Printing ghosting is one of the common printing failures. Although it is generally impossible to directly observe the silhouette, it increases the area of ​​the dots and deteriorates the sharp angle of the edge, which affects the tone and color reproduction of the image, and reduces the clarity of the image. Seriously affected the printing quality. There are many specific reasons for ghosting, including printing machinery, printing technology, and paper. The types of general ghosting are divided into three categories, namely horizontal ghosting, vertical ghosting and irregular ghosting. I will briefly introduce the causes and solutions of these three types of printing ghosting.
1. Horizontal ghosting of printing ghosting
Horizontal ghosting means that shallow shadows appear on the left and right sides of the dots or lines in the axial direction, and their positions are relatively fixed, and the ghosts are light and heavy. I think that horizontal ghosting is generally caused by the following three reasons:
Ghost caused by axial displacement of the two rollers during operation
The thrust bearing of the cylinder of the offset printing press is a component to prevent the axial movement of the cylinder. If the thrust bearing is worn or loose, there is a gap. Under the action of the axial thrust of the helical gear, the cylinder will run in series and produce lateral ghosting The machine's axial fine-tuning mechanism is loose, and the bearings are worn, which will cause the axial displacement of the printing plate cylinder and the rubber cylinder under normal working conditions, resulting in lateral ghosting. Solution: You should pay attention to the maintenance of the printing machine at ordinary times, and it can be avoided to replace the bearing with serious wear in time.
Ghosting caused by axial paper error
Such failures are generally due to inaccurate paper transfer caused by the axial movement of the nagging tooth shaft, which produces ghost images. Solution: Adjust the gap between the two ends of the roller gripper shaft and the end surface of the sleeve.
Ghosting caused by ruffled paper
The paper with a lotus leaf edge is squeezed toward the trailing edge under the pressure of the first color printing and gradually moved inwards due to the printing pressure of the first color. The folded paper is released again, and the amount of this folding and releasing is random, resulting in that the previous print remaining on the blanket of the next unit and the current print cannot completely overlap, resulting in ghosting. Most of this ghosting occurs at the two corners of the trailing edge of the first color, and there is no middle. The solution is to dry the paper and make the paper flatter before printing.
2. Vertical ghosting of printing ghosting
Longitudinal ghosting means that the light shadow appears before and after the axial direction of the dots or lines, and its position is fixed. The ghosting is light and heavy, and it is divided into partial and entire layouts. Jinshiyuan Government believes that vertical ghosting is generally caused by the following three reasons:
The blanket cannot be completely reset after each transfer, resulting in ghosting
Excessive pressure between the rollers or improper configuration of the roller radius. The displacement of the blanket under the action of the friction of the imprinting surface is large, and it cannot be completely reset after each transfer, resulting in ghosting. Solution: Reasonably adjust the lining data of the plate cylinder and rubber cylinder to make them meet the requirements of synchronous rolling; reduce the printing pressure under the premise of ensuring ink transfer.
Ghosting caused by a stretchy blanket
The blanket is not stretched tightly, the displacement is large during the rolling process, and it cannot be reset by the tension. There are two cases of the blanket not stretched tightly: First, the overall stretch is not tight, causing a large area of ​​ghosting; The second is that the rubber cloth is cut obliquely or the iron splint is not well fashioned, resulting in partial tension and partial ghosting. This kind of ghosting mostly occurs in the trailing part. Generally, ghosting only occurs in the first few dozens. Solution: If the blanket is not stretched as a whole, re-tighten it; if the local stretch is not tight, check whether the blanket is cut skewed or not installed properly, find out the cause and correct it.
Ghosting caused by misalignment of the printing plate or cracking of the printing plate leading to misalignment of the printing plate during operation
Solution: Tighten the printing plate; if the printing plate has cracked, you need to change the plate.
3. Irregular ghosting of printing ghosting
Irregular ghosting refers to imprinting ghosting (neither horizontal ghosting nor vertical ghosting) that occurs when the double-diameter cylinder offset press is in continuous operation. Irregular ghosting can be caused by the printing press itself or by the printing process. The reason of the machine is mainly that the double-cylinder double-claws are not installed with enough precision. The printing process operation problem is mainly due to the long-term use of the dental pad is worn and the accuracy is reduced. Usually pay more attention to maintaining the machine to keep the machine in good running state, the ghosting situation will be controlled, and the quality of the printed products will be improved.
Printing ghosting is often a demon that printing masters can't get away with, but as long as you learn more about printing technology and continue to sum up experience, you will stay away from the demon and restore the true image!
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