The water roller sticky ink of offset printing machine has two types: water roller, water transfer roller sticky ink, string water roller and water bucket roller sticky ink. The former is fiber fabric sticky ink, the latter is metal sticky ink. The sticky ink of the water roller will affect the normal water delivery. In severe cases, it will cause the printing plate to be dirty, paste, and even the product will be scrapped. Water roller ink sticking failure is the most common and difficult problem to overcome in offset printing. The specific reasons are analyzed as follows. 1. Lipophilicity of metals At present, the water rollers of offset presses are generally chrome-plated rollers, and the hydrophilicity of chromium is greater than that of lipophilicity. Northerner, j2108. J2203, J2204. In the J2205 offset press, the water bucket roller and the water roller are chrome-plated rollers, which are basically not sticky to ink, but are not sticky at all. The amount of rotation of the water bucket roller is controlled by the walking teeth, and the rotation is slow, and the water film on the surface is thin, so it is easy to lose water. If there is more ink sticking on the water transfer roller, the ink sticking on the water bucket roller is also easy, resulting in uneven water delivery and affecting product quality. Therefore, it is necessary to scrub the sticky ink on the surface of the water bucket roller and the string water roller frequently to prevent the accumulation of ink, and to maintain the good hydrophilicity of the water bucket roller and the string water roller. 2. Water supply operation is not standardized The method of watering operation has a great influence on the amount of ink sticking to the water roller flannel. Because the flannel is made of fiber, although it has been degreased, it still has the characteristics of lipophilicity and hydrophilicity. If the ink sticks first, it is not easy to stick water, so try to avoid the water roller sticking the ink first and then sticking the water during the operation. Before the new water roller is put on the machine, many experienced operators will wipe it repeatedly with a damp cloth. On the one hand, make it full of water, on the other hand, wipe off the surface of the fiber fluff, which is beneficial to prevent ink sticking and hair loss. The general operation method is to install the machine on the new water roller, let the machine run first, and then add water to the water roller. The water should be added as much as possible. The new water roller is most forbidden to close the printing plate without enough water. After the ink roller is dropped, due to insufficient water, it will get dirty and paste, the fleece cover has been glued with ink, and it is difficult to refill the water. If you feel that the new water roller is not sure about the water supply after idling, you can first drop the water roller, and then manually drop the ink roller. Pay attention to the layout. If the water content of the layout is too small, you should immediately lift the ink roller and then add water. specification. 3. Bad Plate Pad In some offset presses, the ink sticking at both ends of the water roller is very serious. Some people think that it is caused by the emulsification of the ink on the two ends of the ink roller, but a closer observation reveals that it is actually caused by poor plate liner. If the liner paper under the printing plate is the same size as the printing plate. During the operations such as plate washing and gumming, the liner paper will be soaked in water and wet. The paper immersed in water will be deformed and expanded, and the pressure between the printing plate and the water roller will be increased. Instead it will stick ink. If the liner paper under the printing plate is much shorter than the printing plate, the pressure between the two ends of the printing plate and the water roller will be lost, and the ink will not stick to the water roller. In the end, these accumulated inks will come into contact with the water roller again, causing serious ink sticking at both ends of the water roller, and gradually expanding toward the middle, affecting water delivery. As a result, the sticky ink at both ends of the printing plate also expands, creating a vicious cycle, which causes the two ends of the blanket and the impression cylinder to be filled with ink, and the two-color machine will have a color mixing failure. Therefore, the length of the liner paper in the printing plate should be emphasized. Generally, the printing plate length of J2108 offset printing machine is 940mm, and the length of the liner paper should be 920-930mm. The liner paper damaged at both ends or soaked with water and dirt should be replaced in time. 4. The nature of fountain solution The fountain solution in the bucket is not tap water, but a certain proportion of water and phosphate. Chromate is formulated with a certain amount of hydrophilic colloid. This stock solution formula is very beneficial to the inorganic salt layer of the printing plate, so many Ty is still in use until now. However, this formula has not solved the problem of sticking ink to water roller flannel. The main reason is that cotton fibers become rough and sticky after being corroded by such acidic substances. In recent years, the wetting powder specially produced for printing has not only removed chromic acid which is harmful to human body, but more importantly, its wetting performance and cleaning effect are particularly good. Because the surface tension of the new fountain solution is reduced by 50% compared to the chromate red syrup used in the past, it can achieve the best wetting and penetration effects. At the same time, because the surfactant has a strong detergency, it can clean the plate surface. It can also clean the water roller flannel, and the ink sticking phenomenon of the water roller flannel is greatly reduced. In short, the operator should study the method of maintaining the water roller to make it non-sticky or less sticky, so as to prolong its service life. In recent years, the wetting powder specially produced for printing has not only removed chromic acid which is harmful to human body, but more importantly, its wetting performance and cleaning effect are particularly good. Because the surface tension of the new fountain solution is reduced by 50% compared to the chromate red syrup used in the past, it can achieve the best wetting and penetration effects. At the same time, because the surfactant has a strong detergency, it can clean the plate surface. It can also clean the water roller flannel, and the ink sticking phenomenon of the water roller flannel is greatly reduced. In short, the operator should study the method of maintaining the water roller to make it non-sticky or less sticky, so as to prolong its service life.
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What are the causes of the ink sticking failure of the water roller of the offset press?