Paper roll wrinkling is a common problem in drum printing, which will affect the overprint accuracy of multi-color printing, and also bring serious printing quality problems. Serious wrinkling will even lead to paper tape fracture. This article will share the common causes and solutions of paper roll wrinkling in drum printing.
Because of the sudden wrinkle failure after replacing the new paper, we stopped the machine and directly checked the paper roll. No problem was found by naked eye observation, and there was no bulge on the edge of the paper. However, when the paper tape is tightened after startup, we can see that the paper roll begins to loosen, and one side of the wrinkled paper becomes significantly loose relative to other positions of the paper tape.
Some paper rolls are packed with two rolls of paper and wrapped with a plastic waterproof layer along the circumference of the paper roll, but the connection between both sides and the paper roll body is not completely covered by the waterproof layer. Even in some places, gaps can be seen in the paper bag, and moist air will enter, which will lead to the problem of paper wrinkling during printing. In this case, it generally only affects the edge of the paper, and the paper roll will not deform. Firstly, the paper on the outer layer of the paper roll can be cut into thin slices by the slitter, and the cut thin slices can be put into the workshop to absorb water evenly before being used for lithography, and then the paper roll can be printed after 3 ~ 4 orders are cut on the machine, and the fold fault disappears. Sometimes, after cutting off the outer layer, the paper roll with severe moisture will still have slight wrinkles. You can adjust the tenter roller on the paper frame or the tension of the paper tape to reduce the printing speed. In this case, there will be a lot of work, but at least normal production can be guaranteed. Of course, try to avoid this when buying paper.
It should be noted that the moisture content of the web should be maintained at least 3%. If it is lower than this limit, it is easy to generate static electricity during printing, and even cause electrical equipment failure of the printing press. At the same time, the low water content of the paper will also cause the adhesion error of the paper and the difficulty of post press processing such as folding.
How to smooth the wrinkled paper?
1. Slightly wet the paper with distilled water and clamp the paper between the absorbent materials. If the paper is wet, try to clamp the paper with two sheets of blotting paper, wool felt or other absorbent material. Kitchen tissue also has water absorption, but the pattern on the tissue may be printed on the surface of the paper to be treated.
2. Clamp the paper clamped by the above method between the two weights again. After clamping the paper with absorbent material, place it on a flat and hard surface, smooth obvious wrinkles with hands, and put a flat weight on it to completely cover the paper. Usually, a stack of heavy and big books is good.
3. Check every day until the paper becomes dry. After drying, the paper flattens and most wrinkles disappear. However, it will take some time to achieve this effect. It is recommended to check every day. Once the absorbent material is found to be wet, replace it with a new one. It takes 3 to 4 days for the wet paper to dry completely. If you only spray a little water on the paper, the paper will be completely dry in less than two days.
In case of wrinkle failure, carefully observe, analyze and try more. Once problems are found, take bold measures. We have encountered serious wrinkling of the paper, and we need to completely solve the wrinkling problem. However, we found that the head of the triangle is not on the midpoint line, overprint is not allowed, and the middle of the RTF roller cannot be cut on the midpoint line. So we moved the position of the RTF roller, and then moved the position of the plate locating pin on the plate cylinder, and finally solved all the problems. In short, we should start with simple and easy methods when we encounter problems. As long as the goal of solving the problem can be achieved, nothing can be moved.
