An Example of Printing Quality Failure of Offset Printing Machine

Four-color lithographic printing press is favored by users because of its convenient operation, high degree of automation, and stable quality of printed products. However, as with other high-performance printing presses, the printing machine will inevitably suffer from some printing quality failures. Among them, printing ghosting and overprinting are not allowed to be common failure phenomena in the printing process, and ghosting and overprinting are not allowed to have quality failures in various forms and causes in daily production. Recently, our company has a Heidelberg four-color machine in the production because of the poor handling of the roller's teeth, and occasional irregular ghosting and overprinting are not allowed.

The machine was printing four-color label products with 105g / m2 coated paper. The size of the printed sheets was 36mm × 78mm, and 30 pages were printed and 10 semi-finished products were printed on the plate, 2 plates were longitudinally stitched, and 5 plates were printed horizontally. The order of printing on the machine is as follows: the first group is printed in K-color, the second group is printed in C-color, the third group is printed in M-color, and the fourth group is printed in Y-color. In this way, the black text and the C-color layout pattern on the external trailing area of ​​the printed sheet at the middle of the printing sometimes appear ghost phenomenon, and the black ghost phenomenon is more pronounced. The printed sheet is also on the outer Y color layout and the M color layout longitudinal position. Obviously overprinting is not allowed, that is, Y-color layout longitudinal and bite spacing becomes smaller from about 0.8mm to 1.2mm. Sometimes the creases appear laterally on the outer surface of the printed sheet. When the operator first analyzes and judges the failure, he or she is mistaken for the fourth group of rollers depending on the appearance of the Y-color plate. The tripods have problems with the teeth or pads on the edge of the printed sheet, and the teeth and pads of the transfer and embossing cylinders are repeatedly adjusted, but overprinting and ghosting failures still occur. At the same time as we were unable to do anything about the printing failure, we suddenly learned from the M color group that there was a short period of time when the edge of the sheet was occasionally torn and wound into the rubber roller. As a result, a serious inspection of the teeth of the M-color group drum facing the outside was performed. Finally, it was found that the group of impression cylinders corresponded to the phenomenon that the biting teeth on the outer edge of the sheet were not tight enough. After adjusting the bite pad to increase the bite pressure, a continuous printing test was conducted. As a result, the above failure phenomenon was completely eliminated.

Originally, because the third group of impression cylinders corresponded to the bite of the sheet edge due to lack of bite pressure, sometimes the sheet moved back and forth in a small section of the outer edge of the sheet during the imprinting process, and each time the displacement was displaced. It is also not the same. There are many tearing edges and rolling in the rubber roller. At least when the outer edge of the printed sheet enters the fourth color group, the longitudinal layout overprinting is inaccurate. Since the printed sheet rests on the outer edge, In the third group, longitudinal displacement occurred during printing. When the fourth group was transferred to the fourth group, the first 3 colors of the imprint of the printed sheet (K, C, M) appeared in the position of the rubber roller of the fourth color group. A certain degree of change, then, the phenomenon of ghosting appeared when the next sheet was reprinted. Among them, due to the small text on the black layout, ghosting is more noticeable. The cyan layout has a slight ghosting phenomenon. The magenta layout is thicker, and it is dominated by continuous typography. , so the naked eye can not see the ghosting phenomenon of the layout, but only see that there is a clear overprinting inaccuracy with the yellow version.

The appearance and elimination of the above-mentioned faults give the author a deep inspiration. During the printing process, various kinds of printing failures may occur at any time. The characteristics of the faults may be varied and sometimes even complicated. Changeable, but no matter what kind of failure, simple or complex, worth mentioning occasionally, frequent occurrences, regular occurrences, no regular occurrences, they always have some appearance. The results of performance and some internal factors, as long as we are good at observing carefully in the usual production practice, carefully analyze and study the phenomenon of failure, step by step inspection and processing, you can quickly and accurately eliminate all kinds of printing quality Failure, so that equipment resume normal production as soon as possible, so that advanced equipment to play its due role.