Ink and ink balance control of lithographic offset printing (3)
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Fifth, analysis of the phenomenon of imbalance of ink and water balance
How to achieve the balance of ink and water, operators should not only understand and study the organic relationship between ink and wash, the constraints between each other and the law of subtle changes between them, but also analyze and discuss the adverse consequences caused by the imbalance of ink and wash.
1 Analysis of the phenomenon that there is less water and less ink: During the printing process, the printing plate has a certain water film in the blank part. When the water film and the oil can compete, it will not be stained by the ink on the ink roller. Too small, the amount of water layer can not resist the adsorption of the ink on the blank part, then the blank part will be stained with ink, resulting in hanging dirty. If the amount of ink supply is small, the printed product will be dull, light gray, and the imprint is not real. The imprint is covered with snowflake-like white spots. In this state, although the "ink-ink balance" is reached, this "ink-ink balance" is not the "ink-ink balance" we want.
2 analysis of the phenomenon of less water and more ink: at this time, the most likely to produce uneven printing ink color, hanging dirty, a part or large layout due to lack of water caused by paste, paste. At the same time printed imprinted ink is also deep, The printed matter becomes black and the dots are not clear, especially for the reproduction of fine dots, and the images are indistinguishable.
3 Analysis of the phenomenon of less water and less ink: If the moisture of the layout is too large, it will spread to the surface of all the ink rollers to form a certain thickness of the water layer, which hinders the normal transfer of the ink, and the emulsification speed of the ink is accelerated, and the ink color of the print is gradually unsaturated. The picture is lighter, the writing is imaginary, gray, hairy, hairy, dull and dull. There is dizziness around the imprint, the image is not clear, no level.
4 Analysis of the phenomenon of water and large ink: When the water content of the plate is excessive, the ink color will become lighter, and it will often be blindly considered that the ink supply amount is small, so the ink quantity is continuously increased, and the ink emulsification loses stability after a long period of cycle. The vicious cycle of unbalanced ink and ink causes the ink to be heavily emulsified and accumulates on the surface of the ink roller, making printing impossible.
Sixth, ink and water balance of commercial rotary machines
As the commercial ink roller, the ink and wash balance should be controlled from the following aspects:
First, what is ink? The purpose of using fountain solution in offset printing is mainly to form a water film that repels the ink in the blank portion of the printing plate to resist the expansion of the ink on the graphic to the blank portion, preventing the dirty plate; and supplementing the damaged hydrophilic layer during the printing process. Maintain the hydrophilicity of the blank portion of the plate; reduce the surface temperature of the plate. The water for the rotary machine is composed of pure water, dampening solution and alcohol. The use of pure water can prevent algae from forming on the dampened water pipe wall and cause blockage. The amount of alcohol used is 8-11%. The dampening solution has an electrical conductivity of 9 to 11 and a pH of 4.8 to 5.2. The best value of these values depends on the long-term practice and summary of the operators. The ink is dispersed in the binder by very fine pigments and fillers, and after grinding, it becomes a relatively stable fluid colloidal suspension. Commercial rotary inks are generally thermoset (ie, hot-drying inks), so their drying properties, oil content, and water solubility are very different from oxidative drying inks and sorption drying inks. The latitude is large, the water volume is difficult to grasp, the tolerance is small, and the emulsification degree of the ink is not easy to grasp. Generally, the ink manufacturer is required to provide the matching solution (adapted), because it has been optimized by several professional experiments and productions. And we need long-term exploration to master.
Second, the operator's mastery of the plate and the ability to understand the proof. Confirm whether the dot and the density of the printing plate meet the requirements and whether it is suitable for the rotary printing requirements. Because the rotary printing speed is fast (generally up to 30,000 rpm), and it is B-B type, if the printed version is not enough to eat ink, and the black layer of the proof is thicker, the operator only needs to zoom in to get closer to the sample color. The amount of ink, in this way, the excess ink is accumulated in the ink roller, which will cause the ink or ink to be heavily emulsified, causing the printed matter to be dirty and destroying the balance of ink and water, and then increasing the amount of water has nothing to do. In addition, the products printed on the rotation are not required to be large, as long as the field is saturated, if the difference between the proof and the actual printing is not analyzed, the amount of ink is increased, which in turn causes print quality problems.
Third, the adjustment of water glue. The adjustment of water glue is more important, especially the adjustment of the water transfer roller and the water proof glue requires moderate adjustment of the water glue (the printing ink width is 8-9mm with the printing plate, and the ink printing width of the water transfer roller is 5-6mm). Too big or too small is not conducive to water transfer. What's more important is that both ends should be leveled. If the ends are not flat, then at the time of printing, there will be a water at one end and a small water at one end, so that when the water balance at the small end of the water is good, the water at the other end must be large. If the water is reduced at the same time, the other end will break the ink and water balance due to small water, resulting in a dirty plate. In short, if the water gel is not leveled, it will definitely have large water or small water, which will lead to serious emulsification and will not reach the best state of ink balance. The same is true for the adjustment of the ink.