Sheet-fed offset printing presses often have the phenomenon that the ink color of the same printed matter is darker and lighter before printing on the printed matter with a larger graphic area or on the ground. Due to the influence of the layout and structure of the machine itself.
1. The influence of the cylinder structure In the process of the inking roller inking the printing plate, when the inking roller is in the empty position of the plate cylinder, the inking roller does not ink, the amount of ink accumulated on the inking roller is large, and then the roller rolls forward, each The inking roller injects ink to the front of the plate with the largest amount of ink. As the inking roller rolls and injects ink, the amount of ink on the inking roller gradually decreases. When it reaches the trailing part of the plate, the amount of ink on the inking roller Already very few. This can easily cause the ink color to become darker and lighter.
2. The influence of the arrangement of the ink rollers The ink rollers of the inking device are generally divided into two groups: inking and receiving. Different models have different arrangements of the two rollers. The ink path of the evenly-distributed ink roller arrangement is divided into two, and the four ink rollers are evenly inked. For this ink roller arrangement, if the adjustment is not correct, the last two ink rollers will not be able to replenish ink, even ink, and recover excess With the effect of the ink layer, the printed matter is extremely prone to appearing deep and shallow. The inking roller is more in front and less inking type. The first two inking rollers account for 90% and the second two are 10%. Such a distribution generally does not produce the phenomenon that the ink color of the printed matter is darker and lighter.
3. Process remedies and precautions in operation
(1) Ink rollers that are too smooth and aging should be replaced in time to ensure good ink transfer performance of the ink roller and sufficient ink storage on the surface of the ink roller, so that the ratio of the amount of ink consumed for printing to the ink storage of the ink roller is as small as possible. This can enhance the ability of the ink roller to adjust the amount of ink itself, so that the ink color of the printed matter is consistent.
(2) Master the fluidity and viscosity of the ink, because the fluidity and viscosity of the ink directly affect the ink transmission speed and the ink storage capacity of the ink roller.
(3) Strictly control the moisture of the plate surface, prevent excessive emulsification of the ink, and ensure the normal transmission and adhesion performance of the ink.
(4) For the layout of the evenly distributed ink path, when adjusting the pressure of the form ink roller, the first two should be heavier and the second two should be lighter. 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 between the inking roller and the plate surface. Because the rotation of the inking roller should rely on the equivalent friction force on both sides, if the pressure difference between the two sides is too large, the rotation of the inking roller on the surface of the inking roller or plate will become frictional sliding instead of pure frictional rotation, which will affect the ink. The normal transmission of the film affects the uniform coating of the plate by the ink roller.
(5) To increase the printing pressure by padding paper in the light-colored ink, it can also play a certain remedial role.
How to repair the damage of the rubber roller After a J2205 offset printing machine of this factory has been working for a period of time, there is a crack on the edge of the lower uniform ink roller of the first color group relying on the doctor blade. At first, it was considered not a big problem, but after a short period of time, the ink penetrated into the cracks, the rubber cracks began to expand and fell off the ink roller one by one. So immediately shut down, remove the rubber roller, and wipe the ink on the rubber roller with gasoline, then use a knife to cut the ink that has penetrated into the crack a little outward, and then use 502 instant adhesive to follow the knife edge Apply it once, and then apply it again in a few minutes. After about 20 minutes, dry the part around with fine sandpaper, and then reinstall the rubber roller to work. Facts have proved that this method works very well. In addition, due to improper normal operation, some heavy rubber rollers took off a small piece of rubber due to injury. At this time, they should be wiped clean in time, and scraped off with a blade, and then use 302 modified acrylic adhesive Spread it evenly on the top, and when it reaches the strength of use, then smooth it with fine sandpaper to use it on the machine.
Cushions in various shapes, sizes, and designs, and they are often covered with fabric or leather.
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