Reasons for paper wrinkling during offset printing

Mechanical reasons 1. Uneven pressure in the paper transfer table's platen roller. The paper is subjected to axial force during the transfer process, causing the paper to bulge in the middle at the front specified position and forming creases after imprinting.
2. Impression roller clamping gripping force is not equal If the embossing roller grips on both sides of the jaw force is not enough, then the paper's drag at the wrinkle; if one side of the lack of force, the corresponding drag edge Wrinkle; if the middle force is insufficient, the middle part of the paper wrinkles.
3. Improper paper transfer In the process of transfer of paper before imprinting, if the mismatch is caused and the length of the paper at the crepe is changed, the wrinkle is likely to wrinkle.
4. The unevenness of the pad When the paper is pinched, if the pad is not flat, the edge of the paper will be wavy and the part of the mouth will wrinkle.
5. The position of the paper edge and the cavities is not correct. After the paper is positioned, if the paper is pinched by the tusks, the edges of the paper are uneven and wrinkles occur.
6. The ink on the surface of the embossing cylinder adheres too thick The thick ink on the surface of the embossing cylinder adheres to the surface of the embossing paper and causes local short-distance wrinkling and deformation.

Causes of paper 1.Knock paper marks too deep and too dense Due to improper paper punching, knocking paper marks is too deep and too dense. When printing, the folds at the knocking paper are easy to wrinkle.
2. The direction of the paper strands When the paper enters the machine imprint, if it is a straight thread, it will easily cause wrinkling.
3. Excessive moisture content of the paper When the moisture content of the paper is too large, the fibers of the paper itself expand, and during the imprinting process, the expanded fibers are narrowed by the enlargement, and the dendritic creases tend to extend toward the direction of the drag.
4. The impact of environmental temperature and humidity Changes in the environment temperature and humidity, resulting in uneven moisture content of the paper, such as the surrounding water content greater than the middle, resulting in lotus leaf, printing paper wrinkles.

Remedy After the occurrence of paper wrinkling, take specific measures to ensure printing efficiency and quality. For wrinkles caused by the above reasons, the following measures can be taken to overcome them.
First, the print sheet is appropriately knocked to improve the printability of the paper so as to eliminate wrinkles of the next color print.
Second, adjust the roller tusks to make the force even, so that the printed sheet is in the correct position of the tusks, to eliminate the wrinkle failure caused by paper transfer misalignment.
Third, when imprinting, ensure that the paper is flat and close to the impression cylinder.
In addition to mechanical reasons and the paper itself, improper use of liners can also cause paper wrinkles. If the lining is too soft, there are bumps, inconvenient conditions, or the lining is not tight, it will cause the paper to wrinkle. Therefore, you should also pay attention to the lining process to prevent wrinkling caused by loose packing.

Source: 21st Century Fine Chemicals Network

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