How to improve product quality, reduce costs, speed up the book publishing cycle, and win the market is an urgent problem for enterprises to solve. Only through digitalization and standardization throughout the entire process of printing production, through hard work of internal skills, and strengthening of basic management, can we gain a firm foothold in competition with satisfactory quality and reasonable cost. Practice has proved that quality is not tested but produced, and through a standardized and standardized management model, controlling every link in production is a feasible way to stabilize quality. The establishment of standards in each link is the basis for stable quality. This article will discuss the data standardized operation settings of the Heidelberg Harris V-30 semi-commercial rotary machine based on the specific conditions of the equipment used by the author.
Water and ink balance control settings
In the printing process operation, whether the "water-ink balance" is mastered or not directly affects the quality of the product. To this end, to learn offset printing and do beautiful work, we must first fully understand the meaning of water-ink balance.
The water-ink balance of lithographic printing is a dynamic balance, that is: at a certain printing speed and printing pressure, the supply amount of the dampening liquid is adjusted so that the volume ratio of the dampening liquid contained in the emulsified ink is between 15% and 26% , To form a water-in-oil (W / O) emulsion ink, with the minimum water supply to compete with the amount of ink on the printing plate.
In the actual printing operation, many operators do not pay attention to the water-ink balance, but only realize the "water-ink balance" when serious emulsification occurs after printing for a period of time, causing the ink roller to de-ink, the print is sticky, and the ink color is dull and dull. The importance of control. Therefore, in order to control the "water and ink balance" of the V-30 eight-color rotary machine, we should proceed from the following aspects:
1. Selection of wetting fluid
The purpose of the wetting fluid of the offset printing press is mainly to form a water film that repels the ink in the blank part of the printing plate, resists the expansion of the ink in the graphic part to the blank part, and prevents the dirty version; The hydrophilic salt layer maintains the hydrophilicity of the blank part of the printing plate; reduces the surface temperature of the printing plate.
In theory, the wetting fluid of the rotary printing press should consist of pure water, fountain solution, and alcohol. The use of pure water can avoid the formation of algae on the walls of dampening pipes and block the transmission of dampening fluid. However, in actual production, due to the different production conditions and water quality of various manufacturers, the pH value, surface tension, hardness, temperature, ambient temperature and humidity, etc. should be considered when selecting the fountain solution, and a set of standard control data is set through experiments. To ensure the long-term stability of the wetting fluid in printing.
①pH value. The pH value is an indicator to measure the acidity and alkalinity of the wetting fluid. Wetting liquids with too low or too high pH values ​​are not suitable for wetting the printing plate. If it is too high, the cleaning ability of the plate is poor, and the blank part is easy to get dirty; if it is too low, the surface of the plate will be severely corroded, which may affect the ink. Pass and dry. In actual production, due to the consideration of changes in various factors, it is generally better to control it at 4.7 to 5.5. The pH value of the wetting liquid is mainly determined by the amount of the dampening solution added. If the amount is large, the pH value is low and the acidity is strong. Through actual measurement, using the factory tap water to control the concentration of the fountain solution is 4% to 5%, to ensure that the pH value is within the above range. At the same time, in the printing process, we must pay close attention to the pH value of the wetting fluid to eliminate the printing failures caused thereby.
②Surface tension. The alcohol dampening system adopted by V-30, in which the alcohol concentration determines the surface tension of the wetting fluid. Therefore, as long as the alcohol concentration is adjusted, the surface tension of the wetting fluid can be made close to the surface tension of the ink, which can meet the requirements of lithography. Here, the surface tension of alcohol (2.25 × 10-3N / m) is much smaller than that of water (7.28 × 10-1N / m). As shown in Figure 1, the surface tension of aqueous solution increases with the alcohol concentration. Significantly decreased, the curve was gentle after reaching a certain concentration, and was basically stable within the surface tension of the ink (3.0 ～ 3.6 × 10-2N / m). Actual measurement, using our tap water, at a conventional concentration of 4% to 5% of the fountain solution, take 8% to 11% of alcohol, the wetting liquid can spread well on the surface of the printing plate, and can achieve a satisfactory water-ink balance.
