Effect of improper proportion of alcohol-free dampening solution on printing
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In recent years, in the domestic alcohol-free fountain solution market, excellent brands have emerged, and the tolerance and compatibility have been greatly improved, and the practical application has become more and more extensive. Now we will briefly discuss several issues that need to be paid attention to during the application of alcohol-free dampening solution.
Alcohol-free dampening solution has the following common characteristics: lower surface tension, working fluid conductivity is controlled at about 1200μS, working fluid pH range is 4.5±0.5, crystal precipitation is not easy to occur, and water pipelines are not easily blocked. However, if the proportion is improperly added, it may affect the printing process and even hinder the normal production.
First, the proportion is too high
Although the alcohol-free fountain solution is not new, most captains are not yet proficient in the actual use. The water tank capacity of each machine is not fixed. The workshop does not have a container with a specific capacity to configure the working fluid. Moreover, the staff also The operation habit of using alcohol is retained, and it is added by feeling. "If you don't print it, you can add a cup"; therefore, the case of excessive alcohol-free dampening solution is too high. Although the pH buffer system is set in the formulation, when the addition ratio is too high, the buffer system fails, causing the pH of the working fluid to be too low. During the interview, the author repeatedly found that the pH of the working fluid reached 3 or even lower.
1.1 too low pH affects the printing durability of the printing plate
Excessive acidity will seriously affect the printing durability of the printing plate, causing the dot of the printing plate to fall off, and the sand in the blank area of the printing plate is seriously corroded, resulting in a pattern phenomenon. In addition, the parts such as the sink roll of the offset water circuit are made of a metal material, and the excessively acidic working liquid will corrode it after long-term immersion.
The standard method of alcohol-free use is to add the alcohol-free fountain solution to the water according to a certain ratio, prepare the working fluid, store it in a fixed container, and operate it by hand, and take it as needed.
1.2 too low pH affects printing quality
Too low pH of the working fluid will also increase the emulsification tendency of the ink, affecting the drying speed of the ordinary offset printing ink. When the special paper is encountered and the length of the machine is not adjusted in time, it is easy to cause the back of the printed product to be dirty and serious. Will cause the printed products to be scrapped. Therefore, the pH of the working fluid should be monitored in time to avoid economic losses.
1.3 Affecting ink and water balance
The formula of the alcohol-free dampening solution contains a chemical component such as a wetting agent instead of alcohol. When the addition ratio is too high, it is easy to cause ink path ink transmission obstacles, and the printing plate is poorly inked, which makes the printing ink color lighter and affects the printing. Work properly.
Second, the addition ratio is too low
If the proportion of alcohol-free dampening solution is too low, the acidity of the working fluid will be too weak, and the formation of the hydrophilic layer in the blank area of the printing plate will be slowed down. The inorganic salt layer in the blank area of the printing plate cannot be replenished in time, so that the hydrophilicity and oleophobicity of the blank area are reduced. Leading to the paste; in order to make the printing go on, the captain must raise the water level and increase the speed of the water supply motor, so the wear and failure rate of the water supply motor will inevitably increase.
Third, the temperature of the workshop changes
Due to seasonal changes, regional differences between North and South, and cost control, the temperature in the offset shop is difficult to stabilize at the theoretical value, and according to the author's experience in testing Fushilai® HD-31 free alcohol dampening solution on site, The temperature in the offset shop is also difficult to be constant during the day; these unstable factors inevitably affect the state of the working fluid, especially for alcohol-free fountain solutions.
In order to ensure the stability of the water supply system to the plate water supply, the working fluid must have a certain viscosity. When printing with alcohol, because the alcohol solution has a certain viscosity, it can ensure the stability of the water supply to the printing plate water supply, and the refrigeration effect will be generated as the alcohol volatilizes, which is beneficial to the cooling of the plate surface, ensuring the water level stability and the smooth printing; In the case of alcohol-free dampening solution, there is no alcohol in the working fluid at this time. If the heat of the plate cannot be dissipated in time, the temperature of the plate will increase, the moisture of the plate will evaporate too quickly, and the machine will heat up. If the ambient temperature rises and there is no refrigeration effect caused by alcohol volatilization, if the water tank cooling effect is poor, the water temperature of the water tank cannot be stably maintained at 10 °C, and the water temperature of the water tank rises faster, further causing obstacles to water supply and water shortage. Serious, the situation of paste and water level is inevitable.
Therefore, for users who use alcohol-free fountain solutions, it is especially important to strictly control the ambient temperature of the workshop and the water temperature of the tank. Although, Fresnel® HD-31 Free Alcohol dampening solution optimizes the formula to minimize the water level from the perspective of the formulation and reduce the adverse effect of the shop temperature on the printing, but strictly control the addition ratio to avoid the proportional misalignment and strict control. Water tank water temperature and other requirements are also essential.
For paper, ink and plate, alcohol-free fountain solutions are insignificant, but they are responsible and can have a huge impact on print quality. Printed material service providers and workshop production personnel should study hard at work, pay enough attention, adapt to new things as soon as possible, and hope to jointly promote green printing work steadily forward.