Causes and solutions of ghosting in the hottest of

2022-08-21
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Reasons and solutions for ghosting in offset printing

in the process of offset printing newspapers and other products, due to many reasons, such as the rubber blanket is not tight, the printing plate is not tightened when loading, the plate cylinder, rubber cylinder, embossing cylinder gears and bearings are seriously worn, and the printing pressure is too large, it is easy to cause the disadvantages of ghosting and double shadow in offset printing books and periodicals. The appearance of ghosting in newspapers and periodicals will seriously affect the quality of printed products and readers' reading. Whenever you see the ghosting products, you will have a feeling of shaking your eyes, numb hair, and unable to read

there are ghosting faults in offset printing, including poor mechanical accuracy, paper factors, and the reasons for improper adjustment of various components. In case of ghosting faults in work, comprehensive analysis should be carried out to find out the root cause of the problem, so as to solve the actual problems

in particular, the ghosting of projects, technologies and standards going out can be divided into longitudinal and transverse ghosting. ① the ghosting failure of patterns, lines and points, which is perpendicular to the axis line of the drum, is called longitudinal ghosting; ② The fault of ghosting of patterns, lines and points is parallel to the axis line of the drum, or parallel at a small angle, which is called horizontal ghosting. In case of small points, patterns and lines, you can use a 5-10 times magnifying glass to observe and eliminate the problem of ghosting. First of all, you should make clear whether it is a vertical ghosting or a horizontal ghosting, determine the type and orientation area of ghosting, and come up with a solution to the problem

I. faults and solutions of longitudinal ghosting

1. The main reason for the faults of longitudinal ghosting is that it is not tight when loading the blanket. Offset printing differs from other printing methods in that; Offset printing uses the indirect printing method of the elastomer in the middle of the rubber drum. There are two situations when the blanket is not tight. One is that the whole rubber is not tight, so that the rubber cylinder, the printing plate cylinder and the embossing cylinder cannot be reset in time under the printing pressure, resulting in a large area of ghosting; Second, when the blanket is cut, there is a skew or the iron splint is not in place, resulting in local tension, causing local ghosting

solution: when cutting the blanket, the radial direction must be taken as the stressed direction of the blanket, that is, the radial direction of the blanket should surround the drum, and the radial direction of the blanket should be perpendicular to the axial direction of the drum. When cutting, the four sides of the blanket should be at right angles, and the diagonals should be equal. Only in this way can the rubber blanket bear equal force on the drum and ensure the product quality. If the cutting is not correct and skewed, the force on the blanket will be uneven, and there will be uneven stripes on the surface of the blanket, resulting in unclear points, local point elongation and deformation

when loading the blanket, after the preparation work is done, put the drag tray to the bite of the rubber drum, install the iron splint of the bite of the blanket, tighten it slightly and put the liner into it, so that the disc machine reaches the drag tip, install the iron splint of the drag tip of the blanket, tighten the iron splint of the drag tip, and fully tighten the blanket. Pay attention that the liner should not wrinkle when loading the blanket. When tightening the blanket, it is required to drag both sides of the tip bite at the same time, and do not tighten it on one side. The new rubber has good elasticity and scalability. The tightening of the blanket should be carried out step by step. Tighten once, wait for the offset press to close and jog at low speed for 3~5min, and then continue to tighten if it is not tightened. In addition, the rubber blanket liner is required to be flat and neat

2. The printing plate is not tightened, resulting in ghosting. Due to carelessness and carelessness in the work, the printing plate did not have a tight double image. It is characterized by large-area or local longitudinal ghosting and double ghosting. The fastening screws used to pull the plate are fastened with a wrench. The tension should be consistent. The European Organization for harmless medical treatment (HCWH) has taken measures to keep patients away from medical devices containing PVC and DEHP in a balanced manner. It is necessary to avoid the printing plate being rolled under the action of pressure, causing slight protrusions and slippage, resulting in product ghosting. In addition, the tension is too large when pulling the printing plate, causing the splints at both ends of the printing plate to be pulled apart, or the plate base to become thinner, Cause fracture and partial ghosting after printing

solution: in case of longitudinal ghosting, check whether the printing plate is tightened and whether the two ends of the biting and trailing tip are excessively broken by tension. The printing plate that is not tightened should be tightened. If the biting is damaged, it should be reprinted. When loading the plate, the printing plate and the backing paper should be laid flat, the clamping screws of the fastening plate should be tightened, and the tension of the pulling screws should be uniform to avoid ghosting caused by longitudinal sliding

