Because of the thick ink layer in gravure, the problem of poor drying is always present. The printing characteristics of gravure printing are wet stacking and wet. Although there is a long drying channel, the ink of the previous color group is not dry when the gravure printing is stacked, but a film is formed on the surface of the ink layer to prevent the latter color The ink of the group reverses the ink of the previous color when superimposed.
Seven reasons why gravure products are not dry
1. The gravure mesh is deep, sometimes the depth reaches 60Î¼m, the amount of ink is large, and drying will be difficult.
2. In order to ensure the transfer of high-gloss small dots, slow drying agent must be added in the gravure printing process, which will also affect the drying effect of the ink.
3. The comprehensive balance of the mixed solvent is not easy to grasp, causing a large amount of slow drying agent to stay.
4. In some printing processes, the last color is printed with white ink, and then rewinding. The distance between the drying and rewinding station is too short, and drying is difficult. And the bottom of the white ink tray requires the ink to have a good hiding power, which can only thicken the ink layer. Generally speaking, the amount of white ink is the largest in all colors.
5. During film printing, the temperature of the drying device should not be too high, and the drying tunnel should not be too long, otherwise the film will be stretched and deformed, affecting the accuracy of overprinting and the length of the product. The commonly used method is to use low temperature and large air volume, and use volatile method in the drying process to discard evaporation.
6. The dependence of solvent volatilization on environmental conditions. When the air pressure in the environment is relatively low, it is difficult to effectively control the drying efficiency with a mechanical exhaust device.
7. The ink layer on the surface of the printed matter has a boundary layer with the atmosphere (the foreign counterpart is called "Boundarylayer", some people translate it as "mirror film"), this is a layer containing hot air and solvent vapor Mixture, the temperature is higher. When the ink is dried under the action of high temperature, the liquid solvent in it will evaporate and move to the boundary layer. If there is no solvent in the boundary layer, the solvent vapor will be easily transferred to the atmosphere. However, as the concentration of solvent vapor in the boundary layer continues to increase, the evaporation rate of the solvent will decrease. When the solvent vapor in the boundary layer tends to be saturated, the evaporation process will stop. The traditional gravure drying process does not pay attention to the existence of the boundary layer and ignores the role of evaporation in drying. Although the industry has made some improvements to the curve of the drying channel of the gravure printing machine, the air resistance is reduced and the air volume is increased. Without the boundary layer that does not flow with air, some unvolatile residual solvent in the ink will still be wrapped in it.
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