(3) Concentration control of fountain solution
The concentration of the fountain solution refers to the amount of the original solution contained in the fountain solution. The stock solution is generally a wetting powder or a stock solution.
When many printing plants use fountain solution, they only pay attention to the pH of the fountain solution within the required range (pH value is 5.0 to 6.0), and ignore the concentration of fountain solution. Due to the addition of more buffer to some fountain solutions, when the concentration of fountain solution changes greatly, its pH (ie, PH value) does not change significantly. Therefore, it is unscientific to control the pH value only .
Because the change of the fountain solution concentration changes its chemical composition, which affects the water-ink balance. Changes in the concentration of fountain solution will also cause changes in the concentration of surfactants, thereby causing changes in surface tension. Too high concentration in the fountain solution will cause emulsification of the ink and hinder the drying of the blot. During high-speed printing, due to temperature factors, Mg (HCO3) 2 and Ca (HCO3) 2 in the fountain solution will decompose and generate insoluble CaCO3 calcium carbonate and MgCO3 magnesium carbonate in water are attached to the water roller, which is easy to prevent water transmission and have dirty plate faults. Therefore, it is necessary to soften the water before preparing. Therefore, the concentration of fountain solution is a key factor influencing the quality of printing. We must control the concentration of fountain solution while maintaining a stable acidity (PH value).
In order to make the printed graphics and text bright and clear, and the blank layout is not dirty, the concentration of the fountain solution must be reasonably adjusted according to the specific printing conditions to ensure that high-quality printed products are printed.
1. Paper performance and fountain solution concentration
When the printing paper is loose in texture or contains dust in the paper, due to the high viscosity of the printing ink, the paper wool and paper powder will often accumulate on the blanket during imprinting, which will inevitably increase the friction of the printing plate and make the printing plate easily dirty In this case, the concentration of fountain solution should be appropriately increased; when printing on paper with high flatness and high tightness, especially when printing on coated paper and glass cardboard, the fountain solution should be appropriately reduced. concentration.
2. Ink performance and fountain solution concentration
Due to the different properties of printing inks, their viscosity, fluidity and acid resistance are also different. The response to the concentration of fountain solution will also be different accordingly, so the concentration of fountain solution should be adjusted as appropriate. Generally speaking, the principle of using the density of fountain solution is as follows: when printing red ink, the concentration is greater than printing black ink; when printing black ink, the concentration is greater than printing cyan ink; while when printing dark ink, the concentration is greater than The density of printing light-colored ink.
3. The amount of desiccant and the concentration of fountain solution
When printing multi-color plate products, in order to accelerate the drying speed of the ink, it is necessary to add dry oil to the ink, which also makes the particles of the ink thicker and the viscosity increases, so the fat sensitivity of the blank part of the printing plate surface increases, so it is easy to produce paste Edition ills. Based on this situation, the amount of stock solution should be increased appropriately.
4. Concentration of printing plate and fountain solution
The layout structure of printed products is diverse, ranging from solid layouts to lines and textured layouts. If the layout is full of lines and text, because of its large ink-carrying area, the concentration of fountain solution should be adjusted appropriately. If it is all the screen version, the concentration of fountain solution should be adjusted lower.
5. Ambient temperature and fountain solution concentration
When the temperature of the printing environment rises, the molecular movement of the substance will inevitably accelerate, the ink fluidity will increase, and at the same time, more free fatty acids can be decomposed, making the printing plate surface prone to dirty phenomenon, so when the temperature is high, the fountain solution should be increased concentration.
6. Printing speed and fountain solution concentration
Due to the thixotropic characteristics of the ink, when the printing speed is high, the friction coefficient of the ink roller of the printing machine is large, it is easy to heat and make the ink thin, the coloring power is reduced, and the color of the ink is pale. Printing ink color, so that the printing plate is prone to appear dirty. Therefore, when the printing speed is high, the concentration of fountain solution should be appropriately increased.
7. If the printing pressure is high and the texture of the blanket and liner is too hard, the concentration of fountain solution should also be considered appropriate. In order to achieve a better anti-dirt effect. The above shows that the concentration of fountain solution should be comprehensively considered according to various specific situations.
Determination of the concentration of fountain solution:
The concentration of fountain solution can be determined by measuring the conductivity. Experiments have shown that there is a certain linear relationship between the concentration change of fountain solution and its conductivity change, that is, the greater the concentration, the greater the conductivity, so it should be changed Find a certain value within the range as its best wetting effect value. We should use soft water when formulating the fountain solution, to ensure that its pH value is between 4.5 and 5.5, and the conductivity should be proportionally changed between 1200 and 600us / cm.
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