An Analysis of "Ghosting" Problems in Newspaper Printing

People who often read newspapers often find one or more thin lines that are significantly shallower than the printed text on some large-format pictures or textured strips in newspapers. This is called “ghosting”. Most of them are "missing ghosts." Ghost shadows are imprints or shadows of unknown origin.

Due to the timeliness of the newspapers, the strong political nature, the short production cycle, and the fast printing speed, once the “ghosting” phenomenon occurs, it will seriously affect the printing quality. The waste of raw materials will affect the image of individuals and companies, and it will affect the national image and cause political accidents. To truly understand the root causes of the “inkless ghosts”, we must understand the composition of the ink supply system of the printing press and the ink transfer mechanism.

First, the composition of the printing press ink supply system

The ink supply systems for newspaper web presses and general sheet-fed offset presses are composed of ink fountains, ink fountain rollers, ink transfer rollers, ink fountain rollers, and ink fountain rollers. Sheetfed offset presses generally have 20-26, and rotary presses generally have only 7-11 needles. If the ink supply speed cannot keep up, it will result in insufficient supply of required ink. The task of the ink supply system is simply the two tasks that must be accomplished: First, the ink from the ink fountain is more quickly beaten by the ink roller; second, the ink roller is used for each rotation of the printing plate. The printing plate has a full and uniform amount of ink.
As we all know, to make ink transfer well, the following conditions must be met:
1. The ink layer breaks in the middle when two surfaces of the ink delivery members that are in contact with each other are separated.
2. One of the two transfer surfaces that are in contact with one another should undergo compression deformation to ensure reliable contact between the ink molecules and the transfer surface. In the ink printing system of the newspaper printing press, the material of the ink transfer roller is required to have good ink-receptive performance, and the viscosity of the printing is used properly to ensure that the ink layer breaks in the middle thereof, and the soft roller and the hard roller are also required to be interposed. Placement allows reliable contact between the ink and the transfer member.

Second, "ghosting" phenomenon and solutions

According to my study and analysis of the newspaper industry, there are mainly the following aspects:

1, poor pressure debugging

The printing pressure and the contact pressure between the various ink rollers are not in the optimum printing state, causing a partial lack of ink and forming a "ghost image." Each ink roller is required to contact with each other to ensure the normal transmission of ink, but it can not be too clear or too heavy, affect the ink supply caused by insufficient ink supply, resulting in "ghosting" phenomenon. According to common sense, the solid lines on the general layout are not easy to produce "ghosting", but due to improper adjustment of the pressure between the ink rollers, affecting the supply of normal ink volume transmission water, it will also produce "ghosting" phenomenon. As long as the pressure is readjusted to ensure the smooth and uniform delivery of ink, the "ghosting" phenomenon can be eliminated. However, if the printing pressure is too light, there will be printing and hair vomit in the printed products, and serious water ripples will occur.

2, roller gear and bearing gear wear

The journal of the printer drum shaft is equipped with a helical gear to transmit power and precise positioning. Due to the high speed and long working time of the printer, the printer is naturally very serious. It is easy to make the gap large when the gears are engaged, causing the pressure between the longitudinal rollers to slip and the slight misalignment between the gears, causing “ghosting”. To solve this problem, it is necessary to replace the gears and bearings; reduce the center distance of the roller, so that the roller gap is reduced, and the gear meshing is controlled within 0.1mm.

3, blanket, printing plate is not tightened

The incomprehensibility of the blanket can cause the blanket cylinder to fail to reset in time after being pressurized or to be skewed when the blanket is cut, making the partial stretch not tight, resulting in "ghosting." Plates can cause "ghosting" due to inaccurate work. Carefully check in the work, these failures can basically be ruled out.
4, newspaper layout needs to be improved

The layout is designed with thick solid lines, isolated lines or decorative lines. These lines are perpendicular to the direction of the printer's ink roller, and the lines have pictures on both sides or shallower textured lines that are perpendicular to the roller. Then on these textured strips, it is easy to produce "ghosting." The reason is that the thick solid lines in the printing, the local consumption of ink is large, and the lines are often on both sides of the blank part. Due to the structural characteristics of the printing press, the local ink roller could not timely replenish the required ink in time, causing a "ghosting" phenomenon. As long as you are familiar with the above principles, it will not happen that you pay a little attention to "ghosting" when you typesetting.