3. Ghosting caused by serious wear of drum gears and bearings. The offset press is equipped with a helical gear with high precision on the Journal of the drum shaft, which transmits more than 80% of the power, and is stable and high precision. In addition to transmitting power, it also has the function of accurate positioning

due to 6000 sheets/h when the offset press is in normal operation, the machine speed is fast and the working time is long, so the wear will be serious. It is easy to mesh the gears with too large time gap, which will cause mutual slip between the longitudinal rollers when pressing, and the contact between the gears is slightly misaligned, resulting in ghosting

solution: if the offset press has serious wear between the rollers, generally, the machine should be overhauled and the gears and bearings should be replaced; Reduce the center distance of the drum, make the drum clearance smaller, and control the gear meshing side clearance within 0.1mm

4. Ghosting caused by excessive pressure between rollers. When the pressure between the rollers is too large, especially when the pressure adjustment between the rubber roller and the embossing roller is too large, due to the large deformation displacement of the blanket under pressure, it cannot be completely reset after embossing, resulting in a large area of longitudinal ghosting

solution: when most of the page ghosting occurs, check whether the printing pressure between the rollers is too large. The pressure between the plate cylinder, rubber cylinder and impression cylinder should be adjusted appropriately, and the pressure between the plate cylinder and rubber cylinder should be adjusted to 0 15mm, the pressure between the rubber drum and the embossing drum is adjusted to 0 25mm。

5. The local and large-area ghosting caused by the lifting and warping of the paper, the uneven arch and the expansion and deformation of the paper are mainly caused by the poor internal quality of the paper itself and the improper adjustment and treatment of the paper. Due to the problems of the paper, it is difficult to adjust the paper teeth, side gauge and paper conveyor during offset printing. The paper has uneven and uneven moisture, and cannot be spread out, which is often prone to ghosting

solution: Hang and adjust the paper again. Offset printing requires that the paper has uniform water content, good flatness, high smoothness, small paper flexibility, strong water resistance, no galling, no powder removal, tight texture, and appropriate ink absorption

II. Faults and solutions of horizontal ghosting

1. Horizontal ghosting is mainly caused by the horizontal movement of the drum. The specific features are that the direction of the ghosting is parallel to the axis line of the drum, the sliding bearing at the shaft end of the drum is seriously worn, and the clearance is too large, or it is caused by the loosening of the nut of the core bearing after the high temperature and high humidity test at 85 ℃ and 85% RH for 1000 hours

solution: replace the seriously worn sliding bearing, find out the rotating drum, and tighten the nut of the sliding bearing. This kind of double shadow can be eliminated

2. Both longitudinal and transverse ghosting are closely related to the quality of the paper itself and the poor adjustment and hanging treatment of the paper. If the paper is arched, it will cause ghosting, especially the "lotus leaf edge" of the trailing part will be arched, and transverse ghosting will occur at both ends of the trailing part

solution: Hang and adjust the paper again to make the water content of the paper uniform before it can be printed on the machine. Two conditions must be met for the paper to print normally:

1. The water content of the paper before printing should be uniform and adapt to the ambient temperature and humidity of the printing workshop

2. During the printing process, the ambient temperature and humidity should be stable, and the influence of other factors on paper moisture should be reduced. Windows should not be opened during production

the reasons for paper wrinkling are as follows: first, the water content of the paper is uneven; Second, the printing machine is faulty, and the paper biting teeth, the paper feeder and the side gauge are not adjusted properly

the paper has the problem of bow and wrinkle ("Ruffle edge") in the trailing part. On the one hand, it is the ink stacking of the embossing cylinder, which should be cleaned in time; In addition, one aspect is the reason for the uneven water content at the trailing tip of the paper

solution: re hang and adjust the treatment, remove the moisture and blow the air, so that the moisture in the middle of the paper is uniform and consistent with that around Parker company, so as to reduce the problem of ghosting

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