In the offset printing process, the curved or dendritic irregular marks formed on the surface after the paper is pressed are called wrinkles or wrinkles. Wrinkling of paper is a very troublesome problem. It not only causes trouble for production, but also affects the accuracy of overprinting. Wrinkled paper sheets can also become unqualified products. Below, the author discusses the causes and solutions of paper wrinkling from the aspects of machinery and paper itself for your reference.
1. The uneven pressure on the transfer roller
The paper is subjected to axial forces during the transport process, causing the paper to bulge in the middle when the paper is pre-positioned, forming wrinkles after imprinting.
2. The pressure of the impression cylinder grips the teeth
If the pressure on both sides of the impression cylinder rubs against the teeth, the wrinkling of the paper is wrinkled; if the strength of one side is not enough, the corresponding drag edge wrinkles; if the middle strength is not enough, the middle part of the paper Wrinkle.
3. Improper paper transfer
In the transfer process of the paper before the imprinting, if the improper fit, resulting in changes in the paper length of the crepe mouth, the dragging part is liable to wrinkle.
4. The tooth pad is uneven
When the paper is choked, if the pad is not flat, the edge of the paper will be wavy and the crease will partially wrinkle.
5. The position of the paper edge and tooth decay is incorrect
After the paper is positioned, if the paper is pinched by cavities, the edges of the paper are uneven and wrinkles may occur.
6. The ink on the surface of the impression roller is too thick
The thick ink sticking on the surface of the impression cylinder will make the paper unsmooth when it is imprinted, and it will also produce local short-distance wrinkling and deformation.
1. Tap the paper mark too deep, too dense
Due to improper paper knocking, the paper-knocking traces are too deep and too dense, and creases are easily generated at the creases of the knocked paper during printing.
2. The direction of the paper silk
When the paper enters the machine imprint, if it is a straight wire, it will easily cause wrinkles.
3. The paper has too much moisture
If the moisture content of the paper is too large, the fibers of the paper itself will expand. During the imprinting process, the expanded fibers will be narrowed due to the enlargement, and the dendritic creases tend to extend toward the direction of the dragging.
4. Influence of ambient temperature and humidity
Temperature and humidity changes in the environment, resulting in uneven moisture content of the paper, such as the surrounding water content greater than the middle, resulting in lotus leaf edge, printing paper wrinkles.
Method of exclusion
After a paper wrinkle failure occurs, measures must be taken in a targeted manner so that printing efficiency and quality can be guaranteed. 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.
There are many factors that cause wrinkling in printing paper. Once the paper is found to be wrinkled, it should be carefully analyzed according to the specific circumstances, to find the cause, and to prescribe the right medicine in order to eliminate the problem in time.
Reprinted from: Printing Technology
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