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2024

How to eliminate ghosting in offset printing?

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During the offset printing process, the occurrence of "ghosting" faults on continuously printed products is called "ghosting". In the actual production process, there are many factors that lead to the appearance of ghosts and shadows.
1. Types of "Ghost Shadow"
In general, "ghost shadows" can be divided into mechanical "ghost shadows" and technological "ghost shadows". Mechanical ghosting is caused by mechanical action, mainly influenced by factors such as printing pressure, ink rollers, and printing plates. The process of ghosting is caused by chemical changes in ink during the printing process, which are greatly affected by the production environment.
According to the positive and negative images of printed materials, "ghost shadows" can be further divided into positive images, "ghost shadows", and negative images, "ghost shadows". The darker part of the pattern color of the printed product itself is called the positive image, which forms a lighter "shadow" in its circumferential extension compared to the positive image, known as the positive image "ghost shadow", as shown in Figure 1a; The lighter part of the pattern color of the printed product itself is called a negative image, and the darker "shadow" formed by the extension in its circumferential direction compared to the negative image is called the "ghost shadow" of the negative image.
2. The formation conditions of "ghost shadows"
Unreasonable layout design or improper adjustment of the printing machine during the offset printing process are the main reasons for the appearance of "ghosting" on printed products, specifically:
① There is a pattern or text at the head of the printing plate that requires a large amount of ink;
② There is a pattern at the end of the printing plate that requires a large amount of ink and has a large area;
③ The distance between the pattern and solid parts in the direction of the plate head and tail is exactly a multiple of the diameter of the ink roller.
The ghosting of offset printing is an avoidable malfunction, and its focus is on prevention to avoid the occurrence of such malfunctions.