Viscosity is the size of the cohesion of the ink, and it is also the most important control indicator in ink applications. Ink viscosity is too low, it will cause the color light, dot enlargement, high light spot deformation, uneven ink transfer and other defects; Ink viscosity is too high, will affect the anilox roller transfer ink performance, ink uneven, sometimes color and India Not deep, but at the same time it can easily lead to dirty, dirty, blistering, quit and other ills.
Viscosity is the size of the cohesion of the ink, and it is also the most important control indicator in ink applications. Ink viscosity is too low, it will cause the color light, dot enlargement, high light spot deformation, uneven ink transfer and other defects; Ink viscosity is too high, will affect the anilox roller transfer ink performance, ink uneven, sometimes color and India Not deep, but at the same time it can easily lead to dirty, dirty, blistering, quit and other ills.
1, the temperature of the ink viscosity
The influence of the workshop temperature on the printing quality is better than 60%~85% relative humidity.
The viscosity is most sensitive to the temperature difference between winter and summer. When the temperature is high, the water evaporates quickly and the drying is fast. During operation, it is necessary to pay attention to prolonging the drying time or increasing the speed of the machine. When the temperature is low, the water evaporates slowly and the ink drying is slow. In the operation, the ink drying speed can be increased or increased. Open drying device. When used in winter, the ink will freeze easily below 0°C. If the ink freezes, it can be placed in a room with high temperature, and it can be dissolved naturally. After mixing, it can be used continuously.
In actual production, when a printer with a squeegee is used, the amount of ink transferred when the temperature is too low is not as stable as when the temperature is slightly higher. An increase in the temperature of the ink causes the viscosity to decrease. As a result, the density of the print is reduced and the ink layer is thinned. To maintain consistency in print quality, it is necessary to maintain consistent ink viscosity. The printer must attach great importance to the influence of the ink temperature, and the temperature of the ink to be used before printing should be stabilized at the temperature of the printing shop. This measure is very important, otherwise the ink density in the printing process will have more obvious changes.
2. Thixotropic effect on ink viscosity
Thixotropy refers to the increase of the fluidity of the ink under stirring by external force, and the ability of the fluid to gradually decrease and resume its original state after ceasing stirring. After the ink has been left for a long time, some poorly stabilized inks tend to precipitate and delaminate. There is a phenomenon of false thickening. At this time, it can be fully stirred, and after a certain period of stirring, the above problems naturally disappear. When using fresh ink, be sure to mix evenly beforehand and make dilution adjustments. Or it is expected that after a certain amount of ink on the machine, the viscosity will decrease, because the thixotropy of water and ink in the machine can improve the fluidity of the ink. When the printing is normal, the ink fountain must also be stirred regularly, especially with a high content of white pulp.
3, PH value of the ink viscosity
The pH value of another index that needs to be controlled in the ink-and-wash application has a normal range of 8.5-9.5. At this time, the printing performance of the water-based ink is the best, and the quality of the printing product is the most stable. As ammonia is constantly evaporating during the printing process, the operator will occasionally add new inks and various additives to the ink, so the PH value of the ink may change at any time. Using a standard pH meter, you can easily measure the pH of the ink. When the PH value is higher than 9.5, the alkali is too strong, the viscosity of the water-based ink decreases, the drying speed becomes slower, the water resistance becomes worse, and the paste plate easily occurs. When the PH value is lower than 8.5, the alkalinity is too weak, the water The viscosity of the base ink will increase, and the ink will tend to dry, blocking the plate and the anilox roller, causing the plate to be dirty and causing bubbles. The influence of PH value on the printability of the aqueous ink is mainly manifested in the viscosity stability and dryness of the ink and the dot definition. As the PH value increases, the ink viscosity decreases and the drying speed also slows.