Factors affecting offset ink transfer and transfer during book printing
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The printing process is the process of ink transfer and transfer. How can I make the ink transfer correctly according to the needs of the production process? What are the factors that affect the ink delivery? How do they match between them?
First, the transmission of offset ink
1. Transfer from the ink fountain to the ink fountain roller. The ink in the ink fountain always keeps good contact with the ink fountain roller, so that the ink is evenly transmitted by the ink fountain. This depends mainly 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 silk end should not be too short, and the rheology should be good. If the ink in the ink fountain has a high yield value, the viscosity is small, and the ink is poor, because it lacks the necessary adhesion to the ink fountain roller, so it is necessary to smash the ink fountain from time to time to ensure good contact between the ink and the ink fountain roller. Otherwise, the front and back of the printed matter will be weak due to the gradual disengagement of the ink from the ink fountain roller. Also pay attention to the ink storage in the ink fountain, to maintain a certain range, and strive to achieve uniform ink.
2. Transfer from the ink fountain roller to the ink roller. Since the offset printing machine ink roller is intermittently rotated, the ink outputted by the ink fountain roller is always an arc-shaped ink strip, and the width of the ink strip can be adjusted. In the printing process, the transfer mode of the thin ink layer and the wide ink strip is better than that of the thick ink layer and the narrow ink strip, so that the ink can be evenly beaten as soon as possible. After the ink is transferred from the ink fountain roller to the ink roller, it can be squeezed, stretched, and broken frequently within a few seconds by a plurality of ink-dispensing rollers, and can be quickly evenly beaten, depending on the ink-dispensing roller. Whether the number of roots and the diameter are mutually prime, whether the ink transfer route is reasonable, whether the ink is balanced, whether the adsorption force on the surface of the ink roller is good, the ink infusion device of the offset printing machine is mostly a long ink circuit device, and the ink is completed by using more than ten ink rollers. Pass. In addition, the radial runout of the inking roller and the axial movement of the inkjet roller cause the ink to be subjected to certain radial and axial shear stresses. During the transfer of the ink, a large amount of heat is released by the extrusion of the ink roller, so that the temperature of the ink rises. For example, when the temperature of the workshop is 25, the ink temperature on the ink roller will reach 40 to 50 after the machine is continuously operated for half an hour.
3. Transfer from the ink roller to the printing plate. In offset printing, the printing plate is wetted by a water roller, and then the ink roller and the printing plate are in full contact to supply ink to the graphic portion of the printing plate. Generally, when the water film of the printing plate is 1 mm, the ink on the ink roller can be blocked from being inked in the blank portion. If the water film in the blank part of the printing plate is too thin, it will be dirty, the water film will be too thick, and the ink will be emulsified excessively. Therefore, the water supply over the assembly damages the effect of the ink roller transferring ink to the printing plate, so it is necessary to control the ink balance.
Second, the transfer of offset ink
1. Conversion from printing plate to blanket. Since offset printing is indirect printing, the ink 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 oleophilic and hydrophobic properties, and the blanket and the printing plate should be reasonable. Uniform pressure, when the printing image part is transferred to the blanket, the printing image part also needs to save a part of the ink, so that the protection can not be underestimated, and it is also indispensable.
2. Transfer from the blanket substrate. When the imprinted ink layer is transferred from the blanket to the print, the pressure between the blanket and the substrate is uniform. The ink-receiving performance of the substrate itself should be good, and it must have sufficient strength. The surface should be smooth and the thickness should be uniform to print a good product. Transfer of the imprinted ink to the surface of the substrate can generally be divided into three steps: the imprinted ink layer and the substrate are in contact with the initial stage of transfer. The imprinted ink layer is subjected to a pressing force, and under the action of the plate pressure, the ink is pressed into the undulating capillary pores of the substrate surface and the printed ink layer is broken. At this time, the ink layer undergoes tensile fracture due to the occurrence of centrifugal force and cavitation, but due to the better wetting property of the ink on the surface of the substrate, a part of the imprinted ink layer is transferred to the surface of the substrate. After the imprinted ink layer is divided into two, the imprinted ink transferred on the surface of the substrate is continuously absorbed into the paper by capillary adsorption. For a substrate with a smooth surface and low absorption, whether the imprinted ink layer can be adsorbed on the surface of the substrate is mainly faster than the ink on the surface of the substrate, which is faster than the interaction between the ink and the substrate. force.