Factors affecting the transfer effect of offset printing ink
Time:2025-10-27
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The transfer of offset printing ink
1、The transfer from the ink fountain to the ink fountain roller
The ink in the ink fountain must always maintain good contact with the ink fountain roller to ensure that the ink is evenly discharged from the ink fountain. This mainly depends on the rheological properties of the ink: the thixotropy should not be too large, the yield value should not be too high, the viscosity should not be too small, the filament head should not be too short, and the rheological properties should be good, etc. If the ink in the ink fountain has a high yield value and low viscosity, its ink discharge performance will be poor because it lacks the necessary adhesion to the ink fountain roller.
Therefore, it is necessary to frequently clean the ink fountain to ensure good contact between the ink and the ink fountain roller. Otherwise, as the ink and the ink fountain roller gradually come into contact, the printed matter will be darker at the beginning and lighter at the end. In addition, attention should be paid to the ink reserve in the ink fountain for network printing design, which should be kept within a certain range to ensure uniform and consistent ink application.
2、The transfer from the ink fountain roller to the ink roller
Because the ink fountain roller of the offset printing machine rotates intermittently, the ink output by the ink fountain roller is always in the form of arc-shaped strip-shaped ink strips, and the width of the ink strips can be adjusted.
During the printing process, the transfer method of thin ink layers and wide ink strips is better than that of thick ink layers and narrow ink strips, which can make the ink evenly mixed as soon as possible. After the ink is transferred from the ink fountain roller to the ink roller, it is frequently squeezed, sheared, stretched and broken by several ink distribution rollers within a few seconds. Whether it can be quickly and evenly distributed also depends on the number of ink distribution rollers and whether their diameters are prime numbers, whether the ink transfer route is reasonable, whether the ink and water are balanced, and whether the surface adsorption force of the ink roller is good.
The ink delivery devices of offset printing machines are mostly long ink path devices, which use more than ten ink rollers to complete the ink transfer. In addition, the radial runout of the ink transfer roller and the axial movement of the ink transfer roller will both subject the ink to certain radial and axial shear stresses. During the ink transfer process, the ink is squeezed by the ink roller, releasing a lot of heat and causing the ink temperature to rise. For instance, when the workshop temperature is 25 degrees, after the machine has been running continuously for half an hour, the ink temperature on the ink roller will reach 40 to 50 degrees.
3、Transfer from the ink roller to the printing plate
During offset printing, the water roller first wets the printing plate, and then the ink roller and the printing plate come into full contact to supply ink to the graphic and text parts of the printing plate. When the water film of a general printing plate is 1mm, it can prevent the ink on the ink roller from adhering to the blank area. If the water film on the blank part of the printing plate is too thin, it will get dirty; if it is too thick, the ink will emulsify excessively. Therefore, excessive water supply will damage the effect of ink transfer from the ink roller to the graphic part of the printing plate. Thus, it is essential to maintain a good balance between ink and water.
4、Conversion from the printing plate to the blanket
Since offset printing is an indirect printing process, the ink on the image part of the printing plate must pass through the blanket to be transferred to the surface of the substrate. Therefore, the surface of the blanket should have good lipophilic and hydrophobic properties. There should be reasonable and uniform pressure between the blanket and the printing plate. When the image part of the printing plate is transferred to the blanket, some ink should also be retained on the image part of the printing plate. The protective role of talent cannot be underestimated and is indispensable.
5. Transfer from the blanket to the substrate
When the ink layer is transferred from the blanket to the printed matter, the pressure between the blanket and the substrate should be uniform. The substrate itself should also have good ink collection performance, sufficient strength, a smooth surface and uniform thickness to print good products.
The transfer of printed ink to the surface of the substrate can generally be divided into three steps: the initial stage of the transfer when the printed ink layer comes into contact with the substrate. The ink layer of the print is subjected to squeezing force. Under the pressure of the printing plate, the ink is pressed into the uneven capillary pores on the surface of the substrate.
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Cavitation phenomenon and fracture of the imprinted ink layer
At this point, due to the occurrence of centrifugal force and cavitation, the ink layer undergoes tensile fracture. However, because the ink has a good wetting property on the surface of the substrate, a part of the printed ink layer is transferred to the surface of the substrate. After the printed ink layer is split in two, the printed ink transferred to the surface of the substrate continues to penetrate into the paper through the adsorption effect of capillary pores. For substrates with smooth surfaces and low absorbency, whether the printed ink layer can adhere to the substrate surface mainly depends on the affinity of the substrate surface for the ink and the interaction force between the ink and the substrate molecules.
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