The positioning of the plate center on the substrate is the first step to correct plate calibration.
The so-called layout center positioning is actually to accurately position the pictures and texts on the printing plate on the substrate, so as to meet the requirements of overprint and post press processing. For our more common printed matter, it is to completely print the graphic parts we need to print on the surface of the substrate, and have a margin to meet the requirements of the finished product, as well as some special requirements for post press processing.
·For different plates and substrates, the positioning of the plate center shall follow the following principles:
1. In order to ensure that the subsequent work of printing (cutting, binding, etc.) can be carried out accurately and smoothly, unless it is not allowed, it is generally required to parallel the layout center frame (dotted line in figure I) with the edge of the substrate (thick black frame in figure I).
2. If the print center is small and the substrate is large, the print center shall be centered up, down, left and right on the substrate.
3. When the layout center is large and the substrate area is compact, at least ensure the cutting distance of the image and text edge (as indicated by the red arrow in Figure 1 is the cutting distance).
4. For the printing plate with corner lines, generally print all four corner lines and ensure the same size of its mouth. When it is impossible to ensure that all four corner lines are printed, under the condition of not affecting the clarity of the picture and text of the mouthpiece, the size of the mouthpiece can be appropriately reduced to make all the corner lines dragged slightly printed.
5. According to the graphic characteristics of the printed piece and the characteristics of the offset printing process, the positioning edge of the top of the printed piece or the printing sheet shall be larger and the non positioning edge of the anchor or the printing sheet shall be smaller as far as possible.
6. On the premise of ensuring the correct position of the layout center, for multi-color printing, the error between colors shall not exceed 0.1mm, and the front and back overprint shall generally not exceed 0.5mm.
·In the actual production operation, in addition to strictly following the work order, we also have the following considerations:
1. Due to cutting, the actual printing paper can not completely ensure that the edges of the paper are completely neat (i.e. there is deviation in the cutting size). Therefore, when correcting the layout, we should move the center of the plate to the regular edge according to the error degree of the paper size.
2. When there are pictures and texts at the mouth of the printing plate center, especially for "bleeding" printing, try to drag the plate center slightly. This has two advantages. First, it can ensure that the pictures and texts in its mouth can be printed as much as possible; Second, it can reduce the damage to the image and text part due to serious version loss at its mouth.
3. Some products with special binding requirements should be carefully analyzed. For example, as shown in Figure 2, the figure requires that the initial steps of binding should be completed after 1 and 2 roll folding, which requires us to reach the same distance a and distance b when correcting the printing plate, Or a is slightly less than B (if a is greater than B, the left edge will be folded at B when folding twice, which will lead to binding difficulties).
There are many problems that should be paid attention to in the actual printing work, which are not listed here. Above, we briefly introduced several problems that should be paid attention to when correcting the printing plate. We should know the position of the plate center on the substrate.
The overprint between colors and between front and back of the printing plate is actually the same as the positioning operation means of the printing plate on the substrate. It only needs to pull each color printing plate to the predetermined positioning position of the printing plate (or in other ways, as described below). This paper will not discuss it more.
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