(III) Concentration Control of Fountain Solution
The concentration of the fountain solution refers to the amount of the stock solution contained in the fountain solution. The stock solution is generally a wetting powder or dampening stock solution.
When many printers use the fountain solution, they only pay attention to the pH of the fountain solution to be controlled within the required range (pH 5.0 to 6.0), ignoring the concentration of the fountain solution. As more buffers are added to some fountain solutions, the pH (pH) of the fountain solution will not change significantly when the concentration of the fountain solution changes greatly. Therefore, it is unscientific to control only the pH value. .
Because the concentration of fountain solution changes its chemical composition, thus affecting the ink balance. Changes in fountain solution concentration can also cause changes in surfactant concentration, causing changes in surface tension. If the concentration in the fountain solution is too high, the ink will be emulsified and the drying of the imprint will be hindered. In the high-speed printing process, Mg(HCO3)2 and Ca(HCO3)2 in the fountain solution will be decomposed due to temperature factors, resulting in insolubilization. CaCO3 calcium carbonate and MgCO3 magnesium carbonate in water are attached to the water roller, which can easily stop the water transfer and cause dirty plate failure. Therefore, it is necessary to soften the water first and then prepare it. Therefore, the concentration of the fountain solution is a key factor affecting the quality of the printed product. We must control the concentration of the fountain solution while maintaining a stable pH value.
In order to make the prints of the prints vivid and clear, and the blank layouts cannot be dirty, the density of the fountain solution must be rationally allocated according to the specific printing conditions to ensure the printing of high quality prints.
1, paper performance and fountain solution concentration
When the texture of the printing paper is loose or dust is contained in the paper, due to the stickiness of the printing ink, the paper wool and the paper powder often deposit on the blanket, which will inevitably increase the friction of the printing plate and make the printing plate dirty easily. In this case, the concentration of the fountain solution should be increased appropriately; when the printed surface has high flatness and tightness, especially when printing coated paper and glass cardboard, the fountain solution should be properly reduced. concentration.
2, ink performance and fountain solution concentration
Due to the different properties of printing inks, the properties such as viscosity, flowability, and acid resistance are also different. The reaction to the concentration of the fountain solution will also be different. Therefore, the concentration of the fountain solution should be adjusted as appropriate. In general, the principle of using the concentration of the fountain solution is: the concentration of the printed red ink is greater than the concentration of the printed black ink; the concentration when printing the black ink is greater than the concentration of the printed blue ink; and the concentration when printing the dark ink is greater than The density of printed light ink.
3, the amount of desiccant and fountain solution concentration
When printing multi-color plate products, in order to speed up the drying of the ink, the ink needs to be placed in a desiccated oil, which also causes the ink particles to become thicker and the viscosity to increase, so that the sense of grease in the blank area of â€‹â€‹the printing plate is increased, and thus the paste is liable to be generated. Edition ills. Based on this situation, the amount of raw liquid should be appropriately increased.
4, printing plate and fountain solution concentration
The layout of printed products is varied, with both on-site layouts and lines and textured layouts. If the layout is full of lines, text-based, because of its larger ink-carrying area, the concentration of fountain solution should be adjusted to some increase. If all are cable screens, the concentration of fountain solution should be reduced appropriately.
5, ambient temperature and fountain solution concentration
When the temperature of the printing environment increases, the molecular motion of the material will inevitably accelerate, the fluidity of the ink will increase, and more free fatty acids will be decomposed at the same time. This will make the printing plate easier to produce dirt. Therefore, when the temperature is high, the dampening fluid should be properly increased. concentration.
6, printing speed and fountain solution concentration
Due to the thixotropic characteristics of the ink, when the printing speed is high, the ink roller of the printing machine has a large coefficient of friction, which tends to cause the ink to become thin due to heat generation. This causes the tinting strength of the ink to decrease and the ink color to fade. In this case, the amount of ink required to be increased can be increased. Printing ink, this printing plate is prone to dirty. Therefore, when the printing speed is high, the concentration of the fountain solution should be appropriately increased.
7. If the printing pressure is high and the blanket and liner are hard, the concentration of fountain solution should also be considered. In order to achieve better anti-dirty effect. The above situation shows that the concentration of fountain solution should be comprehensively considered according to various specific conditions.
Concentration of fountain solution:
The concentration of the fountain solution can be measured by the method of measuring the electrical conductivity. It is proved through experiments that there is a linear relationship between the change of the concentration of the fountain solution and the change of the electrical conductivity. That is, the greater the concentration, the greater the electrical conductivity. Therefore, it should be changed. Find a certain value within the range as its optimum wetting effect value. We should use soft water when formulating the dampening solution to ensure that its pH is between 4.5 and 5.5, and the conductivity should be proportionally changed between 1200 and 600us/cm.
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