The four-color lithographic printing machine is favored by users for its easy operation, high degree of automation, and stable quality of printed products. However, like other advanced printing machines, some printing quality failures are unavoidable in this machine. Among them, printing ghosting and overprint inaccuracy are common failure phenomena in the printing process, while ghosting and overprint inaccuracy quality failures have various manifestations and causes in daily production. Recently, our company has a Heidelberg four-color machine in production because of the poor transfer of the gripper paper of the roller, and occasionally irregular ghosting and overprinting are not allowed.
At the time, the machine was printing four-color label products of 105g / m2 coated paper. The size of the printed sheet was 36mm × 78mm. The layout was printed with 30 open semi-finished products and 10 small plates were printed. Two plates were printed vertically and five plates were printed horizontally. The color sequence of the printing on the machine is as follows: the first group is printed with K color version, the second group is printed with C color version, the third group is printed with M color version, and the fourth group is printed with Y color version. In this way, the black text and the C color layout pattern of one version of the outer trailing part of the printed sheet sometimes appear ghosting phenomenon, the black ghosting phenomenon is more obvious, and the longitudinal part of the printed sheet is also outside the Y color layout and the M color layout. Obviously, the inaccurate situation of overprinting occurs, that is, the distance between the longitudinal direction of the Y-color layout and the bite becomes smaller by about 0.8mm to 1.2mm. Sometimes the printed sheet is creased horizontally on the outer trailing part. At the beginning, when analyzing and judging the fault, the operator always misunderstood the fourth group according to the appearance of the inaccurate appearance of the Y-color version on the outer layout. There is a problem with the teeth or pads on the tripod facing the outer edge of the printed sheet. The teeth and pads corresponding to the transfer and impression rollers have been adjusted repeatedly, but overprinting and ghosting problems still occur from time to time. Just when we were at a loss for printing failures, we suddenly got a small piece of paper from the M color group to the outside, and the edge of the paper was occasionally torn and rolled into the rubber roller. This feature was inspired. So, the teeth of the M-color cylinder facing outwards were carefully inspected, and finally found that the teeth of the group of impression cylinders corresponding to the teeth of the outer printed sheet had insufficient bite. After adjusting the dental pad to increase the bite pressure, a continuous printing test was carried out. As a result, the above failure phenomenon was completely eliminated.
It turned out that due to the lack of bite pressure, the teeth of the third group of impression cylinders corresponding to the edge of the printed sheet, sometimes the printed sheet moved backward in a small section toward the outer edge of the paper during the imprinting process, and the magnitude of the displacement occurred each time. It is also different, most of them appear torn paper edges and are rolled into rubber rollers, or less so that when the outer edge of the printed sheet enters the fourth color group, there is an inaccurate longitudinal overprinting phenomenon, and because the printed sheet is located near the outer edge Longitudinal displacement phenomenon occurred in the third group printing. When handing over to the fourth color group, the imprints (K, C, M) of the first three colors of the printed sheet were also transferred when the position of the rubber cylinder of the fourth color group was transferred. A certain amount of change, so the ghost phenomenon appeared when the next printing sheet was reprinted. Among them, because there are many small texts in the black layout, ghosting is more obvious, and the logo pattern of the cyan layout has a slight ghosting phenomenon. The magenta layout is mainly due to the thicker text and the continuous screen layout is mainly used. Therefore, the ghost phenomenon of the layout cannot be noticed by the naked eye, but only the obvious overprinting phenomenon between the yellow version and the yellow version can be seen.
The appearance and elimination process of the above faults give the author a deep enlightenment. In the printing process, various printing faults may occur at any time, and the characteristics of the faults may be diverse, sometimes even complex. Changeable, however, no matter what kind of failure, simple or complicated; occasional or frequent; regular appearance, irregular appearance, their appearance always has some appearance As a result of characteristic performance and some internal factors, as long as we are good at careful observation in the usual production practice, carefully analyze and study the fault phenomenon, and carry out inspection and processing in an orderly manner, we can exclude all kinds of printing quality quickly and accurately The failure will enable the equipment to resume normal production as soon as possible, so that advanced equipment can play its due role.
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