Causes of paper pleating in offset printing

Paper is a film-like substance formed by the intertwining of fine plant fibers. Thus, the basic composition of paper is plant fibers. The fibers have a hygroscopic effect and the air contains a certain amount of moisture. As long as the paper touches the air, it will continue to be in moisture balance with the air. In offset printing, paper pleating is a common hurdle, but if it is not resolved in time, the quality of the product will be poor and direct and indirect economic losses will be greater. There are three reasons for the pleats caused by offset printing: one is the quality of the paper itself, the other is the improper storage environment and the printing environment, and the third is the improper use of the machine. First, the paper itself caused by the quality of 1. The thickness of the paper should be uniform and the structure of the paper should be loose or tight. Appearance quality should not have light transmission, creases, ridges, spots, cellulose, blemishes, translucent spots, holes, holes, shiny and matt scratches, cracks, incisions, joints. 2. The tightness of the paper edges on both sides of the web must be the same. There should be no "dumplings" and the cylindricity of the web should be guaranteed. 3. Static paper. Paper static electricity is due to the friction between the paper and the paper, which results in some electrons on the surface of one paper and less electrons on the surface of the other paper. In particular, when the environment is relatively dry, the paper has less insulation due to less moisture, and thus the paper with less electrons is difficult to replenish lost electrons from the air. Rotary machines use web paper, which has little effect on the static electricity of the paper when it is fed continuously. After printing, water is absorbed and the conductivity of the paper is improved, and the static electricity is greatly reduced. Generally does not affect the following process. The typographic printing machine uses a single sheet printing, so when the paper is separated from the paper feeding section, it will be difficult to separate due to the attraction between the static electricity of the paper, and it is easy to cause paper failures such as double sheets, multiple sheets, and wrinkles. At the take-up section, the paper is misaligned due to the static electricity of the paper, causing troubles for the following printing and cutting. There are two main methods of treatment: one is to increase the humidity of the workshop, sprinkle some water on the ground, and hung paper in the workshop. The second is the use of air ionization methods to neutralize the electrostatic charge on the paper to eliminate static electricity. This device is harmless to the human body and has no side effects. Second, the paper storage environment and improper printing environment caused by the paper storage environment should have clean, ventilated, dark, moisture and other conditions 1. The storage of the webs should be stacked vertically with the tube upright, to avoid stacking the cartridges horizontally, as this will destroy the cylindricity of the web. 2. Store lithographic paper flat, stacking should not fold. Not even vertical. 3. The ambient temperature of the paper is controlled at 20-25°C. The relative humidity is controlled within the range of 50%-70%. Unable to install air conditioners, humidifiers and other equipment. 4. Do not unpack the paper when it is stored. Paper baskets should be placed on the floor, do not lean against the wall to avoid moisture. Paper baskets should be protected from light, otherwise it is easy to make the paper's moisture content drop sharply and the paper will be deformed and brittle. If it is heated, the mechanical strength of the paper will decrease, making the papers stick to each other and cannot be used. 5. The difference in temperature and humidity between the printing environment and the paper storeroom should not be too large. And when you start printing and do other quasi-work, it is best to isolate the cut paper temporarily from the environment (for example, by covering it with a plastic cover) to avoid rapid imbalance of moisture in different environments. Third, the use of improper adjustment of the machine 1. Improper printing pressure adjustment. Printing pressure may be large or small, and paper pleating may occur. The printing pressure will be adjusted to the best when installing the machine, but after a period of use, the printing pressure will change, especially the rotary machine, high speed, and high wear. More often, the printing pressure should be measured and the printing pressure adjusted to be slightly smaller than the machine requirements. 2. Automatic feeding failure. At present, the offset printing machines used in China are basically overlapped paper feeding methods. Therefore, the occurrence of paper pleating troubles can be summarized as the following: 1 The paper bristle brush causes the separation paper to break: The role of the paper blocking brush is to control Double sheet. Since the bristle brush becomes short and the elasticity is ineffective after the paper bristle brush is used for a period of time, it is easy to break the paper when the paper of 60 g/m2 or less is separated, so that the paper is pleated during printing. The solution is to replace the brushes that are too short in time and adjust the distance the brushes extend. 2 Presser foot touches the paper edge: Because the position of the presser foot pressing against the paper edge is not correct, when the paper is separated, the front end of the paper presser foot breaks the paper edge, which causes the paper to gather during printing. The solution is to adjust the position of the presser foot and the platen, and adjust it when printing different sizes of paper. 3 paper skew caused by swinging the gingiva is less than the edge of the paper and pleated; the position of the paper feeding part is not accurate; paper foot uneven blowing; presser foot eccentric shaft wear; the paper suction nozzle pressure paper is too low; Feeding suction nozzle cam inaccurate positioning; feeding roller and feeding suction nozzle are not matched correctly; bearing on paper feeding roller or paper feeding roller is worn; line belt is loose and inconsistent; paper is stuck; two suction nozzles are not sucking The same as, or inconsistent with the distance from the paper; air pump outlet pressure or suction pressure is too low. To solve the above-mentioned failure of paper feed skew, simply press the manual of the paper feeding department to adjust and repair it; it will not be explained one by one here. 4 paper feed time is too early: when the typography machine is running, the paper feed time is too early to make the paper rushed into the front gauge to cause the paper to go through the position. If the fangs do not reach the edge of the paper, it reaches the middle of the paper. Paper is pleated when printed. The solution is to adjust the relative position of the adjusting plate on the axis of the paper feeding section; for example, if the North man machine is adjusted to the current setting, the paper is about 7 mm from the front rule. 5 Whether it is stacking inside the machine or stacking outside the machine; the quality of the stacking of the paper stacks plays an important role in the quality of the paper feeding. Therefore, when stacking, the heart must be: Packed paper, flattened, broken, broken paper is loaded into the paper basket. In addition, in order to ensure that the thin paper can be positioned accurately and stably, and prevent the impact of the impact force caused by the upturn or squatting on the edge of the paper, the enamel is not good for the paper, resulting in pleated. The easiest way to do this is to perform a knocking process (such as a splayed shape) on the paper bar and the side gauges. To ensure the smooth transport of paper, accurate positioning. (To be continued) (Author: Tianjin Daily Printing Press, Tianjin Institute of Light Industry) Editor-in-Chief/Ou Dingjun