Small knowledge of special paper characteristics
发布时间：
2022-08-23 10:09
During the printing process, the paper will be deformed to a certain extent under the action of printing pressure and peeling tension. For paper with large plastic deformation, after leaving the embossing area, the deformation cannot be recovered, resulting in a large overprinting error. 1. Printing pressure and paper deformation: Paper is a material with plastic deformation, and the plastic deformation characteristics of different papers are different. Under the action of large printing pressure, the width and the length of the two corners of the trailing tip will change.
There is a slight expansion, resulting in inaccurate overprinting, especially in the trailing part of the paper. The greater the printing pressure, the more obvious the deformation of the paper, so when printing the same batch of products, the pressure of each color printing plate should be as consistent as possible, but sometimes the pressure should be adjusted according to the specific situation, for example, the printing pressure of a multi-color offset press There is often a random group of decreasing numbers. The deformation of the paper is closely related to the silk thread of the paper. Considering the general offset printing machine, the overprinting error caused by the deformation of the paper under the action of printing pressure is more difficult to adjust in the axial direction than in the radial direction. The paper should be as parallel as possible to the longitudinal direction of the paper and the axial direction of the cylinder, and the direction of the silk threads of the printing paper for the same batch of products must be the same to ensure the overprinting accuracy. , Under the action of printing pressure, due to the existence of fan-shaped deformation of the paper, the images that require high overprint accuracy or the parts that play an important role in the theme should be arranged near the mouth during prepress processing and plate making. , Because when printing, the deformation of the paper near the mouth is small, and it is easy to overprint accurately. 2. Paper peeling tension and paper deformation: The paper after printing in the nip area is held by the roller grippers, forcing it to separate from the blanket, and the ink on the printing plate is used as a medium, which is strongly adhesive. The sheet sticks to the blanket surface. At this time, the fibrous tissue on the printed sheet is subjected to two forces, one is the downward gripping force of the gripper on the paper, and the other is the upward adhesion force of the ink to the paper. The directions of these two forces are opposite. When the printed sheet is peeled off from the blanket, the trailing tip of the paper is easily curled and does not fit with the impression cylinder, forming a folding angle called the peeling angle. If the adhesiveness of the ink is large, the longer the time for the printed sheet to be peeled and pulled down by the gripper, the larger the peeling angle, the greater the peeling tension, the greater the peeling deformation of the paper, the longer the paper is in the radial direction of the drum, and the overprinting. Accuracy drops.
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