How to make imposition is more conducive to overprinting accurately

1 In the offset printing process, when the paper is subjected to the roller embossing force, the width of the printed sheet and the length of the two corners at the tip of the sheet will be slightly expanded. The greater the pressure, the more stretched it becomes trapezoidal, resulting in inaccurate overprinting, especially at the two corners of the paper dragging section. Therefore, the subject areas with high requirements for overprinting accuracy should be arranged as far as possible at the time of plate making, because the graphic distortions during printing are small and easy to register.

2 The larger the number of sheets, the greater the amount of paper deformation due to changes in water content and printing pressure. In the case of printing a high-precision product with a small number of prints, it may be considered to reduce the number of spells in the multi-patch plates and print them with smaller-sized papers to improve the overlay accuracy.

3 After the fibers of the paper are completely wetted, the increase in diameter is much greater than the increase in the length, so when the moisture content of the paper changes. The rate of expansion along the length of the fiber is less than the rate of expansion in the transverse direction. In offset printing, it is difficult to adjust the size of the plate or blanket along the axis of the roller. The circumferential image size can be adjusted slightly by changing the pad thickness of the plate cylinder; on the other hand, in order to facilitate the stability of the positioning and the limitations of the machine structure. In production, the long side of the paper is always printed in the axial direction of the drum, while in the case of the same elongation, the longer the length, the greater the amount of elongation. Therefore, when printing thick paper. Generally, the length of the fiber, which makes the elongation of the paper smaller, is printed along the axial direction of the roller to facilitate accurate overprinting. When composing, it is necessary to consider how to cut the paper fiber in the axial direction of the printing roller as far as possible, and what size the paper will be after cutting, and then use an appropriate imposition method to cooperate with it.