Yingkou Guanhua Offset Printing Co., Ltd. In multi-color printing, the phenomenon that the ink printed before can make the ink after the printing adhere well is generally called overprinting. Overprinting is the key to the quality of color prints. Overprinting effect is not good often will appear the following printing failure: 1, hue is blurred; 2, dew; 3, crystallization; 4, paste version and so on. What are the main factors that affect overprinting? 1. Adhesion of ink In the printing process, the ink film is separated and transferred to the surface of the ink roller, printing plate and substrate in turn, relying on the adhesion between the ink and these surfaces, and the adhesion is separated and transferred in the ink film. In the process, the action time is very short, and it is periodic. The separation of the ink film is always subject to its own resistance. The ability to separate ink resistance is called stickiness. Wet multicolor printing When the following conditions are met (others are ideal) overprinting is generally better. F1 ≥ F2 + F12 F1: Cohesion of the first color ink; F2: Cohesion of the second color ink; F12: Adhesion between the first color and the second color ink The experiment shows that: In the four-color printing, the color sequence is Y→ In the case of M→C→BK, the adhesiveness of the ink is 7.5, 5.5, 5.0, and 4.5 in order, and the overprinting effect is relatively good. However, in actual printing, due to other reasons, we do not print all of them in this order. In this way, we must require that different colors of ink be fully agitated and then re-inked during deployment, so that a reasonable viscosity can be ensured. From the above analysis, it is known that the adhesion between the ink ink film requires that the first color adhesion force is greater than the secondary color ink adhesion force, and the adhesion force should be reduced in order to ensure that the overprint effect can achieve the desired effect. 2. Overprinting time interval Whether it is a monochrome machine or a multi-color machine, when the overprinting of each color and the second color is overprinting, the ink is required to be dried to a certain extent, otherwise the overprinting of the next color is liable to occur. Dot printing and other printing failures. The following table lists some experimental data where the ink is printed first, then overprints the second color at different time intervals: (See the figure below, see next page.) Print interval M+CC+YY+M Wet-print FB (g/m2) FB (g / m2) FB (g / m2) 0.5300.4052 hours 0.4840.3100.43500.0900.4800.386 hours 0.5000.2400.4500.03224 hours 0.4880.1540.4710.0170.4740.300 a week 0.4980.104 0.4780.0200.4950.140 The first color The time interval between the ink and the second color ink has little effect on the F value, but the B value is smaller due to the increase in the time interval of the overprint. It can be seen from the above data that the time interval of overprinting affects the adhesion of the ink. Larger, printing (monochrome printing) must ensure a certain time interval, but neither too short nor too long, which requires us to explore the actual printing. In the printing process, try to choose the appropriate time interval, especially for the Yingkou Guanhua Offset Co., Ltd. YK4700 series can be overprinted small offset press, the general user is generally printed in a batch of all the color of the job after printing and then overprint The second color, so special easily affect the overprint effect. 3. The plastic viscosity of the ink Plastic flow properties: When the fluid is subjected to a small external force, when the shear stress between the flow layers has not reached a certain value, the fluid does not produce relative flow, only when the external force increases, between the flow layer When the shear stress exceeds a certain limit, the fluid begins to generate relative flow. For ink, a special plastic fluid, because the dispersed phase is a pigment, the shape of the pigment particles is very complicated, and the dispersion of the particles is also very high, and its influence on the fluidity of the ink is also very complicated, which is not specifically described here. Only use some simple data to analyze: The ink flow characteristics (Pa s) rB (N/m2) rB/Y21.5150075M25.32900115C15.01650110 From this data: When the ink is overprinted, in the plastic ink with high viscosity Overprinting of inks with a small plastic viscosity results in a larger B value than printing inks with a higher plastic viscosity than inks with a lower plastic viscosity. In the multi-color overprinting, when selecting the ink color sequence, the plastic viscosity of the ink should be successively decreased according to the printing color sequence, so that the overprinting effect can be basically guaranteed. 4. Ink crystallization Dry multicolor printing, the first color of the ink quickly dried, the printed surface smooth and smooth, glassy, ​​so that the second color ink can not be attached to it, the superimposed effect deteriorated, the formation of ink spots, which It is crystallized. Therefore, when printing, the drying time should be extended as much as possible so that it can reach a certain drying time. In the actual printing, agents that inhibit the rapid drying of the surface can be added, such as Vaseline, butter, and the like. In short, the overprint effect is an important factor in the quality inspection and control of the printed matter. The influencing factors are far more than these. Here I will only discuss the factors we have noticed in the study. Of course, in actual printing, good prints can only be obtained when the factors affecting the quality of printed products in the printing process are controlled to the best state. ·Editor Li Yonglin·