Among the four printing methods of flat concave and soft hole, only one method is obviously different from the other three printing methods on the principle of ink transfer. This is lithography, which is what we usually call offset printing.
The most basic printing principle in offset printing is to use the two rules of incompatibility of oil and water, and selective adsorption of the printing plate to keep the ink and water balanced on the printing plate to achieve the transfer of the dots, and to achieve clear images and full colors Effect. This is where the term ink balance is derived.
4. Measures and control methods to ensure the balance of water and ink
1 During the printing process, the printing plate must have a solid graphic and blank foundation to maintain lipophilic and hydrophilic stability.
2 On the premise of ensuring that the printing plate is not stained, the water supply volume is controlled to the smallest possible range (the water supply of the plate should be 26%), and the water supply volume and the ink volume are in a relatively stable state, so as to ensure the printed matter The ink color is consistent before and after and the printing operation is stable.
3 Master the principle of less water and thick ink. The less water here refers to the premise that the blank part of the layout is not stained. The so-called thick ink is also based on less water. Ink is emulsified due to large water, and the ink layer cannot be thick. From the transfer process of offset ink, it can be seen that in a water supply and ink supply, a total of three times the mixing and emulsification of ink and water, it is impossible to maintain a strict boundary between water and oil. . Therefore, the ink-water balance in offset printing can only be a relative concept, and a perfectly ideal ink-water balance does not exist. As long as the optimal balance is reached, the ideal print can be printed.
4 Select the size of the ink according to the material type of the printing plate. The water volume of the PS version can be appropriately smaller, the water volume of the PVA version can be slightly larger; the water volume of the smooth paper can be smaller, the rough paper can be larger, and the machine runs fast , The water volume can be slightly smaller, and it can be larger at low speeds.
5 Environmental conditions, temperature and humidity can not be ignored. Since the moisture on the layout is distributed in two forms, direct and indirect, while the moisture on the layout meets the needs of water-ink balance during printing, most of it is distributed to the space.
6 The PH value of fountain solution must be controlled (generally controlled at about 4.5 to 5.5). In addition, since the PH value of the offset printing paper surface has a great influence on the PH value of the fountain solution, it is best to measure the PH value of the paper. If the PH value of the paper is too low, the PH value of the fountain solution should be increased slightly; on the contrary, if the PH value of the paper is too high, the PH value should be appropriately lowered so that it can neutralize the OH- of the paper, thereby buffering Excessive PH value of fountain solution. According to the conclusions stated in relevant materials and practice, when the paper PH value is 9, the fountain solution PH value is 4; when the paper PH value is 8, the fountain solution PH value is 5 is better.
7 Use the method of scientific instrument detection to control the water-ink balance. Because the ink obtained in the state of water-ink balance must have thick ink color and consistent density, the change of water-ink balance in the printing process can be detected by continuously measuring the density. When the density value reaches the standard value range, it can be concluded that the water-ink balance is normal.
In addition, in the work, in addition to the offset printing process of water and ink, the operator should also consider the different types of raw and auxiliary materials used (paper, ink, plates, blankets, etc.) and the differences in working environment and other related factors , So that the ink can reach or basically reach the balance suitable for the printing process.
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