Analysis of deep and shallow faults in front of printed matter in offset printing
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When a sheet-fed offset printing press prints a large print area or a solid version of the printed matter, it often appears that the same print is dark and shallow before the ink, which is caused by the fact that the process is not properly controlled. The influence of the layout and structure of the machine itself.
1. Impact of the drum structure
In the process of inking the ink onto the printing plate, when the inking roller is in the empty position of the printing plate cylinder, the inking roller does not ink, the amount of ink accumulated on the ink roller is large, and then the roller rolls forward, each inking roller The ink is inked to the front position of the printing plate with the largest amount of ink. As the inking roller continuously rolls the ink, the amount of ink on the ink roller is gradually reduced, and when the roller is pushed to the printing plate tip, the amount of ink on the inking roller is already small. This is very easy to cause the ink to be deep and shallow.
2. Influence of ink roller arrangement
The ink roller of the inking unit is generally divided into two groups: upper ink and ink receiving. Different models and two sets of ink rollers are arranged differently. The ink path of the evenly distributed ink roller is divided into two ways, and the four ink rollers are evenly inked. For the arrangement of the ink roller, if the adjustment is improper, the latter two ink rollers can not be replenished, inked and recovered. The role of the ink layer, the print is very prone to the phenomenon of deep before and after shallow. The ink is more than before the ink roller, the first two ink rollers account for 90%, the latter two are 10%, such distribution generally does not produce a deep and shallow phenomenon before the ink color.
3. Process remedies and precautions in operation
(1) The ink roller that is too smooth and aging should be replaced in time to ensure good ink transfer performance of the ink roller and sufficient ink storage capacity on the surface of the ink roller, so that the ratio of the amount of ink consumed by printing to the ink storage amount of the ink roller is as small as possible. This enhances the ability of the ink roller to adjust the amount of ink itself, making the ink color of the print consistent.
(2) Master the fluidity and viscosity of the ink, because the fluidity and viscosity of the ink directly affect the ink transport speed and the ink storage capacity of the ink roller.
(3) Strictly control the moisture of the plate to prevent excessive emulsification of the ink and ensure the normal transmission and adhesion of the ink.
(4) For the uniform distribution type ink path layout, when adjusting the pressure of the plate roller, the first two should be heavier, the latter two should be lighter, and the contact width between each other is generally adjusted to 6mm, 6mm, 4mm from front to back. 4mm. The pressure between the inking roller and the inking roller should be equal to the contact pressure of the inking roller with the surface of the printing plate. Because the rotation of the inking roller should rely on the bilateral equivalent friction force, if the pressure difference between the two sides is too large, the rotation of the inking roller on the surface of the ink roller or the printing plate will become a frictional sliding instead of a pure frictional rotation, which affects the ink. The normal transmission affects the uniform coating of the ink roller on the layout.
(5) Increasing the printing pressure in the shallow ink pad can also provide a certain remedial effect.