(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 print paper texture loose or paper contains dust, due to the sticky printing ink, imprinting often make paper hair, paper powder piled on the blanket, it is bound to increase the printing plate The friction makes the plate easy to get dirty. In this case, the concentration of the fountain solution should be increased appropriately; when the printing surface has a high degree of flatness and tightness, especially when printing coated paper and glass cardboard. , you should properly reduce the fountain solution concentration.
2, ink performance and the concentration of the fountain solution due to the different nature of printing inks, its viscosity, fluidity and acid resistance and other properties are also different, the response to the concentration of the fountain solution will be a correspondingly different, it should be adjusted as appropriate fountain solution concentration. 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 density printing color plate products, in order to make the ink drying faster, the need to add dry oil in the ink, this also makes the ink particles thicker, viscosity increases, so the printing layout The sense of fatness in the blank area increases, and it is easy to produce paste defects. Based on this situation, the amount of raw liquid should be appropriately increased.
4. Concentration of printing plate and dampening solution The layout structure of printing products is various, including both on-site layout and line and screen layout. 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 concentration of dampening solution When the temperature of the printing environment increases, the molecular movement of the material must accelerate, the fluidity of the ink increases, and more free fatty acids can be decomposed at the same time, so that the printing plate surface is likely to produce a dirty phenomenon. When the height is high, the concentration of the fountain solution should be increased.
6, printing speed and fountain solution concentration Because the ink has thixotropic characteristics, when the printing speed is high, the ink roller friction coefficient of the printing machine is large, easy to heat to make the ink thinning, so that the tinting strength is reduced, the ink is light, this time Need to increase the amount of ink to increase the printing ink color, so that the printing plate is prone to dirt. 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.
Source: Print Information