An Analysis of the Causes of a Case of Offset Printing and Reflections

The author has witnessed such a thing, a factory into a second-hand goods imported four-color four-color offset. After a few days of debugging, foreign operators will not be able to print products that meet the quality requirements after the installation of the foreign equipment into the factory. It is very easy for the printing plates to have troubles with dirty plates and floral plates. .

The main reason why the printed products do not meet the quality requirements is that they are prone to produce dirty plates and floral plates, and it is easy to make the plate unusable. In the case of faults in the offset printing process of domestic offset printing machines, the reason is not difficult to analyze, generally The pressure between the water roller and the plate is too large or the pressure between the plate roller and the plate is too large.

As we all know, in the transmission process of the offset press, due to the compression deformation of the water roller, there is a certain linear velocity difference with the plate cylinder, so the surface of the water roller and the printing plate will produce friction, and when the water roller and the layout of the plate are awarded When the ink layer is protected, the fountain solution is brought into contact with the worn surface, the plate grain is destroyed, the specific surface area is reduced, the stability of the inorganic salt layer is destroyed, and the blank part is made susceptible to fat and produces a dirty plate. Patterned part of the photosensitive layer also suffers wear and tear resulting in poor performance of the new ink and pattern.

In the offset printing process, the printing ink roller has the most friction, and the surface ink, some of the ink pigment particles are coarse, will produce a large friction when the pressure reaches a large, so that the sand is subject to wear, the ink pattern will have significant wear. Therefore, the excessive pressure between the printing roller and the printing plate will make the blank part of the printing plate dirty, and the printing part will be patterned.

The long-term operation of the domestic machine by the chief of the equipment responsible for commissioning operations is a breeze in the analysis, judgment, and processing of such offset faults. In the commissioning process, it is also mainly used for the water roller and plate, and the ink roller. Several adjustments were made to the pressure between the plates, but they were not effective and the failure could not be ruled out.

Is the second-hand equipment itself has not been accurate or there are defects, and re-adjustment will not help, or lack of practical experience in the adjustment of such equipment, do not grasp the position in place? Or is it wrong to determine the cause of the fault?

For this purpose, the operator of the station was invited to debug. After the master arrived, he also adjusted the pressures slightly. The trouble was eliminated, the quality of the printed matter reached the requirements, and the equipment was used normally. From the analysis of the structure of the offset press, the difference between the domestic machine and the foreign device is that the domestic machine adopts the weeping liquid dampening, the foreign device uses the alcohol dampening, the domestic machine uses the water roller velvet cloth, and the foreign device does not use the package. Flannel, but with a roller. The existence of these differences is precisely the difference between the pressure and the adjustment of the pressure. If there is no practical experience in this area, the pressure adjustment method (and adjustment parameters) adopted by the domestic machine will be used to apply high speed. The pressure values ​​of the foreign equipment are obviously not adjusted to the proper pressure value, and they cannot eliminate the existing faults. Asked the master to adjust the whereabouts of the master, the master introduced several reference pressure parameters and then said: "It is also very important to feel by hand, familiar with nature will be handy." The “sense of hand” that the master said is the practical operation experience in the actual adjustment process. This point is very important, if there is no practical operation, there is no meticulous study and experience accumulation in the production operation, this "feeling by hand" is not felt. This will have the same experience for operators who operate foreign machines or operate domestic machines. (Chen Jinru, Printing Factory, Putian County, Fujian Province)