To check whether it is caused by paper expansion, it is usually to compare the cross marks on the four corners of the plate with those on the printed matter. However, the practical method is to observe the cross marks on the printed matter and check whether there is relative displacement between the colors. Because no matter the displacement between colors is translational, oblique or both, as long as the displacement direction is the same, the angle is the same, and the interval is the same, it can be concluded that the paper is not stretched. For this kind of simple displacement not caused by the expansion and contraction of the paper, first check whether the paper cutting (size, right angle) meets the requirements. No problem. It could be a mechanical problem inside the press. It should be noted that when using thin paper with weak rigidity, especially when printing photo albums at high speed, the above displacement may be caused by insufficient function of registration mechanism.
Check whether the overprint error of each paper is caused by paper stretching. When the printing performance of each album is significantly different, it may be due to the overprint adjustment mechanism or the right angle of the paper. If the colors are the same or similar, the reason may be that there are problems with the roller and gear teeth in the printing process after the two colors are printed. Check the color that appears. When all the colors of the monochromator are not accurate, it can be determined that the reason is poor paper cutting or large humidity changes in the whole printing process. If only a specific color appears, you can determine the cause because there is a problem with the printer itself. However, if only the displacement of the color is large, and it is normal after two colors, it may be caused by warpage, low water content, wave bending and other reasons. This problem can be corrected by absorbing the soaking water after color printing. Check in which part of the paper has nothing to do with the overprint is not accurate, the displacement of each part of the paper is the same. However, due to the expansion and contraction of the paper caused by the overprint is not accurate, the degree of displacement is proportional to the distance, that is, the farther away from the mouth or side gauge, the more serious the displacement.
The above introduces the basic method of judging the cause by observing the samples with inaccurate color registration. We need to know the position of the teeth and side gauges, the printing sequence, and whether the multi-color printing is monochrome or multi-color. It is also necessary to master several samples of continuous printing.