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I. Causes of Paper Wrinkling in Offset Printing
1. Uneven pressure on the presser wheels of the paper feeding table
During the paper conveying process, the paper is subjected to axial force, causing the middle part of the paper to bulge when it reaches the initial positioning position, and forming wrinkles after the pressing process.
2. The clamping force of the paper clamping teeth on the pressing roller is uneven.
If the pressure on both sides of the paper feeding teeth of the embossing cylinder is insufficient, the trailing edge of the paper will wrinkle; if the pressure on one side is insufficient, the trailing edge of the corresponding side will wrinkle; if the pressure in the middle is insufficient, the middle part of the paper will wrinkle.
3. Improper paper connection(Note: The term "connection" is not standard in English and may need to be rephrased for clarity. A possible translation could be "incorrect paper "connection.)
During the paper transfer process before stamping, if the coordination is improper and the length of the paper at the edge of the notch changes, the trailing part is prone to wrinkling.
4. Uneven height of the cushioning pad
When the paper is caught, if the jaw pad is uneven, the paper edge will form a wavy shape and the area around the jaw opening will become slightly wrinkled.
5. The position of the paper edge and the jaw pad is inaccurate.
After the paper is positioned, if the paper is slightly caught by the teeth, it will cause the paper edges to be uneven and result in wrinkling.
6. The ink adhered to the surface of the impression cylinder is too thick.
The excessive ink adhering to the surface of the embossing cylinder causes the paper to not lie flat during embossing, and also leads to local short-interval wrinkling and deformation.
7. Paper-related reasons
A. The indentation marks on the paper are too deep and too dense:
Because the force applied during the paper tapping process was improper, the tapping marks became too deep and too dense. During the printing process, wrinkles were prone to occur at the folding creases of the paper.
B. Direction of paper fibers:
When paper is fed into the machine for pressing, if it has straight grain, it is likely to cause the paper fibers to wrinkle at the thread ends.
C. Excessive moisture content in paper:
If the moisture content of the paper is too high, the fibers of the paper will expand. During the pressing process, the expanded fibers will shrink from being enlarged to narrower, which is prone to cause branch-like wrinkles that extend from the mouth to the tail end.
D. Impact of environmental temperature and humidity:
Changes in environmental temperature and humidity cause uneven moisture content in the paper. If the moisture content around the paper is higher than that in the middle, it will result in "veiled edges". During printing, the paper is prone to wrinkling.
II. Effective solutions for paper wrinkling in offset printing
When paper wrinkling problems occur, targeted measures should be taken to ensure printing efficiency and quality. For wrinkles caused by the above reasons, the following measures can be adopted to overcome them:
First, appropriately emboss the printing sheets to enhance the printing adaptability of the paper, thereby achieving the goal of eliminating wrinkling in the subsequent color printing.
Second, adjust the teeth of the roller so that the pulling force is uniform, ensuring that the printed sheets are in the correct position relative to the teeth, thereby eliminating the creasing problem caused by improper paper alignment.
Thirdly, during the pressing process, ensure that the paper is flat and tightly adhered to the pressing cylinder.
