A double-color machine in our factory has a kind of ghost image, which is more special. Now we describe the phenomenon, the cause and the elimination method for reference by colleagues.
When printing a batch of four-color jobs, taking into account the technical requirements, first print solid yellow and black. The yellow version has a solid area of ​​530mm × 480mm (paper format is 560mm x 540mm), the black version has only one row of text, 170mm from the mouth, and the text size is about 10m? Big black letters and a black bar with a length of 60mm × 5mm. Put black in the color group and yellow in the lower group. When printing at start-up, a ghosting fault occurs, which is characterized by a row of black characters at the mouth of the mouth at two rows of ghost images at a distance of 382 mm from the mouth of the mouth. Approximately 300 copies were printed, and the ghost position was fixed. Stop to find the reason, there is no problem with the printing plate. From the analysis of ghosting characteristics, there is no possibility that the printing plate is not tensioned, the blanket is not tight, and the roller moves. Is it possible that the printability of the ink is poor and causes ghosting? So the ink in the ink fountain was stirred and found to be very fluid and the viscosity was too small. After inquiring the operator, due to the cold weather at that time, the ambient temperature was lower than -8 ℃, and the workshop temperature was only about 10 ℃. A large amount of No. 6 ink was added to change the ink's suitability. From this, it was preliminarily concluded that it was the ghost caused by the ink. After the ink roller was cleaned and the ink was replaced, the situation improved and the ghosting faded. After the water roller was replaced, ghosting was eliminated and printing was normal.
The main reason is that the ink causes ghosting. Adding too much ink to the ink increases the fluidity and reduces the viscosity, so that the ink is not firmly inked on the printing plate, causing part of the ink to be transferred to the water roller through the printing plate. After the second inking, a ghost image with a fixed position and a light but clear imprint appears, and the distance between the ghost image and the normal imprint is about 210mm, which is exactly equal to the circumference of the water roller.
This example shows that in the cold winter, especially in some offset printing workshops with poor conditions, the ink is very hard when the temperature is low. In order to improve its printability, an appropriate amount of ink must be added, but do not add more Because a certain amount of heat will be generated with the operation of the machine, it can change the temperature, viscosity, fluidity and other characteristics of the ink accordingly. If the added auxiliary doses such as ink-adjusting oil or viscosity-removing agent are too much, some unexpected failures will occur, which will affect the normal production schedule.
Author: Gansu Zhangye Flying Mayan Yu color printing plant
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