Can a lithographic printer fully control the water ink balance wetting phenomenon of the NCR series of thermal paper special UV ink products while operating on the printing machine every day? In fact, he relies on experience.
During the printing process, a printer provides water, ink, and printing, adding various auxiliary agents to water and ink to achieve various effects. Although he is not very familiar with the functions of these auxiliary agents, he often relies on experience to do so. Therefore, we believe that lithography printers should understand some factors that affect the balance of ink and water in offset printing, and should use correct scientific theories and experimental results to control the phenomenon of ink and water balance. Therefore, this article collects definitions of terms related to ink and water balance, in order to enable printing professionals to better understand the relationship between ink, bucket liquid, and printing, so that these knowledge can truly understand and correctly control the role of ink and water.
In offset printing, the water roller on the printing plate is used to moisten it first. The blank part of the printing plate is hydrophilic and adsorbs a certain amount of water, while the image and text part is hydrophilic but does not adsorb water; By relying on the plate ink roller to apply ink to the printing plate, a certain amount of ink will be absorbed in the image and text section. Then, through imprinting, the moisture and ink are transferred to the paper through the plate roller and rubber roller. The difficulty in this process is the balance of ink and water, and there are seven factors that affect the balance of ink and water in offset printing: the surface tension of the ink, the surface tension of the fountain solution, the interfacial tension between water and ink, the wettability between ink and printing plate image and text, the wettability between water and printing plate blank, and the wettability between oil ink and printing plate blank The wettability of water and the graphic and textual parts of the printing plate. The selective adsorption of liquid on the flat plate first depends on polarity and non polarity, as well as the affinity of the same polarity and the non affinity of different polarities; On the other hand, it depends on the surface tension of the liquid. In addition, the blank part of the printing plate is made up of high-energy surfaces that first come into contact with any liquid, so during offset printing, water must be used first before ink to enable the printing plate to selectively adsorb and print normally.
1. Surface tension
The force that a liquid resists its surface expansion is called surface tension. If the liquid is surrounded by air, the liquid molecules attract each other. The molecules on the liquid surface are attracted to the liquid center by the internal molecules. Different inks have different surface tension; The surface tension of ink will change after it contains water; The composition and content of the fountain solution vary, and its surface tension also varies. For example, after adding alcohol, its surface tension significantly decreases, the contact angle with the printing plate decreases, and the wetting effect is better.
2. Interfacial tension
The force that two substances that form an interface tend to reduce their common contact area is called interfacial tension. Interface tension occurs between liquids and solids or at the interface between two incompatible liquids. The interfacial tension between liquid and solid is inversely proportional to the wetting ability. The smaller the interfacial tension, the smaller the contact angle, and the stronger the wetting ability. In offset printing, when the fountain solution droplets on the image and text area of the printing plate, or even on the ink layer of the image and text area, only slight changes occur, mainly in the form of water droplets (with a large contact angle), indicating a high interfacial tension; But if it drips onto the non graphic part of the printing plate, due to the low interfacial tension between the fountain solution and the non graphic part of the printing plate, it will quickly spread out. We know that if the water supply is stopped, the non graphic and textual parts of the printing plate will also quickly ink and become dirty; If the ink supply is stopped,