③ Hardness. In theory, pure fountain water is used to prepare fountain solution, and tap water is used in practical applications. The hardness value of different water quality is shown in Table 1. At this time, the hardness should not be too high, otherwise it may cause: rubber and ink roller crystallization, Increased plate wear. Therefore, it is best to choose the ideal water with a total hardness of 8 to 25 ° dH. In view of the existing water quality conditions of our factory, we can only use: pH value = 7.3 ~ 8.0, the total hardness is about 25 ° dH of high-hardness alkaline water, we have adopted an appropriate increase in the amount of fountain solution (5% ) To ensure that the pH value of the fountain solution meets the requirements, and at the same time pay attention to cleaning the water pipeline during maintenance to keep it clean and unobstructed.
④Wetting fluid temperature. In actual production, we control the temperature of the wetting fluid to about 10 ° C, which is helpful to reduce the surface temperature of the printing plate, reduce the evaporation of alcohol, reduce the amount of wetting fluid, and ultimately help control the water-ink balance.
⑤Environmental temperature and humidity. The control of environmental temperature and humidity is also very important. It must be ensured that the temperature of the workshop is controlled at 18 ° C to 25 ° C and the humidity is in the range of 50% to 70% to avoid excessive temperature. The amount used increases the cost, and the main thing is to affect the amount of water supply. Poor control of the water and ink balance will cause the printed product to be dirty. In summary, the data and standardized settings of V30 eight-color rotary wetting fluid are shown in Table 1:
project
pH value
Ideal hardness ° dH
Alcohol concentration%
Dampening solution concentration%
Workshop temperature ° C
Workshop humidity%
Wetting fluid temperature ° C
data
4.7 ～ 5.5
8 ～ 12
8 ～ 11
4 ～ 5
10
18 ～ 25
50 ～ 70
It is difficult to control the ink-water balance if the printing dampening fluid does not take the road of standardization and dataization. One will cause the emulsification of the ink to seriously affect the product quality and the effective performance of the equipment. The amount of fountain solution causes the pH value of the dampening solution to become unstable and increase the cost. More importantly, when there are quality and process problems, it is difficult to find the cause and apply the medicine. In this regard, we also have a lesson.
When the V-30 of our factory was just put into use, due to our insufficient understanding of the standardization and dataization of the dampening system, during daily printing, we did not pay attention to the determination of the pH value of the selected dampening solution. Rotating dampening solution is sufficient. The alcohol setting value is around 8%. The temperature of the water is often higher than 10 ° C. Due to the number of power outages and other factors, the cold water circulation system of the V-30 cannot work properly, resulting in water tank lubrication. The temperature of the wet liquid is often in the range of 30 ～ 40 ℃, which causes the total water volume to be controlled higher and higher during the printing process. As the amount of alcohol increases, the printed products often get dirty, and the ink fountain roller deinks, which affects the normal printing, not to mention the power of advanced equipment. In this case, on the one hand, we exchange and analyze the reasons with other relevant personnel, on the other hand, we look up the relevant information to find the panacea. The painful lessons let us bring the data and standardized control of the water tank dampening system to an important position. First, the original fountain solution with a pH value of 6 was changed to a rotary fountain solution with a pH value of 4.5. The amount of the fountain solution was 3%, the alcohol concentration was set to 11%, and the water temperature was adjusted. It is controlled below 10 ℃, and the pH value of the wetting fluid after preparation is about 5.5. Two high-power air conditioners and four exhaust fans are installed in the workshop to make the workshop's temperature and humidity reach the standard. After several years of implementing digital and standardized control of the water tank wetting fluid, we have made great progress in the control of water and ink balance, which has greatly benefited us.
2. Water roller pressure adjustment
The adjustment of the water roller is more critical, especially by the adjustment of the plate water roller and the string water roller, which requires moderate adjustment intensity. We have repeatedly tried to find that it is appropriate to set the plate water roller and the printing plate to have 6-7mm, and the water roller to have 5-6mm, and pay attention to the leveling of both ends, too large or too small are not conducive to the transmission of the wetting fluid, sometimes one end The balance state is good, but the water volume at the other end is large. At this time, if the water volume is reduced at the same time, the water and ink balance will be destroyed at one end due to the too small water volume, causing a dirty version. In short, the water roller is not leveled, and there will definitely be a state of large or small water, resulting in serious emulsification of the ink and the optimal state of water-ink balance.
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