How to eliminate the "ghosting" of offset printing?

In the offset printing process, the "phantom" fault that appears on the continuously printed products is called "ghostshadow". In the actual production process, there are many factors that can lead to the appearance of "ghosting".

1. The type of "ghost"

Under normal circumstances, "ghosting" can be divided into mechanical "ghosting" and craft "ghosting". Mechanical "ghosting" is caused by mechanical action and is mainly influenced by factors such as printing pressure, ink rollers, and printing plates. Process "ghosting" is caused by chemical changes in the ink during the printing process. Such "ghosting" is greatly influenced by the production environment.

According to the positive and negative images of the printed matter, "ghosting" can be further classified into positive image "ghosting" and negative image "ghosting". The part of the printed matter with a darker pattern color is called a positive image. It forms a "shadow" with a lighter color compared to the positive image in the circumferential direction, which is known as the "ghost shadow" of the positive image, as shown in Figure 1a. The part of the printed matter with a lighter pattern color is called the negative image. The "shadow" formed along its circumferential direction, which is darker in color compared to the negative image, is known as the negative image "ghost".

2. The formation conditions of "ghosts"

Unreasonable layout design or improper adjustment of the printing machine during offset printing is the main reason for the appearance of "ghosting" in printed products, specifically:

① There are patterns or characters that require a large amount of ink at the head of the printing plate.
② At the end of the printing plate, there are patterns that require a large amount of ink and have a large area.
③The distance between the pattern part and the solid part in the direction of the head and tail of the printing plate is exactly in a multiple relationship with the diameter of the ink roller.

The "ghosting" in offset printing is a avoidable fault. The key lies in prevention to avoid the occurrence of such faults.

ISGO has a team of experienced professional designers. The designers will design a suitable and personalized product image based on the different materials, structural differences, shape characteristics, and size requirements of the printed products, in combination with the brand culture of the clients. When changing the design and layout, they will reasonably design the layout. An appropriate layout arrangement can ensure that the grinding rollers have sufficient ink application time. Make the ink volume of the entire page even and technically minimize the appearance of ghosting as much as possible.

Of course, the appearance of "ghosts" can also be avoided from the following aspects:

(1) Adjust the ink supply corresponding to the "ghost" area.
(2) Increase the ink transfer force of the ink transfer roller. If the ink rollers in the ink supply system cannot ensure the uniformity of the ink layer on the ink rollers, "ghostimages" will also occur. Therefore, the method of increasing the momentum of the ink roller string can be adopted to avoid the appearance of "gghost".
(3) Adjust the pressure. To avoid the occurrence of such "ghosting", the operator should adjust the pressure between each ink roller in the ink supply system to an optimal state.
(4) Check the tightness of the rubber blanket, the tightness of the printing plate, and whether the gears of the cylinder are worn.