A special ghosting fault in the two-color machine
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When printing a batch of four colors, considering the process requirements, first print the ground yellow and black. The yellow version has a field area of 530mm × 480mm (the paper format is 560mm x 540mm). The black version has only one row of text, 170mm from the cornice, the text size is about 10mm2, and there are two areas of 30mm2 at the outer distance of 300mm. Large black body and a black bar with a vertical length of 60mm × 5mm. Put black in the color group and yellow in the color group. When starting printing, there is a ghosting fault, which is characterized by a row of black characters at the mouth of the mouth showing two rows of ghosts at 382 mm from the mouth, and the large characters and black bars appearing ghosts at the longitudinal tip. About 300 sheets were printed and the ghost position was fixed. The reason for the downtime is that there is no problem with the plate. From the analysis of the ghost image, there is no possibility that the printing plate is not tightened, the blanket is not tight, and the drum is swaying. Is it because the ink is poorly printed and causes a ghost? Then the ink in the ink fountain was stirred and found to be very fluid and the viscosity was too small. Upon inquiry to the operator, due to the cold weather at that time, the ambient temperature was lower than -8 ° C, and the workshop temperature was only about 10 ° C. A large amount of No. 6 varnish was added to change the ink suitability. Thus, it is preliminarily concluded that it is a ghost caused by the ink. After cleaning the ink roller and replacing the ink, the situation has improved and the ghosting has been lightened. After replacing the water roller, the ghosting is eliminated and the printing is normal.
The reason is mainly because the ink causes ghosting. An excessive amount of varnish is added to the ink, the fluidity is increased, and the viscosity is lowered, so that the ink is not inked on the printing plate, so that part of the ink is transferred to the water roller through the printing plate, and the water roller performs the printing plate while feeding the water. The second inking occurs, so that the position is fixed, the print is light but clear, and the distance between the ghost and the normal print is about 210 mm, which is exactly equal to the circumference of the water roll.
This example shows that in the cold winter, especially in some poor printing offset workshops, the ink is very hard at lower temperatures. In order to improve the printability, it is necessary to add a proper amount of varnish, but don't add more Because the machine generates a certain amount of heat, it can change the temperature, viscosity, fluidity and other characteristics of the ink accordingly. If there are too many auxiliary doses such as varnish or de-adhesive added, some unexpected failures will occur, which will affect the normal production schedule.