Lithographic Offset Printing Strikes in the Balance of Water (2)

Fourth, ensure the ink and water balance measures and control methods

1 During the printing process, the printing plate must have a solid graphic basis and a blank basis to maintain the stability of the lipophilic and hydrophilic.

2 Under the premise of ensuring that the printing plate is not stained, the amount of water supply should be controlled within the smallest possible range (the water supply of the layout should be 26%), and the amount of water supply and the amount of ink should be kept in a relatively stable state. Ink consistency before and after the ink and stable printing operations.

3 Master the principle of less ink and thicker water. There is less water here, assuming that the blank part of the layout is not stained. The so-called ink thickness is also based on less water. Due to the large amount of water caused by ink emulsification, the ink layer cannot be thick. From the process of the transfer of the offset ink, it can be seen that in a single water supply and ink supply, a total of three ink mixing and emulsification occur. It is impossible to maintain a strict boundary between water and oil. . Therefore, the balance of water and ink in offset printing can only be a relative concept, and the perfectly ideal ink-water balance does not exist. As long as the best balance is achieved, the ideal print can be printed.

4 Select the size of the ink according to the material type of the printing plate. The PS version can be smaller and the PVA version can be slightly larger. The smooth paper can be slightly smaller, the rough paper can be slightly larger, and the machine can run faster. The amount of water can be slightly smaller and can be larger at low speeds.

5 Environmental conditions and temperature and humidity cannot be ignored either. As the layout water is distributed in both direct and indirect forms, the layout moisture meets the needs of the ink-and-wash balance during printing, and most of them are distributed to the space. The higher the ambient temperature, the faster the emission will be.

6 The pH of fountain solution must be controlled (typically around 4.5 to 5.5). In addition, since the pH of the surface of the offset printing paper has a great influence on the pH of the fountain solution, it is preferable to measure the pH of the paper. If the pH value of the paper is too low, the pH of the fountain solution should be slightly increased. On the other hand, if the pH of the paper is too high, the pH of the paper should be properly reduced so that it can neutralize the OH- of the paper. Excessive increase in pH of fountain solution. According to relevant data and conclusions drawn from practice, when the pH value of the paper is 9, the pH of the fountain solution is 4; when the pH value of the paper is 8, the pH of the fountain solution is 5 as good.

7 Use scientific instrumentation to control the ink balance. Because the ink obtained under the ink-balanced state is necessarily thick and uniform in density, the change in water-ink balance during the printing process can be detected by continuously measuring the density. When the density value reaches the standard value, it can be concluded that the ink balance is normal.

In addition, in addition to considering the offset transfer process of water and ink, the operator should also consider the different types of raw and auxiliary materials used (paper, ink, plate, blanket, etc.) as well as working environment differences and other related factors. , so that the ink reaches or basically meets the balance required for the printing process.

V. Analysis of the phenomenon of imbalance of ink and wash

In order to achieve ink-water balance, operators must not only understand and study the organic connections between ink and water, their constraining factors, and the patterns of their delicate changes. They should also analyze and explore the adverse consequences caused by the imbalance of ink and wash.

1 The phenomenon of small water and small ink is analyzed: In the printing process, there is a certain water film on the blank part of the printing plate. When the water film and the oil can contend, it will not be stained by the ink on the ink roller. If it is too small, the amount of water layer can not resist the adsorption of ink on the blank part, then the blank part will be accompanied by ink, resulting in hanging dirty, less ink supply will make the printed product with no gloss, pale gray, imprinted, The imprint is filled with snowflakes and white spots. In this state, although the "ink balance" has also been achieved, this "ink-and-ink balance" is not the "ink-ink balance" we want.

2 Analysis of the phenomenon of water, water, ink and more: At this time, the ink is most likely to be unevenly printed, dirty, and a certain part or large area of ​​the layout will cause paste and paste. The printed products become black and dark, and the outlets are not clear, especially for the reproduction of subtle outlets, and the images cannot be clearly separated.

3 Analysis of the phenomenon of water, ink and less: If the water content of the layout is too large, gradually spread to all the surface of the ink roller to form a certain thickness of the water layer, which hinders the ink to accelerate the emulsification speed of the ink, and the blotting ink gradually becomes unsaturated. The text becomes lighter, and the writing is imaginary, grayish, hairy, hairy, and dull. There is a faint ambience around the blot, the image is not clear, and there is no hierarchy.

4 Analysis of the phenomenon of water, ink, and more: When the water in the layout is excessive, the ink color will become shallow, and the amount of ink supply will be blindly considered to be low, thus increasing the amount of ink, and the ink will lose its stability after a long cycle. The vicious cycle of ink and ink imbalance leads to severe emulsification of the ink, which accumulates on the surface of the ink roller, making printing impossible.