People who often read newspapers often find one or more thin lines that are significantly lighter than the printed graphics on some large-format solid pictures or decorative stripes on the newspapers. Most of them are "black ink ghosts". Ghosts are imprints or shadows of unknown origin.
Due to the newspaper's timeliness, strong political nature, short production cycle, and fast printing speed, once the "ghost" phenomenon occurs, it will seriously affect the printing quality. It causes waste of raw materials, ranging from the impact on the image of individuals and companies, and the impact on the image of the country, causing political accidents. To truly understand the root cause of the "ink-deficient ghost image", it is necessary to understand the composition of the ink supply system of the printing press and the ink transmission mechanism.
1. Composition of printing machine ink supply system
The ink supply system of the newspaper rotary machine and the general sheet-fed offset printing press is composed of an ink fountain, an ink fountain roller, an ink transfer roller, a string ink roller and an ink roller. Sheet-fed offset presses generally have 20-26, and rotary presses generally have only 7-11 because of their high speed. If the ink supply speed cannot keep up, it will cause insufficient supply of required ink. The work tasks of the ink supply system are simply two tasks that must be completed: one is to distribute the ink from the ink fountain more concentratedly through the ink roller; the other is to apply the ink roller to the plate every time the plate rotates. The printing plate has a comprehensive and uniform amount of ink supply.
As we all know, to make the ink transfer well, the following conditions must be met:
1. When the surfaces of the two ink transfer parts that are in contact with each other are separated, the ink layer breaks in the middle.
2. At one of the two transfer surfaces that are in contact with each other, compression deformation must occur to ensure reliable contact between the ink molecules and the transfer surface. In the inking system of the newspaper printer, the material of the inking roller is required to have good ink affinity, and the viscosity of the printing should be appropriate to ensure that the ink layer is broken in the middle, and the soft roller and the hard roller should be made between them. Only the placement can ensure reliable contact between the ink and the transfer member.
2. The occurrence and solution of "ghost" phenomenon
According to my study and analysis of the newspaper industry, there are mainly the following aspects of ghosting
1. Poor pressure debugging
The printing pressure and the contact pressure between the various ink rollers are not in the optimal printing state, resulting in a partial lack of ink and the formation of "ghost images". The ink rollers are required to contact each other to ensure the normal transmission of the ink, but they cannot be too clear or too heavy, which affects the amount of ink and causes insufficient ink supply, resulting in a "ghost" phenomenon. According to common sense, the thin solid lines on the general layout are not easy to produce "ghost images", but due to the improper pressure adjustment between the ink rollers, which affects the supply of normal ink transfer water and also produces "ghost images". As long as the pressure is readjusted to ensure smooth and uniform ink transfer, the "ghosting" phenomenon can be eliminated. However, if the printing pressure is too light, there will be no printing, false printing, and serious water ripples in the printed products.
2. Wear of roller gear and bearing gear
Helical gears are installed on the journal of the printing machine cylinder shaft to transmit power and precise positioning. Due to the fast running speed and long working time of the printing press, the wear is naturally serious. It is easy to make the gap when the gears are engaged too large, causing the longitudinal rollers to slide together and the contact between the gears is slightly misaligned, causing "ghosting". To solve this problem, gears and bearings must be replaced; reduce the center distance of the drum to reduce the gap between the drums, and the gear meshing should be controlled within 0.1mm.
3. Blanket, the printing plate is not tight
The lack of tightness of the blanket causes the blanket roller to fail to reset in time after being pressed or skews when the blanket is cut, making the partial stretch not tight, thus causing "ghosting". Because the printing plate is not meticulous and does not tighten, it can also cause "ghosting". Careful inspection during work, these failures can basically be eliminated.
4. The newspaper layout needs to be improved
Use thick solid lines, regional isolation lines or decorative lines to design the layout. These lines are perpendicular to the ink roller of the printer, and there are pictures on both sides of the line or there are lighter decorative stripes perpendicular to the ink roller. Then, on these mesh decorative pieces, it is easy to produce "ghost images". The reason is that the thick lines in the printing process consume a large amount of ink locally, and the sides of the lines are often blank parts. Due to the structural characteristics of the newspaper printer, the instant ink roller cannot partially replenish the required ink in time, causing a "ghost image" phenomenon. As long as you are familiar with the above principles, a little attention to "ghosting" in typesetting will not happen.
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