are mutually squeezed, so that the ink on the ink roller contains - constant moisture. . The water roller and the graphic part of the printing plate press each other, so that the ink layer of the printing plate graphic part also contains - fixed moisture. The more blank parts of the print and the greater the amount of water applied to the roller, the more water is squeezed into the ink. In addition, there are also many surface active substances in fountain solution and ink. It can be seen that ink emulsification in lithography is unavoidable. The problem is how to control the size of the emulsification value and the stability of the emulsification value. The ink balance of the lithographic printing should be understood as the adjustment of various factors. In the blank part of the printing plate, the minimum amount of water is used to compete with the ink to form a microscopic emulsified ink, and the emulsification value of the ink is stabilized. The ink on the layout is less, and the water content is less; the layout ink is also more moisture. Only in this way can a slightly stable emulsion ink be formed. It is difficult to measure the slight emulsification value in actual production, but one point is obvious: the larger the emulsification value, the greater the disadvantages. For example, network outlets have been severely expanded, stencils, inks are not stable, the back of the product is dirty, and the prints are not easily dried. Second, the ink balance control In the printing process, controlling the ink-water balance is related to many aspects. For example: the ratio of the amount of ink and water adjustment, the nature of the fountain solution itself, the concentration and temperature of the fountain solution, the nature of the ink itself, the ink roller pressure, the ambient temperature and humidity, and the like. In old-fashioned machines, the control of these aspects is basically based on feelings. Based on experience, there are many variables that exist. In actual printing, it is easier to find if there is less water. Because the layout of water to a certain extent, the layout will be dirty. Therefore, ink and water imbalance occurs, and most of the water is too large. If it is not adjusted in time, it will cause serious emulsification of the ink. For the first two years, workers at a printing plant said that their desktop machines (old-fashioned machines) printed and approved products. The entire layout (four-way) was only about 20 black letters of the first size. They had adjusted the amount of ink and ink to a minimum ( The fountain roller and the ink fountain roller have almost stopped), but when printed over 2000 sheets, the ink is severely emulsified, causing the back of the printed sheet to be seriously dirty. Indiscriminately, we could only wash the ink roller and re-energize the ink. However, the underlying problem has not been solved. More than 2,000 pieces of old and new problems have appeared again and again. Analyze the reasons, on the one hand, they have not adjusted the ink-water balance in this case. On the other hand, the objective condition is also very important. Modern offset presses, even if the ink and ink pathways are set to separate states, the actual situation is also very different. Compared with the Heidelberg CP2000 offset press water delivery system using the old offset press, there are many differences: 1. The dampening system of the Heidelberg CP2000 offset press uses a continuous water supply. The hopper roller and metering roller are independent drive components. The amount of water supply can be adjusted by the bucket roller and the metering roller, and the gap size of the metering roller can also be adjusted. 2. This machine generally uses alcohol fountain solution. The alcohol fountain solution has a relatively low surface tension and good spreadability. A small amount of water in the blank portion of the printing plate can form a uniform water film, which greatly reduces the amount of water supplied to the plate surface. only- 3. The machine is equipped with a rotary fluid circulation (which must be equipped with alcohol fountain solution) and an automatic control system. Can strictly control the alcohol concentration, the concentration of the original solution, and the temperature of the fountain solution, thereby controlling the surface tension and pH of the fountain solution. 4. With respect to each ink zone, the dampening system is provided with an axial blow which can quickly volatilize excess dampening fluid in a certain area. 5. The machine's ink roller is equipped with a circulating fluid that can control the temperature, so as to achieve the control of the ink temperature of the entire ink leveling system and reduce the change of the ink viscosity in the printing process. 6. Equipped with a powerful CP console, which can pre-fall, fine-tune the amount of ink; pre-run dampening fluid, dampening and set tracking dampening, set the ink volume and speed characteristics, and so on. These factors are directly related to the issue of ink and water balance. Therefore, even if a modern offset press is set to separate ink and ink, conventional offset presses cannot match it. In other words, it is relatively easy for a modern offset press to control the ink-water balance. Third, the characteristics of ink and water roads As mentioned earlier, the ink balance of lithography is to form a slightly stable emulsified ink. If it is the separation of ink and ink, it will take a certain amount of time (inking) to achieve this balance. The more ink, the longer it usually takes. In other words, the ink is unstable during this period. If the ink path is set to communicate, - printing starts, and the first fountain roller feeds the plate, which is an emulsified ink. If all factors affecting the balance of water and ink have been effectively controlled, the ink balance can be reached within a relatively short number of prints and remain stable, so that the product ink is faster and uniform. Further analysis, the use of alcohol fountain solution, the water film on the water roller can be very thin. Therefore, while the water roller transfers water to the blank part of the printing plate, the ink of the printing plate graphic part is also transmitted to the water roller more or less. If the ink channels are in communication, a considerable part of the ink delivered to the water roller is returned to the ink roller. The more ink on the layout, the more ink is returned to the ink roller. In the middle of printing, if the machine is idle for some reason and then printed, it is not easy to cause the first few sheets of ink to be particularly dark, or to make the ink relatively normal. However, if you set up the separation of ink and ink, the situation will be different. As the machine is running idle, the ink layer's ink layer thickness redistributes quickly and the ink layer thickness increases. After imprinting, the ink delivered to the printing plate suddenly increased, especially for products with a large amount of ink. There are usually two cases: one situation is that there is more water on the water roller, and the ink on the printing plate cannot be transmitted to the water roller basically. Therefore, the thickness of the ink layer on the ink roller will return to normal, and the ink on the ink sheet will be Return to normal (specific number of sheets related to ink path design). In the second case, the water on the roller is less, and the ink on the plate is partially transmitted to the roller. If the ink roller pressure is relatively correct, the ink balance control is better, and the ink on the water roller will slowly be taken away again by the printing plate—partially stabilizing the ink color. If the ink roller pressure is not proper and the ink balance is not satisfactory, the ink on the water roller will form a “dead inkâ€, and the more the ink is accumulated, the more time it is necessary to shut down, and then the ink on the water roller is turned on. Observe some manufacturers of four-color machine, if it is set to the state of ink and water separation, mostly the first case, that is more water on the water roller, the water roller is basically not ink.
Rooted with a water roller, there is no need for a water roller flannel cover.