Causes and countermeasures of wrinkling in printing paper

At present, lithographic printing is the main printing method of printing plants, and lithographic printing is not allowed to print overprint due to paper wrinkles, and the ink color is uneven, and even printing cannot proceed, delaying the delivery period. Paper wrinkling is one of the most common and difficult problems for printers. The paper analyzes some of the main reasons for paper wrinkling and measures to prevent wrinkling.
There are two reasons for the printing paper to wrinkle: First, the machine is improperly adjusted; second, the paper is uneven (because of uneven water content). In actual work, the following principles can be used to judge whether the machine is the cause of the machine or the cause of the paper. 1 The same machine is used to print this type of paper. Wrinkles of another type of paper are not wrinkled. Most of the reasons are due to paper. 2 Switch the cut paper back and forth and left and right to the machine. If the machine is always wrinkled at a certain position, it indicates that the machine is improperly adjusted; if it is fixed on a part of the paper, it is a cause of the paper. 3 The same two (or several) machines are printed on the same type of paper, some machines are wrinkled, and some machines are not wrinkled. This indicates that the wrinkled machine is not properly adjusted.
First, the printing machine causes 1. Improper adjustment of the printer feeding device. When Feida dispenses paper, the two paper feed nozzles are not synchronized, and the paper pressure on both sides is not equal, which can easily cause skewed paper feeds. The formation of paper skew and arching, which is one of the reasons for wrinkles.
2. Impression force of impression cylinder grippers is not uniform, and the fact that the dental pads of the row of teeth are not on the same plane is a common cause of wrinkling.
The above problems in the adjustment of the printing machine can be adjusted by experienced masters and treated symptomatically.
Second, the paper causes Paper uneven moisture caused by the paper is not smooth, is the main reason for printing paper wrinkles. After the paper enters the printing shop from the paper mill or warehouse, the environmental humidity of the two places is different. The moisture content of the paper is constantly balanced with the humidity of the surrounding environment. The moisture content of the paper increases or decreases with the ambient humidity. When the paper basket is stored, the four sides are easily in contact with the surrounding air. When the humidity of the printing shop is higher than the humidity of the paper mill or the warehouse, the paper absorbs moisture and stretches on all four sides, but the middle elongation is small, and the paper will lose its original straight skin. The edge becomes "foliolate"; conversely, the paper loses more moisture on all four sides and shrinks, resulting in a "tight edge" phenomenon. Especially when the external climate changes drastically, the deformation of the paper is obvious when it rains.
Because the paper appears "foliage" and "tight edges", it must be wrinkled during printing. In order to prevent and eliminate paper deformation, the following measures should be taken:
1. Hang the paper. Units that have paper-hanging equipment should put spare paper 2 to 4 days ahead of time into the hanging paper room for hanging pictures, so that the temperature and humidity in the paper room can be similar to that of the workshop, and the natural wind can be blown.
2. The workshop and paper room must maintain a certain temperature and humidity in different seasons. Units without air conditioning need to install ventilation fans and open and close doors and windows in time.
3. As far as possible, the use of horizontal silk crepe paper to print can reduce wrinkles, because the paper horizontal wire stretches small, and the longitudinal wire stretches.
4. When the sheet loses moisture and appears “tight”, it can be sprinkled with water around the paper stack and the machine or humidified by a humidifier. All have good results.
5. In case of rushing or inferior paper that is deformed more when hanged, the pad inside the blanket cylinder may be partially removed. The specific method is to remove the eraser and pad from the machine, place it on the table, cut the pad of the outer part of the pad with scissors, and then put the eraser. In this way, the diameter of the portion other than the imprinted portion of the blanket is smaller. When the paper is squeezed from the blanket cylinder to the impression cylinder, the part of the pressing force outside the print is small, and paper with poor flatness can also pass. This can avoid or reduce wrinkles.