How to effectively improve the surface tension of dampening solution during printing
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What is the balance of ink and water? The concept of static is that the water in the blank part of the printing plate does not infiltrate the ink in the graphic part. But in reality this is impossible. Because the oil-water incompatibility is only relative, under certain conditions, for example, the agitation of the force and the action of the surfactant, the oil and water will dissolve into an emulsion. In the process of water transfer and inking of lithographic printing, the ink and dampening solution are always in the force extrusion process. The inking roller and the blank part of the printing plate are mutually squeezed, so that the ink on the inking roller contains water. . The water roller and the printing plate image portion are mutually squeezed, so that the ink layer in the graphic portion of the printing plate also contains water. The more blank parts of the print and the greater the amount of water on the water roller, the more water is squeezed into the ink. In addition, a variety of surface active substances are also present in fountain solutions and inks. It can be seen that ink emulsification in lithography is unavoidable, and the problem is how to control the size of the emulsification value and the stability of the emulsification value. Because the ink balance of lithographic printing should be understood as adjusting various factors, the minimum amount of water is used to compete with the ink in the blank portion of the printing plate to form a micro-emulsified ink, and the emulsified value of the ink is stabilized. The amount of ink on the plate is small, and the water content is small; This will result in a slightly stable emulsion ink. It is difficult to measure the actual emulsification value in actual production, but one thing is obvious: the larger the emulsification value, the more disadvantages it produces. For example, the outlets are seriously enlarged, the paste plate, the product color is unstable, the back of the product is dirty, and the print is not easy to dry.
Second, ink balance control
The printing process, controlling ink and water balance is related to many aspects. For example: the ratio of the amount of ink to the amount of water, 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 temperature and humidity of the environment, and the like. On old-fashioned machines, the control of these aspects is basically based on feelings. Based on experience, there are great variables. In actual printing, if the water is small, it is easier to find. Because the layout is so low that the water is too small, the layout will be dirty. Therefore, the imbalance of ink and ink occurs, and most of the water is too large. If it is not adjusted in time, it will cause serious emulsification of the ink. In the past two years, workers at a printing factory said that their machine (old-fashioned machine) printed-batch products had only about 20 black letters on the entire layout (four open), and they adjusted the amount of ink to a minimum ( The bucket roller and the ink fountain roller have almost stopped. However, when more than 2,000 sheets are printed, the ink is severely emulsified, causing the back of the sheet to be seriously viscous. It is only necessary to wash the ink roller and refill the new ink, but the fundamental problem has not been solved. After more than 2,000, the old problem is repeated. The reason for the analysis is that they did not adjust the ink-and-wash balance in this case. On the other hand, the conditions of objective existence are also very important. Modern offset presses, even if the ink path is set to a separate state, the actual situation is very different. There are many differences between the infusion system of the old-fashioned offset press and the Heidelberg CP2000 offset press water delivery system:
1. The dampening system of the Heidelberg CP2000 offset press is loaded with continuous water supply. The bucket roller and metering roller are a separate transmission component. The amount of water supply can be adjusted by the stepless speed of the water fountain roller and the metering roller, and the size of the water is adjusted by the gap between the water fountain roller and the metering roller.
2. This machine generally uses alcohol dampening solution. The surface tension of the alcohol dampening solution is relatively low, and the spreadability is good. 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. Only - with a water roller, no need to use a water-swept cloth cover.
3. The machine is equipped with a sputum circulation (which must be provided with alcohol fountain solution) and an automatic control system. The surface tension and pH of the fountain solution can be controlled by strictly controlling the alcohol concentration, the concentration of the stock solution, and the temperature of the fountain solution.
4. With respect to each ink zone, an axial blowing is provided in the dampening system to allow excess dampening fluid in a certain area to evaporate quickly.
5. The machine's inkjet roller is provided with a circulating fluid that can control the temperature to control the ink temperature of the entire ink distribution system and reduce the viscosity change of the ink during the printing process.
6. Equipped with a powerful CP console, which can pre-wet and fine-tune the ink volume; pre-damp the dampening solution, post-wet the plate, set the tracking dampening, set the ink volume and speed characteristic curve, and so on.
These factors are directly related to the problem of ink and water balance. Therefore, the modern offset printing machine, even if it is set to separate the ink path, the traditional offset printing machine can not be compared with it. That is to say, it is relatively easy for modern offset presses to control ink and water balance.
Third, the characteristics of the ink road
It has been mentioned above that the ink balance of lithography is to form a slightly stable emulsion ink. If the ink path is separated, it will take a certain amount of time (printing) to achieve this balance. The more the amount of ink, the longer it usually takes. That is to say, the ink color is unstable during this period. If the ink path is set to communicate, the printing is started, and the first ink roller is supplied with an emulsion ink. If the factors affecting the balance of ink and water have been effectively controlled, the ink balance can be reached and stabilized in a relatively short number of prints, so that the ink color of the product is uniform and uniform.
Further analysis, using an alcohol dampening solution, the water film on the toilet roll can be thin. Therefore, while the water roller transfers water to the blank portion of the printing plate, the ink of the printing plate portion is more or less transferred to the water roller. If the ink paths are connected, a considerable portion of the ink delivered to the water roller is returned to the ink roller. The more the amount of ink on the plate, the more ink is returned to the ink roller. In this way, if the machine is re-printed after a certain operation in the middle of printing, it is not easy to cause the ink of the first few sheets to be particularly dark, or to make the ink color relatively normal.
And if it is set to separate the ink path, the situation is different. Since the thickness of the ink layer of the ink roller is quickly redistributed while the machine is running empty, the thickness of the ink layer is increased. After embossing, the ink delivered to the printing plate suddenly increases, especially for products with a large amount of ink. There are usually two cases: one case is that the water roller has more moisture, and the ink on the printing plate cannot be basically transferred to the water roller, so the ink layer thickness on the ink roller is restored to normal, and the ink color on the printing sheet is only Return to normal (the number of sheets is related to the ink path design). No.: In both cases, the water on the water roller is less, and the ink on the plate is partially transferred to the water roller. If the pressure of the ink roller is relatively correct, the ink balance control is better, and the ink on the water roller is slowly taken away by the printing plate - part of which makes the ink color stable. If the ink roller pressure is not good and the ink balance is not ideal, the ink on the water roller will form "dead ink", and even more and more, sometimes have to stop, wash the ink on the water roller and then open. Observe the four-color machine of some manufacturers. If it is set to the state of separation of ink, most of them are the first case, that is, the water roller has more moisture, and the water roller is basically not inked.